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A MAJOR PROJECT REPORT ON
Submitted in partial fulfillment of the award of degree of Master of Technology in Energy management. Submitted by Swati Bajpai Guided by Dr R C Chaudhary Reader
SCHOOL OF ENERGY & ENVIORNMENTAL STUDIES (FACULTY OF ENGINEERING SCIENCES) DEVI AHILAYA VISHWA VIDHALAYA, INDORE 452017 MAY-2012
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CERTIFICATE
The Project title “Design and Analysis of Solar Inverter”
Submitted by Swati Bajpai who has worked under my supervision and guidance, is approved for the submission for the partial fulfillment of the degree in Master of Technology in Energy Management
Date:
Guided by Dr R C Chaudhary Reader
SCHOOL OF ENERGY & ENVIRONMENTAL STUDIES (FACULTY OF ENGINEERING SCIENCES) DEVI AHILYA VISHWA VIDHYALAYAINDORE- 452 017 MAY-2012 2
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Table of Content: SL NO.
DESCRIPTION
PAGE.NO.
1 1.1 1.2 1.3 1.4 1.5 1.6
Solar Energy Solar Energy Facts Solar Energy for home Advantages of Solar Energy Why solar energy? Applications for solar energy Common Solar Equipments
2 2.1 2.2 2.3 2.4 2.5 2.6
How photovoltaic cells work Voltage-Current (V-I) Characteristic Types of Solar Panel Crystalline Silicon Thin Film Concentrators Thermophotovoltaics
3 4 4.1 4.2 4.3 4.4 4.5
How Solar System Works. Consumption Detail Per Month of Electricity Light Bulb Washing Machine Color TV Refrigerate Iron
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5 5.1 5.2
How an Inverter Works. PWM Inverters. Schematic Layout
6 7 8
Result Conclusion Refrences
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Solar Energy Solar electricity is the energy which is extracted by Sun using solar power plants. Sun is the richest source of energies like light and heat. Huge amount of energies are available for us to take and make big impact on our electricity requirements. Our sun throws as much amount of energy on earth in one day which is equivalent to the energy requirement for the entire year For better understating about what solar energy is and how it generated we need to know bit more about Sun which provide us with this amazing source of energy. Solar energy is radiant energy which is emitted by Sun. One interesting question which one may ask is how sun manages to provide such amount of radiant energy constantly, what does sun possess which in result produces such massive amount of energy ? It is obvious that all this energy comes from within the core of sun. This huge ball is full of gases like hydrogen and helium, hydrogen atoms however is present on larger scale. Energy is formed because of nuclear fusion reaction when hydrogen atoms combine to form helium; this entire process takes place in the core of the sun which is the hottest part. Extreme high pressures and temperatures are formed due to nuclear fusions reaction which in result hydrogen atoms to break apart and their nuclei to combine or fuse. One helium atom is formed when four nuclei of hydrogen are fused together; however helium atoms posses lesser mass then four hydrogen atoms. During the nuclear fusion reaction some of the matter is lost which is release into the space, this matter comes out into space as radiant energy. Sun surface is about 109 times bigger then surface of the earth. It takes millions of years for energy generated from the center of the sun to reach to the surface of the sun. Our mother earth is about 149.63 * 106 kilometers away from the sun, and light takes about 8 minutes and 31 seconds to reach to the surface of the earth. Light from the sun travels 186,262 milers per second to reach to earth. Energy emitted from the sun which reaches earth is in massive amount and can be extremely dangerous for mankind on earth if direct exposure is made. Earth posses layer of ozone which filters all harmful radiant energy and allows only that light and heat energy to the surface of earth which benefits living organisms. The energy which finally reaches earth is very low to the amount of energy filtered, yet this amount of energy is sufficient to provide enough electricity to the earth for entire year. Some portion of energy is reflected back 6
into space, little portion is used to evaporation process, some amount of energy is utilized by land, oceans and plants, still rest of the energy is up for us to take and produce solar electricity out of it. The Sun is made of atoms too. Mostly they are ionized, so we should think of the Sun as being made of nuclei and electrons. We can find out by analyzing sunlight, as we will see shortly. The result
About 75% (by mass) H.
About 25% (by mass) He.
A small amount of heavier elements.
The middle of the Sun is a very hot gas. It is ionized: all of the electrons have been ripped away from the nuclei because it is so hot. The nuclei available are mostly 1H, quite a lot of 4He, and a few 2H and 3He. (There are a few other types, but they are not so important for us.) What is happening in the middle of the Sun is analogous to burning methane: C H4 + 2 O2 --> C O2 + 2 H2 O In this reaction, the final molecules have less internal energy than the starting molecules. Since energy is conserved, the extra energy is released as energy of motion of the molecules. That is the gas gets hotter. The amount of energy involved is 5.5 eV each time the reaction above happens. As we have seen, much more energy than that must be involved in the reactions inside the Sun and other stars. The evidence is strong that the overall reaction is "burning" hydrogen to make helium: 4 1H + 2 e --> 4He + 2 neutrinos + 6 photons
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The high energy photons produced by the nuclear process don't get far. They are absorbed and heat the gas. The helium remains in the middle of the Sun. The neutrinos easily zip out of the Sun. (Neutrinos easily zip through most anything, reacting with matter only rarely.)
In this reaction, the final particles have less internal energy than the starting particles. Since energy is conserved, the extra energy is released as energy of motion of the nuclei and electrons in the solar gas, the production of lots of low energy photons and, finally, the energy of the neutrinos, which just zip right out of the Sun. That is the gas gets hotter and has lots of photons (and neutrinos). The amount of energy involved is 26 MeV = 26 x 10 6 eV each time the reaction above happens. Solar Energy is the energy received from the sun that sustains life on earth. For many decades solar energy has been considered as a huge source of energy and also an economical source of 8
energy because it is freely available. However, it is only now after years of research that technology has made it possible to harness solar energy.
