Solar energy is the radiant energy produced by the Sun. It is both light and heat. It, along with secondary solar-powered resources such as wind and wave power, account for the majority of the renewable energy on Earth.
The Earth receives 174 petawatts(PW) of solar radiation at the upper atmosphere. 30% of that is reflected back to space and the rest is absorbed by clouds, oceans and land masses. Land surfaces, oceans, and atmosphere absorb solar radiation, which increases their temperature. Warm air containing evaporated water from the oceans rises, causing convection. When the air reaches a high altitude, where the temperature is low, water vapor condenses into clouds and causes rain. The latent heat of water condensation increases convection, producing wind.
Incoming Solar Energy
The total solar energy absorbed by Earth’s atmosphere, oceans and land masses is approximately 3,850,000 exajoules (EJ) per year. In 2002, this was more energy in one hour than the world used in one year. Photosynthesis captures approximately 3,000 EJ per year in biomass. The amount of solar energy reaching the surface of the planet is so vast that in one year it is about twice as much as will ever be obtained from all of the Earth’s non-renewable resources of coal, oil, natural gas, and mined uranium combined.
Energy absorbed by the oceans and land masses keeps the surface at an average temperature of 14°C. Green plants convert solar energy into chemical energy through photosynthesis. Our food supply is completely dependent on solar energy. After plants die, they decay in the Earth, so solar energy can be said to provide the biomass that has created the fossil fuels that we are dependent on.
Humans harness solar energy in many different ways: space heating and cooling, the production of potable water by distillation, disinfection, lighting, hot water, and cooking. The applications for solar energy are only limited by human ingenuity. Solar technologies are characterized as either passive or active depending on the way the energy is captured, converted, and distributed. Active solar techniques use photovoltaic panels and solar thermal collectors to harness the energy. Passive techniques include orienting a building to the Sun, selecting materials with thermal mass properties, and using materials with light dispersing properties.
Our current dependence on fossil fuels is slowly being replaced by alternative energies. Some are fuels that may eventually become useless, but solar energy will never be obsolete, controlled by foreign powers, or run out. Even when the Sun uses up its hydrogen, it will produce useable energy until it explodes. The challenge facing humans is to capture that energy instead of taking the easiest way out by using fossil fuels.
Sunlight is abundant and it is everywhere. More and more emphasis on the use of this abundant energy source has led to the maximum development in this field. The solar energy can be utilized through various means form building concentrating solar power systems, photovoltaic, solar heating systems , solar cars, solar batteries, solar satellite systems , solar updraft power houses and solar lighting systems. Concentrate solar power systems use mirrors and lenses to store light and heat carrying photons. Photovoltaic effect can be used by deploying solar cells. Solar lighting system can be used by designing the architecture to support day lighting procedure. Solar lighting reduces the load and dependence on electric lighting systems. Solar cars contain e solar panels installed on the roof top of the car. These solar panels convert the sunlight into electric charge and furthermore it can be stored into battery to be used later on. Solar updraft power plants are another addition in the application of the solar energy. These power houses are designed to support the heating of air through sunrays. This hot air rises to the tower and then it runs the turbines to support electricity generation. Solar power satellite is an expensive way to produce electricity form unhindered sunlight day and night.
Solar Power Systems
Depending upon your needs and where you live, there are a variety of solar power systems that could work for you.
- Solar Power System
Solar Power Systems – Grid-Tied (On Grid)
Most people install grid-tied solar power systems -most often in cities, suburbs and industrial areas where access to utility-generated power is available. You can supplement your solar powered electricity with utility-generated energy if you use more electricity than the solar power system supplies.
When your solar power system produces more electricity you need, you can sell the excess to the PG&E, who delivers the clean, renewable energy to other customers. Consequently, the good you do for the environment doesn’t stop at your home or office. Even neighbors without solar power can draw upon the renewable energy of the sun – while you bank credit to offset the utility-generated power you use at night.
- Grid Tied Solar Power System
Solar Power Systems – Grid-Tied with Battery Backup
Solar energy panels combined with batteries and generators for grid-tie applications couple the clean, power supplied by solar panels with the assurance that you will have electricity even during power outages that last for extended periods. During the day, the solar panels generate electricity as needed and charges batteries. If more power is required, or the batteries begin to run low, the natural gas or propane generator kicks in to recharge the batteries. It automatically shuts off when the batteries are fully charged.
- Grid Connected with Battery Bank
Solar Power Systems – Off-Grid
Standalone, or off-grid, solar power systems consist of solar panels and a battery bank. They are typically used in rural areas and regions where there is no access to the utility grid. They may also be appropriate where the grid is somewhat close to the site, but expensive to bring in – for example, across a neighbor’s property. We have installed a number of systems with battery back-up where the grid is available but where the homeowner has experienced unreliable power in the past or believes that he/she will be subject to power outages in the future. We have seen a number of property owners install battery back-up system just for philosophical reasons, for the desire to be independent of the grid and the “gaming” to which utility companies and their power suppliers have subjected customers in the past.
