Renewable Energy Sources by M A Qadeer

M A Qadeer Siddiqui

Renewable Energy Sources

By

Md Abdul Qadeer Siddiqui

0

M A Qadeer Siddiqui

Renewable Energy Sources

RENEWABLE ENERGY SOURCES

Md Abdul Qadeer Siddiqui B-Tech (Automobile Engineering) Bhaskar Engineering College (JNTU Hyderabad)

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Dedicated to... My friends Azeem, Akram and Imran for motivating me and …………………. To my teacher Sandhya Rani Mam for Her blessings……….

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Preface This book ―Renewable Energy Sources‖ caters the need of JNTU-H specially. Each topic is explained in simple way to make student understand and comprehend the subject. Effects of environmental, economic, social, political and technical factors have led to the rapid deployment of various sources of renewable energy-based power generation. The incorporation of these generation technologies have led to the development of a broad array of new methods and tools to integrate this new form of generation into the power system network. This book, arranged into eight sections, tries to highlight various renewable energy based generation technologies. Renewable Energy Resources is a numerate and quantitative text covering subjects of proven technical and economic importance worldwide. Energy supply from renewables is an essential component of every nation‘s strategy, especially when there is responsibility for the environment and for sustainability. This book considers the timeless principles of renewable energy technologies, yet seeks to demonstrate modern application and case studies. Renewable Energy Resources supports multi-disciplinary master degrees in science and engineering, and also specialist modules in science and engineering first degrees. Moreover, since many practicing scientists and engineers will not have had a general training in renewable energy, the book has wider use beyond colleges and universities. Each chapter begins with fundamental theory from a physical science perspective, then considers applied examples and developments, and finally concludes with a set of problems and solutions. The whole book is structured to share common material and to relate aspects together. Therefore the book is intended both for basic study and for application.

The corrections, suggestions and feedbacks from the readers are always appreciated and duly acknowledged. You can reach the author at [email protected]

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CONTENTS

1) PRINCIPLE OF SOLAR RADIATION ………………………………….5 2) SOLAR ENERGY COLLECTION ………………………….………….13 3) SOLAR ENERGY STORAGE AND APPLICATION ………..21 4) WIND ENERGY ………………………………………………………35 5) BIO MASS …………………………………………………………45 6) GEROTHERMAL ENERGY………………………63 7) OCEAN ENERGY………………………….70 8) DIRECT ENERGY CONVERSION ………………88

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CHAPTER 1) PRINCIPLES OF SOLAR RADIATION ROLE AND POTENTIAL OF NEW AND RENEWABLE ENERGY ROLE A broad range of different global energy scenarios confirms that the exploitation of energy efficiency potentials and the use of renewable energies play a key role in reaching global CO2 reduction targets. In scenarios aiming at the stabilisation of greenhouse gas concentration at 450 ppm equivalent, the contribution of renewables to global primary energy supply reaches between 31% (Greenpeace/EREC, Energy [R]evolution) and 23% (IEA World Energy Outlook 2008, 450 Policy Scenario) in 2030. By 2050, renewables are expected to contribute between 56% (Greenpeace/EREC, Energy [R]evolution) and 35% (IEA Energy Technology Perspectives, BLUE Map) to primary energy supply. Differences in the share of renewables across scenarios are partly due to different assumptions on the potentials for increasing energy efficiency. Compared to other scenarios, the more ambitious reduction of energy demand in the Greenpeace/EREC Energy [R]evolution scenario facilitates higher shares of renewables in energy consumption. In the IEA scenarios, also nuclear and fossil technologies with carbon capture and storage (CCS) are considered to be essential elements for achieving the climate protection targets. In particular the use of CCS in the IEA WEO scenario leadsto high CO2 abatement costs, as CCS is not expected to gain economic competitiveness before 2030. It remains unclear what constraints the market uptake of more cost effective renewable options in the IEA scenarios. While all scenario studies analysed provide a wealth of detailed information on various technical and economic issues, there is a general lack of reporting key assumptions in a comprehensive and transparent way, which sometimes makes comparison across studies difficult. All studies analysed are particularly weak in providing data on the heating sector, which in spite of its large contribution to fuel consumption and CO2 emissions in general is treated as a second priority only. A more transparent documentation of basic assumptions and constraints is desirable for any future scenario work. POTENTIAL The largest electricity generation potential on a global scale is seen for the solar technologies concentrating solar thermal power plants (CSP) and PV, followed by wind 5

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onshore and ocean energy. The global potential for direct thermal use of solar and geothermal energy several times exceeds global low temperature demand. The potential for CSP and PV electricity generation is particularly large in Africa. Wind onshore potentials are high in North America, while Latin America has abundant biomass resources. Current global final energy consumption is less than 5% of the overall projected technical renewable energy potential.

SOLAR ENERGY OPTION

ENVIRONMENTAL IMPACT OF SOLAR POWER The sun provides a tremendous resource for generating clean and sustainable electricity without toxic pollution or global warming emissions.

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The potential environmental impacts associated with solar power — land use and habitat loss, water use, and the use of hazardous materials in manufacturing — can vary greatly depending on the technology, which includes two broad categories: photovoltaic (PV) solar cells or concentrating solar thermal plants (CSP). The scale of the system — ranging from small, distributed rooftop PV arrays to large utility-scale PV and CSP projects — also plays a significant role in the level of environmental impact. Physics of Sun The sun is a huge ball of hot gas subject to the action of gravitational forces that tend to make it shrink in size. This force is balanced by the pressure exerted by the gas, so that an equilibrium size prevails. The core of the sun which extends from the centre to about 20% of the solar radius is at an extremely high temperature of around 15.7×106 K and pressure of 340 billion times earth‘s air pressure at sea level. Under these extremes, a nuclear fusion reaction takes place that merge four hydrogen nuclei or protons into an αparticle (helium nucleus), resulting in the production of energy from the net change in mass due to the fact that the alpha particle is about 0.7%less massive than the four protons. This energy is carried to the surface of the sun in about a million years, through a process known as convection, where it is released as light and heat (Hufbauer 1991). Figure shows the internal structure of the sun: the radiative surface of the sun, or photosphere, is the surface that emits solar radiation to space and has an average temperature of about 5,777 K. Localized cool areas called sunspots occur in the photosphere. The chromosphere (around 10,000 K) is the region where solar flares composed of gas, electrons, and radiation erupts.

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The solar constant The solar constant is defined as the quantity of solar energy (W/m²) at normal incidence outside the atmosphere (extraterrestrial) at the mean sun-earth distance. Its mean value is 1367.7 W/m². The spectral distribution is given in the figure. At shorter wavelengths you can see the Fraunhofer absorption lines.

Extraterrestrial and Terrestrial Solar Radiation Extraterrestrial radiation Extraterrestrial radiation (

) is the intensity (power) of the sun at the top of the Earth‘s

atmosphere. It is usually expressed in irradiance units (Watts per square meter) on a plane normal to the sun. It varies throughout the year because of the Earth‘s elliptical orbit, which results in the Earth-Sun distance varying during the year in a predictable way. This effect can be represented empirically with the following equations:

, where mean sun-earth distance and

is the solar constant (

).

is the

is the actual sun-earth distance depending on the day of

the year.

, where where

,

is the day of the year (integer). 8

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Terrestrial radiation  

energy emitted from the Earth and atmosphere detectable both day and night

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Earth's ambient temperature - 300K Earth radiates 160,000 times less than the sun essentially all energy is radiated at (invisible) thermal infrared wavelengths between 4-25um maximum emission occurs at 9.7um

Solar Radiation on Tilted Surface The power incident on a PV module depends not only on the power contained in the sunlight, but also on the angle between the module and the sun. When the absorbing surface and the sunlight are perpendicular to each other, the power density on the surface is equal to that of the sunlight (in other words, the power density will always be at its maximum when the PV module is perpendicular to the sun). However, as the angle between the sun and a fixed surface is continually changing, the power density on a fixed PV module is less than that of the incident sunlight. The amount of solar radiation incident on a tilted module surface is the component of the incident solar radiation which is perpendicular to the module surface. The following figure shows how to calculate the radiation incident on a tilted surface (Smodule) given either the solar radiation measured on horizontal surface (Shoriz) or the solar radiation measured perpendicular to the sun (Sincident).

Instruments for measuring solar radiation

Instrumentation Actinometer is the general name for any instrument used to measure the intensity of radiant energy, particularly that of the sun. Actinometers are classified according to the quantities that they measure:

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A pyrheliometer measures measures the intensity of direct solar radiation. It is so designed that it measures only the radiation from the sun's disk (which has an apparent diameter of ½°) and from a narrow annulus of sky of diameter 5° around the sun's disk. A pyranometer measures global radiation (the combined intensity of direct solar radiation and diffuse sky radiation). It measures solar irradiance from the solid angle 2pi onto a plane surface. When mounted horizontally facing upwards it measures global solar irradiance. If it is provided with a shade that prevents beam solar radiation from reaching the receiver, it measures diffuse solar irradiance. A pyrgeometer measures the effective terrestrial radiation. It measures the atmospheric infrared radiation spectrum that extends approximately from 4.5 µm to 100 µm.

A multi-filter rotating shadowband radiometer measures direct normal, diffuse horizontal and total horizontal solar irradiance. A radiometer is an instrument designed to measure the radiated electromagnetic power. When used in solar energy applications, it is usually desirable for radiometers to respond the same to equal amounts of energy at all wavelengths over the wavelength range of the radiation to be measured. Most radiometers therefore work by using a thermopile to measure the temperature rise of a sensitive element whose receiving surface is painted dull black. Instruments for measuring solar irradiance using a photovoltaic cell as the sensitive element have a non-uniform spectral response. An alternative method of measuring solar radiation, which is less accurate but also less expensive, is a sunshine recorder. Sunshine recorders measure the number of hours in the day during which the sunshine is above a certain level (typically 200 mW/cm2). Data collected in this way are used to determine the solar insolation by comparing the 11

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measured number of sunshine hours to those based on calculations and including several correction factors. Campbell Stokes Recorders are the instruments that are used to measure sunshine. These are one of the most important tools in meteorology. They are just important as the rain gauge for example.

SOLAR ENERGY RADIATION DATA According to Mathias Aarre Maehlum, Energy Informative, one year‘s worth of solar energy (radiant light and heat from the sun) reaching the surface of the earth would be twice the amount of all non-renewable resources, including fossil fuels and nuclear uranium. The solar energy that hits the earth every second is equivalent to 4 trillion 100watt light bulbs. Furthermore, the solar energy that hits one square mile in a year is equivalent to 4 million barrels of oil. Thus, the potential of solar energy is immense.

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CHAPTER 2) SOLAR ENERGY COLLECTION

Glazed flat-plate collectors Glazed flat-plate collectors are very common and are available as liquid-based and airbased collectors. These

collectors

are

better

suited

for

moderate

temperature

applications where the demand temperature is 30-70C and/or for applications that require heat during the winter months. The liquid-based collectors are most commonly used for the heating of domestic and commercial hot water, buildings, and indoor swimming

pools.

The air-based collectors

are

used

for

the

heating

of

buildings, ventilation air and crop-drying.

Glazed flat-plate collector In this type of collector a flat absorber efficiently transforms sunlight into heat. To minimize heat escaping, the plate is located between a glazing (glass pane or transparent material) and an insulating panel. The glazing is chosen so that a maximum amount of sunlight will pass though it and reach the absorber. Unglazed flat-plate solar collectors In North America unglazed flat-plate collectors currently account for the most area installed per year of any solar collector. Because they are not insulated, these collectors are best suited for low temperature applications where the demand temperature is below 30C. By far, the primary market is for heating outdoor swimming pools, but other markets exist including heating seasonal indoor swimming pools, pre-heating water for car washes and heating water used in fish farming operations. There is also a market potential for these collectors for water heating at remote, seasonal locations such as summer camps. 13

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Unglazed flat-plate collectors Unglazed flat-plate collectors are usually made of black plastic that has been stabilized to withstand ultraviolet light. Since these collectors have no glazing, a larger portion of the sun‘s energy is absorbed. However, because they are not insulated a large portion of the heat absorbed is lost, particularly when it is windy and not warm outside. They transfer heat so well to air (and from air) that they can actually ‗capture‘ heat during the night when it is hot and windy outside! Unglazed perforated plate collectors The key to this type of collector is an industrial-grade siding/cladding that is perforated with many small holes at a pitch of 2-4 cm. Air passes through the holes in the collector before it is drawn into the building to provide preheated fresh ventilation air. Efficiencies are typically high because the collector operates close to the outside air temperature. These systems can be very cost-effective, especially when they replace conventional cladding on the building, because only incremental costs need be compared to the energy savings.The most common application of this collector is for building ventilation air heating. Other possible components for this system are: a 20-30cm air gap between the building, a canopy at the top of the wall that acts as a distribution manifold, and by-pass dampers so that air will by-pass the system during warm weather.Another application for this collector is crop drying. Systems have been installed in South America and Asia for drying of tea, coffee beans, and tobacco. Currently there is a project underway with funding through the Technology Early Actions Measures (TEAM) for the monitoring of 10 crop drying systems in 8 countries in South and Central America and Asia.

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Back-pass solar collectors Air-based collectors use solar energy to heat air. Their design is simple and they often weigh less than liquid-based collectors because they do not have pressurized piping. Airbased collectors do not have freezing or boiling problems. In these systems, a large solar absorber is used to heat the air. The simplest designs are single-pass open collectors. Collectors that are coated with a glaze can also be used to heat air for space heating. This type of collector may be integrated in the building and combined with thermal mass such as in the Trombe wall described at the National Renewable Energy Laboratory. Concentrating solar collectors By using reflectors to concentrate sunlight on the absorber of a solar collector, the size of the absorber can be dramatically reduced, which reduces heat losses and increases efficiency at high temperatures. Another advantage is that reflectors can cost substantially less per unit area than collectors.This class of collector is used for hightemperature applications such as steam production for the generation of electricity and thermal detoxification. These collectors are best suited to climates that have an abundance of clear sky days and therefore are not so common in Canada. Stationary concentrating collectors may be liquid-based, air-based, or even an oven such as a solar cooker.There are four basic types of concentrating collectors: 1. Parabolic trough 2. Parabolic dish 3. Power tower 4. Stationary concentrating collectors Air based solar collectors The energy collected from air-based solar collectors can be used for ventilation air heating, space heating and crop drying. The most common application in Canada is for ventilation air heating. Three types of air-based collectors : Type of collector

Ventilation Air Heating

Space Heating

Crop Drying

Unglazed perforated plate

Very Good

Poor

Very Good

Glazed flat-plate

Good

Poor

Good

Back Pass

Fair

No

Fair-Good

Trombe wall

No

Good

No

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Designs for the first three collector types are simple. The collectors usually weigh less than liquid-based collectors because they do not have pressurized piping. Another advantage of air-based collectors is that they do not have freezing or boiling problems. All four of these air-based collectors can be integrated into buildings and form part of a building‘s envelope. These first three collectors are described in more detail on each of their own pages; the trombe wall is described in detail at the U.S. National Renewable Energy Laboratory web site. NRCan has developed two free software programs for analysis of solar air heating systems. SWIFT (Solar Wall International Feasibility Tool) can be used for job quotations and system design for ventilation air heating and crop drying applications for the first three system types. RETScreen is useful for conducting quick pre-feasibility studies of the cost effectiveness of proposed unglazed perforated plate collector installations. Batch solar collectors One hundred years ago, water tanks that were painted black were used as simple solar residential water heaters. Today their primary market is for residential water heating in warm countries. In Canada, they can be effectively used in campgrounds and for residential water heating in temperate climates such as Vancouver Island; during winter the tanks must be protected from freezing or they must be drained. Modern batch collectors have a glazing that is similar to the one used on flat plate collectors and/or a reflector to concentrate the solar energy on the tank surface. Because the storage tank and the solar absorber act as a single unit, there is no need for other components. On an area basis, batch collector systems are less costly than glazed flat-plate collectors but also deliver less energy per year. Solar cookers Though there are many types of solar cookers, all of them have a couple of basic components: 

Concentrator or lens to increase the available solar energy and insulation to reduce heat loss.