Some of the modern Solar Energy systems consist of magnifying glasses along with pipes filled with fluid. These systems consist of frontal glass that focuses the sun’s light onto the pipes. The fluid present in the pipes heats up instantly. In addition they pipes are painted black on the outside so as to absorb maximum amount of heat. The pipes have reflective silver surface on the back that reflects the sunlight back, thus heating the pipes further. This reflective silver surface also helps in protecting everything that is on the back of the solar panel. The heat thus produced can be used for heating up water in a tank, thus saving the large amount of gas or electricity required to heat the water.
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Solar Energy Facts Solar Energy is already being successfully used in residential and industrial settings for cooking, heating, cooling, lighting, space technology, and for communications among other uses. In fact, fossil fuels are also one form of solar energy stored in organic matter. With fossil fuels making major impact on the environment and raising issues of pollution and global warming, solar energy has increased in its importance to industries and homes. While the reserves of fossil fuels are restricted, there is no limitation to the availability of solar energy. With improvement in solar energy technology and the increase in prices of fossil fuel, solar energy is gradually becoming more and more affordable. In addition, there is additional cost in the form of importation and transportation, required for oil, coal and gas. On a surface on the Earth’s orbit, normal to the sun, solar radiation hits at the rate of 1,366 Watt Per Meter Square. This is known as solar constant. While 19% of this energy gets absorbed in the atmosphere, 35% gets reflected by clouds. So, the solar energy that reaches sea level is much reduced. In the last few years, the cost of manufacturing of photovoltaic cells has gone down by as much as 5% in a year and the percentage of government subsidies have gone up. This means that every year, it is becoming more and more affordable to use Solar Energy. In 2004, the global solar cell production increased by as much as 60%. The amount of energy released by a single Kilo Watt of solar energy unit is equivalent to burning as much as 76 Kg of coal that releases over 135 Kg of carbon dioxide. As per energy industry giant, Shell more than 50% of the global energy in 2040 is going to be in the form of renewable energy. Solar Energy for home In the last few years the number of photovoltaic installations on homes connected to utility grid has grown significantly. And, the demand for Solar Energy has grown due to policies in green pricing from utilities and government rebate programs. The demand has also grown due to the 10
interest of households to get electricity from renewable, non-polluting and clean source. However, most of the users are interest in solar energy, but they can pay only a limited premium for it. The returns on the initial high costs of installation are in the form selling solar energy to the grid at premium rates and also in the form of long-term savings that come in the form of not having to pay any utility bills. When you have a solar system that is connected to the utility grid, the regular generation of electricity is used at home and the excess electricity is exported to the utility. In this type of setup you would not require any batteries because any additional demand will be met from the grid supply. However, if you want to be free of the grid, battery storage will be required to supply power during nighttime and during cloudy or stormy conditions. Vacation homes or holiday homes that don’t have access to the grid can utilize Solar Energy in a more cost-effective manner as compared to relying on the grid for running wires to the remote location. People living in remote areas having sufficient sunlight can get reliable power in the form of solar energy. The basic components required in the solar power system consists of a solar panel, battery for storing all the energy gathered during daytime, a regulator and essential switches and wiring. These types of systems are commonly known as Solar Home Systems (SHS). Solar Energy Cost When you want to install Solar Energy system at home, you would require it to be sufficient for meeting all electricity requirements in home for a day plus it should generate enough power to store for 3 to 5 days for contingency purpose. Such a system would keep supplying power and getting charged when the days are sunny. During rain or winters it would be able to keep backup charge for a couple of days until the sun emerges. This means that such a solar power system is going to supply you a regular flow of electricity. Solar panels are one of the most important factors in the generation of Solar Energy. On an average, 1 Sq. Ft. of Solar Panel generates 10.6 Watts of power. And, the cost of 1 Sq. Ft. of Solar Panel is approximately Rs. 4,500. 10.6 Watt of power is sufficient to light a room. So, if
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you want to power appliances like television, refrigerator and computer, you would need more solar panels. You would have to consider solar grid-tie, and install 60 to 70 solar panels on the roof to meet the overall electricity requirement of your home. You must know that the cost of installing solar panels is not at all cheap.
Advantages of Solar Energy Solar Energy has more advantages than you can point out the disadvantages. When it comes to considering solar power as mainstay source of energy for home and industrial settings, it beats all other conventional sources of energy. Once the initial cost of installation is met, the electricity generated by solar panels is free of cost. In a stand-alone solar power system you don’t have to pay any utility bills. Another positive in installing solar power systems is that government offers lots of rebates and incentives to cover the initial cost. You can also sell the additional electricity generated by your system. Sometimes the utility company will give you credits for selling the excess amount of electricity. Another good thing about solar power is that the cost of the technology is decreasing almost every few months and the efficiency is improving significantly. Today, you can find different types of solar solutions that are more convenient to install. Solar Energy is a renewable and clean source of energy and you don’t have to pay any transmission cost. This is because the energy would be produced and consumed at the same place. Depending upon your budget, you can get all or a part of your electricity requirements fulfilled by solar energy. When batteries are used in the system to store electricity you can become entirely independent of the grid. This also means that you don’t have to get bothered by power failures in the grid, as you would be able to enjoy seamless supply of electricity. Before we delve into the discussion of why solar energy is so needed in the world today, we’ll first look into what solar energy really is. By definition, solar energy is that beaming light and heat that is generated from the sun. Solar energy has been used by human beings since time
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immemorial. Solar power is used in a widespread of the ever so progressing technologies of the world. The radiation that comes from solar energy along with the resultant solar energized resources such as wave power, wind, biomass and hydroelectricity all give an explanation for most of the accessible renewable energy that is present on earth. However, only an infinitesimal portion of the existing solar energy is used. So the question of why solar energy, that persists in the minds of many, is because solar energy can prove to have an immense amount of constructive and helpful impact on you and on the environment as a whole. Contrasting to the fossil fuels that we consume and use on a daily basis, solar energy does not fabricate the excessively injurious pollutants that are liable for the greenhouse effect which is known to lead to global warming. Solar power use reduces the quantity of contamination and toxic waste, not to forget pollution that the engendering plants have to produce. Global warming is an issue of great interest. In the recent times, with more awareness about the harmful effects of global warming, the issue is taken with great interest. There is in point of fact a massive belief that the use of fossil fuel is a contributing factor to the cause of global warming, which will ultimately result in the demise of the planet altogether. Probably the best part about why solar energy is that it is a renewable source of energy, which basically means that it will stay there forever, it will be consumed for all practical human usages. Oil, coal etc, is all bound to finish one day and eradicate from the face of the planet. So why not put them in the storage and use something more useful, is a basic question that many people have today.