It may cost you as high as $50 per foot to bring utility power to your property, after which you’ll continue to pay for power forever. It’s often less expensive to add a solar energy system from the start and be your own power company. You can add the solar power system cost to your mortgage, reducing the combined costs of mortgage and utility bills.
When your off-grid solar power system produces excess electricity during the day, it is used to charge the batteries. When the sun’s not shining, electricity is drawn from the batteries to power the home or business. The advantage is greater independence for you. The disadvantage is greater complexity and cost.
Solar Power System – Direct DC
Simple, direct DC solar power systems produce energy where and when it’s needed. Common uses include powering water pumps and fans. There is no complex wiring, so storage and control systems aren’t required. Small systems are easy to transport and install.
- Solar Power Solutions (DC System)
Hybrid Power Systems
Hybrid power systems combine various sources of electrical generation, and are well suited for electrification. Solar and wind technologies are modular, and seasonal variations of sun and wind often complement each other.
When it comes to the future, solar energy is looking strong. People are now realizing that in the long term, Solar Energy provides a financially viable option. The upfronts costs might be high, but in the long term, everyone can save money by using Solar Energy.
Today, the declining cost and increasing efficiency of solar energy technology has given rise to practical applications on earth – from powering personal electronic devices, homes and factories to generating utility-scale power.
The first commercial use of photovoltaic cells nearly 50 years ago was powering communications satellites in near-earth orbit. Solar Energy provides a huge advantage for satellites because they can be launched into orbit without the added weight of a fuel supply.
Saving money is something that everyone is looking to achieve when it comes to solar energy. The great advantage of solar energy is that it utilizes a free energy resource; the sun. By utilizing the power of the sun, solar energy systems can create electricity. In fact, even if extra energy is produced, this can actually be sold to utility providers at a profit. Solar energy does not just save people money, but it can also make them money too.
A lot more people these days are focused on doing what is right for the environment. This includes things like producing energy. Power plants use a lot of non-renewable energy resources to provide our homes with power. Solar energy systems do not damage the environment in any way, so are good for the future of the planet.
One of the major advantages of solar energy is the lack of maintenance that is required in the long term. The systems do need slight maintenance every now and then, but in the long term, the costs are minimal. This means that once the initial investment has been made, there is little that a owner of a solar energy system really needs to do.
The cost of solar cells is decreasing and the efficacy of these cells is increasing. Moreover the process of generating electricity by using bio fuels is getting expensive and hard. The reason is that production of the essential bio fuels like coal oil and gas are limited to the few countries. This is the reason why most of the underdeveloped countries of the world are switching to the solar power plants. These power plants generate electricity at lower cost as compared to the bio fuels. These solar power plants can support the personal as well as industrial applications. Solar energy can support the launch of satellite into the orbit. This helps to lower the weight of satellite by replacing its fuel with solar heat. The solar energy power plants are really simple to install without indulging into the hassle of wires. Solar energy is free and it is everywhere, this attribute has given it an edge over the other types of energy applications.
Solar Energy is fast becoming the most popular way to power the home. There are literally hundreds of advantages, which most manufacturers will focus on. Not everything to do with solar energy is actually positive though. There are actually quite a lot of disadvantages when it comes to producing Solar Energy.
One of the main disadvantages when it comes to Solar Energy is the fact that the intial setup costs are extremely high. Buying a Solar Energy system can cost in the region of thousands. For a lot of people, this simple means that they are priced out of the market. For others, it means is takes years for them to start gaining based on their initial investment. Over time, this will change, as the cost of energy rises and the cost of materials to produce Solar Energy systems reduces.
Another thing to consider when using Solar Energy to produce electricity, is that the systems tend to take up a lot of space. In order to produce a lot of energy, sometimes a whole garden area or roof of a property will need to be used in order to get enough Solar Energy.
Of course, this also relies on the position and strength of the sun, which changes on a daily basis. This means that on days when the sun is blocked or not as strong, then the Solar Energy systems will not produce much in terms of energy. This is one of the major disadvantages of Solar Energy that a lot of people do not think of.
We have used the Sun for drying clothes and food for thousands of years, but only recently have we been able to use it for generating power.The Sun is 150 million kilometres away, and amazingly powerful.
Just the tiny fraction of the Sun’s energy that hits the Earth (around a hundredth of a millionth of a percent) is enough to meet all our power needs many times over.
In fact, every minute, enough energy arrives at the Earth to meet our demands for a whole year – if only we could harness it properly.
Solar Energy Basics
Solar is the Latin word for sun—a powerful source of energy that can be used to heat, cool, and light our homes and businesses. That’s because more energy from the sun falls on the earth in one hour than is used by everyone in the world in one year. A variety of technologies convert sunlight to usable energy for buildings. The most commonly used solar technologies for homes and businesses are solar water heating, passive solar design for space heating and cooling, and solar photovoltaics for electricity.
Businesses and industry also use these technologies to diversify their energy sources, improve efficiency, and save money. Solar photovoltaic and concentrating solar power technologies are also being used by developers and utilities to produce electricity on a massive scale to power cities and small towns.
