Standalone solar PV system depends mainly upon solar energy. So it is need to design system in proper way, so that solar...
Seminar Report on “DESIGN ASPECT OF STANDALONE PV SYSTEM”
Presented By MALIK SAMEEULLAH (
[email protected])
Submitted to School of Renewable Energy and Efficiency National Institute of Technology
1
Introduction
Climate change is generally accepted as being the greatest environmental challenge facing our world today. Together with the need to ensure long-term security of energy supply, it imposes an obligation on all of us to consider ways of reducing our carbon footprint and sourcing more of our energy from renewable resources. In just one year the Earth‘s surface receives as much solar energy as two times the total reserves of the Earth‘s non-renewable resources of coal, oil, natural gas, and mined uranium combined. Only 15000 sq. km of total 200,000 sq. km of Thar desert on the Western part of India‘s State of Rajasthan, can produce from solar radiation, total electricity which would be more than equal to all the installed capacity of coal and other power plants in India. As India and other emerging economies develop, their per capita consumption and carbon emissions are expected to increase dramatically. This has raised serious concerns about their effects on global warming. Even during the global downturn in 2008-09, the Indian economy registered a GDP growth of 6.5%. Its greenhouse gas emissions have risen correspondingly. At present India is the third largest GHG emitting country; however, in per capita terms the contribution (1.8 tons) is much below the global average of 4.2 tons.
The Jawaharlal Nehru National Solar Mission (JNNSM) is one of the eight missions of India‘s National Action Plan on Climate Change (NAPCC) 3 that elucidates the nation‘s vision for solar technology: installation of 22GW of solar capacity by 2022 – this, by no means is a small task, given that India had a mere 10.28 MW of installed solar capacity in 2010. The objectives and goals of JNNSM are as follows: increase supply of grid–connected solar power to 1GW by 2013, 10 GW by 2017, and to 20 GW by 2022; promote off–grid applications equivalent to 2GW; distribute 20 million solar home lighting systems in rural areas; expand the area occupied by solar thermal collectors to 20 million square meters by 2022. Due to its geographical location, India has an enormous capacity of solar energy. Solar energy is utilized in different way like on grid solar PV plant, off grid solar PV system, solar thermal power plant and for heating purpose etc. 2
India is sitting on huge untapped solar Photo Voltaic off grid opportunities, given its ability to provide energy to untapped remote rural areas, the scope of providing backup power to cell towers and its inherent potential to replace precious fossil fuels. The off-grid opportunities are significant, given the cost involved in off-grid applications when compared to huge financial investments to be made to set up grids.
3
Chapter 1
1.1 Solar Resources The sun is the Earth‘s nearest star and the source of virtually all the Earth‘s energy, producing 3.8 × 1023 kW of power in huge nuclear fission reactions. Most of this power is lost in space, but the tiny fraction that does reach the Earth, 1.73 × 1016 kW, is thousands of times more than enough to provide all of humanity‘s energy needs. Energy can also be harvested from the sun directly for heating, drying, cooking, distilling, raising steam and generating electricity. Many types of equipment can be used to collect solar energy. These include flat plate solar thermal panels and evacuated tubes, which harvest solar energy for heating water, and solar concentrators that focus the rays of the sun into high energy beams to produce heat for electricity generation (known as concentrated solar power or CSP.
1.2 Converting Solar Energy 1. Solar energy to chemical energy: Green plants transform solar energy to chemical energy in sugar and cellulose by the process of photosynthesis (all biomass contains chemically stored solar energy). Unfortunately, we have not yet developed a way to directly transform solar energy into chemical energy. 2. Solar energy to heat energy: Solar heating devices transform solar energy into heat that is used for drying, water-heating, space-heating, cooking and distilling water. CSP plants convert water to steam that is used to generate electricity. Solar thermal energy is most easily used in applications that require relatively small amounts of heat. 3. Solar energy to electrical energy: Solar electric devices (solar PV cells) transform solar energy into electrical energy. This can be used to directly power electrical devices such as pumps and fans.
