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 | SOLAR ENERGY TECHNOLOGY How Do Solar Cells Work? In the 1950s scientists tinkering with semiconductors found that by introducing small, minutely controlled amounts of certain impurities called dopants to the semiconductor matrix, the density of free electrons could be shepherded and controlled. The dopants, similar enough in structure and valence to fit into the matrix, have one electron more or less than the semiconductor; for example, doping with phosphorus, which has five valence electrons, produces a (negative) n-type semiconductor, with an extra electron which can be dislodged easily. Aluminum, boron, indium, and gallium have only three valence electrons, and so a semiconductor doped with them is (positive) p-type, and has holes where the missing electrons ought to be. These holes behave just like electrons, except that they have an opposite, positive charge. Holes are theoretical, but so are electrons, and either or both may or may not exist, but we know for sure that if one exists, they both do, because we cant create something out of nothing in the physical world. It is important to understand that, although loosely bonded or extra carriers exist in a substance, it is still neutral electrically, because each atoms electrons are matched one for one by protons in the nucleus.The fun begins when the two semiconductor types are intimately joined in a pn-junction, and the carriers are free to wander. Being of opposite charge, they move toward each other, and may cross the junction, depleting the region they came from, and transferring their charge to their new region. This produces an electric field, called gradient, which quickly reaches equilibrium with the force of attraction of excess carriers. This field becomes a permanent part of the device, a kind of slope that makes carriers tend to slide across the junction when they get close.When light strikes a photovoltaic cell, atoms are bombarded with photons, and give up electrons. When an electron gets lopped off an atom, it leaves behind a hole, which has an equal and opposite charge. Both the electron, with its negative charge, and the hole, with its positive charge, begin a random walk generally down the gradient. If either carrier wanders across the junction, the field and the nature of the semiconductor material discourage it from recrossing. A proportion of carriers which cross this junction can be harvested by completing a circuit from a grid on the cells surface to a collector on the backplane. In the cell, the light pumps electrons out one side of the cell, through the circuit, and back to the other side, energizing any electrical devices found along the way. |
 | Solar Cell battery diagram |
For decades people who live off-grid, not connected to utility electric transmission lines, have generated their own power with solar energy. Now, people who live on the grid can economically install and obtain the benefits of solar and renewable energy systems. GENERATE GREEN POWER: Generate electricity with the sun, wind or waterproducing no pollution or emissions. GAIN POWER INDEPENDENCE: With the use of batteries, or eventually stored hydrogen, you can rely on your own generating capacity, and not on public utilities. ENSURE RELIABLE POWER: With a battery back-up system, you can keep your appliances running during utility power outages. CREATE SAFE, CLEAN POWER: Unlike fossil fuel back-up generators, solar creates no noise, smell or pollution and requires no fuel storage. FEED GREEN POWER BACK TO THE UTILITIES: In many states, you can send your home-generated power back to the utility and get credit for the power you feed into the utility grid. OBTAIN TAX CREDITS AND REBATES: Tax credits and rebates are available in many states to people and businesses who install solar powered products.
By harnessing the power of the sun, wind or water, people all over the world produce their own pollution-free reliable electricity. Technological advances, government assistance, the need for reliable power, and the desire to reduce the use of fossil fuels have made renewable energy systems attractive to people in the United States and worldwide.Solar technology makes it possible for home and business owners to have dependable power from renewable sources. Mass production has significantly reduced the price of renewableenergy systems and their components. Solar and battery-based backup power systems can ensure reliable power even when the utility grid is down. When the utility grid is working, systems feed solar-generated electrons back into the utility grid. The use of renewable sources such as wind, water and sun, increases our energy self-sufficiency and fosters economic and national security. As more families, individuals and businesses generate their own renewable electricity we will reduce pollution,provide more electricity for all to use, reduce the use of fossil fuels, and make the electricity on the grid greener. Deregulation has created an atmosphere of change in the United States. We are experiencing higher electricity rates and electricity shortages. Laws, referred to as Net Metering, allow solar-energy-system owners to feed their generated electricity back to the utility. The system owner receives a credit or payment for solar electrons fed into the grid. In other words, you pay only for the net electricity you consume - the amount of electricity you take from the utility minus the amount you generate and feed back from your solar system. With a solar electric system, you can provide yourself with some protection from the fluctuating prices of fuel, because your systems fuel is the sun. Additionally, state, local and federal tax incentives and rebates have made obtaining a system more economical. Types of Power SystemsPower systems vary in design depending