The energy from the sun can be used to overcome the energy crisis generated by the scarcity of resources like oil and gas. Solar energy is free and it is everywhere. That is why now more and more countries have switched to processes which help them conserve the heat and light from sun.
Access of Sun to Earth
Sun is a part of solar system and it completes its rotation around the earth in 365 days. When the sunrays travel a long way from sky to earth they carry with them the heat and light of sun. Our earth is capable of absorbing this heat. 30% of the solar energy is sent back while the remaining 70% is consumed by the oceans, rivers, land and clouds. This solar energy is also responsible for rain. It is this energy which completes the water cycle for us. The water vapors accumulate in the air and when they are carried to some higher altitude, these vapors compress themselves to clouds and they shower rain. We receive 3, 85,000EJ energy every year which is sufficient to meet the energy requirement of solar projects. It is not the sun which is responsible for global warming it is the industry and businesses run by man who is responsible. The widespread devastation of forests for bio fuels has affected the mechanism of greenhouse effect hence there is now more heat in summer than which can be tolerated.
Uses & Applications of Solar Energy
The development and research in the field of alternative fuel generation has also given rise to improvement in the utilization of solar energy. The various applications of solar energy include solar power houses, solar vehicles, cooking, water purification, solar lighting and use of solar thermal energy. The most recent progress in the field of solar energy consumption is the introduction of the concept solar thermal energy. This is the way to harness solar rays to generate heat from them. This process is used to heat water using evacuated tube collectors and glazed flat plate collectors. Thermal solar energy is also used to disinfect water form the germs using sunrays. The heat from the sunrays eliminates the bacteria present in the tap water; this process is called water treatment. Solar energy is also used to cook food in solar cookers. These cookers are specifically designed to store heat of sun to utilize later on. Another amazing dimension of solar heating is the “Process Heat”. Parabolic dish antennas and scheffler reflectors facilitate this process and the heat stored in this way is used for industrial applications. This process is not only helpful in generating electricity but it also produces steam. Some other applications include solar ponds and solar power houses.
Electricity Generation from Sunlight
Electricity today has become essential for our survival. However with the passage of time the cost of production and consumption has also increased. This has forced mankind to look for the alternative ways to generate electric current. The heat from the sun is converted to electricity using Photovoltaic. The use of Photovoltaic was limited to very small applications like solar calculators. However now this mechanisms is used to generate electricity in very large power houses of up to 14MW. This is an economical way to produce electricity however every solar power house requires a strong backup support usually form wind power houses. However for the purpose of using Photovoltaic at home one can maintain a backup system by using batteries.
How Solar Power Works or How Solar Energy Works
The light and heat generated by sun can be conserved for diverse energy and power applications. Solar energy source of energy is under the phase of development and experimentation. Solar energy valuable energy is capable of providing heating, ventilation and fuel alternatives. Sun is an abundant energy resource and most of all it comes with the environment friendly package. Hence it is a common thought now that this energy source would lead towards its way to the end of this century.
Chemical Reaction in the Sun
The sun is the ruling star in of our solar system. This useful star provides us comfort, energy and growth. It is the presence of sunlight that we are able to grow plants and cultivate our barren land. Hydrogen consumed during nuclear fusion present in the sun generates radiant energy. This process helps the solar rays to reach earth in the form of very small energy packets called photons. These photons are absorbed by our oceans and land. When the sunrays reach to earth they interact with the oceans and rivers. The heats present in the sunlight facilitate the process of evaporation. It is in this process that water vapors, winds and cyclones are produced. If we implant aerodynamic wind mills in the way we can generate electricity from this process as well.
Solar Energy Working
If we store sunlight for constant 20 days we can replace a yearly reserve of coal, natural gas and oil. The energy present in the earth’s outer atmosphere is about 1300 Watts, which reduces to 1000Watts when it finally reaches the earth. The solar energy works only if we store it. Solar energy collectors are now implanted to store this energy. These are large flat black containers which are covered by glass. These solar energy collectors are placed ate the roof tops or in large barren land which is specifically allocated to solar energy consumption. The collector contains pipes which carry liquid in them. The liquid is a mixture of alcohol and water. This process either heats the water or air (the air is carried through the radiators to the building).the working of solar energy is also dependent upon how we utilize and transform it.
Conversion of Solar Energy
The solar energy is converted to chemical energy when plants use it to perform the process of photosynthesis. Hence solar energy works by utilizing its light and heat effectiveness. The solar energy is converted into thermal solar energy by directly converting the heat from the sun into thermal energy. When the power of the sunrays is converted into the electricity with the help of chemical reaction in the solar cells, it is an example of Photovoltaic conversion of energy. It is important to understand here that solar energy works naturally to facilitate the growth of plant and the working of our echo system. However now there are many artificial ways to make use of the solar energy. This solar energy works for us humans if we store it using different storage devices like the panels, solar cells and scheffler reflectors. Simple examples of solar cooker will explain how this solar energy works? Solar cooker is comprised of metal foil. This metal foil is capable of storing heat. When we place this solar cooker under sun for an entire day .it stores enough heat in it for the purpose of cooking food later in the evening. These solar cookers were invented to prevent immense deforestation in the rural areas. These cookers are an inexpensive and environment friendly way to cook food. The reason for environment friendliness is that these cookers do not generate harmful gases like carbon monoxide.