Often there is also an oven type cavity to place food into for cooking. Hot dog cookers, which do not need an 'oven' can also be made.Solar cookers are commonly able to reach cooking temperatures of 90-150 C (200-300 F) and some can even reach 230 C (450 F)! With these temperatures, it is possible to cook virtually any food as long as it is sunny outside.Making and using solar cookers can be a fun and educational school project. Liquid-based solar collectors Liquid-based collectors use sunlight to heat a liquid that is circulating in a "solar loop". The fluid in the solar loop can be water, an antifreeze mixture, thermal oil, etc. The solar loop transfers the thermal energy from the collectors to a thermal storage tank. The type of collector you need depends on how hot the water must be and the local climate. The most common liquid-based solar collectors are:

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Glazed flat-plate Unglazed flat-plate Vacuum tube Batch collector Concentrating

Parabolic dish systems A parabolic dish collector is similar in appearance to a large satellite dish, but has mirrorlike reflectors and an absorber at the focal point. It uses a dual axis sun tracker. A parabolic dish system uses a computer to track the sun and concentrate the sun's rays onto a receiver located at the focal point in front of the dish. In some systems, a heat engine, such as a Stirling engine, is linked to the receiver to generate electricity. Parabolic dish systems can reach 1000 °C at the receiver, and achieve the highest efficiencies for converting solar energy to electricity in the small-power capacity range.

Parabolic dish collector with a mirror-like reflectors and an absorber at the focal point Parabolic trough system Parabolic troughs are devices that are shaped like the letter ―u‖. The troughs concentrate sunlight onto a receiver tube that is positioned along the focal line of the trough. Sometimes a transparent glass tube envelops the receiver tube to reduce heat loss. Parabolic troughs often use single-axis or dual-axis tracking. In rare instances, they may be stationary. Temperatures at the receiver can reach 400 °C and produce steam for generating electricity. In California, multi-megawatt power plants were built using parabolic troughs combined with gas turbines.

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Parabolic trough system Power tower system A heliostat uses a field of dual axis sun trackers that direct solar energy to a large absorber located on a tower. To date the only application for the heliostat collector is power generation in a system called the power tower. A power tower has a field of large mirrors that follow the sun's path across the sky. The mirrors concentrate sunlight onto a receiver on top of a high tower. A computer keeps the mirrors aligned so the reflected rays of the sun are always aimed at the receiver, where temperatures well above 1000°C can be reached. High-pressure steam is generated to produce electricity.

Power tower system Stationary concentrating solar collectors Stationary concentrating collectors use compound parabolic reflectors and flat reflectors for directing solar energy to an accompanying absorber or aperture through a wide acceptance angle. The wide acceptance angle for these reflectors eliminates the need for a sun tracker. This class of collector includes parabolic trough flat plate collectors, flat plate collectors with parabolic boosting reflectors, and solar cookers. Development of the first two collectors has been done in Sweden. Solar cookers are used throughout the world, especially in the developing countries.

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Vacuum tube solar collectors Vacuum (also ―evacuated‖) tube solar collectors are amongst the most efficient and most costly types of solar collectors. These collectors are best suited for moderate temperature applications where the demand temperature is 50-95C and/or for very cold climates such as in Canada‘s far north. Like with glazed flat-plate solar collectors, applications of vacuum tube collectors include heating of domestic and commercial hot water, buildings, and indoor swimming pools. Due to their ability to deliver high temperatures efficiently another potential application is for the cooling of buildings by regenerating refrigeration cycles. Vacuum (also “evacuated”) tube solar collectorsVacuum tube solar collectors have a selective absorber for collecting sunlight that is in vacuum-sealed tube. Their thermal losses are very low even in cold climates. Orientation of Solar Collector For best performance, you need around 100 square ft of unshaded south-facing space for every kilowatt of electricity. The amount of solar radiation will be less if your roof faces SE or SW.

Photo Credit: NREL.gov

The condition of your roof is important, too. Ensure the roof can hold the weight of the system (about 3-5lb per square foot) and that the roofing material will last as long as the PV system (25-30 years).

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Solar thermal energy collector

Glazed plate solar collector 20

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CHAPTER 3) SOLAR ENERGY STORAGE AND APPLICATIONS Solar energy Storage

1) Thermal

2) Electrical

3)Chemical

4) Mechanical

5)Electromagnetic

1-Capacitor 2-Inductor 3-Battery 1-Chemical 2-Thermochemical

1-Sensible: a- Water storage b- Pebble bed Storage 2-Latent Heat

1-Pumped hydro electric 2- Compressed air 3- Flywheel

LATENT HEAT STORAGE SYSTEM

Scheme of of a solarthermal power plant with integrated storage capacity .

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Latent heat storage system use the energy absorbed or released during the isothermal phase change of materials. A first selection of suited storage materials is based on the melting temperature which should be close to the saturation temperature which is dependent on the pressure of the steam. Since systems using direct steam generation are operated at pressures T-s diagramm power plant with integrated storage capacity between 30 and 100bar the melting temperature of phase change materials (PCM) should be in the range of 230°C and 330°C. Due to cost aspects metallic materials like tin or lead can‘t be used, instead salts like sodium nitrate or potassium nitrate are typical candidate materials. A direct contact between storage material and steam is not possible, so thermal energy has to be transferred within the storage material. Cost effective storage systems demand high internal heat fluxes, which depend mainly on the heat conductivity of the storage material. Nonmetallic storage materials usually show low heat conductivities, especially the solid phase behaves like a thermal isolator. Essential for the development of cost effective storage systems is the increase of the effective heat conductivity in the storage material. DISTOR include research on three different concepts for PCM-storage: 





innovative composite materials made from PCM and materials showing a high thermal conductivity minimization of the average distance for heat transfer within the storage material, e.g. by encapsulation of the storage material application of an intermediate heat transfer medium for transfer of thermal energy between the pipes of the steam system and the storage material

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Stratified Storage Theoretical principles:

How can the physical properties of the heating water in a stratified storage tank be optimally utilised? Quite simple – by considering the following principle demands: 1. The layer system or other inserts built into the tank must not consist of metallic materials. Metals are good heat conductors and would quickly compensate for/mix up different temperature layers again. 2. No heat exchangers may be located inside the heat exchanger: This "thermal stirrers" would generate unwanted currents and destroy temperature layers, or mix up layers with different temperatures.

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4. A largely calm ("laminar") inflow of relatively large amounts of water into the tank volume is only possible through multi-chamber systems: Depending on the velocity, flows into pipes always generate overpressure or underpressure (venturi effect). 5. Preliminary sorting into different temperature levels (hot, warm, cool) is generally necessary, as there would otherwise be dynamic, turbulent currents within the tank because of excessive temperature differences and at the same time great height differences, also caused by thermal lift and descent rates (natural law of gravity). Perfect implementation





Stratified storage tank OSKAR-10/... from ratiotherm The thermal hydraulic 5-chamber layer insert of OSKAR-10/... comprises a heatresistant but bad heat conducting, that is, heat insulating plastic, and depending on the tank size and required volume flow one or more basic main pipe/s with correspondingly sized internal "inflow and stratification chambers". The supply or withdrawal of heat flows takes place via this layer insert with its sophisticated connection system, exactly suited to OSKAR-10/... and its areas of application and also made of heat resistant, thick-walled plastic pipes with good thermal insulation properties; in other words: the charging and discharging of OSKAR-10/… Because of the significantly larger cross-sections of this chamber system, compared to the connecting pipes, the flow rate (dynamic, kinetic energy) of the storage medium water is reduced to a minimum. Due to the extremely slow flow of the water, which is hardly moving, and the integrated water deflections in the chambers, the effect of a calm lift or descent according to the physical law of gravity (warm water is lighter than cold water), can develop without interference. The classical problem:

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The classic problem: Each supply flow mixes the entire tank content to a smaller or greater degree. This quickly causes the tank to have a uniform temperature level. The temperature level is often not sufficient to operate the heating system or heat the domestic water. The costly consequence of these systems is being reheated by the burner. Why temperature layers?

The different heat generators (solar, wood, etc.) largely vary in their output rating and thus also deliver very different temperatures. If they are not mixed but stored in layers, their energy content is fully preserved and can be used advantageously for heating or domestic hot water heating. Mechanical stratified storage tanks often work with external tank connections at different heights. The heat flows are then supplied directly to the tank content with different temperatures using control technology. The many lateral connections thereby constitute a drawback: They penetrate the tank insulation thereby causing increased "heat loss" of the tank. Furthermore, detrimental effects on existing temperature layers in the tank can hardly be avoided. The necessary control technology for "mechanical" stratified storage tanks is extremely expensive, depending on the system, and is the basis for the entire range of problems regarding maintenance, failure and wear. Running costs for servicing and maintenance are inevitable.

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Thermal hydraulic stratified storage tanks

with single chamber systems and integrated heat exchangers for utilising solar power function relatively well. The handling of larger volume flows and/or different return temperatures from consumer circuits represents a problem, however, often causing a mixing of the temperature layers



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The thermal hydraulic stratified storage technology developed by ratiotherm - with the 5-chamber layer inserts in OSKAR-10/... or special layer inserts in ratiotherm special stratified storage tanks - sorts out different temperature levels using a connection system especially suited exactly to the respective storage tank type. All connections are inserted into the tank at the bottom from underneath and emerge in the corresponding temperature zone of the multi-chamber system of the layer insert These calming and layer chambers let the heat flows rise and descend in the centre of the tank like in a "lift" in a completely calm and current-free manner. The supply and withdrawal of heat flows into or out of the corresponding temperature layers of the tank volume range takes place according to temperatures. In practice, most of the temperature zones are reached with this method.

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SOLAR POND

The sun is the largest source of renewable energy and this energy is abundantly available in all parts of the earth. It is in fact one of the best alternatives to the non-renewable sources of energy. One way to tap solar energy is through the use of solar ponds. Solar ponds are large-scale energy collectors with integral heat storage for supplying thermal energy. It can be use for various applications, such as process heating, water desalination, refrigeration, drying and power generation. The solar pond works on a very simple principle. It is well-known that water or air is heated they become lighter and rise upward e.g. a hot air balloon. Similarly, in an ordinary pond, the sun‘s rays heat the water and the heated water from within the pond rises and reaches the top but loses the heat into the atmosphere. The net result is that the pond water remains at the atmospheric temperature. The solar pond restricts this tendency by dissolving salt in the bottom layer of the pond making it too heavy to rise. A solar pond has three zones. The top zone is the surface zone, or UCZ (Upper Convective Zone), which is at atmospheric temperature and has little salt content. The bottom zone is very hot, 70°– 85° C, and is very salty. It is this zone that collects and stores solar energy in the form of heat, and is, therefore, known as the storage zone or LCZ (Lower Convective Zone). Separating these two zones is the important gradient zone or NCZ (Non-Convective Zone). Here the salt content increases as depth increases, thereby creating a salinity or density gradient. If we consider a particular layer in this zone, water of that layer cannot rise, as the layer of water above has less salt content and is, therefore, lighter. Similarly, the water from this layer cannot fall as the water layer below has a higher salt content and is, therefore, heavier. This gradient zone acts as a transparent insulator permitting sunlight to reach the bottom zone but also entrapping it

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there. The trapped (solar) energy is then withdrawn from the pond in the form of hot brine from the storage zone. Though solar ponds can be constructed anywhere, it is economical to construct them at places where there is low cost salt and bittern, good supply of sea water or water for filling and flushing, high solar radiation, and availability of land at low cost. Coastal areas in Tamil Nadu, Gujarat, Andhra Pradesh, and Orissa are ideally suited for such solar ponds. Solar Pond at Bhuj The Bhuj Solar Pond is a research, development, and demonstration project. The construction of the 6000 m2 pond started in 1987 at Kutch Dairy, Bhuj as a collaborative effort between Gujarat Energy Development Agency, Gujarat Dairy Development Corporation Limited, and TERI under the National Solar Pond programme of the Ministry of Non-Conventional Energy Sources. TERI carried out execution, operation, and maintenance of the Bhuj Solar Pond. The solar pond is 100 m long and 60 m wide and has a depth of 3.5 m. To prevent seepage of saline water, a specially developed lining scheme, comprising locally available material, has been adopted. The pond was then filled with water and 4000 tonnes of common salt was dissolved in it to make dense brine. A salinity gradient was established and wave suppression nets, a sampling platform, diffuses for suction and discharge of hot brine, etc. were also installed. This pond has been successfully supplying processed heat to the dairy since September 1993, and is, at present, the largest operating solar pond in the world. SOLAR APPLICATIONS SOLAR HEATING/COOLING Solar heating & cooling (SHC) technologies collect the thermal energy from the sun and use this heat to provide hot water, space heating, cooling, and pool heating for residential, commercial, and industrial applications. These technologies displace the need to use electricity or natural gas. Today, Americans across the country are at work manufacturing and installing solar heating and cooling systems that significantly reduce our dependence on imported fuels. We need smart policies to expand this fast‐growing, job‐producing sector.

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SOLAR DISTILLATION Solar distillation is a relatively simple treatment of brackish (i.e. contain dissolved salts) water supplies. Distillation is one of many processes that can be used for water purification and can use any heating source. Solar energy is a low tech option. In this process, water is evaporated; using the energy of the sun then the vapour condenses as pure water. This process removes salts and other impurities. Solar distillation is used to produce drinking water or to produce pure water for lead acid batteries, laboratories, hospitals and in producing commercial products such as rose water. It is recommended that drinking water has 100 to 1000 mg/l of salt to maintain electrolyte levels and for taste. Some saline water may need to be added to the distilled water for acceptable drinking water. Solar water distillation is a very old technology. An early large-scale solar still was built in 1872 to supply a mining community in Chile with drinking water. It has been used for emergency situations including navy introduction of inflatable stills for life boats. There are a number of other approaches to desalination, such as photovoltaic powered reverse-osmosis, for which small-scale commercially available equipment is available; solar distillation has to be compared with these options to determine its appropriateness to any situation. If treatment of polluted water is required rather than desalination, slow sand filtration is a low cost option. Energy requirements for water distillation The energy required to evaporate water, called the latent heat of vaporisation of water, is 2260 kilojoules per kilogram (kJ/kg). This means that to produce 1 litre (i.e. 1kg as the density of water is 1kg/litre) of pure water by distilling brackish water requires a heat input of 2260kJ. This does not allow for the efficiency of the system sued which will be less than 100%, or for any recovery of latent heat that is rejected when the water vapour is condensed. It should be noted that, although 2260kJ/kg is required to evaporate water, to pump a kg of water through 20m head requires only 0.2kJ/kg. Distillation is therefore normally considered only where there is no local source of fresh water that can be easily pumped or lifted. Solar dryers Solar dryers are devices that use solar energy to dry substances, especially food. These are of two types Direct: Direct solar dryers expose the substance to be dehydrated to direct sunlight. They have a black absorbing surface which collects the light and converts it to heat; the substance to be dried is placed directly on this surface. These driers may have enclosures; glass covers and/or vents to in order to increase efficiency.

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Indirect: In indirect solar dryers, the black surface heats incoming air, rather than directly heating the substance to be dried. This heated air is then passed over the substance and exits through a chimney, taking moisture from the substance with it. PHOTOVOLTAIC ENERGY CONVERSION Solar energy is leading the green revolution. If you're considering installing a solar photovoltaic (PV) system on your home, you don't need to know how the PV cells work. Your solar contractor knows the details, and they know which types of panels to use in a given application. But PV systems cost a lot of money, and customers are generally interested in knowing as much as possible about the details. The more you understand, the better your own decision-making process will be. A standard PV cell is a thin semiconductor sandwich, with two layers of highly purified silicon. Photovoltaic arrays are nothing more than huge matrices of interconnected semiconductor sandwiches. Usable PV systems comprised all sorts of equipment that protects the user from electrical shock, stores the electricity in battery banks, and converts the direct current (DC) into alternating current (AC), which is what people use in their houses. But at the heart of each system is a simple conversion process.

A photovoltaic cell changes light into electricity.

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A basic cell is around 1/100th of an inch thick, with a wide range of surface areas. A typical life span is over 25 years, and there are cells in place that have produced electricity reliably for over 40 years. This longevity is ultimately due to the coatings and framing structures that protect the cells. A module is an assembly of individual cells, connected in series and parallel arrangements designed to yield optimum performance.

In a series connection, voltage is additive, while in a parallel connection, current is additive. A typical PV cell produces around half a volt of electrical output. When 36 PV cells are connected in series, the result is an 18-volt module. A module or panel is a number of individual cells interconnected and housed into a finished product. A typical PV module in a residential application measures around 2.5 feet by 5 feet, in either bluish or black. Frames are either aluminum-colored or black, with the latter being the overwhelming choice of most homeowners these days (they just look better). It's possible to achieve a wide range of voltage and current outputs, depending on how the individual cells are connected together. The amount of power a module can produce is a function of the total surface area, as well as the amount of sunlight that strikes the module. Typical modules are rectangular and are available in a variety of sizes and configurations. Small modules (the kind used in hand-held calculators) output less than a single watt of power, while a typical residential module produces around 200 watts of power, more or less.