Why solar energy? Because, it is ultra clean, natural and a sustainable source of energy that you can utilize in the use of making solar electricity, solar heating appliances, solar cooling appliances and also solar lighting appliances. Another key aspect of using solar energy is that it has massive financial benefits. They can generally be seen in the reduction of your utility bills. As you would be consuming solar power for the electricity that you use, the heating, the cooling and the lighting of your environment. Statistically, in the United States, Americans are known to be consuming 25% of the world’s oil 13
production on a daily basis. On the whole, the planet is being drained of its oil resources and the energy prices are only bound to go up. To only mend your own personal cost of energy needs is probably one of the smartest things to do and not to forget a very valuable future investment, when measured up to the unavoidable rise in the cost of energy in recent times as well as the not so far future. Solar energy systems are very much affordable, and with the help from the local, state and the federal programs that are now available to help in the installation costs, they seem to make much more sense than using other sources of generating energy apart from the solar energy. Conversely, if you take benefit of the law that was passed in 2005, which is mainly referred to as the law of the net metering, you can actually end up saving on the price of the batteries and use extra power back into the utility network, which if you ever have the need to use it, can do so easily. This in short means that the utility corporation actually turns into being your own personal storage facility, with absolutely no extra fund cost to your wallet. On the global front, creating the use of solar energy seems to be one of the best options available. The change in the climate world over is a serious threat to our planet which is causing much of the problems. The emission levels of carbon dioxide that we generate by the constant use of fossil fuel are literally killing our planet. The usage of solar energy will only provide us with a clean environment, a life where we will not have to constantly worry about the ever so reducing resources to provide us with the basic comforts of our life. With net metering, the ever so reasonably priced solar technology and the ultimate willingness to change this situation around, you can augment the energy competence of your home, and in due course accomplish net zero fossil fuel expenditure and utilization. You will also save the planet from dying out by using solar energy!
Applications for solar energy Solar power plants are relatively common than what we have witness in past decay. There are many reasons which we have been discussing through out on different section of website that it is important to adopt some kind of alternative source of power generation before we run out of current sources which produce electricity for us at present. The most obvious and realistic choice
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is solar energy. Solar energy is available in abundant amount on earth and shifting our electricity requirements on solar energy is most likely to be the option in coming future. Solar plants have already start providing electricity to us on different levels and scales. What we have all witness since our childhood is solar power calculator or wrist watch but now thankfully things have moved way on. Solar power gadgets or huge solar power arrays are seen producing massive amount of electricity for domestic and commercial areas. Solar power usage is not constant through out the world. Developed countries more obviously have larger solar power consumption than developing countries. For instance Abengoa Solar launched commercial solar plant in Seville Spain, it produces 20Megwatts of electricity. Solar Applications can be divided into three categories for understanding them better. Solar applications are available in sectors like Residential, Commercial, Industrial and Agriculture. Let’s discuss these sectors in detail and know what work has been done in given sectors.
Residential solar power There are numerous solar powered based devices available in market which are used in residential sector, products like solar power heater, geezer, outdoor garden lights, battery chargers etc. These days’ entire homes can be powered by solar energy. Appropriate solar cells type is used and joined together in modules. These modules of cells are mounted on the roof of the home for direct exposure to the sun light. This sun light is then converted into electricity using solar cells and then transfer into electric system of the house. If power requirement of house is higher then what solar power plant is producing then it can be used supplementary to reduce utility bills and incase if more power is produced than it is required, your electric plant grid station may use net metering and purchase the amount of electricity sent to grid station by your solar power plant. There are systems available which hold battery backups and store the access amount of energy. This energy can be used when conventional electricity is out.
Industrial Solar Power Solar energy applications : solar energy is been in use in industry and provides multiple industrial applications, especially when power is required in remote locations. Solar power can be useful in such industrial applications where small kilowatt energy is required. Some examples of remote location solar powered applications are TV Station, Radio broadcasting towers, 15
repeater stations, radio telephones etc.Solar power also facilitated electricity in transportation signaling system. In Japan, there are cities which are totally equipped with solar power traffic signal systems and does not require conventional electricity to operate. Other transportation system includes navigation systems, light houses in oceans, runway lights on airports, security camera in dark etc. Other industrial applications where solar power is used are environmental, situation equipment and protection systems for well heads, bridges pipelines etc. Such applications where electricity load is high, solar power can prove cost effective by configure hybrid electric power systems, that joints photovoltaic solar power system with small generators that operates on fuel or natural gas. Solar power is highly reliable and can work on locations where conventional electricity is not reachable. Space is one of the examples for it. Satellites are powered by solar power from the day first when first satellite was launched in Space Solar car is another most sophisticated application of solar energy. PV is installed on the surface of the car which converts sun light into electricity to power up a car. Such cars are not yet available for use in market, but they are bound to come for launch commercially very soon in future.
Commercial Solar Power Commercial building like offices, school, clinics, community halls, hospitals etc can also take advantage from solar energy electrification. In office buildings, glass/glass PV modules can provide cover over atria, which provide shaded light inside the building. PV systems can also be installed on vertical wall office building in several ways, Curtain wall system, rain screen over cladding etc.
Solar Energy Equipments for Home Solar energy is not only utilized by governments and industry to produce power but is of many uses to household. There is an array of solar equipments to be used in home. First of all, there are solar panels that are used to produce electric current. This electric current is conserved in a battery at the back. However for the conversion of electric current to the usable energy like alternate current an inverter is used. This inverter turns the direct current into alternate current to support the functioning of electrical appliances. Other solar equipments which can be used at home include solar pool heating systems, solar water heaters, solar ovens and solar cookers. Solar energy can be used directly and indirectly. Direct consumption of solar energy is possible 16
only if we conserve sunlight using solar equipments. However the indirect consumption includes the modules such as passive solar heating. The basic purpose of domestic solar equipments is that the end users can also benefit form this free sources of energy and conserve the electricity produced by using fossils. The design of solar equipments is really simple and small. Domestic solar equipments are adjusted according to the need of the home. For example the solar water heating system can be deployed in your back yard.