Why We Prefer Solar Energy, Reasons to Use Solar Energy
If we observe our environment which is the most abundant and free resource available to us, the answer is solar energy. Hence it is a natural alternative to fossil fuels like oil, gas and coal. The energy from the fossil fuels and water is used to generate electricity at large. The scarcity and wastage of these resources have made them expensive to use. Therefore solar energy is the low cost and safe alternative to the other fuels. There are many reasons to use solar energy like expensive fossils and bio fuels, global warming and development in solar energy utilization.
Expensive Bio Fuels
Solar energy is a renewable energy source which is relatively inexpensive. The reason for its being getting famous is its availability and abundance. While in the case of other bio fuels like oil and gas which are limited to the ownership of few countries this natural resource is free. These countries have monopoly over these resources and it is over their will that the prices of these biofuel like coal and oil fluctuate in the international market. Hence if we work on developing solar energy power plants we can save sufficient amount of tax imposed on importing oil and other biofuels. Development of power house using bio fuels is also an expensive project. All one need is to deploy solar grids. However the solar power project requires minimum initial investment. The deployment of solar grids is scaleable because the more you deploy solar grids the more you produce electricity.
Global Warming and Solar Energy
The use of fuels like oil and gas in homes, cars and industry has brought us to the problem of global warming. The extreme production of harmful gases like carbon monoxide has destroyed the ozone layer hence we receive both the harmful and harmless sunrays. The extreme pollution in our planet has disturbed the smooth working of our echo system. This has resulted in lower rainfalls and dries whether. The use of sun to support industrial processes can help us overcome the worst situation of global warming. It can also help us stop destroying our fertile land from the harmful waste resulting from industrial processes. The governments all over the world are supporting the solar power projects especially in the under developed countries. The south Asian countries like Pakistan, India and Bangladesh are planning major solar power projects to utilize the beneficial solar energy.
Development and Research in the field of Alternative Fuels
The research in the field of alternative fuels has helped scientist to discover renewable energy projects. One such solar project which was initiated in the red sea recently was the experiment of solar ponds. The red is rich in salt content. It is deep and contains heaps of salt. This presence of salt is utilized to store solar heat in it. The temperature in lower salt layers reaches to 90 degrees Celsius which is sufficient to process heat and water. Such developments and more in this field are economical this is another reason why we should switch to alternative energy sources. The solar energy is helpful in generating tax free electricity at home that is why now end users have deployed batteries which support solar electricity generation. Solar energy is of many uses like water treatments, cooking and ventilation. The awareness about using solar cookers in rural areas has also helped to decrease the cut down of trees for cooking purposes. The solar vehicles do not emit harmful gases like other vehicles. hence all in all the profusion and simplicity to use the solar energy has gave us innumerable reasons to use it as a renewable energy source alone or in combination with wind and geothermal energy sources.
Solar Energy History from 400 B.C. to the present day advances.Even when the supply of fossil fuels seemed endless, there were those who were interested in harnessing the power of the sun for energy. In 400 B.C. the Greeks were the first to implement the sun’s rays for heat. During this time they began to orient the placement of their houses to trap solar heat during winter.
SOLAR ENERGY HISTORY – 18th CENTURY
Even though the first solar collector was built by Swiss scientist Horace de Saussure in 1767, it would be another century before French inventor Auguste Mouchout would patent a design for a motor to run on solar energy. His devices turned solar energy into steam power.
SOLAR ENERGY HISTORY – 19th CENTURY
In 1878 the first book about solar energy, A Substitute for Fuel in Tropical Countries was written by William Adams. Using mirrors Adams was able to power a 2.5 horsepower steam engine. His design known as the Power Tower Concept is still in use today. The photovoltaic effect or the production of electricity directly form the sun was discovered by Frenchman Henry Becquerel in 1890. In 1891 American Clarence Kemp received a patent for the first solar water heater.
SOLAR ENERGY HISTORY – 20th CENTURY
The early 1900’s brings more knowledge and improvement to the quest for solar power. In 1904 Henry Willsie built two plants in California. Willsie was the first person to use solar power at night after generating it during the day. Still he was not able to make sales and his solar company folded.
The 1950’s brings more development in the solar energy sector. The first solar water heating system was placed in a commercial building as the primary source for interior heat. The first commercial solar cells was also made available to the public. Space programs made extensive use of solar power from the early 1960’s to present day.
By the end of the 1970’s there were over 100 solar manufacturers in the United States. With the energy crisis of the seventy’s, the realization of the importance of solar energy to replace traditional energy methods became clear. From that point until today solar energy has gradually received more and more interest and support.
Today there is a renewed focus on solar energy. More people are recognizing the need and the advantage of solar power. Solar cells are powering an array of items from household appliances to cars. Solar electric systems now power many homes and commercial businesses. The future of solar power to provide inexhaustible power supply at affordable costs is great.