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Modules are characterized by: 

Cell material, or the type of silicon process that is used



Glazing material



Frame and electrical connections

The most important feature of a cell is the composition of the silicon structure. Single crystalline cells may be cast into an ingot of multiple crystals. Or the crystalline materials may also be deposited as a thin film, which is referred to as amorphous silicon. Individual silicon wafers used to manufacture PV cells are embedded with metallic contacts (wires). The cells are coated with an anti-reflection material so that the maximum amount of sunlight is absorbed into each cell. Single crystalline cells are more efficient than polycrystalline because, in polycrystalline cells, inter-grain boundaries introduce resistance to current flow (which consumes energy). Amorphous silicon is much less expensive to manufacture, but it's only around half as efficient in converting sunlight into useable electrical energy. In practical terms, this means that an amorphous system requires twice the surface area to output the same amount of power. Depending on how much surface area is available, this may or may not be a problem. In most residential applications, suitable roof space is limited, so efficiency is an important factor.

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CHAPTER4) WIND ENERGY SOURCES The energy from the wind can be harnessed by wind turbines to generate electricity and also windmills to pump water. During the 1990s, wind turbines evolved dramatically to become very large and increasingly efficient machines, as a direct result of government policies set in Denmark enabling communities and co-ops to develop wind turbines and encouraging research and development.

Chart: Global Annual Wind Installations (MW) 1980-2005 Capturing and Using Wind Modern wind turbines generate electricity typically around 80% of the time. The output varies depending on wind speed, but over the course of a year, a turbine is designed and expected to generate about 30% of its theoretical maximum output. This is known as its capacity factor, which for conventional power plants is typically 50%. Although the wind does not always blow, one region may be calm while another one is windy. Therefore, overall fluctuations can be significantly reduced if wind turbines are spread out across a country or region. Wind turbines tend to generate more power during the day when it is needed most and less at night, a pattern that corresponds well to electricity demand. Wind power therefore combines well with existing power plants in Canada that can be used only when needed, such as hydro plants, or must-run power plants like biomass that tend to have excess power at night. The energy that is available in the wind is cubically related to the speed at which it is moving. In other words, doubling the wind speed means there is eight times more

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energy. A good wind power site therefore needs to be consistently windy. Even small differences in wind speed can have a large impact on the performance a project. Wind energy can also be used for mechanical work such as water pumping and smallscale power systems for homes and small businesses. Canada has a unique expertise and manufacturing ability for medium-scale electrical systems that are ideally suited for remote community applications and hybrid systems such as wind-diesel. Benefits 

Large-scale wind energy is becoming cost competitive with traditional power generation.



Very low cradle-to-grave impacts.



Wind is abundant all over the world.



Wind patterns tend to follow consumption patterns.



Turbines co-exist nicely with farms, supplying additional income with minimal impact on the usable land.



Wind turbines are very quiet and are less likely to be struck by a bird than a downtown building, a bay window or a car is. Challenges



Significant local visual impact.



Moving parts require maintenance and upkeep.



A consistent and considerable amount of wind is needed.



Bats can be affected or struck by turbines.



Power output is variable and needs overall system integration.

POTENTIAL Global wind power has doubled over the last 3 years, which now accounts for 2% of the world‘s electricity production, and as much as 20% in some countries. It is estimated that 13% of the worlds land area has wind speeds greater than 6.9 m/s at commercial wind turbine heights, this could theoretically produce 40 times the world's current electricity production. Although the total quantity of wind energy potentially available is considerable, there remain obstacles to the substantial expansion of this industry. Critics claim that wind power cannot replace conventional power sources since these still need to be available for when the wind isn‘t blowing, and these are expensive to keep in reserve and waiting on part load, reducing overall energy efficiency. For low contributions, wind power can be considered largely additional, since reserves are always needed to cater for unexpected unavailability of the largest single power source and having a large number of smaller generating units can sometimes be beneficial.

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In addition to providing replacement power, wind plants reduce emissions by forcing the most polluting and inflexible power plants offline with more efficient and flexible types of generation. However, with increasing use of wind energy in the system the proportion of conventional plant wind replaces reduces, and consistent wind power generation requires high voltage connections to wind farms over a wide area. Further expansion of the industry may also require energy storage technologies to balance fluctuations of supply and demand; these include hydroelectricity, compressed air storage and electro-chemical batteries. The latter option is particularly interesting in view of the potential use of battery-electric vehicles in the future since their batteries could be charged overnight when power demand is low and used to supply power during peak demand periods. Peak electricity demand could also be reduced through pricing structures and switching off non-essential appliances. In addition to to replacing carbon intensive electricity production, wind power can drive heat pumps for space heating or charge vehicle batteries for transport, reducing natural gas and petroleum use. These are more efficient methods of producing heat and work than the traditional methods they replace, so direct comparisons of energy cannot usually be made . For example, one popular book grossly underestimated the potential contribution of wind power, partly because it compared the electricity generated from wind turbines with the primary chemical energy in fossil fuel directly. HORIZONTAL AXIS TURBINE In the wind turbine business there are basically two types of turbines to choose from, vertical axis wind turbines and horizontal axis wind turbines. They both have their advantages and disadvantages and the purpose of this article is to help you choose the right system for your application.

Horizontal axis wind turbine dominate the majority of the wind industry. Horizontal axis means the rotating axis of the wind turbine is horizontal, or parallel with the ground. In big wind application, horizontal axis wind turbines are almost all you will ever see. However, in small wind and residential wind applications, vertical axis turbines have their place. The advantage of horizontal wind is that it is able to produce more electricity from a given amount of wind. So if you are trying to produce as much wind as possible at all times, horizontal axis is likely the choice for you. The disadvantage of 37

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horizontal axis however is that it is generally heavier and it does not produce well in turbulent winds. VERTICLE AXIS TURBINE In comes the vertical axis wind turbine. With vertical axis wind turbines the rotational axis of the turbine stands vertical or perpendicular to the ground. As mentioned above, vertical axis turbines are primarily used in small wind projects and residential applications.

This niche comes from the OEM‘s claims of a vertical axis turbines ability to produce well in tumultuous wind conditions. Vertical axis turbines are powered by wind coming from all 360 degrees, and even some turbines are powered when the wind blows from top to bottom. Because of this versatility, vertical axis wind turbines are thought to be ideal for installations where wind conditions are not consistent, or due to public ordinances the turbine cannot be placed high enough to benefit from steady wind.

Wind turbine power ouput variation with steady wind speed. The figure below shows a sketch a how the power output from a wind turbine varies with steady wind speed.

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Cut-in speed. At very low wind speeds, there is insufficient torque exerted by the wind on the turbine blades to make them rotate. However, as the speed increases, the wind turbine will begin to rotate and generate electrical power. The speed at which the turbine first starts to rotate and generate power is called the cut-in speed and is typically between 3 and 4 metres per second.

Rated output power and rate output wind speed. As the wind speed rises above the cut-in speed, the level of electrical ouput power rises rapidly as shown. However, typically somewhere between 12 and 17 metres per second, the power output reaches the limit that the electrical generator is capable of. This limit to the generator output is called the rated power output and the wind speed at which it is reached is called the rated output wind speed. At higher wind speeds, the design of the turbine is arranged to limit the power to this maximum level and there is no further rise in the output power. How this is done varies from design to design but typically with large turbines, it is done by adjusting the blade angles so as to to keep the power at the constant level.

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Cut-out speed. As the speed increases above the rate output wind speed, the forces on the turbine structure continue to rise and, at some point, there is a risk of damage to the rotor. As a result, a braking system is employed to bring the rotor to a standstill. This is called the cut-out

speed and

is

usually

around

25

metres

per

second.

Wind turbine efficiency or power coefficient. The available power in a stream of wind of the same cross-sectional area as the wind turbine can easily be shown to be

If the wind speed U is in metres per second, the density ρ is in kilograms per cubic metre and the rotor diameter d is in metres then the available power is in watts. The efficiency, μ, or, as it is more commonly called, the power coefficient, cp, of the wind turbine is simply defined as the actual power delivered divided by the available power.

The Betz limit on wind turbine efficiency.

There is a theoretical limit on the amount of power that can be extracted by a wind turbine from an airstream. It is called the Betz limit .The limit is μ=16/27≈ 59%

Betz Criterion 40

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What is Betz Law?

We all feel the wind on us when we go for a ride on a motorcycle or on a windy day where you almost are swept off your feet. Wind can be very strong and we experience this power on windy days or storms. With all this wind energy flowing around us, scientists decided to put it to good use specially in these days with more emphasis on global warming there is a lot of pressure to use renewable sources of energy. Wind energy is flowing freely all around us and has not been utilized much. Well, with that in mind, wind farming is being tried and to some extent has been harnessed very successfully. Wind farming makes use of turbines which turn with the speed of the wind and create kinetic energy. This energy is converted to electricity by an electrical grid or generator. Many experiments are being conducted to find the most cost effective and energy efficient solution. But one of the most important inventions was made way back in 1919 by a German physicist; Albert Betz demonstrating the limitations of wind turbines is worrying the scientists. Even today these findings known as Betz Law or Betz limit have been found to be true irrespective of man‘s effort to create different energy efficient wind turbines. Betz law is quite interesting and how a calculation made almost 100 years back holds true even today.

What is Betz Law or Betz Limits? According to Betz law even when all the ideal conditions of energy generation are prevalent we can only derive 59% energy from wind turbines. 100% wind energy generation is simply not possible. Herein the capacity or ability of a generator to convert kinetic energy into electric energy is not under question. Rather the structure and mechanism of wind turbine has limitations in converting the wind energy into 100% kinetic energy owing to which we cannot take full benefit of wind energy.

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Although we are always inclined to get 100% of everything, it‘s not always possible and most of the times nature has its genuine reasons for confining man from achieving his own will. Betz law although was invented in 1919 has been known unknowingly to mankind but in a simpler way. How? Well what happens when you extract 100% energy from any source? The energy becomes empty or dried out. Similarly, if we are successful in deriving 100% kinetic energy from wind energy will there be any air or wind left? No! And then what will rotate the wind turbine? So at least to keep the velocity enough so as to make the wind turbine rotate for energy generation it‘s important that 100% efficiency is not achieved. What is the fundamental basis of Betz law? Betz law basically talks about how a wind turbine cannot extract more than 59.3 % of Kinetic energy from the wind. Under Ideal conditions or theoretically the maximum energy that can be extracted from the wind is called the Power coefficient which is a ratio between the amounts of energy that can be extracted by a Wind turbine to the total energy in the Wind. Power Coefficient (Beth's Coefficient) = Kinetic Energy that is extracted by a Wind turbine/Total energy in the Wind What are the limitations for achieving high efficiency? Usually the most important intention of energy generation is to achieve maximum efficiency within reasonable operational costs. So as to make the turbines cost effective, there would be a need to adapt design trade-offs but this can affect the overall efficiency of the system. So the idea is to get more power from stronger wind by sidelining the efficiency a bit. It has been found that less efficient rotor blades have been found to give more output. Moreover, the speed of wind is always a variable, while the turbines installed will always be of same efficiency and capacity. All these problems are currently being faced by the engineers and hence even today Betz law seems to be relevant.

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CHAPTER 5) BIOMASS The term Bioconversion, also known as biotransformation refers to the use of live organisms often microorganisms to carry out a chemical reaction that is more costly or not feasible nonbi ologically. These organisms convert a substance to a chemically modified form. An example is the industrial production of cortisone. One step is the bioconversion of Progesterone to 11-alpha-Hydroxyprogesterone by Rhizopus nigricans. Another example of this is the conversion of organic materials, such as plant or animal waste, into usable products or energy sources by biological processes or agents, such as certain microorganisms, some Detritivores or enzymes. The conversion of organic materials, such as plant or animal waste, into usable products or energy sources by biological processes or agents, such as certain microorganisms. The Bioconversion Science and Technology group performs multidisciplinary R&D for the Department of Energy's (DOE) relevant applications of bioprocessing, especially with biomass. Bioprocessing combines the disciplines of chemical engineering, microbiology and biochemistry. The Group 's primary role is investigation of the use of microorganism, microbial consortia and microbial enzymes in bioenergy research. New cellulosic ethanol conversion processes have enabled the variety and volume of feedstock that can be bioconverted to expand rapidly. Feedstock now includes materials derived from plant or animal waste such as paper, auto-fluff, tires, fabric, construction materials, municipal solid waste (MSW), sludge, sewage, etc.

AEROBIC AND ANAEROBIC DIGESTION

Aerobic Digestion Aerobic digestion of waste is the natural biological degradation and purification process in which bacteria that thrive in oxygen-rich environments break down and digest the waste. 43

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During oxidation process, pollutants are broken down into carbon dioxide (CO 2 ), water (H 2 O), nitrates, sulphates and biomass (microorganisms). By operating the oxygen supply withaerators, the process can be significantly accelerated. Of all the biological treatment methods, aerobic digestion is the most widespread process that is used throughout the world. Biological and chemical oxygen demand Aerobic bacteria demand oxygen to decompose dissolved pollutants. Large amounts of pollutants require large quantities of bacteria; therefore the demand for oxygen will be high. The Biological Oxygen Demand (BOD) is a measure of the quantity of dissolved organic pollutants that can be removed in biological oxidation by the bacteria. It is expressed in mg/l. The Chemical Oxygen Demand (COD) measures the quantity of dissolved organic pollutants than can be removed in chemical oxidation, by adding strong acids. It is expressed in mg/l. The BOD/COD gives an indication of the fraction of pollutants in the wastewater that is biodegradable. Advantages of Aerobic Digestion Aerobic bacteria are very efficient in breaking down waste products. The result of this is; aerobic treatment usually yields better effluent quality that that obtained in anaerobic processes. The aerobic pathway also releases a substantial amount of energy. A portion is used by the microorganisms for synthesis and growth of new microorganisms.

Path of Aerobic Digestion 44

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Aerobic Decomposition A biological process, in which, organisms use available organic matter to support biological activity. The process uses organic matter, nutrients, and dissolved oxygen, and produces stable solids, carbon dioxide, and more organisms. The microorganisms which can only survive in aerobic conditions are known as aerobic organisms. In sewer lines the sewage becomes anoxic if left for a few hours and becomes anaerobic if left for more than 1 1/2 days. Anoxic organisms work well with aerobic and anaerobic organisms. Facultative and anoxic are basically the same concept.

Anoxic Decomposition A biological process in which a certain group of microorganisms use chemically combined oxygen such as that found in nitrite and nitrate. These organisms consume organic matter to support life functions. They use organic matter, combined oxygen from nitrate, and nutrients to produce nitrogen gas, carbon dioxide, stable solids and more organisms.

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Anaerobic Digestion Anaerobic digestion is a complex biochemical reaction carried out in a number of steps by several types of microorganisms that require little or no oxygen to live. During this process, a gas that is mainly composed of methane and carbon dioxide, also referred to as biogas, is produced. The amount of gas produced varies with the amount of organic waste fed to the digester and temperature influences the rate of decomposition and gas production.

Anaerobic digestion occurs in four steps: • Hydrolysis : Complex organic matter is decomposed into simple soluble organic molecules using water to split the chemical bonds between the substances. • Fermentation or Acidogenesis: The chemical decomposition of carbohydrates by enzymes, bacteria, yeasts, or molds in the absence of oxygen. • Acetogenesis: The fermentation products are converted into acetate, hydrogen and carbon dioxide by what are known as acetogenic bacteria. • Methanogenesis: Is formed methanogenic bacteria.

from

acetate

and hydrogen/carbon

dioxide

by

The acetogenic bacteria grow in close association with the methanogenic bacteria during the fourth stage of the process. The reason for this is that the conversion of the fermentation products by the acetogens is thermodynamically only if the hydrogen concentration is kept sufficiently low. This requires a close relationship between both classes of bacteria.

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The anaerobic process only takes place under strict anaerobic conditions. It requires specific adapted bio-solids and particular process conditions, which are considerably different from those needed for aerobic treatment.

Path of Anaerobic Digestion

Advantages of Anaerobic Digestion Wastewater pollutants are transformed into methane, carbon dioxide and smaller amount of bio-solids. The biomass growth is much lower compared to those in the aerobic processes. They are also much more compact than the aerobic bio-solids. Anaerobic Decomposition A biological process, in which, decomposition of organic matter occurs without oxygen. Two processes occur during anaerobic decomposition. First, facultative acid forming bacteria use organic matter as a food source and produce volatile (organic) acids, gases such as carbon dioxide and hydrogen sulfide, stable solids and more facultative organisms. Second, anaerobic methane formers use the volatile acids as a food source and produce methane gas, stable solids and more anaerobic methane formers. The methane gas produced by the process is usable as a fuel. The methane former works slower than the acid former, therefore the pH has to stay constant consistently, slightly 47

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basic, to optimize the creation of methane. You need to constantly feed it sodium bicarbonate to keep it basic.