Common Solar Equipments Solar energy products are becoming common now. Moreover the development in this sector has taken it to toward some really different inventions like solar hand bags and solar caps. There is a long list of solar equipments ranging from the solar power systems to solar cookers and solar lights. Some important solar equipment include solar street lights, solar lantern, solar panels, solar lamps, solar energy collectors, solar portable kits, solar inverters, solar battery chargers, solar power generators, photovoltaic panels, solar batteries, solar cars, solar cells, solar jackets,solar water pumps, concentrated solar power plants and many more. The use of all these solar equipments doe not put much pressure on your pocket once they are installed.
Some Uses of Solar Equipments Solar panels are used to transform solar heat into electricity. Solar panels can be attached to the existing electricity grids for saving electricity or can be used alone. Solar cookers and ovens can save a lot of electricity used during cooking. The solar energy cookers cook food in the same way but the end product id relatively healthy. Solar street lights can conserve sunlight all day long and stay luminous in the night. Solar heating systems are a cost effective way of transforming water into steam. This useful steam is then used to support the industrial machinery. The use and production of solar equipments is increasing as the world is shifting to alternative and renewable energy sources. Make a simple solar cooker at your home by using cardboard and silver foil. Use it and find out how simple it is use solar appliances. These solar appliances can save a lot of energy for you. In order to make the use of solar equipments common it is important to guide the students about its benefits. This would shift our next generation automatically towards its use.
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How photovoltaic cells work Photovoltaic is the other name for Solar cells, photovoltaic cells are responsible for producing energy out of sun light it receives. Photovoltaic or solar cells are made of special materials which are semi-conductors. These semi-conductors produces electricity when sun light falls onto its surface. Solar electric cells are simple cells to use, they are do not require any thing but sun light to operate, they are long lasting , reliable and easy to maintain. Normally solar panels life time is twenty five years.
Voltage-Current (V-I) Characteristic Extracting the maximum amount of power from the solar panel is difficult due to the nonlinearity of the Voltage-Current (V-I) characteristic. Figure shows the V-I characteristic for Solar Panel
The blue line in Figure 2-1 is the actual V-I characteristic and the pink line corresponds to the power as a function of the voltage (P = I*V). As you can see, the voltage to current relationship is not linear, which makes it a little more difficult to determine the maximum power point. The maximum power point on a linear curve would occur at the midpoint of the V-I characteristic.
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However, in the case of a nonlinear relationship, the power needs to be determined by calculating the voltage to the current. To get the maximum power from the solar panel, the solar panel must always be operated at or very near the point where the power curve is at a maximum, its peak point. However, this operating point will constantly change due to the constantly changing ambient conditions. In fact, the temperature and other affects such as irradiance alter the V-I characteristic changing the operating point that would allow us to pull out the maximum amount of power. As a result, we need to constantly track the power curve and keep the solar panel operating at the point where the maximum amount of power would be achieved. Irradiance is a characteristic that deals with the amount of sun energy reaching the ground. The irradiance reaching the earth in ideal conditions is 1000W/m2. However, this value is altered significantly depending on where you are located geographically, the angle of the sun, and the amount of haze or cloud cover preventing all of the suns energy from reaching the ground. Since solar panels run strictly off the energy emitted from the sun, their output is affected by the changing irradiance. The Figure 2-2 below demonstrates the affect irradiance has on the output of solar panels.
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How photovoltaic cells work, and what are there types. There are many types of solar cell technologies which are under development, but four of them are most commonly used, these technologies are crystalline silicon, thin films concentrators and thermo photovoltaic solar cell technologies. These cells are integrated to other solar power plant components to make electricity available. Let’s study these technologies in detail.
Crystalline Silicon: Crystalline silicon cells are quite widely used in most solar power plants. These types of cells contain two layers, positive layer and negative layer just like in most semiconductors. Positive layer exist on the top side whereas negative layer exists on button. Electric field is created with in these layers. Photons from sun light strikes on semiconductors in result electrons are released, electrons are electric charge. This electricity is transferred as direct current (DC) in panel. There are some cells available which are made from polycrystalline silicon, these type of cells are made of multiple but small in size silicon crystals, these kind of cells are relatively cheaper to be produced but there efficiency is compromised, where as single silicon crystal cells have better performance.
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Applications of silicon solar cell Ordinary silicon cells are smaller in size hence produce small amount of electricity. One silicon cell can be used for powering up calculator or wrist watch. To produce enough energy from these types of cell for lightening up entire home modules of silicon cells are require to be made in which these cells are connected together. These modules are building blocks for solar power. More and more modules are connected together for increasing solar electric power capacity. Arrays of modules are made for power generation in satellites. Thin Film Thin film solar cells are simple, durable lighter and easier to assemble when we compare it with silicon module solar cells. Amorphous is used to build best quality thin film cells. In these form of solar cells atoms arrangement is not in particular order. It is very efficient type of cell; it can convert over 90% of usable solar energy to electricity when it is exposed to light only by using amorphous silicon thin film cell which is only one micron thick. Thin film cells have advantage of being cost effective , they are required lesser amount semiconductor materials.
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Application of Thin Films These types of cells are not produced individually, but they are developed in modules and then joint together to frames and rest of the plant. Thin layers of semiconductors are used to manufacture thin films by using backing materials like plastic or glass. These backing materials are directly coated with anti-reflected materials and protective layers. Thin films are designed to match the shape of backing materials; this enabled these types of cells to be extremely flexible in
Concentrators One can easily understand the working of concentrator cells, they works just as optical lens do. Concept is very much same as in magnifying glass. In concentrator cells light is concentrated using lens to fall on solar cells to produce maximum energy as possible. By using concentrator cells lights intensity is increase by targeting on certain area, which in result increases electricity production. Most of concentrator cells produced these days are made up of crystalline silicon material. But there are materials like gallium arsenide and gallium indium phosphide have proven to be much more effective in performance when compare with silicon in solar cells, there are chances for these cells will increase in use in future.