Solar thermal power is the extended form of solar energy or we can say that it’s the energy required for harnessing the solar energy.
How Solar Thermal Power works?
In this method energy from the sun is used to generate heat.Solar panels are used to gather heat from the sun so that heat is imprisoned and is used for water and space heating in buildings. These panels are located in such a way as to maximize absorption of heat from the sun during the day.The panels hold tubing through which water flow. This tubing is known as solar thermal collectors. In indirect method a non-hazardous anti freeze liquid is utilized instead of water.The sun warms the liquid and it shifts this heat to water held in a tank.
In solar thermal energy plants incoming radiation is trapped by large mirror fields they in turn concentrate the energy towards absorbers.The absorbers receive the concentrated radiation and transfers it thermally to the working medium. The heated fluid is operated as in power stations directly (in case steam or air is used as medium) or indirectly through a heat exchanging steam generator on the turbine unit which then drives the generator.
Different technologies for solar thermal power plants
Three different technologies for solar thermal power plants making useOf concentrating solar energy systems.
1 Parabolic troughs,
2 Central receivers (towers) and
3 Parabolic dishes.
1. Parabolic Trough
This system uses linear concentrators of parabolic shape which have highly efficient surfaces; it can be molded in angular movements towards the sun position and can focus the radiation onto a long line receiving absorber tube. The captivated energy is transferred by a working fluid, and the fluid is then piped to a conventional power conversion system.
2. Central Receivers
This system use heliostats to follow the sun by two axes mechanisms follow the elevation and azimuth angles with the function to reflect the sunlight from several heliostats (device used for tracking the movement of the sun) which are oriented around a tower and then focus it towards a central receiver which is at the top of the tower. This technology serves as an energy input to the power conversion system because it shift solar energy very efficiently by optical means of delivering highly concentrated sunlight to one central receiver unit.
3. Parabolic Dishes Systems
The reflectors focus sun rays on a dish-mounted receiver at its focal point. Within the receiver there is a medium for transferring the heat which uses the solar energy and shifts it to the power transformation setup, which could be mounted in one unit together with the receiver or at the ground. Dish collectors attain highest solar flux and the highest performance of all concentrator types with respect to peak solar concentration and of system efficiency due to its ideal optical configuration and two axis controls for tracking the sun. The dish technology is applicable to off-the-grid power generation, i.e. at remote places or at island situations.
• Solar thermal products and structure are a smart choice for businesses.
• The use of thermal products can accumulate our other natural resources and water for us.
• Thermal heating systems are very useful for businesses like hotels and restaurants.
• The annual cost of heating water can also be minimized by using thermal solar heating systems. For this reason many industries are replacing their energy sources from natural to solar thermal energy.
• This is a new technology and the government is supporting it and provides ease by reducing taxes on these products. The use of solar thermal products gives a corporate image of the commercial users.
• The systems are environment friendly and stop vast quantities of carbon dioxide, nitrous and sulfur dioxide from entering the atmosphere.
• A Solar Hot Water system provides 50 to 70% of water heating nearly free each year. In the months of summer, the system can in reality provide almost all your hot water needs and approximately 50% for the rest of year.
• Solar thermal systems will allow you to save money by improving your building energy rating lessening your energy bills.
• Net metering, is that the extra energy produced during the day by solar source will make your meter run in the opposite direction, so that at night you use the extra energy you have produced in the day time.
• Solar panels are low repairs and trustworthy systems.
• Dispatchable peaking electricity
• High conversion efficiencies
• Hybrid operation
• Dispatch able peeking electricity
• Hybrid operation
Future of Solar Thermal Power
For various commercial applications different technologies involved in the concentration are developing the new techniques and methods for the construction of the high flux solar system which would be of greater value as compared to the present ones. This high flux is efficiently used in commercial and business sectors. This type of solar thermal systems will certainly provide within the next decade a significant contribution to efficient and inexpensive, renewable and clean energy supply.
Photovoltaic (PV) Power
PV is emerging as a major power resource, steadily becoming more affordable and proving to be more reliable than utilities. Photovoltaic power promises a brighter, cleaner future for our children.
In 1839, Edmund Becquerel discovered the process of using sunlight to produce an electric current in a solid material, but it wasn’t until a century later that scientists eventually learned that the photovoltaic effect caused certain materials to convert light energy into electrical energy.
The photovoltaic effect is the basic principal process by which a PV cell converts sunlight into electricity. When light shines on a PV cell, it may be reflected, absorbed, or pass right through. The absorbed light generates electricity.
In the early 1950s, photovoltaic (PV) cells were developed as a spin-off of transistor technology. Very thin layers of pure silicon are impregnated with tiny amounts of other elements. When exposed to sunlight, small amounts of electricity are produced. Originally this technology was a costly source of power for satellites but it has steadily come down in price making it affordable to power homes and businesses.