BIOGAS DIGESTERS TYPES: 1) Floating drum type 2) Fixed Dome type

1) Fixed-dome Plants A fixed-dome plant consists of a digester with a fixed, non-movable gas holder, which sits on top of the digester. When gas production starts, the slurry is displaced into the compensation tank. Gas pressure increases with the volume of gas stored and the height difference between the slurry level in the digester and the slurry level in the compensation tank. The costs of a fixed-dome biogas plant are relatively low. It is simple as no moving parts exist. There are also no rusting steel parts and hence a long life of the plant (20 years or more) can be expected. The plant is constructed underground, protecting it from physical damage and saving space. While the underground digester is protected from low temperatures at night and during cold seasons, sunshine and warm seasons take longer to heat up the digester. No day/night fluctuations of temperature in the digester positively influence the bacteriological processes. The construction of fixed dome plants is labor-intensive, thus creating local employment. Fixed-dome plants are not easy to build. They should only be built where construction can be supervised by experienced biogas technicians. Otherwise plants may not be gastight (porosity and cracks).

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The basic elements of a fixed dome plant (here the Nicarao Design) are shown in the figure below.

Fixed dome plant Nicarao design: 1. Mixing tank with inlet pipe and sand trap. 2. Digester. 3. Compensation and removal tank. 4. Gasholder. 5. Gaspipe. 6. Entry hatch, with gastight seal. 7. Accumulation of thick sludge. 8. Outlet pipe. 9. Reference level. 10. Supernatant scum, broken up by varying level.

picture:Basic function of a fixed-dome biogas plant, 1 Mixing pit, 2 Digester, 3 Gasholder, 4 Displacement pit, 5 Gas pipe

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Function A fixed-dome plant comprises of a closed, dome-shaped digester with an immovable, rigid gas-holder and a displacement pit, also named 'compensation tank'. The gas is stored in the upper part of the digester. When gas production commences, the slurry is displaced into the compensating tank. Gas pressure increases with the volume of gas stored, i.e. with the height difference between the two slurry levels. If there is little gas in the gas-holder, the gas pressure is low.

Digester The digesters of fixed-dome plants are usually masonry structures, structures of cement and ferro-cementexist. Main parameters for the choice of material are:    

Technical suitability (stability, gas- and liquid tightness); cost-effectiveness; availability in the region and transport costs; availability of local skills for working with the particular building material.

Fixed-dome plant in Tunesia. The final layers of the masonry structure are being fixed.[3]

Fixed dome plants produce just as much gas as floating-drum plants, if they are gas-tight. However, utilization of the gas is less effective as the gas pressure fluctuates substantially. Burners and other simple appliances cannot be set in an optimal way. If the gas is required at constant pressure (e.g., for engines), a gas pressure regulator or a floating gas-holder is necessary. Gas-Holder The top part of a fixed-dome plant (the gas space) must be gas-tight. Concrete, masonry and cement rendering are not gas-tight. The gas space must therefore be painted with a gas-tight layer (e.g. 'Water-proofer', Latex or synthetic paints). A possibility to reduce the risk of cracking of the gas-holder consists in the construction of a weak-ring in the masonry of the digester. This "ring" is a flexible joint between the lower (water-proof) and the upper (gas-proof) part of the hemispherical structure. It prevents cracks that develop due to the hydrostatic pressure in the lower parts to move into the upper parts of the gas-holder.

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Types









Renewable Energy Sources

of

Fixed-dome

Plants

Chinese fixed-dome plant is the archetype of all fixed dome plants. Several million have been constructed in China. The digester consists of a cylinder with round bottom and top. Janata model was the first fixed-dome design in India, as a response to the Chinese fixed dome plant. It is not constructed anymore. The mode of construction lead to cracks in the gasholder - very few of these plant had been gas-tight. Deenbandhu, the successor of the Janata plant in India, with improved design, was more crack-proof and consumed less building material than the Janata plant. with a hemisphere digester CAMARTEC model has a simplified structure of a hemispherical dome shell based on a rigid foundation ring only and a calculated joint of fraction, the so-called weak / strong ring. It was developed in the late 80s in Tanzania.

Fixed dome plant CAMARTEC design[1] Climate and Size Fixed-dome plants must be covered with earth up to the top of the gas-filled space to counteract the internal pressure (up to 0,15 bar). The earth cover insulation and the option for internal heating makes them suitable for colder climates. Due to economic parameters, the recommended minimum size of a fixed-dome plant is 5 m3. Digester volumes up to 200 m3 are known and possible.

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Summary Advantages: Low initial costs and long useful life-span; no moving or rusting parts involved; basic design is compact, saves space and is well insulated; construction creates local employment. Advantages are the relatively low construction costs, the absence of moving parts and rusting steel parts. If well constructed, fixed dome plants have a long life span. The underground construction saves space and protects the digester from temperature changes. The construction provides opportunities for skilled local employment.

Disadvantages: Masonry gas-holders require special sealants and high technical skills for gas-tight construction; gas leaks occur quite frequently; fluctuating gas pressure complicates gas utilization; amount of gas produced is not immediately visible, plant operation not readily understandable; fixed dome plants need exact planning of levels; excavation can be difficult and expensive in bedrock. Disadvantages are mainly the frequent problems with the gas-tightness of the brickwork gas holder (a small crack in the upper brickwork can cause heavy losses of biogas). Fixed-dome plants are, therefore, recommended only where construction can be supervised by experienced biogastechnicians. The gas pressure fluctuates substantially depending on the volume of the stored gas. Even though the underground construction buffers temperature extremes, digester temperatures are generally low. Fixed dome plants can be recommended only where construction can be supervised by experienced biogas technicians. Variations: Some companies are now looking into small pre-fab fixed dome plants made of fibreglass which

appears

to

be

a

low

cost

alternative to

construction

intensive masoned plants. A custom made plant can be produced in 2 days and -after transport- installed in less than 1 day! 2) Floating-drum Plants Floating-drum plants consist of an underground digester and a moving gas-holder. The gas-holder floats either directly on the fermentation slurry or in a water jacket of its own. The gas is collected in the gas drum, which rises or moves down, according to the amount of gas stored. The gas drum is prevented from tilting by a guiding frame. If the 52

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drum floats in a water jacket, it cannot get stuck, even in substrate with high solid content.

Floating-drum plant in Mauretania[3] The Drum In the past, floating-drum plants were mainly built in India. A floating-drum plant consists of a cylindrical or dome-shaped digester and a moving, floating gas-holder, or drum. The gas-holder floats either directly in the fermenting slurry or in a separate water jacket. The drum in which the biogascollects has an internal and/or external guide frame that provides stability and keeps the drum upright. If biogas is produced, the drum moves up, if gas is consumed, the gas-holder sinks back. Size Floating-drum plants are used chiefly for digesting animal and human feces on a continuous-feed mode of operation, i.e. with daily input. They are used most frequently by small- to middle-sized farms (digester size: 5-15m3) or in institutions and larger agroindustrial estates (digester size: 20-100m3).

Disadvantages: The steel drum is relatively expensive and maintenance-intensive. Removing rust and painting has to be carried out regularly. The life-time of the drum is short (up to 15 years; in tropical coastal regions about five years). If fibrous substrates are used, the gas-holder shows a tendency to get "stuck" in the resultant floating scum.

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Water-jacket plant with external guide frame: 1 Mixing pit, 11 Fill pipe, 2 Digester, 3 Gasholder, 31 Guide frame, 4 Slurry store, 5 Gas pipe[4] Water-jacket Floating-drum Plants Water-jacket plants are universally applicable and easy to maintain. The drum cannot get stuck in a scum layer, even if the substrate has a high solids content. Water-jacket plants are characterized by a long useful life and a more aesthetic appearance (no dirty gas-holder). Due to their superior sealing of the substrate (hygiene!), they are recommended for use in the fermentation of night soil. The extra cost of the masonry water jacket is relatively modest.

Material of Digester and Drum The digester is usually made of brick, concrete or quarry-stone masonry with plaster. The gas drum normally consists of 2.5 mm steel sheets for the sides and 2 mm sheets for the top. It has welded-in braces which break up surface scum when the drum rotates. The drum must be protected against corrosion. Suitable coating products are oil paints, synthetic paints and bitumen paints. Correct priming is important. There must be at least two preliminary coats and one topcoat. Coatings of used oil are cheap. They must be renewed monthly. Plastic sheeting stuck to bitumen sealant has not given good results. In coastal regions, repainting is necessary at least once a year, and in dry uplands at least every other year. Gas production will be higher if the drum is painted black or red rather than blue or white, because the digester temperature is increased by solar radiation. Gas drums made of 2 cm wire-mesh-reinforced concrete or fiber-cement must receive a gastight internal coating. The gas drum should have a slightly sloping roof, otherwise rainwater will be trapped on it, leading to rust damage. An excessively steep-pitched roof is unnecessarily expensive and the gas in the tip cannot be used because when the drum is resting on the bottom, the gas is no longer under pressure.

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Floating-drums made of glass-fiber reinforced plastic and high-density polyethylene have been used successfully, but the construction costs are higher compared to using steel. Floating-drums made of wire-mesh-reinforced concrete are liable to hairline cracking and are intrinsically porous. They require a gas-tight, elastic internal coating. PVC drums are unsuitable because they are not resistant to UV. Guide Frame The side wall of the gas drum should be just as high as the wall above the support ledge. The floating-drum must not touch the outer walls. It must not tilt, otherwise the coating will be damaged or it will get stuck. For this reason, a floating-drum always requires a guide. This guide frame must be designed in a way that allows the gas drum to be removed for repair. The drum can only be removed if air can flow into it, either by opening the gas outlet or by emptying the water jacket. The floating gas drum can be replaced by a balloon above the digester. This reduces construction costs but in practice problems always arise with the attachment of the balloon to the digester and with the high susceptibility to physical damage.

Types of Floating-drum Plants There are different types of floating-drum plants:       

KVIC model with a cylindrical digester, the oldest and most widespread floating drum biogas plant from India. Pragati model with a hemisphere digester Ganesh model made of angular steel and plastic foil floating-drum plant made of pre-fabricated reinforced concrete compound units floating-drum plant made of fibre-glass reinforced polyester low cost floating-drum plants made of plastic water containers or fiberglass drums: ARTI Biogas plants BORDA model: The BORDA-plant combines the static advantages of hemispherical digester with the process-stability of the floating-drum and the longer life span of a water jacket plant.

Summary Advantages: Advantages are the simple, easily understood operation - the volume of stored gas is directly visible. The gas pressure is constant, determined by the weight of the gas holder. The construction is relatively easy, construction mistakes do not lead to major problems in operation and gas yield.

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Disadvantages: Disadvantages are high material costs of the steel drum, the susceptibility of steel parts to corrosion. Because of this, floating drum plants have a shorter life span than fixed-dome plants and regular maintenance costs for the painting of the drum. GAS YEILD Feedstock

Dry Matter %

Biogas Yield m3/tonne

Feedstock

Dry Matter %

Biogas Yield m3/tonne

Cattle slurry

10

15-25

Potatoes

-

276-400

Pig slurry

8

15-25

Rye grain

-

283-492

Poultry

20

30-100

Clover grass

-

290-390

Grass silage

28

160-200

Sorghum

-

295-372

Whole wheat crop

33

185

Grass

-

298-467

Maize silage

33

200-220

Red clover

-

300-350

Maize grain

80

560

Jerusalem artich.

-

300-370

Crude glycerine

80

580-1000

Turnip

-

314

Wheat grain

85

610

Rhubarb

-

320-490

Rape meal

90

620

Triticale

-

337-555

Fats

up to 100

up to 1200

Oliseed rape

-

340-340

Nettle

-

120-420

Reed canary grass

-

340-430

Sunflower

-

154-400

Alfalfa

-

340-500

Miscanthus

-

179-218

Clover

-

345-350

Whole maize crop

-

205-450

Barley

-

353-658

Flax

-

212

Hemp

-

355-409

Sudan grass

-

213-303

Wheat grain

-

384-426

Sugar beet

-

236-381

Peas

-

390

Kale

-

240-334

Ryegrass

-

390-410

Straw

-

242-324

Leaves

-

417-453

Oats grain

-

250-295

Fodder beet

-

160-180

Chaff

-

270-316 56

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COMBUSTION CHARACTERSTICS OF BIO GAS Fuel types have experienced a transition process since the beginning of the industrial era, from solid fuels, liquid fuels, to the modern era where the objective is to disseminate the utilization of gas fuels. The objective is to find a renewable, cleaner source of energy, easy to manage and with low environmental impact not only at a local level but also globally. Biogas is one of these renewable sources of energy. Biogas is produced from the anaerobic fermentation of organic matter in sanitary landfills and in anaerobic biodigestors of organic solid wastes, from plants and animals. The environmental benefit of the production and use of this fuel is deeply appreciated through the reduction of gas emissions that exhibit a greenhouse effect since it is produced by the organic matter decomposition in agricultural and animal wastes as well as in sanitary landfills. Regarding its use, biogas can be utlized directly as a fuel in heating or power generation processes, as it is stated by Desideri, Di Maria, Leonardo & Proietti (2003) and Zamorano, Pérez, Aguilar & Ridao (2007). The first authors studied the energy potential of biogas produced at a sanitary landfill located in the center of Italy that serves a 400 000 - population town. This work concludes that 60% of the biogas produced at the sanitary landfill can be utilized in internal combustion engines for power generation due to its lower calorific effect, close to 19 000 KJ / Nm3 and given its methane content (greater than 40%). The utilization of the produced biogas represents, according to this publication, a yield close to 100 GW-h/ year. Zamorano et al (2007) conducts a similar work in the city of Granada in the South of Spain, whose landfill serves 300 000 people. An approximate energy potential estimation of 4 500 GW-h/year, greater than the values found in Italy, is reported in this work. This difference is produced because the biogas analysis revealed a 45% methane content in all the biogas produced in the landfill. These works indicate that it is feasible, from the economic standpoint, to utilize the biogas produced in landfills according to the type of technology, being mainly utilized in internal reciprocating combustion engines. The biogas utilization potential in this type of engines reveals that purification is necessary before considering its use as vehicle fuel (The Society of Motor Manufactu-rers and Traders Ltd. - SMMT - 2002). This purification consists in the elimination of certain components such as hydrogen sulphide, chlorine compounds, and ammonia, among others, and the decrease in the percentage of carbon dioxide. Despite the above, its utilization also depends on the knowledge available about its behavior in combustion systems. Therefore, a phenomenological study of the biogas combustion pattern in premixed systems is required, about its combustion properties and characteristic phenomena in premixed systems, in order to gain enough information to be applied in the design, redesign, or optimization of systems operating with this type of fuel. Furthermore, criteria about optimum atmospheric burner design are necessary so biogas can be utilized efficiently and safely in rural areas where organic materials are available. 57

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The objective in this case is to substitute wood logs in the preparation of food, thus contributing to decrease the pressure imposed on rainforest deforestation and avoid respiratory diseases resulting from a deficient wood combustion. Definition of these properties and characteristic phenomena are presented during the development of this work and the methodology described as well. Combined heat and power (CHP) is the simultaneous production of useable heat and electricity. As the process of AD(Anaerobic digestion) requires some heat it is suited to CHP. Whilst coal and gasfired power stations have an efficiency of around 34% and 55% respectively, CHP plants can achieve overall efficiencies in excess of 70% at the point of use. The ratio of heat to power varies dependent on the scale and technology, but typically 30-35% is converted to electricity, 40-45% to heat and the balance lost as inefficiencies at various stages of the process. This typically equates to over 2kWh electricity and 2.5kWh heat per cubic meter, at 60% methane.

BIOGAS AND IC ENGINE Biogas and Internal Combustion Engines Biogas is a mixture of approximately 60 per cent methane (CH4), 40 per cent carbon dioxide (CO2), and traces of hydrogen sulphide (H2S). Biogas has a number of problems as a fuel: 



 

High CO2 content reduces the power output, making it uneconomical as a transport fuel. It is possible to remove the CO2 by washing the gas with water. However, this is expensive (the capital cost in the mid 1980s was US$1200/kW in the UK), although the equipment lifetime can be expected to be much longer than the engine. The solution produced from washing out the CO2 is acidic and needs careful disposal. H2S is acidic and if not removed can cause corrosion of engine parts within a matter of hours. It is easy to remove H2S, by passing the gas through iron oxide (Fe203 -rusty nails are a good source) or zinc oxide (ZnO). These materials can be re-generated on exposure to the air, although the smell of H2S is unpleasant. There is a high residual moisture which can cause starting problems. The gas can vary in quality and pressure.

Engine operation Biogas can be used in both spark ignition and compression ignition engines. The exact amount needed depends upon the methane content of the biogas. However, an approximate substitution figure is:  

1.3 -1.9m3 biogas is approximately equivalent to 1 litre petrol/gasoline 1.5 - 2.1m3 biogas is approximately equivalent to 1 litre diesel 58

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Since the engine will run hotter than with a liquid fuel, the cooling system needs to be efficient or there will be problems with engine wear. The waste heat from the cooling water can be used to heat the digester.