4
1.3 Solar Radiation Principles Sunshine reaches the earth as a type of energy called radiation. Radiation is composed of millions of high-energy particles called photons. Each unit of solar radiation, or photon, carries a fixed amount of energy. Depending on the amount of energy that it carries, solar radiation falls into different categories including infrared (i.e. heat), visible (radiation that we can see) and ultraviolet (very high energy radiation). The solar spectrum describes all of these groups of radiation energy that are constantly arriving from the sun, and categorizes them according to their wavelength. Different solar cells and solar energy collecting devices make use of different parts of the solar spectrum. Solar energy arrives at the edge of the Earth‘s atmosphere at a constant rate of about 1350 watts per square meter (W/m2): this is called the ‗solar constant‘. However, not all this energy reaches the Earth‘s surface. The atmosphere absorbs and reflects much of it, and by the time it reaches the Earth‘s surface, it is reduced to a maximum of about 1000W/m2. This means that when the sun is directly overhead on a sunny day, solar radiation is arriving at the rate of about 1000W/m2. Northern countries (i.e. Europe) have lower annual solar radiation levels than countries nearer the Equator – mainly because they have shorter days in winter. Solar Irradiance: Solar irradiance refers to actual radiation energy striking on per unit area. It is measure in KW per meter square. Value of irradiance depends upon the angle of incidence rays, geographical location and weather condition at that time.
Insolation: Insolation is a measure of energy received on a specified area over a specified period of time. For a particular location and month, Irradiance value 5
change continuously and its value is maximum at noon time. Due to this, insolation value is not a constant quantity. For designing a system, we calculate the average insolation of month. For the rating of Solar PV modules irradiance of 1000 W/ is used. For calculation purpose, Insolation is represent in PSH (Peak Sun Hour). A Site that receives a 5 PSH a day receives the same amount of energy that would have been received if sun had shone for 5 hours at 1000 W/ .
Insolation Measurement S.No Method Abbreviation Definition 1. kWH per sq m2 per kWh/ Quantity of solar energy, in day kilowatt-hours, falling on a square meter in a day. 2. Daily Peak sun hours PSH Number of hours per day during which solar irradiance averages 1000W/m2 at the site.
6
Chapter 2
2.1 Photovoltaic Cells Photovoltaic (PV) cells, or solar cells, take advantage of the photoelectric effect to produce electricity. PV cells are the building blocks of all PV systems because they are the devices that convert sunlight to electricity. Commonly known as solar cells, individual PV cells are electricity-producing devices made of semiconductor materials. PV cells come in many sizes and shapes, from smaller than a postage stamp to several inches across. They are often connected together to form PV modules that may be up to several feet long and a few feet wide. Energy bands in material, called semiconductor are separated from material and insulator as there conductivity falls between them. And since separation between energy bands varies from one semiconductor to other there conductivity varies over a large range by adding impurities and by optical excitation. For instance, energy gap for InAs is small, about 0.36 eV, while the energy gap for CdS is large about 2.42 eV. Photons in the sun‘s spectrum have energy in the range 0.3 eV to 4.5 eV, high enough to excite electrons in semiconductors to higher energy levels. This concept is used to generate electricity from PV cells. 2
nd
Zn Cd
Elemental Semiconductor used in solar photovoltaic Device 3rd 4th 5th B C Al Si P Ga Ge As In Sb
6th S Se Te
In order to collect the energy of a photon in the form of electrical energy through solar cells, the following series of actions should take place: (a) increase in the potential energy of carriers (generation of electron-hole pair) and (b) separation of carriers. On absorption of a photon, the difference in energy level results in an increase in potential energy of electrons and also keep the excited electrons in the higher energy level for a long period than its relaxation time to the ground state in valence band. This increases the probability of charge separation and extraction of work from the device. For separation of charge asymmetry in the semiconductor device is required. 7
Combination of a P-type semiconductor and N-type semiconductor or a P-N junction has such asymmetry which provides a built in electric field at the junction. When light shines on a solar cell, a large number of electron-hole pairs created. Due to asymmetry in the p-N junction, the generated electrons tend to flow from P-side to N-side and the generated holes tend to flow from N-side to P-side, resulting in the separation of the charge carriers which can flow in the external circuit delivering the work to the load.
2.2 Parameters of Solar cell: The current voltage relationship of a solar PV module can be given by following equation: )
)
Where is current generated due to light, is series resistance of PV modules, n is ideality factor, is reverse saturation current, T is temperature and k is boltzman constant.
The various parameter of solar PV module include short circuit current, open circuit voltage, Fill factor (FF), efficiency, peak power, series resistance and shunt resistance.
