Non-conventional energy sources notes

1) Explain renewable energy, mention various forms of the same and elaborate on its potential in Indian Scenario. Ans. Renewable energy sources are sources that are continuously replenished by natural processes. For example, solar energy, wind energy, bio-energy - bio-fuels grown sustainably, hydropower etc., are some of the examples of renewable energy sources. A renewable energy system converts the energy found in sunlight, wind, falling-water, seawaves, geothermal heat, or biomass into a form, we can use such as heat or electricity. Most of the renewable energy comes either directly or indirectly from sun and wind and can never be exhausted, and therefore they are called renewable. Solar: India receives solar energy in the region of 5 to 7 kWh/m2 for 300 to 330 days in a year. This energy is sufficient to set up 20 MW solar power plant per square kilometre land area. Wind Energy : India has been rated as one of the most promising countries for wind power development, with an estimated potential of 20,000 MW. Biomass fuels account for about one-third of the total fuel used in the country. It is

the

most important fuel used in over 90% of the rural households and about 15% of the urban households. Using only local resources, namely cattle waste and other organic wastes, energy and manure are derived. Thus the biogas plants are the cheap sources of energy in rural areas Cogeneration : Cogeneration improves viability and profitability of sugar industries. Indian sugar mills are rapidly turning to bagasse, the leftover of cane after it is crushed and its juice extracted, to generate electricity. This is mainly being done to clean up the environment, cut down power costs and earn additional revenue. According to current estimates, about 3500 MW of power can be generated from bagasse in the existing 430 sugar mills in the country. Around 270 MW of power has already been commissioned and more is under construction.

2) What is the need of non conventional energy resource? Renewable energy sources also called non-conventional energy, are sources that are continuously replenished by natural processes. For example, solar energy, wind energy, bio-energy bio-fuels grown sustain ably), hydropower etc., are some of the examples of renewable energy sources A renewable energy system converts the energy found in sunlight, wind, falling-water, seawaves, geothermal heat, or biomass into a form, we can use such as heat or electricity. Most of the renewable energy comes either directly or indirectly from sun and wind and can never be exhausted, and therefore they are called renewable. However, most of the world's energy sources are derived from conventional sources-fossil fuels such as coal, oil, and natural gases. These fuels are often termed non-renewable energy sources. Although, the available quantity of these fuels are extremely large, they are nevertheless finite and so will in principle 'run out' at some time in the future Renewable energy sources are essentially flows of energy, whereas the fossil and nuclear fuels are, in essence, stocks of energy Various forms of renewable energy Solar energy Wind energy Bio energy Hydro energy Geothermal energy Wave and tidal energy

3) Define solar Radiation? Solar radiation refers to the electromagnetic radiation that reaches the Earth from the Sun. At an average distance of 150 million kilometres from the Sun, the outer atmosphere of Earth receives approximately 1367 W/m² of insolation (World Meteorological Organisation). This varies by around ±2% due to fluctuations in emissions from the Sun itself as well as by ±3.5% due to seasonal variations in distance and solar altitude.

4) Define Solar declination Solar declination is the angle between the sun’s rays and a plane passing through the equator. The solar declination depends only on the day of the year. The declination is also equal to the latitude at which the sun is directly overhead at solar noon on the given day. The declination is positive when the sun is directly overhead north of the equator (December 21 through June 21) and it is negative when the sun is directly overhead south of the equator (June 21 through December 21). The solar declination, δ, can be calculated from the equation: δ = (23.45o)sin[360 o (284 + n)/365] Where n is the day number in the year, with January 1 as 1. The solar declination has a maximum value of + 23.45 o on June 21 and a minimum value of – 23.45 o on December 21. Example: What is the value of the solar declination on February 15? Solution: The value of n for February 15 is 31 + 15 = 46 Equation (3), with the value 46 substituted for n becomes: δ = (23.45)sin[360(284 + 46)/365] = (23.45 o)sin[325.5 o] δ = -13.3 o 5) Define Solar Hour Angle( ω) The Solar Hour Angle is a measure of the position of the sun relative to solar noon at a given time at any given location on the earth. The hour angle, ω, is zero when the sun is directly overhead (local solar noon). It is negative before local solar noon and is positive in the afternoon. The hour angle changes by 15 o each hour, or one degree in 4 minutes. Solar time can be calculated from the following equation: Solar Time = local standard time + ET + (lst – llocal)(4 min/degree)

