JAI OH SURYA BHAGAVAN!!
PHOTOVOLTAIC CELL:
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Photovoltaic
energy is the conversion of sunlight into electricity. A
photovoltaic cell, commonly called a solar cell or PV, is the
technology used to convert solar energy directly into electrical
power. A photovoltaic cell is a non mechanical device usually
made from silicon alloys.
Photovoltaic cells are cells which are directly capable of converting light energy into electricity. -They are made of semiconductors such as thin slices of crystalline silicon or gallium arsenide. They, as mentioned above, are capable of converting solar energy directly into electricity. -The simplest of photovoltaic cells may generate power only enough to run solar powered calculators and watches. Still more complexly designed photovoltaic cells are able to provide electricity to houses and electric grids. -But these usually provide insufficient, i.e., low power to remote, unattended devices like buoys, weather and communication satellites, and equipment aboard spacecrafts. Various Application of SPV's -Solar energy can also be used to meet our electricity requirements. Through Solar Photovoltaic (SPV) cells. Electricity generated by SPVs can either be used as it is or can be stored in the battery. This stored electrical energy then can be used at night. SPV can be used for a number of applications such as: a. domestic lighting b. street lighting c. village electrification d. water pumping e. desalination of salty water f. powering of remote telecommunication repeater stations g. railway signals and so on. -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. SPVs are being used in satellites like INSAT-2B, 3B.The solar cell was first developed by Chepin, Fuller and Pearson in 1954. They used diffused silicon p-n junction. Then the cadmium-sulphide solar cell was developed. Later on semi-conductors like Gas, In As, etc were developed and used to make solar cells. A solar cell essentially consists of a P-N junction diode embedded in a glass or clear plastic package. Only one side of the package is kept transparent and the other side of the package is either painted black or enclosed in a metallic case. The surface layer of the P-type junction material is made extremely thin so that the incident photons may easily penetrate to reach the junction. Metal contacts are made at whole N-side and at the ends of P-side. The contact on P-side acts as anode while that on N-side acts as cathode. When sunlight is incident on the P-surface through a transparent window, it penetrates to the junction. This energy is sufficient to break covalent bonds, thus creating electrons and holes on both sides of junction. The flow of these charge carriers constitutes the minority current. This current is directly proportional to the intensity of illumination and it also depends upon the surface area of junction being illuminated. The open circuit voltage depends upon the illumination. Hence power-output of a solar cell depends on the intensity of the incident sunlight.
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