Compression / ignition engines Biogas will not self-ignite in a diesel engine. Therefore, it is necessary to use a little diesel (approximately 20 per cent) to ignite the fuel. The biogas enters the engine via the air inlet system, after the air filter. This needs a small modification to the air intake system (see figure3 ). This option also allows for the engine to be operated on diesel fuel alone in periods when there is insufficient biogas.

An engine requires 0.6- 0.7m3 of biogas/kWh. Therefore, a 5kW generator running for three hours needs about 10m3. This is a large volume of biogas. Spark ignition engines These are not commonly used as stationary engines. They can, however, operate on 100 per cent biogas, since the spark ignites the biogas/air mixture. The same modifications to the air intake system are required as for a diesel engine.

Operating experience A large amount of operating experience has now been built up in India, China and Nepal on using biogas engines. There are conflicting views on the problems of long-term operation and engine wear. Problems may be encountered with the valves sticking, since these normally rely on the liquid fuel to provide some lubrication. Likewise, the piston also obtains some lubrication from the fuel and without this there is cylinder wear, which eventually leads to loss of power.

The use of gas engines would avoid these problems, although these are expensive compared to an internal combustion engine. However, evidence suggests that many of the most common problems encountered with all engines, irrespective of fuel, could be avoided if people were trained in simple maintenance; for example, in tightening bolts and changing or topping up lubricating oil. Loss of lubrication oil is one of the most common causes of engine failure and manufacturers are now incorporating an automatic cut-off device to protect the engine.

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ECONOMIC ASPECTS A Biogas unit can yield a whole range of benefits for their users, the world, society and the environment in general, the key benefits include; (1) Production of energy (heat, light, electricity). (2) Transformation of organic wastes into high quality fertilizer. (3) Improvement of hygienic conditions through reduction of pathogens, worm eggs and flies. (4) Workload reduction; mainly for women, in firewood collection and cooking. (5) Environmental advantages through protection of forests, soil, water and air. Production of energy (heat, light, electricity) Methane is the valuable component under the aspect of using biogas as a fuel. Biogas use, replacing conventional fuels like kerosene or firewood, allows for the conservation of environment. It therefore, increases its own value by the value of i.e. forest saved or planted. Biogas is able to substitute almost the complete consumption of firewood in rural households. 1 m3 Biogas (approximately 6 kWh/m3) is equivalent to: Diesel, Kerosene (approx. 12 kWh/kg) 0.5 kg Wood (approx. 4.5 kWh/kg) 1.3 kg Cow dung (approx. 5 kWh/kg dry matter) 1.2 kg Plant residues (approx. 4.5 kWh/kg d.m.) 1.3 kg Hard coal (approx. 8.5 kWh/kg) 0.7 kg 60

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City gas (approx. 5.3 kWh/m3) 1.1 m3 Propane (approx. 25 kWh/m3) 0.24 m3 Large units and/or communal units produce biogas in large quantities and can be used to power engines and generators for mechanical work or power generation. Transformation of organic wastes into high quality organic fertilizer The biogas digester is fed with cow dung slurry at a design rate, which is governed by local parameters. The output from the digester (digested manure) is actually a high quality organic fertilizer. This fertilizer is very important where the farmers do not have the resources to buy chemical fertilizers frequently. If you compost chicken manure, for example, the finished compost will have in it only 1.58 to 2%o nitrogen. The same manure digested in a bio-gas plant will analyze 6% nitrogen. The digested slurry must be immediately utilized - and properly applied - as fertilizer, each daily kg can be expected to yield roughly 0.5 kg extra nitrogen, as compared with fresh manure. If the slurry is first left to dry and/or improperly applied, the nitrogen yield will be considerably lower. This nitrogen is already present in the manure. The nitrogen is preserved when waste is digested in an enclosed bio-gas plant, whereas the same nitrogen evaporates away as ammonia during open air composting. The bio-gas plant is the perfect fertilizer-making machine and it has been tested all over the world. There is no better way to digest or compost manure and other organic material than in a bio-gas plant. One can compare the bacteria in a digester tank to fish worms. Fish worms help the soil by eating organic matter, passing it through their bodies and expelling it as very rich fertilizer. They live by breaking waste material down into food for plants. It is the same with the bacteria in a methane digester. It is all very natural.

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CHAPTER 6) GEOTHERMAL ENERGY

RESOURCES Geothermal energy is the heat from the Earth. It's clean and sustainable. Resources of geothermal energy range from the shallow ground to hot water and hot rock found a few miles beneath the Earth's surface, and down even deeper to the extremely high temperatures of molten rock called magma. Almost everywhere, the shallow ground or upper 10 feet of the Earth's surface maintains a nearly constant temperature between 50° and 60°F (10° and 16°C). Geothermal heat pumps can tap into this resource to heat and cool buildings. A geothermal heat pump system consists of a heat pump, an air delivery system (ductwork), and a heat exchangera system of pipes buried in the shallow ground near the building. In the winter, the heat pump removes heat from the heat exchanger and pumps it into the indoor air delivery system. In the summer, the process is reversed, and the heat pump moves heat from the indoor air into the heat exchanger. The heat removed from the indoor air during the summer can also be used to provide a free source of hot water. In the United States, most geothermal reservoirs of hot water are located in the western states, Alaska, and Hawaii. Wells can be drilled into underground reservoirs for the generation of electricity. Some geothermal power plants use the steam from a reservoir to power a turbine/generator, while others use the hot water to boil a working fluid that vaporizes and then turns a turbine. Hot water near the surface of Earth can be used directly for heat. Direct-use applications include heating buildings, growing plants in greenhouses, drying crops, heating water at fish farms, and several industrial processes such as pasteurizing milk. Hot dry rock resources occur at depths of 3 to 5 miles everywhere beneath the Earth's surface and at lesser depths in certain areas. Access to these resources involves injecting cold water down one well, circulating it through hot fractured rock, and drawing off the heated water from another well. Currently, there are no commercial applications of this technology. Existing technology also does not yet allow recovery of heat directly from magma, the very deep and most powerful resource of geothermal energy. Many technologies have been developed to take advantage of geothermal energy - the heat from the earth. NREL performs research to develop and advance technologies for the following geothermal applications: 

Geothermal Electricity Production Generating electricity from the earth's heat.

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Geothermal Direct Use Producing heat directly from hot water within the earth.



Geothermal Heat Pumps Using the shallow ground to heat and cool buildings.

Renewable Energy Sources

The centre of the Earth is around 6000 degrees Celsius - easily hot enough to melt rock. Even a few kilometers down, the temperature can be over 250 degrees Celsius if the Earth's crust is thin. In general, the temperature rises one degree Celsius for every 30 - 50 meters you go down, but this does vary depending on location .In volcanic areas, molten rock can be very close to the surface. Sometimes we can use that heat. Geothermal energy has been used for thousands of years in some countries for cooking and heating. The name "geothermal" comes from two Greek words: "geo" means "Earth" and "thermal" means "heat". GEOTHERMAL WELLS Geothermal wells are wells which tap into the natural geothermal energy found beneath the Earth‘s crust. Geothermal energy is thermal energy generated and stored in the Earth. Thermal energy is the energy that determines the temperature of matter. Earth‘s geothermal energy originates from the original formation of the planet, from the radioactive decay of minerals, from volcanic activity, and from solar energy absorbed at the surface. Geothermal wells have been used for several decades as an adjunct to existing heating and cooling systems. The systems are designed to use the Earth‘ s relatively constant subsurface temperature along with a heat exchanger to either add to or remove heat from a dwelling. What is Geothermal Electricity? Even though the surface of Earth can get quite cold at times, the area beneath the Earth‘s crust has a relatively stable temperature and it is usually very hot. Geothermal energy utilizes this heat to generate electricity called the ‗Geothermal electricity‘ and to provide heating to various structures. The energy can either be used directly, in the form of geothermal wells which connect to sources of water and steam heated by the earth, or indirectly, in the case of systems which pump water through hot regions under the Earth‘s crust.

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What are the different types of geothermal wells? Geothermal wells also known as geo exchange systems have 2 basic designs. They are: Open looped system: in an open looped system, ground water is pumped from water well into a heat exchanger located in a surface dwelling. The water drawn from the earth is then pumped back into the aquifer through a different well, or in some cases the same well. Alternatively, the ground water could be discharged to a surface of water body. In the heating mode, cooler water is returned to the earth, while in the cooling mode, warmer water is returned. Closed loop system: In a closed loop system, an opening (either borehole or trench) is made in the earth. A series of pipes are installed into the opening and connected to a heat exchange system in the dwelling. The pipes form a ―closed loop‖, and are filled with a heat transfer fluid. The fluid is circulated through the piping from the opening into the heat exchanger and back. The system functions in the same manner as the open looped system, except there is no pumping of ground water.

How is geothermal well constructed? The methods and equipment used to drill geothermal wells are similar to those used to drill oil and gas wells. High-temperature and Steam-dominated Reservoirs: The drilling fluid-also called drilling mud-is circulated through the well to bring the cuttings back to the surface and to cool the well. After a well is drilled, often beyond 5,000 feet, steel pipe, called casing, is cemented in place by pumping cement into the annulus (space between the casing and the rock formation). The casing and cement prevent fluids in different zones from mixing with each other or with the produced fluids. It is essential to cement all of the annular space behind the casting. Cement prevents the casing from expanding when heated and helps prevent corrosion. Low-temperature, Water-dominated Reservoirs: Wells in low-temperature, water dominated reservoirs are usually less than 1,000 feet deep. Typically, the well is cased and cemented to appoint above the production zone to prevent polluted surface waters coming from contaminating shallows, water-bearing zones. The standard for this type of well resemble those for other water wells.

How many geothermal wells are there and how much water is produced? There are about 470 steam wells and 230 high-temperature, hot wells in 10 hightemperature geothermal fields in California. In 2005, over 324 billion kilograms of water was produced from these wells. In addition, there are several hundred low-temperature geothermal wells in the state for which the Division has no records. 64

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TYPES OF GEOTHERMAL SYSTEMS There are two basic geothermal system types: Hydrothermal and Hot Rock or Enhanced Geothermal Systems. Normally conventional hydrothermal reservoirs are found in fractured volcanic rocks where temperatures are relatively high near the surface such as in New Zealand. However, geothermal reservoirs are found in non volcanic areas where the crustal heat flow is sufficient to produce high temperatures and the rocks are permeable to allow the production of large volumes of fluid. Greenearth Energy's domestic and international exploration and development focus is on conventional geothermal (Hydrothermal) systems. In Australia the focus is on Hot Sedimentary Aquifer (HSA) systems. In Indonesia the focus is on Volcanic Systems.

FIGURE 1: Schematic of Geothermal Systems

The extraction of heat from hot rocks is achieved by pumping water into the rocks at depth using an injection well, and subsequently withdrawing it from a production well at a much higher temperature after it has flowed under pressure through fractures in the hot rocks. Hot rocks are hot due to the heat which is generated at depth being trapped by the insulating effect of overlying rocks and sedimentary cover usually over 3000 metres in thickness. 65

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USES FOR GEOTHERMAL ENERGY Direct uses for low and moderate temperature resources typically up to 150oC involves using the heat in the water directly (without a heat pump or power plant) for such things as heating of buildings, industrial processes, greenhouses, aquaculture (growing of fish) and resorts. Figure 2 provides an overview of such applications at varying temperatures.

FIGURE 2: Temperature ranges for Direct Heat Applications

POWER GENERATION USING GEOTHERMAL ENERGY Most geothermal power plants operating today are "flashed steam" power plants using high temperature water from production wells. Released from the pressure of the deep reservoir, part of the water flashes (explosively boils) to steam and the force of the steam is used to spin the turbine generator. In a binary power plant the working fluid (usually isobutane or isopentane) boils and flashes to a vapor at a lower temperature than water does, so electricity can be generated from reservoirs with lower temperatures. 66

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Binary power plants have virtually no emissions but are relatively less efficient. Figure 3 provides a schematic of a typical binary power plant arrangement.

Figure 3 Schematic of Binary Cycle Power Plant Source: Oregon Institute of Technology (modified by Greenearth Energy) to take account of the change of the cooler to air cooling rather than vapour (evaporative) cooling.

Conventional hydrothermal systems have well-demonstrated economic and technological viability. Some geothermal fields have been supporting cost-effective, dependable electrical power generation for over 50 years. Ongoing advances in binary geothermal power-plant technology have lowered the temperature requirement for electrical power generation, and also improved the bottom-line economic viability of many conventional hydrothermal resources. TECHNOLOGIES HARNESSING ENERGY Technology Mile-or-more-deep wells can be drilled into underground reservoirs to tap steam and very hot water that drive turbines that drive electricity generators. Four types of power plants are operating today:

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Flashed steam plant The extremely hot water from drill holes when released from the deep reservoirs high pressure steam (termed as flashed steam) is released. This force of steam is used to rotate turbines. The steam gets condensed and is converted into water again, which is returned to the reservoir. Flashed steam plants are widely distributed throughout the world. Dry steam plant Usually geysers are the main source of dry steam. Those geothermal reservoirs which mostly produce steam and little water are used in electricity production systems. As steam from the reservoir shoots out, it is used to rotate a turbine, after sending the steam through a rock-catcher. The rock-catcher protects the turbine from rocks which come along with the steam. Binary power plant In this type of power plant, the geothermal water is passed through a heat exchanger where its heat is transferred to a secondary liquid, namely isobutene, iso-pentane or ammonia–water mixture present in an adjacent, separate pipe. Due to this double-liquid heat exchanger system, it is called a binary power plant. The secondary liquid which is also called as working fluid, should have lower boiling point than water. It turns into vapor on getting required heat from the hot water. The vapor from the working fluid is used to rotate turbines. The binary system is therefore useful in geothermal reservoirs which are relatively low in temperature gradient. Since the system is a completely closed one, there is minimum chance of heat loss. Hot water is immediately recycled back into the reservoir. The working fluid is also condensed back to the liquid and used over and over again. Hybrid power plant Some geothermal fields produce boiling water as well as steam, which are also used in power generation. In this system of power generation, the flashed and binary systems are combined to make use of both steam and hot water. Efficiency of hybrid power plants is however less than that of the dry steam plants. Enhanced geothermal system The term enhanced geothermal systems (EGS), also known as engineered geothermal systems (formerly hot dry rock geothermal), refers to a variety of engineering techniques used to artificially create hydrothermal resources (underground steam and hot water) that can be used to generate electricity. Traditional geothermal plants exploit naturally occurring hydrothermal reservoirs and are limited by the size and location of such natural reservoirs. EGS reduces these constraints by allowing for the creation of hydrothermal reservoirs in deep, hot but naturally dry geological formations.EGS techniques can also extend the lifespan of naturally occurring hydrothermal resources. Given the costs and limited full-scale system research to date, EGS remains in its infancy, with only a few research and pilot projects existing around the world and no commercial-scale EGS plants to date. The technology is so promising, however, that a number of studies have found that EGS could quickly become widespread.

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Potential In India

      

It has been estimated from geological, geochemical, shallow geophysical and shallow drilling data it is estimated that India has about 10,000 MWe of geothermal power potential that can be harnessed for various purposes. Rocks covered on the surface of India ranging in age from more than 4500 million years to the present day and distributed in different geographical units. The rocks comprise of Archean, Proterozoic, the marine and continental Palaeozoic, Mesozoic, Teritary, Quaternary etc., More than 300 hot spring locations have been identified by Geological survey of India (Thussu, 2000). The surface temperature of the hot springs ranges from 35 C to as much as 98 C. These hot springs have been grouped together and termed as different geothermal provinces based on their occurrence in specific geotectonic regions, geological and strutural regions such as occurrence in orogenic belt regions, structural grabens, deep fault zones, active volcanic regions etc., Different orogenic regions are – Himalayan geothermal province, Naga-Lushai geothermal province, Andaman-Nicobar Islands geothermal province and non-orogenic regions are – Cambay graben, Son-NarmadaTapi graben, west coast, Damodar valley, Mahanadi valley, Godavari valley etc. Puga Valley (J&K) Tatapani (Chhattisgarh) Godavari Basin Manikaran (Himachal Pradesh) Bakreshwar (West Bengal) Tuwa (Gujarat) Unai (Maharashtra) Jalgaon (Maharashtra) 69

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CHAPTER 7) OCEAN ENERGY The ocean can produce two types of energy: thermal energy from the sun's heat, and mechanical energy from the tides and waves. Oceans cover more than 70% of Earth's surface, making them the world's largest solar collectors. The sun's heat warms the surface water a lot more than the deep ocean water, and this temperature difference creates thermal energy. Just a small portion of the heat trapped in the ocean could power the world. Ocean thermal energy is used for many applications, including electricity generation. There are three types of electricity conversion systems: closed-cycle, open-cycle, and hybrid. Closed-cycle systems use the ocean's warm surface water to vaporize a working fluid, which has a low-boiling point, such as ammonia. The vapor expands and turns a turbine. The turbine then activates a generator to produce electricity. Open-cycle systems actually boil the seawater by operating at low pressures. This produces steam that passes through a turbine/generator. And hybrid systems combine both closed-cycle and opencycle systems. Ocean mechanical energy is quite different from ocean thermal energy. Even though the sun affects all ocean activity, tides are driven primarily by the gravitational pull of the moon, and waves are driven primarily by the winds. As a result, tides and waves are intermittent sources of energy, while ocean thermal energy is fairly constant. Also, unlike thermal energy, the electricity conversion of both tidal and wave energy usually involves mechanical devices. A barrage (dam) is typically used to convert tidal energy into electricity by forcing the water through turbines, activating a generator. For wave energy conversion, there are three basic systems: channel systems that funnel the waves into reservoirs; float systems that drive hydraulic pumps; and oscillating water column systems that use the waves to compress air within a container. The mechanical power created from these systems either directly activates a generator or transfers to a working fluid, water, or air, which then drives a turbine/generator. 70

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What is OTEC Ocean Thermal Energy Conversion (OTEC) is a marine renewable energy technology that harnesses the solar energy absorbed by the oceans to generate electric power. The sun‘s heat warms the surface water a lot more than the deep ocean water, which creates the ocean‘s naturally available temperature gradient, or thermal energy.