on what energy sources are used and what purpose they must fulfill. The next few pages have information to help you design the systems listed below.Utility-Intertie Solar SystemsSometimes called gridtie, these systems can be used anywhere that the electric utility allows net metering, where a solar or wind powered system turns your electric meter backwards when it is producing more power than you are using. This type of system provides no back-up power when utility power fails.Utility-Intertie Solar Systems with Backup A utility-intertie system with battery backup feeds excess solar electricity to the grid and provide back up power when the utility grid is down. With this type of system you sacrifice some power generation efficiency in exchange for power whenever there is a power failure. The amount of backup power depends on the size of the battery and electrical loads.Off-Grid Power SystemsThis type of power system is independent of the utility grid. It can use solar electric modules, a wind generator or a micro-hydroelectric generator or a combination of any or all of them to produce your electric power. The owner of this type of system often uses a gas or diesel generator for backup when the power system does not meet all of the users needs. Determine What System Meets Your NeedsUse the charts and worksheets on the following pages to become familiar with the design of these systems and consult your solar power system professional installer to pick out the exact components.State and Federal IncentivesThere is a federal tax incentive called the Energy Credit that allows businesses to take a 15% credit for renewable energy equipment (solar electric, solar thermal and wind powered systems). In addition, there is an accelerated 5-year depreciation schedule that allows businesses to write 100% of the systems cost off their taxable income over the first five years. Many states offer rebates and tax incentives to home owners to lower the installed cost of a utility connected power system.If you have access to the world wide web, look at http://www.dsireusa.org/ for more information about incentives in your area. |
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SOLAR GRID-TIE POWER About residential grid-tie systems A basic grid-tie system, as shown below consists of solar cells and a Xantrex grid-tie inverter. Solar cells take the Sun's energy and turn it into DC electricity. The Xantrex inverter turns the DC electricity generated by the solar cells into utility grade AC power for use in your home or business. To enjoy the benefits of green power production and protect your family from blackouts, you can choose a Xantrex grid-tie system with batteries and a generator, as shown in Figure 2. When utility power fails, your Xantrex power system will automatically provide power to run your home security system, refrigerator, lights, computer and other vital appliances. A grid-tie system is an effective way to reduce your dependence on utility power, lower your electric bills, increase green energy production and improve the environment. Recommended Grid-Tie Products Xantrex GT 3.0 Xantrex SW with GTI SOLAR OFF-GRID POWER About residential off-grid systems A basic off-grid system consists of a renewable energy source, which generates DC power, a battery bank that stores the DC power, and a Xantrex inverter. Our inverter is the intelligent center of a renewable energy system, seamlessly converting DC power to clean and reliable AC electricity for your needs. The off-grid system pictured here is a solar electric hybrid system that offers additional automatic features. It consists of solar panels, a battery bank, our top-of-the-line Xantrex SW Plus Inverter/Charger, a charge controller that manages battery charging, and a generator. When the sun is up, the solar panels generate power to charge batteries and provide electricity. At night, the Xantrex inverter/charger automatically runs your electrical equipment from your battery bank. The generator provides additional back-up battery charging capability for extended periods of cloudy weather. The Xantrex inverter/charger can automatically start the generator and initiate a recharge cycle when the battery bank is depleted, or a load is too large for the batteries to support independently. You can even have a connection to the grid should you want to use utility power. Xantrex manufactures a complete range of power products to suit various budgets and electricity requirements. From complete power systems that come ready to install from our factory, to components that can be integrated into a system by one of our expert dealers, Xantrex has a system to meet your needs. |
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The sun is the natural source of energy for an independent water supply. Solar pumps operate anywhere that the sun shines, and the longer it shines, the more water they pump. When it's cloudy, they pump less water, but often you need less water when it is cloudy. Photovoltaic modules, the power source for solar pumping, have no moving parts, require no maintenance and last for decades. A properly designed solar pumping system will be efficient, simple and reliable. Solar water pumping systems operate on direct current. The output of the solar power system varies throughout the day and with changes in weather conditions. The nature of variable electricity in the form of direct current (DC) is quite different from conventional, steady alternating (AC) current from the utility grid or a generator. To use solar energy economically, the pumping system must utilize the long solar day, drawing a minimum of power. This means pumping slower than conventional pumps. Pumping at rates of less than 6 GPM requires different mechanisms from the conventional (centrifugal) pumps.Small solar pumps are unique, both electrically