Solar (PV) Cells
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"I'd put my money on the sun and solar energy. What a source of power! I hope we don't have to wait until oil and coal run out before we tackle that." - Thomas Edison, 1931

4540 square miles of Solar Panels (8 billions of 200w solar panels) could meet all current national energy needs (4 trillion kWh)!
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"Every hour, enough of sunlight energy reaches the Earth to meet the world's energy demand for a whole year."

The amount of power solar panels produce is determined by the quality of the solar panel, solar cells and technology used in making the solar panel.

There are mainly 4 types of solar cells: mono-crystalline, poly-crystalline, amorphous and thin-film (CIS, CIGS).

Mono-crystalline efficiency is in 16% range. PV cell is made from pure mono-crystalline silicon with almost no defects or impurities. High purity mono cells are used to make computer CPU chip, relatively low purity cells are used for solar module. The most common size of mono-crystalline cell is 5x5 (125x125mm) and 6x6 (156x156mm). The bigger the size, the harder is to make. Mono-crystalline has a lifetime of 25 to 30 years under normal circumstance.

Poly-crystalline efficiency is in 13% range. PV cell is produced using numerous grades of mono-crystalline silicon. This is less expensive to manufacturing due to simpler processes involved in production compared with mono-crystalline. The most common size of mono-crystalline cell is 5x5 (125x125mm) and 6x6 (156x156mm). Poly-crystalline has a lifetime of 20 to 25 years under normal circumstance.

Amorphous efficiency is in 10% range. Silicon composed of silicon atoms in a thin layer rather than a crystal structure. It absorbs light more effectively than crystalline so cells can be thinner. Thin film technology can be used in rigid, flexible, curved and foldaway modules. The have a lower cost than crystalline cells but have a lower efficiency. Amorphous has a lifetime of less than 10 years under normal circumstance.

Thin-film efficiency is in 11% range. PV cell is the most efficient material in poor light conditions, whilst also being an extremely sturdy, vandal-proof PV. The lifetime on thin-film is uncertain.

Solar energy is the conversion of sunlight into electricity through a photovoltaic (PVs) cell, commonly called a solar cell. A photovoltaic cell is made from silicon alloys.

Sunlight is composed of photons, or particles of solar energy. These photons contain various amounts of energy corresponding to the different wavelengths of the solar spectrum. When photons strike a photovoltaic cell, they may be reflected, pass right through, or be absorbed. Only the absorbed photons provide energy to generate electricity. When enough sunlight (energy) is absorbed by the material (a semiconductor), electrons are dislodged from the material's atoms. Special treatment of the material surface during manufacturing makes the front surface of the cell more receptive to free electrons, so the electrons naturally migrate to the surface. When the electrons leave their position, holes are formed. When many electrons, each carrying a negative charge, travel toward the front surface of the cell, the resulting imbalance of charge between the cell's front and back surfaces creates a voltage potential like the negative and positive terminals of a battery. When the two surfaces are connected through an external load, electricity flows.

The photovoltaic cell is the basic building block of a PV system. Individual cells can vary in size from about 1/2 inch to about 4 inches across. However, one cell only produces 1 or 2 watts, which isn't enough power for most applications. To increase power output, cells are electrically connected into a packaged weather-tight module. Modules can be further connected to form an array. The term array refers to the entire generating plant, whether it is made up of one or several thousand modules.

The performance of a photovoltaic array is dependent upon sunlight. Climate conditions (e.g., clouds, fog) have a significant effect on the amount of solar energy received by a PV array and, in turn, its performance. The chart below shows solar insolation in kilowatt-hours per square meter per day in many US locations. Also, the environmental impact of a photovoltaic system is minimal, requiring no water for system cooling and generating no by-products. Photovoltaic cells, like batteries, generate direct current (DC) which is generally used for small loads (electronic equipment). When DC from photovoltaic cells is used for commercial applications or sold to electric utilities using the electric grid, it must be converted to alternating current (AC) using inverters, solid state devices that convert DC power to AC.

DOE-Get Sun PowerNREL-Solar Irradiance ChartPV Progress & Challenges
BEF Grant for Oregon or WashingtonGo Solar California Handbook Florida Solar Incentives
10 Steps Go SolarFAQ on Federal Solar Tax CreditsGreen Energy Ohio
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