8
2.3 Solar PV modules A solar PV module can be considered as a big solar cell (array of several solar cell connected in series and parallel) with large voltage and current output than a single solar cell. The ways in which interconnection of solar cells is obtained in a thin film technology and in a wafer based technology are different. One solar cell produce 0.5-0.6 V voltage and current of range 4-5 A. For charging battery of 12 V, we need an input voltage around to 18 V. So 18 cells solar PV module is used. These day solar PV modules are available with the power rating ranging from 3W to 300 W.
Type of Solar PV modules 1. Monocrystalline Module: Monocrystalline, as the name suggests, is constructed using one single crystal, cut from ingots. This gives the solar panel a uniform appearance across the entire module. These large single crystals are exceedingly rare, and the process of 'recrystallising' the cell is more expensive to produce. 2. Polycrystalline silicon, or multicrystalline silicon, (poly-Si or mc-Si): it is made from cast square ingots — large blocks of molten silicon carefully cooled and solidified. Poly-Si cells are less expensive to produce than single crystal silicon cells, but are less efficient. 3. Thin film cell: Thin film modules use non-crystalline PV material that can be deposited in fine layers on various types of surfaces. Although they only accounted for about 10 per cent of all solar PV production in 2008, their portion of the market is growing rapidly. It is expected that thin film technology costs will drop much faster than that of crystalline silicon technology. 4. Organic cell: Organic solar cells are a relatively novel technology, yet hold the promise of a substantial price reduction (over thin-film silicon) and a faster return on investment. These cells can be processed from solution, hence the possibility of a simple roll-to-roll printing process, leading to inexpensive, large scale production.
9
2.4 Solar PV system A Photovoltaic system (informally, PV system) is an arrangement of components designed to supply usable electric power for a variety of purposes, using the Sun (or, less commonly, other light sources) as the power source. PV systems may be built in various configurations: 1. 2. 3. 4. 5.
Off-grid without battery (Array-direct) Off-grid with battery storage for DC-only appliances Off-grid with battery storage for AC & DC appliances Grid-tie without battery Grid-tie with battery storage
StandAlone (Off-grid) solar PV system Standalone PV system is best suited for a location where grid is not available. For low power application like houses, water pump and load of mobile tower, standalone PV system is used. Main difference as compare to on-grid solar PV is that in this system power cannot flow from PV system to grid. Off grid PV system used battery bank for storage of energy.
10
The major balance-of-system equipment are: 1. Batteries Batteries accumulate excess energy created by your PV system and store it to be used at night or when there is no other energy input. Batteries can discharge rapidly and yield more current that the charging source can produce by itself, so pumps or motors can be run intermittently. There are two types of batteries; i. Lead Acid Batteries ii. Nickel Cadmium Batteries 2. Charge controller A solar charge controller is needed in virtually all solar power systems that utilize batteries. The job of the solar charge controller is to regulate the power going from the solar panels to the batteries. Overcharging batteries will at the least significantly reduce battery life and at worst damage the batteries to the point that they are unusable.
3. Inverter The function of an inverter is to transform the low voltage DC of a lead acid battery into higher voltage AC which may be used to power standard ‗mains‘ appliances. An inverter is necessary where appropriate low voltage appliances are unavailable or expensive or in larger systems where it is necessary to distribute the power over a wide area.
11
Chapter 3
3.1 Designing of Off grid Solar PV system One of the main aim to install off-grid solar PV system is to provide electrical power to a system as per demand. And it is the only source of electrical energy as no grid is available. So, need to select the rating of different component of system in such a manner that it can be able to satisfy the demand of system. On the same time, we also take consideration of economic of system. Some of the basic Principles to Follow When Designing a Quality PV System 1.
2. 3. 4. 5. 6. 7. 8.
A packaged system should be selected that meets the owner's needs. Customer criteria for a system may include reduction in monthly electricity bill, environmental benefits, desire for backup power, initial budget constraints, etc. The PV array should be sized and oriented to provide the expected electrical power and energy. It should be ensured that the roof area or other installation site is capable of handling the desired system size. Sunlight and weather resistant materials for all outdoor equipment should be specified. Array should be located to minimize shading from foliage, vent pipes, and adjacent structures. System should be designed in compliance with all applicable building and electrical codes. The system should be designed with a minimum of electrical losses due to wiring, fuses, switches, and inverters. The battery system should be properly housed and managed, should batteries be required. It should be ensured that the design meets local utility interconnection requirements.
3.2 Step Wise PV system designing It consists mainly of 6 steps as follow: 1. Solar Energy Estimation 2. System Load Estimation 12
3. 4. 5. 6.