- Cells Semiconductor device that converts sunlight into direct current (DC) electricity
- Modules PV modules consist of PV cell circuits sealed in an environmentally protective laminate and are the fundamental building block of PV systems
- Panels PV panels include one or more PV modules assembled as a pre-wired, field-installable unit
- Array A PV array is the complete power-generating unit, consisting of any number of PV modules and panels
A single PV cell is a thin semiconductor wafer made of two layers generally made of highly purified silicon (PV cells can be made of many different semiconductors but crystalline silicon is the most widely used). The layers have been doped with boron on one side and phosphorous on the other side, producing surplus of electrons on one side and a deficit of electrons on the other side.
When the wafer is bombarded by sunlight, photons in the sunlight knock off some of excess electrons, this makes a voltage difference between the two sides as the excess electrons try to move to the deficit side. In silicon this voltage is 0.5 volt
Metallic contacts are made to both sides of the semiconductor. With an external circuit attached to the contacts, the electrons can get back to where they came from and a current flows through the circuit. This PV cell has no storage capacity, it simply acts as an electron pump.
The amount of current is determined by the number of electrons that the solar photons knock off. Bigger cells, more efficient cells, or cells exposed to more intense sunlight will deliver more electrons.
A PV module consists of many PV cells wired in parallel to increase current and in series to produce a higher voltage. 36 cell modules are the industry standard for large power production.
The module is encapsulated with tempered glass (or some other transparent material) on the front surface, and with a protective and waterproof material on the back surface. The edges are sealed for weatherproofing, and there is often an aluminum frame holding everything together in a mountable unit. In the back of the module there is a junction box, or wire leads, providing electrical connections.
Types of PV Modules
Monocrystalline Silicon Panels: Monocrystalline (or single-crystal) silicon solar panels have a return electricity rate of anywhere from 14% to 18%. These panels are made from one continuous sheet of silicon that has pieces of metal nailed to the edges to increase the conductivity and to excite the electrons.
Monocrystalline panels are more expensive than some of the other types of solar panels that you can buy but they are also more effective, so in the long run you’re better off buying these panels if you can afford the up front cost.
Polycrystalline Silicon Panels: Polycrystalline (or multi-crystal) silicon panes have an electricity return rate of about 12%-14% so they are less efficient than monocrystalline silicon solar panels. These panels are made up of lots of individual PV cells that have metal conducting materials nailed to the sides that will help excite the electrons and also connect the cells together.
Polycrystalline silicon panels are the cheapest solar panels to produce so they are usually the cheapest for consumers to buy. The maintenance costs of polycrystalline silicon panels is lower than the maintenance cost of monocrystalline solar panels because if one of the cells on a polycrystalline panel is damaged you can have the individual cell replaced without having to replace the entire panel.
String Ribbon Silicon Panels: String ribbon silicon panels are made in a similar way to the polycrystalline silicon panels and have about the same electricity return rate. The difference between string ribbon silicon panels and polycrystalline silicon panels is that the PV cells in a string ribbon panel are made of strips of silicon attached to metal bars that connect the strips to form a cell. Using strips of silicon to form the cell instead of using one solid square of silicon make the production cost of string ribbon silicon panels a bit lower than the production cost of polycrystalline silicon panels.
Amorphous Silicon Panels: Amorphous silicon panels have the lowest electricity return rate of any type of solar panels. Traditionally amorphous silicon solar panels have an electricity return rate of between 5%-6%. That’s because these panels aren’t made with crystalline silicon. They are composed of a piece of semi conductive metal, like copper, with a thin silicon film over the top that is attached to some metal pieces.
These panels are very cheap to produce but when you’re buying solar panels for home use you need to consider the long term efficiency of the type of panel that you’re buying. Unfortunately, though cheap to begin with they do not produce much energy, therefore amorphous silicon panels are not going to be cost effective in the long run.
PV panels include one or more PV modules assembled as a pre-wired, field-installable unit. The modular design of PV panels allows systems to grow as needs change. Modules of different manufacture can be intermixed without any problem, as long as all the modules have rated voltage output within 1.0 volt difference.
Solar panels generate free power from the sun by converting sunlight to electricity with no moving parts, zero emissions, and no maintenance. The solar panel, the first component of a electric solar energy system, is a collection of individual silicon cells that generate electricity from sunlight. The photons (light particles) produce an electrical current as they strike the surface of the thin silicon wafers. A single solar cell produces only about 1/2 (.5) of a volt. However, a typical 12 volt panel about 25 inches by 54 inches will contain 36 cells wired in series to produce about 17 volts peak output. If the solar panel can be configured for 24 volt output, there will be 72 cells so the two 12 volt groups of 36 each can be wired in series, usually with a jumper, allowing the solar panel to output 24 volts. When under load (charging batteries for example), this voltage drops to 12 to 14 volts (for a 12 volt configuration) resulting in 75 to 100 watts for a panel of this size.
Multiple solar panels can be wired in parallel to increase current capacity (more power) and wired in series to increase voltage for 24, 48, or even higher voltage systems. The advantage of using a higher voltage output at the solar panels is that smaller wire sizes can be used to transfer the electric power from the solar panel array to the charge controller & batteries. Since copper has gone up considerably in the last few years, purchasing large copper wiring and cables is quite expensive.