Where lst is the standard time meridian in the local time zone, llocal is the local meridian, and ET is the equation of time in minutes, given by the equation: ET = 9.87 sin(2B) – 7.53 cos(B) – 1.5 sin(B) Where B = 360(n – 81)/364 degrees

6) Define Solar Altitude Angle The Solar Altitude Angle is the angle between the sun’s rays and a horizontal plane. When the sun is just rising or setting, the altitude angle is zero. When the sun is directly overhead, the altitude angle is 90 o. The solar altitude angle, α, can be calculated for any location and and time from the latitude, Φ, solar declination, δ, and solar hour angle, ω, using the following equation: Solar Altitude Angle, Φ Sin Φ = sin L sin δ + cos L cos δ cos ω Example : Calculate the solar altitude angle, α , for solar noon on February 15, in St. Louis, MO (latitude: 38.75o N) Solution: From above Example , the solar declination, δ , on February 15, is – 13.3 o The hour angle, ω, is zero at solar noon, and the latitude is given in the problem statement as 38.75 o Sin Φ = sin(38.75 o) sin(-13.3 o) + cos(38.75 o) cos (-13.3 O) cos( 0 ) Calculating (with conversion of degrees to radians if needed) gives: Sin Φ = 0.615 Φ = sin-1(0.615) = 0.6624 radians =

37.9 o = Φ

Term

Definition

Solar Noon

Time when the sun is directly overhead position of interest. Each hour away from this position corresponds to a 15odeviation (hour angle).

Zenith Angle (θz)

The angle between the vertical and the line to the sun. This is also the angle of incidence on a horizontal surface for beam radiation. Additionally, the Solar Altitude angle is defined as the compliment of the zenith angle.

Solar Azimuth Angle (γs)

The deviation angle from due South for the projection of the sun's position on the horizontal plane (-180o for Each, +180o for West)

Diagram

Surface Azimuth Angle (γ)

The deviation angle from due South for the surface's normal vector projected onto the horizontal plane (180o for Each, +180o for West)

The angular position of the sun (at solar noon) with respect to the plane of the equator. The angle varies seasonally due to the Earth's tilt and Declination can be calculated for a given day Angle (δ) using: δ = 23.45 sin[ 360 (284 + n) / 365 ] where n is day of the year

Slope (β)

Angle between the collecting surface and the horizontal plane. In order to maximize the solar yield over the entire year, this angle should be set equal to the latitude. Steeper angles can be utilized to optimize for winter months. Likewise, shallow angles are used to optimize solar yield during the summer months.

Irradiance

The rate at which radiant energy is incident on a surface per unit area of surface (W/m2)

Irradiation

The incident energy per unit area on a surface (integration of irradiance over a specific time J/m2

Calculating the Position of the Sun and Angle of Incidence To calculate the sun’s position and the angle of incidence for a known surface at a given time and location. Initial Calculations and known values: Angle of Declination (δ) = 23.45 sin[ 360 (284 + n) / 365 ] Hour Angle (ω)= (Number of Hours from Solar Noon) x 15o Surface Azimuth (γ) = Orientation of surface measured from due South Slope (β): Slope of surface Latitude(Φ) of Location Using these variables the consine of the angle of incidence of beam radiation on the surface is: cosθ = sinδ sinΦ cosβ – sinδ cosΦ sinβ cosγ + cosδ cosΦ cosβ cosω + cosδ sinΦ sinβ cosγ cosω + cosδ sinβ sinγ sinω