OTEC uses the ocean‘s warm surface water with a temperature of around 25°C (77°F) to vaporize a working fluid, which has a low-boiling point, such as ammonia. The vapor expands and spins a turbine coupled to a generator to produce electricity. The vapor is then cooled by seawater that has been pumped from the deeper ocean layer, where the temperature is about 5°C (41°F). That condenses the working fluid back into a liquid, so it can be reused. This is a continuous electricity generating cycle. The efficiency of the cycle is strongly determined by the temperature differential. The bigger the temperature difference, the higher the efficiency. The technology is therefore viable primarily in equatorial areas where the year-round temperature differential is at least 20 degrees Celsius or 36 degrees Fahrenheit. Resource

The oceans cover more than 70% of Earth‘s surface and capture a large part of the sun‘s heat in the upper layers, making them the world‘s largest solar collectors and energy storage system. Utilizing just a small portion of this energy, can cover the global energy need. The energy source of OTEC is free, available abundantly and is continually being replenished as long as the sun shines and the natural ocean currents exist. Various renowned parties estimate the amount of energy that can be practically harvested to be in 71

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the order of 3 to 5 terawatts (1 terawatt is 1012 watts) of baseload power generation, without affecting the temperature of the ocean or the world‘s environment. That‘s about twice the global electricity demand. The oceans are thus a vast renewable resource, with the potential to contribute to the future energy mix offering a sustainable electricity production method. The technology is viable primarily in equatorial areas where the year-round temperature differential is at least 20°C (36°F). Benefits The distinctive feature of OTEC is the potential to provide baseload electricity, which means day and night (24/7) and year-round. This is a big advantage for for instance tropical islands that typically has a small electricity network, not capable of handling a lot of intermittent power.

OTEC benefits Next to producing electricity, OTEC also offers the possibility of co-generating other synergistic products, like fresh water, nutrients for enhanced fish farming and seawater cooled greenhouses enabling food production in arid regions. Last but not least, the cold water can be used in building air-conditioning systems. Energy savings of up to 90% can be realized. The vast baseload OTEC resource could help many tropical and subtropical (remote) regions to become more energy self-sufficient. Synergetic products Fresh Water: The first by-product is fresh water. A small hybrid 1 MW OTEC is capable of producing some 4,500 cubic meters of fresh water per day, enough to supply a population of 20,000 with fresh water. OTEC-produced fresh water compares very favourably with standard desalination plants, in terms of both quality and production costs. Food: A further by-product is nutrient rich cold water from the deep ocean. The cold ―waste‖ water from the OTEC is utilised in two ways. Primarily the cold water is discharged into large contained ponds, near shore or on land, where the water can be used for multi-species mariculture producing harvest yields which far surpass naturally occurring cold water upwelling zones, just like agriculture on land. Cooling: The cold water is also available as chilled water for cooling greenhouses, such as the Seawater Greenhouse or for cold bed agriculture. The cold water can also be used for air conditioning systems or more importantly for refrigeration systems, most likely linked with creating cold storage facilities for preserving food. When the cold water has been used it is released to the deep ocean. 72

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Cold water applications PRINCIPLE UTILIZATION 1. Absorption of waves means generation of waves. A body oscillating in water will produce waves. A big body and a small body may produce equally large waves provided the smaller body oscillates with larger amplitude. This may be utilised for the purpose of wave energy conversion, for instance by a small floating body heaving in response to an incident wave, in particular so if it can be arranged that the body oscillates with a larger amplitude than the wave amplitude. 2. Optimum oscillation for maximum energy capture. In order to obtain maximum energy from the waves it is necessary to have optimum oscillation of the wave-energy converter (WEC). For a sinusoidal incident wave there is an optimum phase and an optimum amplitude for the oscillation. 3. Phase control by latching. In order to obtain the optimum oscillatory motion for maximising the absorbed energy or the converted useful energy it may be necessary to return some energy back into the sea during some small fractions of each oscillation cycle and profit from this during the remaining part of the cycle. For this reason ―optimum control‖ of WECs has also been termed ―reactive control‖. To achieve this in practice it is required to utilise a reversible energy-converting machinery with very low conversion losses. It could, for instance be a high-efficiency hydraulic machinery which can work either as a motor or as a pump.11 To realise the optimum control in practice, a computer with appropriate programme software, and with input signals from sensors measuring the wave1 and/or the WEC‘s oscillatory motion10, is required. It is also necessary to predict the wave some seconds into the future.

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SETTING OF OTEC PLANTS The Earth's oceans are continually heated by the sun, and cover nearly 70% of the earth‘s surface. The secret to harvesting the ocean‘s stored solar energy lies in exploiting the difference in temperature between the warmer water at the surface, and the colder water at greater depth. If the extraction could be made cost-effective, it could provide two to three times more energy than other ocean-energy options, such as wave power. But the small magnitude of the temperature difference makes energy extraction, so far, relatively difficult and expensive. How Does Ocean Thermal Energy Conversion Create Electrical Energy? Perhaps the easiest way to understand ocean thermal energy conversion (OTEC) is by looking at the three primary types of OTEC plant: (1) open-cycle, (2) closed-cycle, and (3) hybrid. All three plants make use of a ―heat engine‖ – a device placed between deep, cold ocean water and shallow, warmer water. As heat flows from the warm water to the cold water, the heat engine uses the energy of the transfer to drive a generator that creates electricity. Closed-cycle Ocean Thermal Energy Conversion Warm surface seawater is pumped through a heat exchanger that vaporizes a fluid with a low boiling point (e.g., ammonia). The expanding vapor turns a turbo-generator to produce electricity. Open-cycle Ocean Thermal Energy Conversion Warm seawater is placed in a low-pressure container, where it boils. The expanding steam drives a turbine attached to an electrical generator. When the ocean water turns to steam, it leaves behind its salt and other contaminants. The steam is then exposed to cold ocean water, condensing it into fresh water for drinking or irrigation. Hybrid Ocean Thermal Energy Conversion Warm seawater enters a vacuum chamber, where it is flash-evaporated into steam (similar to the open-cycle process). The heat of the steam vaporizes ammonia in a separate container, and the vaporized ammonia drives a turbine to produce electricity (similar to the closed-cycle process). Vaporizing the seawater removes its salt and other impurities. When the steam condenses in the heat exchanger, it emerges as fresh, pure water for drinking or agriculture.

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Where Are the Best Locations for OTC Plants? OTEC plants can produce more power where the temperature difference between warm and cold ocean water is greatest. This generally occurs within 20° north and south of the equator, in the tropics. What Is the Record Power Output From an OTEC Plant? In May 1993, an experimental open-cycle OTEC plant at Keahole Point, Hawaii produced 50,000 watts of electricity, breaking the record of 40,000 watts set by a Japanese system in 1982. Has Ocean Thermal Energy Conversion Been Tried in the Past? In 1881, French physicist Jacques Arsene d‘Arsonval proposed tapping the thermal energy of the ocean. A student of d‘Arsonval‘s, Georges Claude, built the first OTEC plant in Cuba in 1930. The system generated 22 kW of electricity using a low-pressure turbine. The Natural Energy Laboratory of Hawaii Authority, established in 1974, is one of the world's leading test facilities for OTEC technology. Hawaii is often said to be the best U.S. location for OTEC, because of warm surface water, excellent access to very deep, very cold water, and because Hawaii has the highest electricity costs in the U.S. Japan has been a major contributor to the development of OTEC technology, primarily for export to other countries. In the 1970s, the Tokyo Electric Power Company built a 100 kW closed-cycle OTEC plant on the island of Nauru. The plant became operational in 1981 and produced about 120 kW of electricity (90 kW was used to power the plant, and the remaining electricity was used to power a school and several other facilities in Nauru). This set a world record for power output from an OTEC system where the power was sent to a real power grid. What Share of the World’s Energy Needs Could OTEC Supply? Some experts believe that if OTEC became cost-competitive, it could provide gigawatts of electrical power, and in conjunction with electrolysis, could produce enough hydrogen to completely replace all projected global fossil fuel consumption. What Barriers Stand in the Way OTEC Power Production? Managing costs remains a huge challenge. OTEC plants require expensive, largediameter intake pipes, submerged at least a kilometer deep in the ocean to bring very cold water to the surface. Cold seawater is a requirement for all three types of OTEC 75

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systems. The cold seawater can be brought to the surface by direct pumping, or by desalinating the seawater near the sea floor, lowering its density and causing it to ―float‖ through a pipe to the surface. Has a Closed-cycle OTEC Plant Ever Been Built? In 1979, the Natural Energy Laboratory and several private-sector partners developed a mini OTEC experiment that achieved the first successful at-sea production of net electrical power from closed-cycle OTEC. (Net power is that which remains after subtracting the power required to run the plant.) The mini OTEC vessel was moored 1.5 miles off the Hawaiian coast and produced enough net electricity to illuminate the ship's light bulbs and run its computers and televisions. In 1999, the Natural Energy Laboratory tested a 250 kW pilot closed-cycle plant, the largest of its kind. Since then, no further tests of OTEC technology have been conducted in the U.S., largely because the costs of energy production today have delayed financing of a permanent, continuously operating plant. What OTEC Projects are on the Drawing Board? Planned OTEC projects include a small plant for the U.S. Navy base on the island of Diego Garcia in the Indian Ocean, to replace existing diesel generators. The plant would also provide 1,250 gallons of drinking water to the base per day. A private firm has proposed building a 10-MW OTEC plant on Guam. And Lockheed Martin‘s Alternative Energy Development team is in the final design phases of a 10-MW closed cycle OTEC pilot system that will become operational in Hawaii in 2012 or 2013. The system will be designed to expand to 100-MW commercial systems in the near future. Does OTEC Have Benefits Beyond Producing Power? Yes, indeed. For example, the cold seawater from an OTEC system can provide airconditioning for buildings. If such a system operated 8000 hours per year in a large building, and local electricity sold for 5¢-10¢ per kilowatt-hour, it could save $200,000$400,000 in annual energy bills (U.S. Department of Energy, 1989). The InterContinental Resort and Thalasso-Spa on Bora Bora now uses OTEC technology to air-condition its buildings. The system passes cold seawater through a heat exchanger, where it cools fresh water in a closed-loop system. The cool freshwater is then pumped to buildings for cooling (no conversion to electricity takes place). Another application is chilled-soil agriculture . When cold seawater flows through underground pipes, it chills the surrounding soil. The temperature difference between 76

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plant roots in the cool soil and plant leaves in the warm air allows many plants that evolved in temperate climates to be grown in the subtropics. Aquaculture, another viable OTEC offshoot, is considered one of the best ways to reduce the financial and energy costs of pumping large volumes of water from the deep ocean. Deep ocean water contains high concentrations of essential nutrients that are depleted in surface waters due to consumption by animal and plant life. This ―artificial upwelling‖ mimics natural upwellings responsible for fertilizing and supporting the largest marine ecosystems, and the largest densities of life on the planet. Cold-water delicacies such as salmon and lobster, and microalgae such as spirulina can also be cultivated in the nutrient-rich cold water from OTEC plants. As described earlier, open-cycle and hybrid OTEC plants produce desalinated wate. System analysis indicates that a 2-megawatt (net) plant could produce about 4300 cubic meters of desalinated water per day (Block and Lalenzuela 1985). OTEC plants can produce hydrogen via electrolysis, using electricity generated by the OTEC plant. Also, minerals can be extracted from seawater pumped by OTEC plants. Japanese researchers have recently found that developments in materials sciences and other technologies are improving the ability to extract minerals efficiently, using ocean energy. What Barriers Stand in the Way of Ocean Thermal Energy Conversion? The obstacles to OTEC as a viable power source are considerable, but probably not insurmountable. Political concerns include the legal status of OTEC facilities located in the open ocean. Costs, of course, also remain uncertain, because so few OTEC facilities have been deployed. One study estimated OTEC power generation costs as low as US $0.07 per kilowatt-hour, compared with $0.05 - $0.07 for subsidized wind systems. How Positive is the Outlook for OTEC Power Generation? Positive factors include the fact that OTEC is a renewable resource without waste products or limited fuel supplies; the vast area in which it is available (within 20° of the equator); freedom from dependence on petroleum; possible development of alternate ocean power sources, such as wave energy, tidal energy, and by extracting methane hydrates; and the possibility of combining OTEC with solar energy, aquaculture, air conditioning, and mineral extraction. Do Technical Difficulties Stand in the Way of OTEC? Unfortunately, yes. For example, OTEC plants often use direct contact heat exchangers, which generate gases that can degrade a plant‘s efficiency. Since the theoretical 77

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maximum efficiency of OTEC plants is 6% to 7%, and present plants operate at slightly lower efficiencies, anything that degrades performance must be considered significant. Other problems include microbial fouling, which lowers thermal conductivity; improper sealing; and parasitic power consumption by exhaust compressors. However, these obstacles are the focus of ongoing research, and seem likely to be solved in the near future. Thermodynamic Cycle

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TIDAL ENERGY AND WAVE ENERGY What is Wave and Tidal Energy? In addition to its abundant solar, wind and geothermal resources, the Pacific Northwest is also uniquely situated to capture the renewable energy of the ocean. Special buoys, turbines, and other technologies can capture the power of waves and tides and convert it into clean, pollution-free electricity. Like other renewable resources, both wave and tidal energy are variable in nature. Waves are produced by winds blowing across the surface of the ocean. However, because waves travel across the ocean, their arrival time at the wave power facility may be more predictable than wind. In contrast, tidal energy, which is driven by the gravitational pull of the moon and sun, is predictable centuries in advance. The technologies needed to generate electricity from wave and tidal energy are at a nascent stage, but the first commercial projects are currently under development, including some in the Pacific Northwest. Like most emerging energy technologies, wave and tidal technologies are currently more expensive than traditional generating resources, but with further experience in the field, adequate R&D funding, and proactive public policy support, the costs of wave and tidal technologies are expected to fol-low the same rapid decrease in price that wind energy has experienced. Potential Worldwide potential for wave and tidal power is enormous, however, local geography greatly influences the electricity generation potential of each technology. Wave energy resources are best between 30º and 60º latitude in both hemispheres, and the potential tends to be the greatest on western coasts. The United States receives 2,100 terawatt-hours of incident wave energy along its coastlines each year, and tapping just one quarter of this potential could produce as much energy as the entire U.S. hydropower system. Oregon and Washington have the strongest wave energy resource in the lower 48 states and could eventually generate several thousand megawatts of electricity using wave resources. 2 Several sites in Washington‘s Puget Sound with excellent tidal resources could be developed, potentially yielding several hundred megawatts of tidal power.3 While no commercial wave or tidal projects have yet been developed in the United States, several projects are planned for the near future, including projects in the Northwest. AquaEnergy Group, Ltd is currently designing and permitting a onemegawatt demonstration wave power plant at Makah Bay, Washington. Ocean Power Technologies has received a preliminary permit to explore construction of North America‘s first utility-scale wave energy facility off the coast of Reedsport, Oregon. With the support of the Oregon Department of Energy, Oregon State University is also seeking funding to build a national wave en-ergy research facility near Newport, Oregon. Several tidal power projects are also being explored in the region. Tacoma Power has secured a preliminary permit to explore a tidal power project at the Tacoma Narrows, one of the best locations for tidal power in the country, and Snohomish County Public 79