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Application of Concentrator cells Concentrator cells are widely used in high tech industries like space and satellites etc, concentrator cells are reliable cells that’s why these cells used in such sensitive and expensive space operations. These cells produce way more energy even by using low quality and less expensive semiconductors materials comparing other solar electric cells. A normal concentrator cell is consist of lens which help focusing sun on perfect spot of cell, assembly of solar cell, device to waste of extra heat, wires for connectivity etc. These units are capable of combining with other units of different shapes and sizes to form bigger modules. Concentrator cells best works in direct sunlight, dry climates. Tracking devices must be used with these types of cells so that they can manage to keep their direction towards sun. Thermo Photovoltaic Thermo Photovoltaic cell uses different technology to produce electricity. Thermo- means heat, these cells converts heat into electricity; rest of it works as same as photovoltaic cells which converts light into electricity. The only difference between thermo-photovoltaic and photovoltaic is that thermo photovoltaic cells uses semiconductor which are designed for long wavelength, invisible light like infrared rays released by hot objects. This way of generating electricity is very neat and clean and also simpler to what we experience in power generation using generators, steam turbines etc. 23
Applications for Thermophotovoltaic Cells
These kinds of cells are very useful as they do not require much of maintenance works. They cannot only convent heat energy from sun into electricity but can also convert heat from any source into electric energy. Heat sources like fuel combustions, combustions of gasses etc. thermophotovoltaic cells like all other types of solar cells do not release any by product which can harm environment, that’s why they are clean sources of energy. Thermophotovoltaic cells can be used in furnaces in future to produce their own electricity, can also be useful in battery charging and power generators
How Solar Power Works There is hardly any one who has not heard about solar energy, and if one knows what solar energy is, it is certain to be known that sun has some thing to do with it. Well sun has almost every thing to do with; it is only sun who manages to provide 1000 watts per square meter. That is enormous amount of energy to take, if we have enough solar cells array to place on open land to capture energy.
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There is one most common example for solar product is calculator which we use in our homes and office. These calculators do not have batteries but operates on solar cells and usually it remains on and do not have off buttons, for them to keep on working only light is required. There are little advance examples for solar power applications available in fewer parts of the world, solar application like solar signals on highways, emergency road signs, emergency call boxes, parking lights and garden lights. Proper solar panels are getting common these days, these solar panels can take up the entire electricity load of home, although this is not yet that common but definitely on the way to be very useful and adoptable in coming future. That time is not that far when most of our homes will be using solar power home. How Solar System Works. To understand how solar power planels work and provide electricity I have broken down its working and processes in to steps for better understanding. These steps are mentioned with the in the order as it happens in given solar plant. Steps like Sun light, Earth surface, Photovoltaic Cells, Weather Station, DC switch, Inverter, Transformer, AC switch, Electric meter. 1. SUN LIGHT: Sun is the only source for light for earth, sun produces enormous amount of energy due to fusion reactions with in its core. Portions of energy are travelled to the surface of the earth; these portions of energy are called photons. Sun light passes through different layers before entering into atmosphere of earth, these layers have specific filtration process which filter harmful energy and light and prevent it to reach on earth. The energy which gets in the atmosphere is reflected and absorbed by earth, crops water, oceans etc and some of the energy is reflected back into space. Rest of the energy is available to take to produce energy from. 2. Earth Surface: Earth receives enormous amount of radiant energy from the sun, even after reflection of most of the energy during traveling from sun to earth. This energy available is still on huge scale to be converted into electricity using solar panels. Sun light is the most important part to complete life cycle of human beings and other living organisms including animals and plants. Combination of sun light, sea and atmosphere
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creates wind pressure which keeps weather systems of earth intact, these winds can also be utilized for producing electricity with help of wind machines. 3. Photovoltaic Cells: The most important component of solar panel which produces electricity is photovoltaic cells. The basic function of photovoltaic cells is to convert sun radiant energy into electricity. The word photovoltaic it self means light energy, photo means light and voltaic means energy. Each photovoltaic cell is packed into modules which are called arrays. These cells produce DC direct current when sun is shining directly over them, produced electricity is then send to building electric system or grid station for next step. 4. Inverter: Inverter is device which converts direct current (DC) into usable Alternative current (AC). Photovoltaic cells produce direct current which inverter converts into alternative current so that it can be consumed by building. Most of electric devices like computers, house lights, air conditioners etc require alternative current (AC) to operate. These are four steps which are must to be taken place for any solar panel to work. However there may be some additional steps which can be installed by different companies to enhance and improve the maintenance and overall performance or entire solar panels. These steps may include, electric meter, weather station device, DC switch disconnection module, Transformer, AC switch disconnection module, data acquisition module, electricity distribution panel module. Electric meter: These electric meters are used for the same purpose as our normal electric meters are used for. They keep the record of energy being consumed which is produced by solar panels. Normally electric energy is measured in watts or kilowatts. Most of solar panels come with electric meters especially when panels are designed to produce energy on large scale. Data acquisition module: Data acquisition module is important module which receives inputs from weather station module and electric meter. It is normally designed in such a way that it gathers important information to calculate weather conditions and output of solar panels. Weather Station module: Weather station is another useful add-on for solar panels. As name suggests it keeps the record of weather conditions. Weathers conditions are very crucial as far as 26
the performance or solar panels are concern, therefore keeping weather conditions as record is important. These modules are normally located near photovoltaic cells or arrays. Weather station normally have anemometer to keep the record for wind speed, pyranometer keeps record for solar energy falling on solar panel arrays and of course thermometer to measure temperature. All these
inputs
are
then
send
to
data
acquisition
module
for
further
processing.