and mechanically. The most efficient pumps are positive displacement pumps; that pump a certain amount of water with each rotation. If it is cloudy or early morning, the pump will receive less energy and run slower. A positive displacement pump will pump approximately ½ as much water with ½ as much energy. Conventional AC pumps are usually centrifugal pumps that turn at high speed to pump as many gallons per minute as possible. They also consume a large amount of power. If you run a centrifugal pump at ½ speed, it pumps ¼ the water. Their efficiency is very low at low speeds and when pumping against high pressure.If your water sources are remote from power lines, add up your long-term costs of fuel and repairs on generators, or the cost of utility line extensions. Now consider the savings with a solar pump that needs attention only once every 2 to 20 years depending on model.Solar powered pumps can provide an equal volume of water per day without the high and inefficient energy demands of a large capacity AC pump. Instead of pumping a large volume of water in a short time and turning off, the solar pump works slowly and efficiently all day. Often a solar pump will work fine in a well with a recovery rate too slow for a conventional AC pump. Solar Submersible Pumps If you are pumping from a well, we have solar pumps that can deliver from 1 gallon per minute (GPM) to over 75 GPM. The smallest pump, the low power diaphragm pump from Shurflo, operates from two 50 to 75 watt solar modules, depending on the head (vertical distance) they are pumping. It can pump 500 to 1000 gallons per day and lift water 200 feet. This pump requires service every 2 to 4 years.If you have a higher lift, need more water or want a pump that does not require service for 15 to 20 years, the Grundfos SQFlex pump is a good choice. The SQFlex can lift water 525 feet and can pump over 20,000 gallons per day at lower lifts. For greater water needs or deeper wells, the Grundfos SQ-series AC submersible pump can easily be powered by an inverter or generator. Larger conventional single and three phase AC pumps, up to 10 HP, can be solar powered with the Aerovironment AC Pump Controller and a large PV array.Surface PumpingSurface pumps are less expensive than DC submersibles, where applicable. A surface pump is not submersible. It can draw water from a dug well, spring, pond, river or tank, and push it far uphill and through a long pipeline to fill a storage tank or to pressurize it for home use or for irrigation, livestock, etc. The pump may be placed at ground level, or suspended in a well in some cases.All pumps are better at pushing than pulling. Surface pumps must be placed no higher than 10 or 20 feet above the surface of the water source at sea level (subtract one foot per 1000 ft. Elevation). Suction piping must be oversized a bit and not allow air entrapment (much like a drain line) and should be as short as possible. Pumps can push very long distances. The vertical lift and flow rates are the primary factors that determine power requirements. Pressurization Many conventional AC powered water systems pump from a well or other water source, into a pressure tank that stores water and stabilizes the pressure for household use. When you turn on water in the house, an air-filled bladder in the tank forces the water into the pipes. When the pressure drops, a pressure switch turns on the pump, refilling and repressurizing the tank. This works fine because of the ability of the AC pump to deliver a volume of water larger than the household uses. This can work in systems with an inverter large enough to run a standard AC pump. However, this will not work with pumps operating directly from PV modules. First, the sun may not be shining when you need pressure. Second, many solar pumps deliver water too slowly to keep up with household use.There are two ways to solve this problem. A non-pressurized water tank can be located high enough above the house for gravity to supply the water pressure. This can be on a hill or a tower. Water pressure in PSI = Head in feet times 0.433. For reasonable pressure the tank needs to be at least 40 feet above the house. If this is not possible, a battery operated pressure booster pump can fill a pressure tank as needed from a storage tank that is filled by a solar pump during the day. The Flowlight Booster pump, as well as the Shurflo 2088 pumps can be used for this purpose. You must use a pump that can deliver the maximum GPM required by the house, or have a pressure tank that is large enough to make up the difference between what the pressure pump can deliver and what is required, for the amount of time it is required. This is called the drawdown volume of the tank. Air filled pressure tanks can be obtained locally from a pump dealer. |
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DO YOU HAVE A GOOD SITE FOR WIND POWER? Wind powered battery charging systems can be cost-effective if the average wind speed is nine miles per hour (mph) or more at the location of the wind generator. If you are using wind in combination with photovoltaic power, it may be cost effective if good wind is available only during part of the year. The power available from the wind is proportional to the cube of the wind speed. When the wind speed doubles, the power delivered is eight times as great . Most wind generators are designed to deliver maximum power at a wind speed of 30 mph. At 15 mph, they will deliver about 1/8 their rated power. A wind generator should be mounted at least 20 feet higher than any obstruction within 300 feet to avoid turbulence. You can expect the power output of a wind generator to decrease roughly 3% for every 1000 feet of elevation. That means that youll get 70% of the power at 10,000 feet elevation. |
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