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Utility District has received preliminary permits for seven other potential tidal power sites in the Puget Sound.4 Wave Energy Technologies There are three main types of wave energy technologies. One type uses floats, buoys, or pitching devices to generate electricity using the rise and fall of ocean swells to drive hydraulic pumps. A second type uses oscillating water column (OWC)devices to generate electricity at the shore using the rise and fall of water within a cylindrical shaft. The rising water drives air out of the top of the shaft, powering an air-driven turbine. Third, a tapered channel, or overtoppingdevice can be located either on or offshore. They concentrate waves and drive them into an elevated reservoir, where power is then generated using hydropower turbines as the water is released. The vast majority of recently proposed wave energy projects would use offshore floats, buoys or pitching devices. The world‘s first commercial offshore wave energy facility will begin operating by the end of 2007 off the Atlantic coast of Portugal. The first phase of the project, which Scottish company, Ocean Power Delivery (OPD) developed, features three ‗Pelamis‘ wave energy conversion devices and generates a combined 2.25 MW of electricity. OPD plans to expand the facility to produce 22.5 MW in 2007.5 Tidal Power Technologies Until recently, the common model for tidal power facilities involved erecting a tidal dam, or barrage, with a sluice across a narrow bay or estuary. As the tide flows in or out, creating uneven water levels on either side of the barrage, the sluice is opened and water flows through low-head hydro turbines to generate electricity. For a tidal barrage to be feasible, the difference between high and low tides must be at least 16 feet. La Rance Station in France, the world‘s first and still largest tidal barrage, has a rated capacity of 260 MW and has operated since 1966. However, tidal barrages, have several environmental drawbacks, including changes to marine and shoreline ecosystems, most notably fish populations.6 Several other models for tidal facilities have emerged in recent years, including tidal lagoons, tidal fences, and underwater tidal turbines, but none are commercially operating. Perhaps the most promising is the underwater tidal turbine. Several tidal power companies have developed tidal turbines, which are similar in many ways to wind turbines. These turbines would be placed offshore or in estuaries in strong tidal currents where the tidal flow spins the turbines, which then generate electricity. Tidal turbines would be deployed in underwater ‗farms‘ in waters 60-120 feet deep with currents exceeding 5-6 mph. Because water is much denser than air, tidal turbines are smaller than wind turbines and can produce more electricity in a given area.7 A pilot-scale tidal turbine facility – the first in North America – was installed in New York‘s East River in December 2006. The developer, Verdant Power, hopes to eventually install a 10 MW tidal farm at the site.8

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Environmental Impacts Unlike fossil-fueled power plants, wave and tidal energy facilities generate electricity without producing any pollutant emissions or greenhouse gases. Since the first wave and tidal energy facilities are currently being deployed, the full environmental impacts of wave and tidal power remain uncertain but are projected to be small. Concerns include impacts on marine ecosystems and fisheries. Environmental impact studies are currently underway and several pilot and commercial projects are undergoing environmental monitoring. The East River tidal turbine pilot project includes a $1.5 million sonar system to monitor impacts on fish populations, for example.9 Careful siting should minimize impacts on marine ecosystems, fishing and other coastal economic activities. Wave and tidal facilities also have little or no visual impact, as they are either submerged or do not rise very far above the waterline. HYDRO POWER PLANT There are three types of hydropower facilities: impoundment, diversion, and pumped storage. Some hydropower plants use dams and some do not. The images below show both types of hydropower plants. Many dams were built for other purposes and hydropower was added later. In the United States, there are about 80,000 dams of which only 2,400 produce power. The other dams are for recreation, stock/farm ponds, flood control, water supply, and irrigation. Hydropower plants range in size from small systems for a home or village to large projects producing electricity for utilities. The sizes of hydropower plants are described below. IMPOUNDMENT The most common type of hydroelectric power plant is an impoundment facility. An impoundment facility, typically a large hydropower system, uses a dam to store river water in a reservoir. Water released from the reservoir flows through a turbine, spinning it, which in turn activates a generator to produce electricity. The water may be released either to meet changing electricity needs or to maintain a constant reservoir level.

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DIVERSION A diversion, sometimes called run-of-river, facility channels a portion of a river through a canal or penstock. It may not require the use of a dam.

PUMPED STORAGE When the demand for electricity is low, a pumped storage facility stores energy by pumping water from a lower reservoir to an upper reservoir. During periods of high electrical demand, the water is released back to the lower reservoir to generate electricity.

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SIZES OF HYDROELECTRIC POWER PLANTS Facilities range in size from large power plants that supply many consumers with electricity to small and micro plants that individuals operate for their own energy needs or to sell power to utilities. Large Hydropower Although definitions vary, DOE defines large hydropower as facilities that have a capacity of more than 30 megawatts. Small/Mini Hydropower Although definitions vary, DOE defines small hydropower as facilities that have a capacity of 100 kilowatts to 30 megawatts. Micro Hydropower A micro hydropower plant has a capacity of up to 100 kilowatts. A small or microhydroelectric power system can produce enough electricity for a home, farm, ranch, or village.

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MINI HYDEL POWER PLANT AND Their ECONOMICS Hydropower is using water to power machinery or make electricity. Water constantly moves through a vast global cycle, evaporating from lakes and oceans, forming clouds, precipitating as rain or snow, then flowing back down to the ocean. The energy of this water cycle, which is driven by the sun, can be tapped to produce electricity or for mechanical tasks like grinding grain. Hydropower uses a fuel—water—that is not reduced or used up in the process. Because the water cycle is an endless, constantly recharging system, hydropower is considered a renewable energy.

When flowing water is captured and turned into electricity, it is called hydroelectric power or hydropower. There are several types of hydroelectric facilities; they are all powered by the kinetic energy of flowing water as it moves downstream. Turbines and generators convert the energy into electricity, which is then fed into the electrical grid to be used in homes, businesses, and by industry.

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Mini hydel power station Mangrol is situated on Right Main canal of Chambal project near R.D. 106070.4 meter emanating from Kota Barrage. The plant have three units of capacity 2 MW each. The main supplier & erector of main generation equipment by M/s BHEL and Civil contractor of power house building is M/s RSBCEE Jaipur.

SALIENT FEATURES

S.NO.

Particulars

a. b. c. d.

Type of Power House Installed Capacity No. of Unit & Capacity Location of Power House

e. f. g. h. i. j. k.

9 Surface Power House. 6 MW 3 Units of 2 Mw each. Near R.D. 106070.4 meter on RMC of Kota Barrage.

Nearest Village MUNDLA, Tehsil Mangrol Distt. Baran. Nearest Railway Station Baran (25 Km.) Supplier & Main erector of M/S BHEL. Main generation equipment. Civil Contractor of PH M/S RSBCC Jaipur. Building Consultants CEA for Electrical works WNPCOS for Civil works. Design head 7.32 meter Design discharge of RMC At 4050 cusecs. PH site. 85

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No. of falls & height Max. Power potential Average Annual Power potential Max. tail water level

5 Nos total head 24.27 ft. 6.94 MW 4.31 MW

EL 241.12 meter. Propeller Axial Flow Horizontal type Kaplan turbine Type of Turbine and Name make :-BHEL. Type of Generator & make Synchronous Make- BHEL. GATES & TRASH RACK. Intake gate 3 Nos. of 4028.4x5049 mm each. Stop-log gate 1 Set of 4028.4 x13800 mm. Draft Tube gate 1 No. of 5278.4x 4167 mm. DISCHARGE CANAL NEAR POWER HOSUE: Full supply level EL 241.12 m. Bed Level EL 237.92m Section Bed width 26.70m, FSD 3.2m Velocity 3 ft/sec. Length 1800 m. CAPITAL COST a cost of power production 11.76 crore. Cost of transmission 5.78 crore. Total capital cost 17.54 crore. Installation cost per MW Rs. 29,233/TRANSMISSION LINE Ist Feedr Mangrol to ayana 33 KV 16 Km. IInd Feeder Mangrol to Baran 33 KV 25 Km. GENERATION SINCE COMMISSINING.

S.No. Financial year 1. 92-93 2 93-94 3. 94-95 4. 95-96 5. 96-97 6. 97-98 7. 98-99 8. 99-2000 9. 2000-2001 10. 2001-02 11. 2002-03 12. 2003-04 13. 2004-05 14. 2005-06 15. 2006-07 16. 2007-08

Generation in (LU) 31.749 62.388 98.767 116.100 110.747 78.221 78.323 19.242 23.963 56.266 NIL 34.8825 83.6985 59.199 80.5815 63.732 86

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17. 18. 19.

2008-09 2009-10 2010-11

39.135 22.05350 32.62350

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CHAPTER 8) DIRECT ENERGY CONVERSION Need for Direct Energy Conversion In direct energy conversion system energy source directly converted into electricity without and working fluid or steam. Direct conversion systems have no moving parts. Need: 1. No conversion of energy into mechanical and to electricity. 2. Less losses in conversion process. 3. More efficient process 4. Cost also reduced but technology required to improve it. CARNOT CYCLE If an engine is continually to convert thermal energy into mechanical energy, it must operate cyclically. At the end of each cycle it must return to its initial configuration, so it can repeat the process of conversion of heat into work over and over again. Steam engines and automobile engines are obviously cyclic -- after one (or sometimes two) revolutions, they return to their initial configuration. These engines are not 100% efficient. The condenser of a steam engine and the radiator and exhaust of an automobile engine eject a substantial amount of heat into the environment; this waste heat represents lost energy. Besides, there are frictional losses. Any device that converts heat into work by means of a cyclic process is called a heat engine. The engine absorbs heat from a heat reservoir at high temperature, converts this heat partially into work, and ejects the remainder as waste heat into a reservoir at low temperature. In this context, a heat reservoir is simply a body that remains at constant temperature, even when heat is removed from or added to it. In practice, the high-temperature heat reservoir is often a boiler whose temperature is kept constant by the controlled combustion of some fuel, and the low-temperature reservoir is usually a condenser in contact with a body of water or in contact with the atmosphere of the Earth, whose large volume permits it to absorb the waste heat without appreciable change of temperature. Figure 21.5 is a flow chart for the energy, showing the heat Q1 flowing into the engine from the high-temperature reservoir, the heat Q2 (waste heat) flowing out of the engine into the low-temperature reservoir, and the work generated. The work generated is the difference between Q1and Q2,

The efficiency of the engine is defined as the ratio of this work to the heat absorbed from the high-temperature reservoir,

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This says that if Q2 = 0 (no waste heat), then the efficiency would be e= 1, or 100%. If so, the engine would convert the high-temperature heat totally into work. As we will see later, this extreme efficiency is unattainable. Even under ideal conditions, the engine will produce some waste heat. It turns out that the efficiency of an ideal engine depends only on the temperatures of the heat reservoirs. CARNOT CYCLE Whether it is coal, oil, gas or nuclear power, 80% of the worlds electricity is derived from heat sources and almost all of the energy conversion processes used convert the thermal energy into electrical energy involve an intermediate step of converting the heat energy to mechanical energy in some form of heat engine. To satisfy this need a wide range of energy conversion systems has been developed to optimise the conversion process to the available heat source.

Despite over 250 years of development since James Watt's steam engine was first fired up, the best conversion efficiency achieved today is only around 60% for combined cycle steam and gas turbine systems. Efficiencies in the range of 35% to 45% are more common for steam turbines, 20% to 30% for piston engines and as low as 3% for OTEC ocean thermal power plants. This page describes some thermodynamic aspects of a variety of representative heat engines. More detailed descriptions of these engines can be found on other pages on this site via the links below. The efficiency of heat engines was first investigated by Carnot in the 1824 and expanded upon by Clapeyron who provided analytical tools in 1834 and Kelvin who stated the Second Law of Thermodynamics in 1851 and finally by Clausius who introduced the concept of entropy in 1865.

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The Carnot Cycle

Figure 1. An ideal gas-piston model of the Carnot cycle. The Carnot cycle consists of the following four processes: I. A reversible isothermal gas expansion process. In this process, the ideal gas in the system absorbs qin amount heat from a heat source at a high temperature Th, expands and does work on surroundings. II. A reversible adiabatic gas expansion process. In this process, the system is thermally insulated. The gas continues to expand and do work on surroundings, which causes the system to cool to a lower temperature, Tl. III. A reversible isothermal gas compression process. In this process, surroundings do work to the gas at Tl, and causes a loss of heat, qout. IV. A reversible adiabatic gas compression process. In this process, the system is thermally insulated. Surroundings continue to do work to the gas, which causes the temperature to rise back to Th.

Thermoelectric Generators

How Thermoelectric Power Generation Works The basic concept of thermoelectric Generators TEG‘s (Seebeck effect) is outlined below to explain to the Layman and also Engineers who are not familiar with the technology. We have been manufacturing TEG Power Generators for the last 10 years. A full 7090

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80% of the interest comes from persons whom have only minimal knowledge of the technology. Based on the requests for pricing and products available, interest in this field has exploded in the last three years. Thermoelectric modules work on two different principal : Peltier Effect: This effect introduce power to the module with a resultant cooling of one side and heating of the other these type of modules are low amp typically in the 6 amp range and are designed for low temperature exposure of NO MORE THAN 100°C to 110°C hot side. Higher temperature exposure will cause the module to either break apart or the soldered couples to melt from high heat making them poor choices for power generation! Seebeck Effect: This effect is created by temperature differential across the module from heating one side and cooling the other side by moving the heat flux away as fast as it moves through the module . You cannot describe a peltier module and say it produced power as many laymen do in the BLOGS. Please describe a Seebeck effect module as a power generator and a Peltier module as a cooling module. Thermoelectric Generators using the Seebeck Effect work on a temperature differentials. The greater the differential (DT) of the hot side less the cold side, the greater the amount of power (Watts) will be produced. Two critical factors dictate power output : The amount of heat flux that can successfully move through the module. The temperature of the hot side less the temperature of the cold side Delta Temperature (DT). Great effort must be placed on the heat input design and especially the heat removal design (Cold Side). The better the TEG Generator construction is at moving heat from the hot side to the cold side and dissipating that heat as it moves thru the module array to the cold side the more power will be generated. Unlike solar PV which use large surfaces to generate power. Thermoelectric Seebeck effect modules are designed for very high power densities, on the order of 50 times greater than Solar PV! Thermoelectric Seebeck Generators using liquid on the cold side perform significantly better then any other method of cooling and produce significantly more net additional power than the pump consumes. For any thermoelectric power generator (TEG), the voltage(V) generated by the TEG is directly proportional to the number of couples (N) and the temperature difference (Delta T) between the top and bottom sides of the TE generator and the Seebeck coefficients of the n and p- type materials.

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The standard material we work with is BiTe. The best efficiency that can be achieved with this material is approximately 6%. But once the material is placed into a constructed module the efficiency drops to 3 to 4% depending on DT because of thermal and electrical impedance! No other semiconductor material can perform as well as BiTe as far as efficiency is concerned at temperatures below 300°C. Other material like PbTe are used but are far less efficient at lower temperatures, and must be used at significantly higher temperatures in the 600°C hot side range and are commercially available but very expensive! The standard material we work with is BiTe. The best efficiency that can be achieved with this material is approximately 6%. But once the material is constructed into a module, efficiency drops to 3 to 4% because of thermal and electrical impedance. No other semiconductor material can perform as well as BiTe as far as efficiency is concerned. Other material such as PbTe are used but are far less efficient, and must be used at significantly higher temperatures (450°C600°C) hot side and are not commercially available! Power output based on (DT) is very predictable and well documented, but access to this information is difficult to find. With power generation the thinner the length or thickness of the module the greater the amp output or rating. You can have a 25 amp * module the same size typically 40 mm x 40 mm as a 3 amp module * in module size, but length or height of the pellet or element determines how much heat can pass thru the module. The ratio of the length compared the actual width x depth determines the overall amperage of the module. As the height of the pellet is shortened ability of heat flux to pass more quickly thru the module allows for greater power generation as long as DT can be maintained. That same 25 amp modules will produce over 8 times the amount of power as the 3 amp module. But 8 times the watts will need to pass thru that 25 amp module in order to produce that power. It is imperative that a DT be maintained. The module simply acts as a bridge. The larger the bridge area to length the greater the flow of heat and resulting power output. Our low temperature modules (TEG2) are high amp modules with contacts that are soldered using AgTn solder on both sides. Although, the temperature of the solder has a 240°C melting point the solder begins to degrade at about 190-200°C . Therefore we recommend the hot side stay below 190C to allow for small temperature variations. Our High Temperature Modules (TEG1) use flame spraying high temperature metal Aluminum on the hot side and can withstand much higher temperatures in the range of 300°C hot side and have considerably larger tolerances when it comes to incidental 92

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higher temperature over shouts. So much so that you can expose the hot side to 320°C intermittently with very little module degradation. This technique is much more expensive to implement and therefore the cost is reflected in the price of the modules. Temperature of the hot side is probably the most critical component when considering Thermoelectric Generators. (DT) Delta T needs to be in the 100°C range to get a viable power output from each modules.