Transformer: Transformer is an important component for any electric system; it makes sure that electricity coming from inverter is compatible with electric voltage of house, building office etc. DC switch disconnection module: This module helps professional solar panel electricians to disconnection solar panel from the rest of its system. When DC switch is off, electricians can do maintenance task on the rest of solar panel components. AC switch disconnect module: This module allows electricians to disconnect electric supply of house or building from photovoltaic system. With AC switch turned off maintenance of solar photovoltaic system can be performed. Electricity distribution panel module: This module is designed to receive energy from solar panels which is then combined with other electricity supply company. From here this energy is passed on electric wiring all over the building, house office etc to run electric appliances.
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Consumption Detail Per Month of Electricity For Average House (approx): For Selected Item:
For Washing Machine
1 Washing Machine 2. Amps rating. 3. Voltage Rating - Usually 230 Volts 4. Amps x Volts = Watts 5. Watts/1000 = kilowatts or kW 6. Hours used in month (use an average) 7. Kilowatts x Hours = Kilowatt Hours or kWh 8. Cost of electricity (in price per kWh) 9. kWh x PAISE = Cost (in paise) to run the Item for 1 month 10. Divide by 100 to get to Cost in Rs to run Item for 1 month 11. Number of the same Items in the house Total Amount
1 Amps 230 Volts 230 Watts .23 kW 20 Hours 4.6 KWh 450 Paise 2070 Paise 20.70 1 21
Rs
items Rs
For Light Bulb
1.Light Bulb 2. Amps rating. 3. Voltage Rating - Usually 230 Volts 4. Amps x Volts = Watts 5. Watts/1000 = kilowatts or kW
0.174 Amps 230 Volts 40 Watts .04 kW 28
6. Hours used in month (use an average) 7. Kilowatts x Hours = Kilowatt Hours or kWh 8. Cost of electricity (in price per kWh) 9. kWh x PAISE = Cost (in paise) to run the Item for 1 month 10. Divide by 100 to get to Cost in Rs to run Item for 1 month 11. Number of the same Items in the house Total Amount
180 7.2 450 3240 32.4 2 65
Hours KWh Paise Paise Rs items Rs
For Color TV
1. Colour TV 2. Amps rating. 3. Voltage Rating - Usually 230 Volts 4. Amps x Volts = Watts 5. Watts/1000 = kilowatts or kW 6. Hours used in month (use an average) 7. Kilowatts x Hours = Kilowatt Hours or kWh 8. Cost of electricity (in price per kWh) 9. kWh x PAISE = Cost (in paise) to run the Item for 1 month 10. Divide by 100 to get to Cost in Rs to run Item for 1 month 11. Number of the same Items in the house Total Amount 29
.87 Amps 230 Volts 200 Watts .2 kW 140 Hours 28 KWh 450 Paise 12600 Paise 126
Rs
1 126
items Rs
For Refrigerate
1. Refrigerate 2. Amps rating. 3. Voltage Rating - Usually 230 Volts 4. Amps x Volts = Watts 5. Watts/1000 = kilowatts or kW 6. Hours used in month (use an average) 7. Kilowatts x Hours = Kilowatt Hours or kWh 8. Cost of electricity (in price per kWh) 9. kWh x PAISE = Cost (in paise) to run the Item for 1 month 10. Divide by 100 to get to Cost in Rs to run Item for 1 month 11. Number of the same Items in the house Total Amount
30
2.174 Amps 230 Volts 500 Watts .5 kW 500 Hours 250 KWh 450 Paise 112500 Paise 1125
Rs
1 items 1125 Rs
For Iron
1. Iron 2. Amps rating. 3. Voltage Rating - Usually 230 Volts 4. Amps x Volts = Watts 5. Watts/1000 = kilowatts or kW 6. Hours used in month (use an average) 7. Kilowatts x Hours = Kilowatt Hours or kWh 8. Cost of electricity (in price per kWh) 9. kWh x PAISE = Cost (in paise) to run the Item for 1 month 10. Divide by 100 to get to Cost in Rs to run Item for 1 month 11. Number of the same Items in the house Total Amount
31
5.21 Amps 230 Volts 1200 Watts 1.2 kW 10 Hours 12 KWh 450 Paise 5400 Paise 5400 1 54
Rs items Rs
For Fan
1. Fan 2. Amps rating. 3. Voltage Rating - Usually 230 Volts 4. Amps x Volts = Watts 5. Watts/1000 = kilowatts or kW 6. Hours used in month (use an average) 7. Kilowatts x Hours = Kilowatt Hours or kWh 8. Cost of electricity (in price per kWh) 9. kWh x PAISE = Cost (in paise) to run the Item for 1 month 10. Divide by 100 to get to Cost in Rs to run Item for 1 month 11. Number of the same Items in the house Total Amount
.174 Amps 230 Volts 40 Watts .04 kW 300 Hours 12 KWh 450 Paise 5400 Paise 5400
Rs
2 items 108 Rs
Total Electric Consumption
SL No. Particulars
Amount (Elec. Bill For 1 Month) 32
1 2 3 4 5 6
Light Bulb Washing Machine Color TV Refrigerate Iron Fan TOTAL
65 21 126 1125 54 108 1499
Cost of Project: Sl No 1 2 3 4 5 6
Particular
Amount
Solar Panel (18v) Battery (12v) Transformer Relay Component Miscellaneous Total
1400 600 220 20 350 200 2790
33
How an Inverter Works So how can an inverter give us a high voltage alternating current from a low voltage direct current. Let's first consider how an alternator produces an alternating current. In its simplest form, an alternator would have a coil of wire with a rotating magnet close to it. As one pole of the magnet approaches the coil, a current will be produced in the coil. This current will grow to a maximum as the magnet passes close to the coil, dying down as the magnetic pole moves further away. However when the opposite pole of the magnet approaches the coil, the current induced in the coil will flow in opposite direction. As this process is repeated by the continual rotation of the magnet, an alternating current is produced.