Inverter Selection Battery Bank size No. of Solar PV module Cost Estimation and optimization
Now discuss the procedure in detail: 1. Solar Energy estimation Insolation level at particular location play a crucial role in designing a system. At particular location, insolation level change over a year and no two locations have same insolation level. Various agency have a solar radiation data, which may be freely available or available by pay service charge. Agency like NASA, IMD, WRDC, RETscreen and metanorm provide radiation data. They use different technique to calculate radiation. So data from different agency may have slightly variation.
Insolation in kWh/m2/day 8 7 6 5 4 3 2 1 0 Jan
Feb
Mar
Apr
May
June
July Agust Sep
Oct
Nov
Dec
Insolation in kWh/m2/day
Figure show the insolation level of New Delhi. From the graph, we found that insolation is minimum in December. If solar PV system is able to satisfy the system load requirement in December month than only PV system is feasible. So in this case we choose December as a design month. Now for design purpose take insolaton 3.9 PSH (3.9kW , 1000 Kw/ for 3.9 hour).
13
2. Calculation of Load For designing, it is essential to know the type of load present and daily energy requirement. Based on daily energy requirement, solar PV system is designed. One has to determine the configuration of PV system and which components (PV panels, load, battery, controllers, diesel generator, etc.) are to be connected in a system. The configuration and design of the system will change depending on 1. The type of the load (AC or DC, light or heavy, etc.), 2. The load requirement (critical/non-critical, reliability, cost, etc.) 3. Its geographical location (wind resources, solar resources, proximity with grid, etc.). Solar PV system is not recommended for heat exchange application (electrical heater, refrigerator, and toaster). So for this type of load many other solar thermal system is available and more efficient.
Point to be noted for calculation of daily load 1. For best system designing daily load calculation is required. 2. Replace conventional lighting system with LED and CFL. 3. Use of energy efficient device is preferred when we switch to solar PV system. 4. Generally load estimation of design month is used to find system requirement. Sheet of Load estimation
Appliance Voltage in V Load (AC/DC) CFL(8*12) 240 V (AC) Fan (1*80) 240 V (AC) TV (1*120) 240 V (AC) PC (2*60) 240 V (AC) Charger 240 V (AC) Point Peak Load Total Daily DC energy demand Total Daily AC energy demand
Power (watts) 96 80 120 120 20
Daily Use (Hours) 9 15 7 6 3
Energy use Energy use (DC) Wh (AC) Wh 864 1200 840 720 60
436 W 0 3684 Wh
14
3. Inverter selection Inverter is used to convert DC into AC. Now energy stored in battery Bank is converted into AC, which is the ultimate requirement of houses. Generally input voltage of inverter is in between 12V to 72V DC and 1 to 30 Amp of current. Output of inverter in general 230 V, 50 HZ. Inverter rating is depend upon the peak load of system and by considering a load demand in future, we always try to make some margin between peak load and rating, as inverter is a costly device and not be replaced again. Generally it is considered that 15% is wasted in between inverter and load point. So we need more Wh as compare to what we calculated based on load. For the above case, actual energy required is calculated by taking ratio of energy use to system efficiency (3684/0.85=4334 Wh). 4. Battery Bank Size 4334 Wh of energy is required to be supplied by the battery and the terminal voltage of the battery bank should be 24 V. The parameters to be considered in sizing of batteries are: 1. Depth of discharge (DoD) of battery; 2. Voltage and ampere-hour (Ah) capacity of the battery; and 3. Number of days of backup. ‗Depth of discharge‘ (DoD) is use to express how much batteries are discharged in a cycle before they are charged again. For 100 Ah battery with DoD of 70% mean it provide energy of 70Ah and after that it need to charge again. Ah capacity of battery= Rating of Battery= Using this two formula, battery size is calculated and for the supply of above energy requirement of 4336 Wh, battery rating is 368 Ah. If backup is considered than rating of battery increase in proportion to no of day of backup. Now if consider for system of one day backup, then Ah rating is just double. So total Ah rating of battery is 737 Ah.
15
For battery of 100Ah, DoD 70% and 12 V Battery bank consists of 16 batteries with parallel combination of 2 series battery.