- Solar Panels
A PV Array consists of a number of individual PV modules or panels that have been wired together in a series and/or parallel to deliver the voltage and amperage a particular system requires. An array can be as small as a single pair of modules, or large enough to cover acres.
12 volt module is the industry standard for battery charging. Systems processing up to about 2000 watt-hours should be fine at 12 volts. Systems processing 2000 – 7000 watt-hours will function better at 24 volt. Systems running more than 7000 watt-hours should probably be running at 48 volts.
Photovoltaic Module Performance
The performance of PV modules and arrays are generally rated according to their maximum DC power output (watts) under Standard Test Conditions (STC). Standard Test Conditions are defined by a module (cell) operating temperature of 25o C (77 F), and incident solar irradiant level of 1000 W/m2 and under Air Mass 1.5 spectral distribution. Since these conditions are not always typical of how PV modules and arrays operate in the field, actual performance is usually 85 to 90 percent of the STC rating.
Today’s photovoltaic modules are extremely safe and reliable products, with minimal failure rates and projected service lifetimes of 20 to 30 years. Most major manufacturers offer warranties of twenty or more years for maintaining a high percentage of initial rated power output. When selecting PV modules, look for the product listing (UL), qualification testing and warranty information in the module manufacturer’s specifications.
- Solar Power System
A photovoltaic cell (PV cell) is a specialized semiconductor diode that converts visible light into direct current (DC). Some PV cells can also convert infrared (IR) or ultraviolet (UV) radiation into DC electricity. Photovoltaic cells are an integral part of solar-electric energy systems, which are becoming increasingly important as alternative sources of utility power.
The first PV cells were made of silicon combined, or doped, with other elements to affect the behavior of electrons or holes (electron absences within atoms). Other materials, such as copper indium diselenide (CIS), cadmium telluride (CdTe), and gallium arsenide (GaAs), have been developed for use in PV cells. There are two basic types of semiconductor material, called positive (or P type) and negative (or N type). In a PV cell, flat pieces of these materials are placed together, and the physical boundary between them is called the P-N junction. The device is constructed in such a way that the junction can be exposed to visible light, IR, or UV. When such radiation strikes the P-N junction, a voltage difference is produced between the P type and N type materials. Electrodes connected to the semiconductor layers allow current to be drawn from the device.
Solar Cell Working
Solar cells, also called photovoltaic (PV) cells by scientists, convert sunlight directly into electricity. PV gets its name from the process of converting light (photons) to electricity (voltage), which is called the PV effect. The PV effect was discovered in 1954, when scientists at Bell Telephone discovered that silicon (an element found in sand) created an electric charge when exposed to sunlight. Soon solar cells were being used to power space satellites and smaller items like calculators and watches. Today, thousands of people power their homes and businesses with individual solar PV systems. Utility companies are also using PV technology for large power stations.
Solar panels used to power homes and businesses are typically made from solar cells combined into modules that hold about 40 cells. A typical home will use about 10 to 20 solar panels to power the home. The panels are mounted at a fixed angle facing south, or they can be mounted on a tracking device that follows the sun, allowing them to capture the most sunlight. Many solar panels combined together to create one system is called a solar array. For large electric utility or industrial applications, hundreds of solar arrays are interconnected to form a large utility-scale PV system.
Traditional solar cells are made from silicon, are usually flat-plate, and generally are the most efficient. Second-generation solar cells are called thin-film solar cells because they are made from amorphous silicon or nonsilicon materials such as cadmium telluride. Thin film solar cells use layers of semiconductor materials only a few micrometers thick. Because of their flexibility, thin film solar cells can double as rooftop shingles and tiles, building facades, or the glazing for skylights.
Third-generation solar cells are being made from variety of new materials besides silicon, including solar inks using conventional printing press technologies, solar dyes, and conductive plastics. Some new solar cells use plastic lenses or mirrors to concentrate sunlight onto a very small piece of high efficiency PV material. The PV material is more expensive, but because so little is needed, these systems are becoming cost effective for use by utilities and industry. However, because the lenses must be pointed at the sun, the use of concentrating collectors is limited to the sunniest parts of the country.
How do Photovoltaics Work?
Photovoltaics is the direct conversion of light into electricity at the atomic level. Some materials exhibit a property known as the photoelectric effect that causes them to absorb photons of light and release electrons. When these free electrons are captured, an electric current results that can be used as electricity.
The photoelectric effect was first noted by a French physicist, Edmund Bequerel, in 1839, who found that certain materials would produce small amounts of electric current when exposed to light. In 1905, Albert Einstein described the nature of light and the photoelectric effect on which photovoltaic technology is based, for which he later won a Nobel prize in physics. The first photovoltaic module was built by Bell Laboratories in 1954. It was billed as a solar battery and was mostly just a curiosity as it was too expensive to gain widespread use. In the 1960s, the space industry began to make the first serious use of the technology to provide power aboard spacecraft. Through the space programs, the technology advanced, its reliability was established, and the cost began to decline. During the energy crisis in the 1970s, photovoltaic technology gained recognition as a source of power for non-space applications.