Now lets consider what a transformer does. A transformer also causes an electric current to be induced in a coil, but this time, the changing magnetic field is produced by another coil having an alternating current flowing through it. Any coil with an electric current flowing through it will act like a magnet and produce a magnetic field. If the direction of the current changes then the Polarity of field changes. Now, the handy thing about a transformer is that, the voltage produced in the secondary coil is not necessarily the same as that applied to the primary coil. If the secondary coil is twice the size (has twice the number of turns) of the primary coil, the secondary voltage will be twice that of the voltage applied to the primary coil. We can effectively produce whatever voltage we want by 34
varying the size of coil.
If we connected a direct current from a battery to the primary coil it would not induce a current in the secondary as the magnetic field would not be changing. However, if we can make that direct current effectively change direction repeatedly, then we have a very basic inverter. This inverter would produce a square wave output as the current would be changing direction suddenly.
This type of inverter might have been used in early car radios that needed to take 12 volts available in the car and produce the higher voltages required to run radio valves (known as in America ) in the days before transistors were widely used in the tubes.
A more sophisticated inverter would use transistors to switch the current. The switching transistors are likely to be switching a small current which is then amplified by further transistor circuitry. This will still be a square wave inverter. 35
The Sine Wave Inverter To get a sinusoidal alternating current from the output of our transformer, we have to apply a sinusoidal current to the input. For this we need an oscillator An amplifying transistor can be made to oscillate by feeding some of the amplified output back to its input as positive feedback. We will all have heard this effect at sometime when someone is setting up a PA or microphone system. If the microphone is too close to the speaker, some of the output from the speaker is fed back to the microphone and inputted to the amplifier again. The positive feedback in an electronic circuit can be tuned using extra components to produce the frequency we require (generally either 50 or 60 cycles per second to mimic mains electricity). If a crystal is used to control this frequency, as in a battery watch or clock, the frequency can be very accurately controlled As with simpler switching transistor circuit, the oscillator will be producing a low current output. This will then need to be amplified by what will be roughly equivalent to a powerful audio amplifier to produce the high current for the primary coil of the transformer (the frequency of mains AC current is roughly equivalent to the lowest notes on a bass guitar).
36
The transformer, while being very useful, does not do something for nothing. While increasing the voltage, the current will be reduced, and the power (voltage x current) will stay the same (less any inefficiency of the transformer). In other words, to get 1Kw of high voltage AC current out, you have put 1Kw of low voltage AC current in.
Grid Tied Inverters If the above example were a grid tied inverter, ie able to feed power back into the national grid, it would need to use a sample of the mains voltage to then be amplified within the inverter, or to synchronize the oscillator with that sample. Grid tied inverters will also sense if there is a "power cut" and disconnect themselves from the grid. If they did not have this facility, in the event of a power cut, your inverter would be attempting to power all your neighbours houses and would present an electrocution risk to anyone working on power lines that had supposedly been turned off.
The Main Inverter Types 1. Square wave or modified sine wave. 2. Sine wave (sometimes described as "Pure Sine wave") 3. Grid-Tied
Square Wave or Modified Sine wave The square wave form will be as shown above right and the modified sine wave form will have had some attempt to round the corners off though will still have some sharp corners or spikes. Compare this to the Sine wave form below right.
37
Many AC appliances will work perfectly well a modified sine wave form wave. Some appliances such as computers, televisions, radios or music centres have in built power supplies that reduce the voltage, rectify it to produce a DC current, and smooth it to give a steady DCvoltage. This process will often smooth out any spikyness that was in the original AC supply. However, any inductive load (one where the power passes through a coil, as in a power supply transformer or a motor) causes the voltage and current to be out of phase (their appropriate graphs do not line up). Modified signwave inverters do not cope with this so well, causing the appliance to use more power than it would otherwise. This extra power consumption will cause the motor or transformer to run hotter than it would otherwise and may reduce it's life. It will also mean that the inverter will need a slightly higher power rating to power the same appliance. There is also the possibility that your television picture may not be as good as it should and anything with
a timer (eg bread
maker)
may not
run at the
correct
speed.
There may also be a noise problem. Any equipment that may give a quiet hum when connected to the mains supply, is likely to give a more annoying buzz. My own experience has shown this to be true with a ceiling fan, particularly when running on the lower speeds. These potential problems will need to be balanced against the price difference (modified sine wave converters will be significantly cheaper than pure sine wave) taking into account the appliances you expect to be using. 38
Grid-Tied A Grid-Tied inverter is capable of synchronising with an existing mains electricity supply (synchronising its sine wave output so that it is at the peak voltage point at the same time as the mains supply). This type of inverter can be used (where your electricity utility company allows it and with a modified meter if required) to enable you to push your spare electricity into the grid system. In some cases your normal electricity meter will simply run backwards when you are supplying power.
A grid tied inverter designed to be used without a battery (and therefore no charge controller), may have MPPT technolology built into it's input circuitry. String Inverters Inverter designed to accept high input voltages (upto 600 volts in commercial systems) may be called String Inverters, refering to the series connected panels, used to produce the higher voltages, being connect as a string. DC Input Voltage You may already have the rest of your system setup and you are already committed to using a particular voltage. You may however still be able to choose. The lower the input voltage you are using, the higher the current you will need to use. If you compare a 12 volt and a 24 volt inverter of the same power rating, the 12 volt item will need to draw twice the current. To carry that current, the cables from your battery to the inverter will need to be 4 times the size. A higher voltage system is likely to be more efficient although you will find that most inverters on the market are either 12 or 24 volts. A 48 volt inverter will be more difficult to find and may therefore be more expensive. AC Output Power
39
Any inverter will have a quoted output power which will be the maximum power level they can provide continuously, measured in watts or killowatts. Inverters will normally however cope with higher levels of power for a short period, enabling them to deal with a short power surge that many appliances will draw at turn on. Practically all electrical appliances will draw extra current for a split second at switch on, including low energy light bulbs. The power output characteristics will vary between different inverters but they may be able to produce 10% over the rated figure for 5 minutes, 50% over for 5 seconds, more for 1 second. Continuous output power capabilities of any inverter may be affected by the battery supplying the DC input voltage. The battery will need to be large enough to be able to supply the high current needed for a large inverter without the battery voltage dropping too low .Continuous output power capabilities may also be affected by the ambient temperature. An inverter that is producing high power will produce heat that is normally dissipated with the help of a fan. If you are experiencing high air temperatures, your inverter may not be able to cope with continuous high outputs without over heating and shutting down. Inverter Efficiency By efficiency, we are really saying, what percentage of the power that goes into the inverter comes out as usable AC current (nothing is ever 100% efficient, there will always be some losses in the system). This efficiency figure will vary according to how much power is being used at the time,
with
the
efficiency
generally
being
greater
when
more
power
is
used.