Battery Bank
5. No. of Solar PV module The parameters of concern for the PV module sizing are: 1. Voltage, current and wattage of the module; 2. Solar radiation at a given location and at given time; 3. Efficiency of the batteries; 4. Temperature of the module; 5. Efficiency of the MPPT and charge controller unit; and 6. Dust level in working environment. 7. Losses in battery and controller during charging are around 20%. Energy supplied by PV panel 5417 Wh
𝟏
𝑬𝒏𝒆𝒓𝒈𝒚 𝒔𝒖𝒑𝒑𝒍𝒊𝒆𝒅 𝒃𝒚 𝒃𝒂𝒕𝒕𝒆𝒓𝒚 𝒍𝒐𝒔𝒔𝒆𝒔 𝒊𝒏 𝒃𝒂𝒕𝒕𝒆𝒓𝒚 𝒂𝒏𝒅 𝒄𝒐𝒏𝒕𝒓𝒐𝒍𝒍𝒍𝒆𝒓 4334/0.8 Wh
𝑬𝒏𝒆𝒓𝒈𝒚 𝒔𝒖𝒑𝒑𝒍𝒊𝒆𝒅 𝒃𝒚 𝑷𝑽 𝑷𝒂𝒏𝒆𝒍 𝑺𝒚𝒔𝒕𝒆𝒎 𝑽𝒐𝒍𝒕𝒂𝒈𝒆 5417/24 Ah
Total Ah generated by Panel 226 Ah
𝑻𝒐𝒕𝒂𝒍 𝑨𝒉 𝒈𝒆𝒏𝒆𝒓𝒂𝒕𝒆𝒅 𝑷𝑺𝑯 𝑷𝒆𝒂𝒌 𝑺𝒖𝒏 𝑯𝒐𝒖𝒓) 226/3.9 Amp
Total Ampere to be produced 57.9 Amp
16
For PV module rating of 100 𝑊 , 12V No of Parallel module required 7 No.
𝑻𝒐𝒕𝒂𝒍 𝑨𝒎𝒑 𝒕𝒐 𝒃𝒆 𝑷𝒓𝒐𝒅𝒖𝒄𝒆𝒅 ∗ 𝟏𝟐 𝒓𝒂𝒕𝒆𝒅 𝑷𝒐𝒘𝒆𝒓 𝒐𝒇 𝑷𝒂𝒏𝒆𝒍 57.9*12/100
Total PV module required =2*7 =14 No. (System voltage is 24 V).
6. Cost estimation Now the system with detail of component size and rating is found out. Solar PV system cost is easily calculated and system size is adjusted further to make solar PV system economically viable for a particular case.
Solar Panel module
Battery Bank
2*7=14 No.
2*8=16 No. Charge controller
Rating
Rating
100 W, 12 V
100 Ah, DoD 70%
Inverter AC Load of 436 W
Rating 0.5 Kw, 24 V input and 240 V output, 50 Hz.
17
S.No
Particulars
Unit
1. 2. 3. 4.
Inverter Battery 100 Ah Solar PV module 100 W Charge Controller Total Cost Take 30% of total cost as Installation charge and protection device cost Total Amount
kW No. No. No.
5.
Rate (INR) 12000 2500 6000 5000
Table 2. Cost Estimation of Solar PV system
18
Qty.
Amount (Rs.)
0.5 kw 16 14 1 Total
6000.00 40000.00 84000.00 5000.00 135000.00 40500.00 175500.00
Conclusion Standalone solar PV system depends mainly upon solar energy. So it is need to design system in proper way, so that solar PV system is able to satisfy load demand. Each parameter considered carefully as its play a crucial role in system designing. In report basic concept of Solar PV system is discussed including principle of working and components detail. Step wise designing calculation help us to make solar PV system economically viable and efficient.
19
Reference 1. Mohamed H. Beshr, Hany A. Khater, Amr A. Andelraouf, ― Modelling of a Residential Solar Stand-Alone Power System‖, Proceedings of the 1st International Nuclear and Renewable Energy Conference (INREC10), Amman, Jordan, March 21-24, 2010 2. Marks Hankins, ―Stand-Alone Solar Electric System‖,Earthscan Expert Series 3. Chetan Singh Solanki, ―Solar Photovoltaics Fundamental, Technologies and Applications‖, PHI 4. Enda Flood, K. McDonnell, F. Murphy and G. Devlin, ―A Feasibilty Analysis of Photovoltaic Solar Power for Small Community in Ireland‖, The Open Renewable Energy Journel,2011, 4, 78-92. 5. ―Performance of Solar Power Plants in India‖, submitted to Central Electricity Regulatory Commission New Delhi in Feb 2011.
20