The zenith angle (θz) can be found setting the slope (β) equal to zero in this equation. With the zenith angle found, the solar azimuth angle (γs) can be calculated as follows: γs = sign(ω) |cos-1 [ (cosθz sinΦ – sinδ) / (sin θz cosΦ) ]

7) write about Solar Radiation Measuring Instruments (Radiometers)? A radiometer absorbs solar radiation at its sensor, transforms it into heat and measures the resulting amount of heat to ascertain the level of solar radiation. Methods of measuring heat include taking out heat flux as a temperature change (using a water flow pyrheliometer, a silver-disk pyrheliometer or a bimetallic pyranograph) or as a thermoelectromotive force (using a thermoelectric pyrheliometer or a thermoelectric pyranometer). Direct normal Solar Irradiance – Pyrheliometers The direct normal component of the solar irradiance can be measured by an instrument called Normal

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Pyrheliometer: (1) protection cap, (2) window with heater, (3) sight, (5) sensor, (7) humidity indicator, (10) cable for heater

A pyrheliometer is an instrument used to measure the direct solar radiation at a given location. Since they need to be pointed directly at the sun, pyrheliometers are typically mounted on a tracking device that follows the sun’s movements. After sunlight enters the pyrheliometer, it is converted to an electrical voltage by a thermopile. This voltage can then be calibrated to give units of watts per square meter, the standard units of solar irradiance. Pyrheliometers are used for scientific research and for placing solar panels. Solar irradiance is a measure of the flux of solar radiation, or the solar energy per unit time, per unit area. It depends on the location of measurement—solar irradiance near the surface of the sun will be much larger than at the distance of Earth. In fact, there are variations in solar irradiance across the surface of Earth; these depend on the amount of atmosphere sunlight must penetrate, and, to a lesser extent, differences in distance from the sun. The average solar irradiance at Earth’s distance from the sun is about 1,366 watts per square meter.

8) Write about Pyranometers? Radiometers designed for measuring the irradiance on a plane surface, normally from solar radiation and lamps. The instruments are used in meteorological research, solar energy research, material testing, climate control in greenhouses, building physics, science and many other applications • To make a measurement of irradiance, it is required by definition that the response to “beam” radiation varies with the cosine of the angle of incidence, – so that there will be a full response when the solar radiation hits the sensor perpendicularly (normal to the surface, sun at zenith, 0 degrees angle of incidence) – zero response when the sun is at the horizon (90 degrees angle of incidence, 90 degrees zenith angle) – and 0.5 at 60 degrees angle of incidence. • Therefore, a pyranometer should have a so-called “directional response” or “cosine response” that is close to the ideal cosine characteristic. • In order to attain the proper directional and spectral characteristics, a pyranometer’s main components are: • A thermopile sensor with a black coating. This sensor absorbs all solar radiation, has a flat spectrum covering the 300 to 50,000 nm range, and has a near-perfect cosine response. • A glass dome: limits the spectral response from 300 to 2,800 nanometers (cutting off the part above 2,800 nm), while preserving the 180 degrees field of view. Another function of the dome is that it shields the thermopile sensor from convection. • The black coating on the thermopile sensor absorbs the solar radiation. This radiation is converted to heat. The heat flows through the sensor to the pyranometer housing. The

thermopile sensor generates a voltage output signal that is proportional to the solar radiation.

(1) sensor, (2, 3) glass domes, (5) cable, standard length 5 m, (9) desiccant. 9) Write about different types of solar energy Collectors?

1)Flat-plate collector Use both beam and diffuse solar radiation, do not require tracking of the sun, and are low-maintenance, inexpensive and mechanically simple.