Efficiency may vary from something just over 50% when a trickle of power is being used, to something over 90% when the output is approaching the inverters rated output. An inverter will use some power from your batteries even when you are not drawing any AC power from A 3Kw inverter may typically draw around 20 watts from your batteries when no AC current is being used. It would then follow that if you are using 20 watts of AC power, the inverter will be drawing
40
watts
from
the
batteries
and
the
efficiency
will
only
be
50%.
A small 200W inverter may on the other hand only draw 25 watts from the battery to give an AC output of 20 watts, resulting in an efficiency of 80%. Larger inverters will generally have a facility that could be named a "Sleep Mode" to increase overall efficiency. This involves a sensor within the inverter sensing if AC power is required. If not, it will effectively switch the inverter off, continuing to sense if power is required. This can 40
usually be adjusted to ensure that simply switching a small light on is sufficient to "turn the inverter on". This does of course mean that appliances cannot be left in "stand-by" mode, and it may be found that some appliances with timers (eg washing machine) reach a point in their cycle where they do not draw enough power to keep the inverter "switched on", unless something else, eg a light, is on at the same time. Another important factor involves the wave form and inductive loads (ie an appliance where an electrical coil is involved, which will include anything with a motor). Any waveform that is not a true sine wave (ie is a square, or modified square wave) will be less efficient when powering inductive loads - the appliance may use 20% more power than it would if using a pure sine wave.
PWM Inverters. Now a days most of the inverters available in the market utilizes the PWM (Pulse Width Modulation) technology. The inverters based on PWM technology are superior in many factors compared to other inverters designed using conventional technologies. The PWM based inverters generally use MOSFETs in the output switching stage. In such cases the inverters are generally termed as PWM MOSFET inverters. The inverters based on PWM technology has a lot of protection and control circuits compared to the traditional inverters.
What is PWM technology PWM or Pulse width Modulation is used to keep the output voltage of the inverter at the rated voltage (110V AC / 220V AC) (depending on the country) irrespective of the output load. In a conventional inverter the output voltage changes according to the changes in the load. To nullify effect caused by the changing loads, the PWM inverter correct the output voltage according to the value of the load connected at the output. This is accomplished by changing the width of the switching frequency generated by the oscillator section. The AC voltage at the output depend on the width of the switching pulse. The process is achieved by feed backing a part of the inverter output to the PWM controller section (PWM controller IC).Based on this feedback voltage the PWM controller will make necessary corrections in the pulse width of the switching pulse 41
generated at oscillator section. This change in the pulse width of the switching pulse will cancel the changes in the output voltage and the inverter output will stay constant irrespective of the load variations. Oscillator circuit Oscillator circuit generates the switching frequency. Generally the oscillator circuit will be incorporated in the PWM IC itself.
Driver circuit Driver circuit drives the output section of the inverter according to the switching frequency. Transistors or Specially designed driver ICs are employed in the driver circuit.The driver circuit is some what similar to a preamplifier. Output section Output section drives the load. It consists of a step up transformer for stepping up the battery voltage to the line voltage and an array of switching MOSFET devices for driving the primary of the step up transformer. The output voltage will be available at the secondary of the step up transformer.
42
Schematic: First of all draw the schematic in DIP TRACE software
43
PCB LAYOUT
44
Inverter PCB Layout Positive:
45
Inverter PCB Layout Negative 46
Result 60 watt inverter 2. Amps rating. 3. Voltage Rating - Usually 230 Volts 4. Amps x Volts = Watts
0.26 Amps 230 Volts 60 Watts 47
5. Watts/1000 = kilowatts or kW 6. Hours used in month (use an average) 7. Kilowatts x Hours = Kilowatt Hours or kWh 8. Cost of electricity (in price per kWh) 9. kWh x PAISE = Cost (in paise) to run the Item for 1 month 10. Divide by 100 to get to Cost in Rs to run Item for 1 month
.06 kW 660Hours 39 KWh 450 Paise 17550 Paise
Total Amount save per month
175
175.5 Rs
Rs
Conclusions To complete this project in an effective manner a thorough understanding of solar technology and important aspects of it is essential. A variety of different applications were researched and determined whether or not they are even feasible at the current state of solar technology. The most feasible application for solar power is for remote locations requiring small quantities of power to run lighting, pumps, and other low power applications. That’s why we design a solar inverter of 60w to fulfill the above requirement. The sun has the ability to give off lots of energy however solar panels can only convert a small amount of solar energy to electrical energy due to inefficiency in solar panel technology. 48
References Aldous, Scott. “How Solar Cells Work.” How Stuff Works. Nov. 2, 2002. . Bogus, Klaus and Markvart, Tomas. Solar Electricity. Chichester, New York. Wiley Press, 1994. Distributed Power Solutions Home Page. 2003. Minneapolis, Minnesota. . Nation Center for Photovoltaics. “Turning Sunlight into Electricity.” 20 Oct. 2002. . National Solar Supply Home Page. 2003 http://www.nationalsolarsupply.com/page.asp?id=18 Neville, Richard C. Solar Energy Conversion. The Netherlands: Elsevier Science, 1995. Optima Batteries Home Page. 1996-2004. Johnson Controls Inc., 49
. Rincón-Mora, Gabriel and Zadeh, Hassan. “Current Sensing Techniques for DC-DC Converters.” 2002. . Sayigh, A.A.M., ed. Solar Energy Engineering. New York, USA: Academic Press, 1977. Ziemer, Rodger. Signals and Systems: Continuous and Discrete 4th Ed. New Jersey, USA: Prentice Hall, 1998.
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