Operation of Photovoltaics
The diagram above illustrates the operation of a basic photovoltaic cell, also called a solar cell. Solar cells are made of the same kinds of semiconductor materials, such as silicon, used in the microelectronics industry. For solar cells, a thin semiconductor wafer is specially treated to form an electric field, positive on one side and negative on the other. When light energy strikes the solar cell, electrons are knocked loose from the atoms in the semiconductor material. If electrical conductors are attached to the positive and negative sides, forming an electrical circuit, the electrons can be captured in the form of an electric current — that is, electricity. This electricity can then be used to power a load, such as a light or a tool.
Continue reading Solar Photovoltaic Technology
Solar water heating systems use free heat from the sun to warm domestic hot water. A conventional boiler or immersion heater can be used to make the water hotter, or to provide hot water when solar energy is unavailable.
Solar Water Heating (SWH) or Solar Hot Water (SHW) systems comprise several innovations and many mature renewable energy technologies that have been well established for many years. SWH has been widely used in Greece, Turkey, Israel, Australia, Japan, Austria and China.
In a “close-coupled” SWH system the storage tank is horizontally mounted immediately above the solar collectors on the roof. No pumping is required as the hot water naturally rises into the tank through thermosiphon flow. In a “pump-circulated” system the storage tank is ground or floor mounted and is below the level of the collectors; a circulating pump moves water or heat transfer fluid between the tank and the collectors.
SWH systems are designed to deliver hot water for most of the year. However, in winter there sometimes may not be sufficient solar heat gain to deliver sufficient hot water. In this case a gas or electric booster is normally used to heat the water.
A solar cooker, or solar oven, is a device which uses the energy of sunlight to heat food or drink to cook it or sterilize it. High-tech versions, for example electric ovens powered by solar cells, are possible, and have some advantages such as being able to work in diffuse light. However at present they are very unusual because they are expensive. The vast majority of the solar cookers presently in use are relatively cheap, low-tech devices. Because they use no fuel and cost nothing to operate, many nonprofit organizations are promoting their use worldwide to help reduce fuel costs for low-income people, reduce air pollution and slow deforestation and desertification, caused by use of firewood for cooking. Solar cooking is a form of outdoor cooking and is often used in situations where minimal fuel consumption is important, or the danger of accidental fires is high.
Low-Tech Solar Cookers
There are a variety of types of solar cookers: over 65 major designs and hundreds of variations of them. The basic principles of solar cooker design are:
- Concentrating Sunlight: A reflective mirror of polished glass, metal or metallised film is used to concentrate light and heat from the sun into a small cooking area, making the energy more concentrated and increasing its heating power.
- Converting Light to Heat: A black or low reflectivity surface on a food container or the inside of a solar cooker will improve the effectiveness of turning light into heat. Light absorption converts the sun’s visible light into heat, substantially improving the effectiveness of the cooker.
- Trapping Heat: It is important to reduce convection by isolating the air inside the cooker from the air outside the cooker. A plastic bag or tightly sealed glass cover will trap the hot air inside. This makes it possible to reach similar temperatures on cold and windy days as on hot days.
- Greenhouse Effect: Glass transmits visible light but blocks infrared thermal radiation from escaping. This amplifies the heat trapping effect.
Types of Solar Cooker
The available designs of solar ovens fall into three main categories: the box, parabolic, and panel designs. The feature common to each oven design is the shiny reflective surface that directs the sun’s rays onto a dark cooking vessel. Each category has advantages when compared on their heating ability, ease of construction, ease and safety of use.
1. Box Cooker Solar Ovens
2. Reflective Panel Solar Cookers
3. Parabolic Solar Cookers
Box Solar Cooker
Box cookers are the most common type made for personal use. There are over several hundred thousand in India alone. Despite the name “box” cooker, they are made in both circular and rectangular shapes. They consist of an enclosed inner box covered with clear glass or plastic, a reflector, and insulation. There is a wide variety of patterns and plans for the box cooker. While they do not heat quickly, they do provide slow, even cooking and are extremely cheap to make. Box cookers are very easy and safe to use, and fairly easy to construct.
Box Solar Cooker
Panel Solar Cooker
Panel cookers are flat reflective panels which focus the sunlight onto a cooking vessel without the inner box common in box cookers. Panel cookers are the easiest and least costly to make, requiring just four reflective panels and a cooking vessel, but they are unstable in high winds and do not retain as much heat when the sun is hidden behind clouds. The diagram shows a panel cooker with a dark cooking vessel and thermometer all wrapped in a plastic oven bag.
Parabolic Solar Cooker
Reflective materials are used to concentrate light and heat from the sun into a small cooking area, making the Sun’s energy more concentrated and therefore more powerful, resulting in the fastest cooking times of all Cooker designs.
Parabolic cookers require more precision to focus the sunlight on the cooking vessel and are therefore the most complex design to build. If the sunlight is not focused exactly on the cooking vessel, the food will not cook efficiently.