Flat Plate Collectors Of the many solar collector concepts presently being developed, the relatively simple flat plate solar collector has found the widest application so far. Its characteristics are known, and compared with other collector types, it is the easiest and least expensive to fabricate, install, and maintain. Moreover, it is capable of using both the diffuse and the direct beam solar radiation. For residential and commercial use, flat plate collectors can produce heat at sufficiently high temperatures to heat swimming pools, domestic hot water, and buildings; they also can operate a cooling unit, particularly if the incident sunlight is increased by the use of a reflector. Flat plate collectors easily attain temperatures of 40 to 70ºC. With very careful engineering using special surfaces, reflectors to increase the incident radiation, and heat-resistant materials, higher operating temperatures are feasible. The main components of a flat plate solar collector: Absorber plate made of any material, which will rapidly absorb heat from sun's rays and quickly transfer that heat to the tubes or fins attached in some manner, which produces a good thermal bond. Tubes or fins for conducting or directing the heat transfer fluid from the inlet header or duct to the outlet. Glazing, this may be one or more sheets of glass or a diathermanous (radiation transmitting) plastic film or sheet.Thermal insulation, which minimizes downward heat loss from the plate. Cover strip, to hold the

other components in position and make it all Watertight.Container or Casing, which surrounds the foregoing components and keeps them free from dust, moisture, etc. Flat plate solar collectors are classified into Water-type (hydronic) collectors, using water as the heattransfer fluid. Air-type collectors, using air as the heat-transfer fluid.

10) Write about Parabolic trough collector?  Consist of parallel rows of mirrors (reflectors) curved in one dimension to focus the sun’s rays. All parabolic trough plants currently in commercial operation rely on synthetic oil as the fluid that transfers heat from collector pipes to heat exchangers

Linear Fresnel reflector

 Approximate the parabolic trough systems but by using long rows of flat or slightly curved mirrors to reflect the sun’s rays onto a downward-facing linear, fixed receiver.  Simple design of flexibly bent mirrors and fixed receivers requires lower investment costs and facilitates direct steam generation. Parabolic dish reflector  Concentrate the sun’s rays at a focal point propped above the centre of the dish. The entire apparatus tracks the sun, with the dish and receiver moving in tandem.  Most dishes have an independent engine/generator (such as a Stirling machine or a micro-turbine) at the focal point.

Heliostat field collector

 A heliostat is a device that includes a plane mirror which turns so as to keep reflecting sunlight toward a predetermined target.

 Heliostat field use hundreds or thousands of small reflectors to concentrate the sun’s rays on a central receiver placed atop a fixed tower.

11) Write about solar water heater? Solar water heating systems use the Solar Energy to heat the water from direct sunlight. These have earned worldwide appreciation because of their immense help in reducing the carbon footprints and to save energy. Water heating needs consume a lion’s share of the energy produced and SWHS aim at reducing this energy need. Solar water heaters are very beneficial to the user because: • Solar water heaters save electricity and thus money; electricity is becoming more and more expensive and its availability is becoming unreliable • Solar water heaters are non-polluting • Solar water heaters are safer than electric geysers as they are located on the roof • A Solar water heating of system off capacity 100LPD (litres per day) can save approximately 1500 units an year and hence can prevent the emission of 1.5 tonnes of CO2 each year. The success of solar water heaters in India can be demonstrated from the fact that more than 20,000 domestic systems are installed every year in the country. 3.1.2 Working: • A typical domestic solar water heater consists of a hot water storage tank and one or more flat plate collectors. • The collectors are glazed on the sun facing side to allow solar radiation to come in. • A black absorbing surface (absorber) inside the flat plate collectors absorbs solar radiation and transfers the energy to water flowing through it. • Heated water is collected in the tank which is insulated to prevent heat loss. • Circulation of water from the tank through the collectors and back to the tank continues automatically due to density difference between hot and cold water (thermo-siphon effect). The main parts of solar water heating system include a solar collector, an insulated tank, supporting stands, connecting pipes and instrumentation. The type and complexity of SWSH is determined by many factors and some of them have been broadly categorised as follows:

• The changes in ambient temperature during the day-night cycle. • Changes in ambient temperature and solar radiation between summer and winter. • The temperature of the water required from the system. • The amount of water required from the system per unit time The systems can be differentiated on the following basis: • The type of collector used • The location of the collector - roof mount, ground mount, wall mount • The location of the storage tank in relation to the collector • The method of heat transfer - openloop or closed-loop (via heat exchanger) • Photovoltaic thermal hybrid solar collectors can be designed to produce both hot water and electricity. Passive System: Passive solar technologies are means of using sunlight for useful energy without use of active mechanical or electrical systems. Conventional Heat Storage Units (CHS) implement passive solar water heating. These are often plate type or evacuated tube collectors with built-in insulated tanks. The unit uses convection (movement of hot water upward) to move the water from collector to tank. Neither pumps nor electricity are used to enforce circulation. A CHS is also known as a compact system or mono-block has a tank for the heated water and a solar collector mounted on the same chassis. Typically these systems will function by natural convection or heat pipes to transfer the heat energy from the collector to the tank. The main advantages of Passive Solar water heating systems are: • No mechanical or electrical parts are present • Very low maintenance • Lower cost • Longer life Active SWHS: Active solar hot water systems employ a pump to circulate water or HTF between the collector and the storage tank. Because the pump should only operate when the fluid in the collector is hotter than the water in the storage tank, a controller is required to turn the pump on and off.

Active systems can tolerate higher water temperatures than would be the case in an equivalent passive system. Consequently active systems are often more efficient than passive systems but are more complex, more expensive, more difficult to install and rely on either mains or PV sourced electricity to run the pump and controller. The use of an electronically controlled pump has several advantages: • The storage tank can be situated lower than the collectors. In passive systems the storage tank must be located above the collector so that the thermo siphon effect can transport water or HTF from collector to tank. • Because of the fact that active systems allow freedom in the location of the storage tank, the tank can be located where heat loss from the tank is reduced, e.g. inside the roof of a house. • New active solar water heating systems can make use of an existing warm water storage tanks ("geysers"), thus avoiding duplication of equipment • Reducing the risk of overheating. If no water from the solar hot water system is used (e.g. when water users are away), the water in the storage tank is likely to overheat. Several pump controllers avoid overheating by activating the pump during the day at during times of low sunlight, or at night. This pumps hot water or HTF from the storage tank through the collector (which can be cool in low light levels), thus cooling the water in the storage tank. • Reducing the risk of freezing. For direct active systems in cold weather, where freeze tolerant collectors or drain down approaches are not used, the pump controller can pump hot water from the water storage tank through the collector in order to prevent the water in the collector from freezing, thus avoiding damage to the metal parts of the system.

12) Write about Passive Solar Space Heating Systems Passive solar space heating – house acts as solar collector and storage facility •

Passive solar space heating – heat flows by natural means, no mechanical devices such as pumps or fans

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Sunlight collected through south-facing windows and the energy is stored in the thermal mass of the building (concrete, water, stone etc.)

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More solar energy transmitted through glass than is lost through the same windows over 24 hrs

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Sunlight is kept out during summer using roof overhangs (sun is higher in the sky)

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Essential elements of a passive solar system:

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Excellent insulation

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Solar collection (south-facing windows)

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Thermal storage

3 Types of passive systems •

Direct gain

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Indirect gain

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Attached solar greenhouse

Direct gain •

Large south-facing windows admit solar radiation

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Thermal mass exposed to direct radiation absorbs radiation

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Thermal mass radiates heat back into the room at night

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Indirect gain –

Collects and stores solar energy in one part of the house and uses natural heat transfer to distribute this heat to the rest of the house

e.g. Trombe wall

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Attached greenhouse – Greenhouse on south-side of house

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Acts as expanded thermal storage wall Windows must be insulated at night Concrete floors and used for energy storage

water

filled

drums

13) Write about Active Solar Space Heating Systems. Active system a. Flat plate or evacuated tube collectors (thermal storage) and mechanical means of delivering heat into the living space b. Working fluid may be water or air c. FPC usually roof-mounted, storage tank in the basement d. Auxillary heaters (electric) may be added for days with poor insolation e. May be vertical mounted (~60% less insolation than roof)