Joule Thomson Effect Joule-Thomson effect, the change in temperature that accompanies expansion of a gas without production of work or transfer of heat. At ordinary temperatures and pressures, all real gases except hydrogen and helium cool upon such expansion; this phenomenon often is utilized in liquefying gases. The phenomenon was investigated in 1852 by the British physicists James Prescott Joule and William Thomson (Lord Kelvin). The cooling occurs because work must be done to overcome the long-range attraction between the gas molecules as they move farther apart. Hydrogen and helium will cool upon expansion only if their initial temperatures are very low because the long-range forces in these gases are unusually weak. The Joule–Thomson coefficient The change of temperature ( T ) with a decrease of pressure ( P ) at constant enthalpy ( H ) in a Joule–Thomson process is the Joule–Thomson coefficient denoted as μJT and may be expressed as: μJT≡(∂T∂P)H The value of μJT is typically expressed in K/Pa or °C/bar and depends on the specific gas, as well as the temperature and pressure of the gas before expansion. For all real gases, it will equal zero at some point called the inversion point and, as explained above, the Joule–Thomson inversion temperature is the temperature where the coefficient changes sign (i.e., where the coefficient equals zero). The Joule–Thomson inversion temperature depends on the pressure of the gas before expansion. In any gas expansion, the gas pressure decreases and thus the sign of ∂ P is always negative. With that in mind, the following table explains when the Joule–Thomson effect cools or heats a real gas:

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For some gases, the Joule–Thomson inversion temperatures at atmospheric pressure are very low: for helium, about 51 K (−222 °C), and for hydrogen, about 202 K (-71 °C). Thus, helium and hydrogen will warm during a J–T expansion at typical room temperatures. On the other hand, nitrogen has an inversion temperature of 621 K (348 °C) and oxygen has an inversion temperature of 764 K (491 °C). Hence, the two most abundant gases in atmospheric air can be cooled by a J–T expansion at typical room temperatures.[10] It should be noted that μJT is always equal to zero for ideal gases. In other words, they will neither heat nor cool during an expansion through an insulated throttling device.

Applications In practice, the Joule–Thomson effect is achieved by allowing the gas to expand through a throttling device (usually a valve) which must be very well insulated to prevent any heat transfer to or from the gas. External work must not be extracted from the gas during the expansion (meaning that the gas must not be expanded through a turboexpander). The effect is applied in the Linde cycle, a process used in the petrochemical industry for example, where the cooling effect is used to liquefy gases, and also in many cryogenic applications (e.g., for the production of liquid oxygen, nitrogen and argon). Only when the Joule–Thomson coefficient for the given gas at the given temperature is greater than zero can the gas be liquefied at that temperature by the Linde cycle. In other words, a gas must be below its inversion temperature to be liquefied by the Linde cycle. For this reason, a simple Linde cycle cannot normally be used to liquefy helium, hydrogen and neon. MHD (Magneto Hydro Dynamic) Generators: Magnetohydrodynamic power generation provides a way of generating electricity directly from a fast moving stream of ionised gases without the need for any moving mechanical parts - no turbines and no rotary generators. Several MHD projects were initiated in the 1960s but overcoming the technical challenges of making a practical system proved very expensive. Interest consequently waned in favour of nuclear power which since that time has seemed a more attractive option. MHD power generation has also been studied as a method for extracting electrical power from nuclear reactors and also from more conventional fuel combustion systems Working Principle The MHD generator can be considered to be a fluid dynamo. This is similar to a mechanical dynamo in which the motion of a metal conductor through a magnetic field

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creates a current in the conductor except that in the MHD generator the metal conductor is replaced by a conducting gas plasma. When a conductor moves through a magnetic field it creates an electrical field perpendicular to the magnetic field and the direction of movement of the conductor. This is the principle, discovered by Michael Faraday, behind the conventional rotary electricity generator. Dutch physicist Antoon Lorentz provided the mathematical theory to quantify its effects.

The flow (motion) of the conducting plasma through a magnetic field causes a voltage to be generated (and an associated current to flow) across the plasma , perpendicular to both the plasma flow and the magnetic field according to Fleming's Right Hand Rule Lorentz Law describing the effects of a charged particle moving in a constant magnetic field can be stated as F = QvB where F is the force acting on the charged particle Q is charge of particle v is velocity of particle B is magnetic field The MHD System The MHD generator needs a high temperature gas source, which could be the coolant from a nuclear reactor or more likely high temperature combustion gases generated by burning fossil fuels, including coal, in a combustion chamber. The diagram below shows possible system components.

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The expansion nozzle reduces the gas pressure and consequently increases the plasma speed (Bernoulli's Law) through the generator duct to increase the power output . Unfortunately, at the same time, the pressure drop causes the plasma temperature to fall (Gay-Lussac's Law) which also increases the plasma resistance, so a compromise between Bernoulli and Gay-Lussac must be found. The exhaust heat from the working fluid is used to drive a compressor to increase the fuel combustion rate but much of the heat will be wasted unless it can be used in another process. 

The Plasma The prime system requirement is creating and managing the conducting gas plasma since the system depends on the plasma having a high electrical conductivity. Suitable working fluids are gases derived from combustion, noble gases, and alkali metal vapours.

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The Gas Plasma To achieve high conductivity, the gas must be ionised, detaching the electrons from the atoms or molecules leaving positively charged ions of the gas. The plasma flows through the magnetic field at high speed, in some designs, more than the speed of sound, the flow of the charged particles providing the necessary moving electrical conductor. Methods of Ionising the Gas Various methods for ionising the gas are available, all of which depend on imparting sufficient energy to the gas. It may be accomplished by heating or irradiating the gas with X rays or Gamma rays. It has also been proposed to use the coolant gases such as helium and carbon dioxide employed in some nuclear reactors as the plasma fuel for direct MHD electricity generation rather than extracting the heat energy of the gas through heat exchangers to raise steam to drive turbine generators. Seed materials such as Potassium carbonate or Cesium are often added in small amounts, typically about 1% of the total mass flow to increase the ionisation and improve the conductivity, particularly of combustion gas plasmas. Containment Since the plasma temperature is typically over 1000 °C, the duct containing the plasma must be constructed from non-conducting materials capable of withstanding these high temperatures. The electrodes must of course be conducting as well as heat resistant .

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Note that 90% conductivity can be achieved with a fairly low degree of ionisation of only about 1%. (Note also logarithmic scale)

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The Faraday Current A powerful electromagnet provides the magnetic field through which the plasma flows, and perpendicular to this field are installed the two electrodes on opposite sides of the plasma across which the electrical output voltage is generated. The current flowing across the plasma between these electrodes is called the Faraday current. This provides the main electrical output of the MHD generator.

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The Hall Effect Current The very high Faraday output current which flows across the plasma duct into the load itself reacts with the applied magnetic field creating a Hall Effect current 97

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perpendicular to the Faraday current, in other words, a current along the axis of the plasma, resulting in lost energy. The total current generated will be the vector sum of the transverse (Faraday) and axial (Hall effect) current components. Unless it can be captured in some way, the Hall effect current will constitute an energy loss . Various configurations of electrodes have been devised to capture both the Faraday and Hall effect components of the current in order to improve the overall MHD conversion efficiency. One such method is to split the electrode pair into a series of segments physically side by side (parallel) but insulated from eachother, with the segmented electrode pairs connected in series to achieve a higher voltage but with a lower current. Instead of the electrodes being directly opposite eachother, perpendicular to the plasma stream, they are skewed at a slight angle from perpendicular to be in line with the vector sum of the Faraday and Hall effect currents, as shown in the diagram below, thus allowing the maximum energy to be extracted from the plasma.

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Power Output The output power is proportional to the cross sectional area and the flow rate of the ionised plasma. The conductive substance is also cooled and slowed in this process. MHD generators typically reduce the temperature of the conductive substance from plasma temperatures to just over 1000 °C. An MHD generator produces a direct current output which needs an expensive high power inverter to convert the output into alternating current for connection to the grid.

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Efficiency Typical efficiencies of MHD generators are around 10 to 20 percent mainly due to the heat lost through the high temperature exhaust. This limits the MHD's potential applications as a stand alone device but they were originally designed to be used in combination with other energy converters in hybrid applications where the output gases (flames) are used as the energy source to raise 98

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steam in a steam turbine plant. Total plant efficiencies of 65% could be possible in such arrangements. 

Experience Demonstration plants with capacities of 50 MW or more have been built in several countries but MHD generators are expensive. Typical use could be in peak shaving applications but they are less efficient than combined-cycle gas turbines which means there are very few installations and MHD is currently not considered for mainstream commercial power generation. HALL EFFECT If an electric current flows through a conductor in a magnetic field, the magnetic field exerts a transverse force on the moving charge carriers which tends to push them to one side of the conductor. This is most evident in a thin flat conductor as illustrated. A buildup of charge at the sides of the conductors will balance this magnetic influence, producing a measurable voltage between the two sides of the conductor. The presence of this measurable transverse voltage is called the Hall effect after E. H. Hall who discovered it in 1879. Note that the direction of the current I in the diagram is that of conventional current, so that the motion of electrons is in the opposite direction. That further confuses all the "right-hand rule" manipulations you have to go through to get the direction of the forces.

The Hall voltage is given by

Show

The Hall effect can be used to measure magnetic fields with a Hall probe.

Faraday’s Law

Faraday's 1st Law of Electrolysis - The mass of a substance altered at an electrode during electrolysis is directly proportional to the quantity of electricity transferred at that electrode. Quantity of electricity refers to the quantity of electrical charge, typically measured in coulomb.

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Faraday's 2nd Law of Electrolysis - For a given quantity of D.C electricity (electric charge), the mass of an elemental material altered at an electrode is directly proportional to the element's equivalent weight.

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FUEL CELL What is a fuel cell? A fuel cell is a device that generates electricity by a chemical reaction. Every fuel cell has two electrodes, one positive and one negative, called, respectively, the anode and cathode. The reactions that produce electricity take place at the electrodes. Every fuel cell also has an electrolyte, which carries electrically charged particles from one electrode to the other, and a catalyst, which speeds the reactions at the electrodes. Hydrogen is the basic fuel, but fuel cells also require oxygen. One great appeal of fuel cells is that they generate electricity with very little pollution–much of the hydrogen and oxygen used in generating electricity ultimately combine to form a harmless byproduct, namely water. One detail of terminology: a single fuel cell generates a tiny amount of direct current (DC) electricity. In practice, many fuel cells are usually assembled into a stack. Cell or stack, the principles are the same. How do fuel cells work? The purpose of a fuel cell is to produce an electrical current that can be directed outside the cell to do work, such as powering an electric motor or illuminating a light bulb or a city. Because of the way electricity behaves, this current returns to the fuel cell, completing an electrical circuit. (To learn more about electricity and electric power, visit "Throw The Switch" on the Smithsonian website Powering a Generation of Change.) The chemical reactions that produce this current are the key to how a fuel cell works. There are several kinds of fuel cells, and each operates a bit differently. But in general terms, hydrogen atoms enter a fuel cell at the anode where a chemical reaction strips them of their electrons. The hydrogen atoms are now "ionized," and carry a positive electrical charge. The negatively charged electrons provide the current through wires to do work. If alternating current (AC) is needed, the DC output of the fuel cell must be routed through a conversion device called an inverter.

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Graphic by Marc Marshall, Schatz Energy Research Center Oxygen enters the fuel cell at the cathode and, in some cell types (like the one illustrated above), it there combines with electrons returning from the electrical circuit and hydrogen ions that have traveled through the electrolyte from the anode. In other cell types the oxygen picks up electrons and then travels through the electrolyte to the anode, where it combines with hydrogen ions. The electrolyte plays a key role. It must permit only the appropriate ions to pass between the anode and cathode. If free electrons or other substances could travel through the electrolyte, they would disrupt the chemical reaction. Whether they combine at anode or cathode, together hydrogen and oxygen form water, which drains from the cell. As long as a fuel cell is supplied with hydrogen and oxygen, it will generate electricity. Even better, since fuel cells create electricity chemically, rather than by combustion, they are not subject to the thermodynamic laws that limit a conventional power plant (see "Carnot Limit" in the glossary). Therefore, fuel cells are more efficient in extracting energy from a fuel. Waste heat from some cells can also be harnessed, boosting system efficiency still further. So why can't I go out and buy a fuel cell? The basic workings of a fuel cell may not be difficult to illustrate. But building inexpensive, efficient, reliable fuel cells is a far more complicated business. Scientists and inventors have designed many different types and sizes of fuel cells in the search for greater efficiency, and the technical details of each kind vary. Many of the choices facing fuel cell developers are constrained by the choice of electrolyte. The design of electrodes, for example, and the materials used to make them depend on the 101

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electrolyte. Today, the main electrolyte types are alkali, molten carbonate, phosphoric acid, proton exchange membrane (PEM) and solid oxide. The first three are liquid electrolytes; the last two are solids. The type of fuel also depends on the electrolyte. Some cells need pure hydrogen, and therefore demand extra equipment such as a "reformer" to purify the fuel. Other cells can tolerate some impurities, but might need higher temperatures to run efficiently. Liquid electrolytes circulate in some cells, which requires pumps. The type of electrolyte also dictates a cell's operating temperature–"molten" carbonate cells run hot, just as the name implies. Each type of fuel cell has advantages and drawbacks compared to the others, and none is yet cheap and efficient enough to widely replace traditional ways of generating power, such coal-fired, hydroelectric, or even nuclear power plants. The following list describes the five main types of fuel cells. More detailed information can be found in those specific areas of this site.

Different types of fuel cells. Alkali fuel cells operate on compressed hydrogen and oxygen. They generally use a solution of potassium hydroxide (chemically, KOH) in water as their electrolyte. Efficiency is about 70 percent, and operating temperature is 150 to 200 degrees C, (about 300 to 400 degrees F). Cell output ranges from 300 watts (W) to 5 kilowatts (kW). Alkali cells were used in Apollo spacecraft to provide both electricity and drinking water. They require pure hydrogen fuel, however, and their platinum electrode catalysts are expensive. And like any container filled with liquid, they can leak.

Drawing of an alkali cell.

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Molten Carbonate fuel cells (MCFC) use high-temperature compounds of salt (like sodium or magnesium) carbonates (chemically, CO3) as the electrolyte. Efficiency ranges from 60 to 80 percent, and operating temperature is about 650 degrees C (1,200 degrees F). Units with output up to 2 megawatts (MW) have been constructed, and designs exist for units up to 100 MW. The high temperature limits damage from carbon monoxide "poisoning" of the cell and waste heat can be recycled to make additional electricity. Their nickel electrode-catalysts are inexpensive Drawing of a molten carbonate cell compared to the platinum used in other cells. But the high temperature also limits the materials and safe uses of MCFCs–they would probably be too hot for home use. Also, carbonate ions from the electrolyte are used up in the reactions, making it necessary to inject carbon dioxide to compensate. Phosphoric Acid fuel cells (PAFC) use phosphoric acid as the electrolyte. Efficiency ranges from 40 to 80 percent, and operating temperature is between 150 to 200 degrees C (about 300 to 400 degrees F). Existing phosphoric acid cells have outputs up to 200 kW, and 11 MW units have been tested. PAFCs tolerate a carbon monoxide concentration of about 1.5 percent, which broadens the choice of fuels they can use. If gasoline is used, the sulfur must be removed. Platinum electrode-catalysts are needed, and internal parts must be able to withstand the corrosive acid.

Drawing of how both phosphoric acid and PEM fuel cells operate.

Proton Exchange Membrane (PEM) fuel cells work with a polymer electrolyte in the form of a thin, permeable sheet. Efficiency is about 40 to 50 percent, and operating temperature is about 80 degrees C (about 175 degrees F). Cell outputs generally range from 50 to 250 kW. The solid, flexible electrolyte will not leak or crack, and these cells 103

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operate at a low enough temperature to make them suitable for homes and cars. But their fuels must be purified, and a platinum catalyst is used on both sides of the membrane, raising costs.

Drawing of a solid oxide cell

Solid Oxide fuel cells (SOFC) use a hard, ceramic compound of metal (like calcium or zirconium) oxides (chemically, O2) as electrolyte. Efficiency is about 60 percent, and operating temperatures are about 1,000 degrees C (about 1,800 degrees F). Cells output is up to 100 kW. At such high temperatures a reformer is not required to extract hydrogen from the fuel, and waste heat can be recycled to make additional electricity. However, the high temperature limits applications of SOFC units and they tend to be rather large. While solid electrolytes cannot leak, they can crack.

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