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Explain briefly how photovoltaic cells are usefu in harnessing solar energy.
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Solar photovoltaic (PV) (also called solar cells) is a technology that directly produces electricity from sunlight (not heat). It is one solar technology which has the greatest potential for use throughout the world. PV cells require little maintenance, have no moving parts, and essentially no environmental impact. They work cleanly, safely and silently. They can be installed quickly in small modules, anywhere there is sunlight.

Working of a Photovoltaic Cell:

  1. A photovoltaic cell is basically a p-n junction, made of semiconductors like Silicon.
  2. When Photons in sunlight hit the semiconductor material of solar panel, one of these 3 things happens:
    • It passes straight through the silicon — lower energy photons
    • It is reflected off the surface
    • It is absorbed by the silicon — if the photon energy is higher than the silicon band gap value, generating an electron-hole pair and sometimes heat, depending on the band structure.
  3. Negatively charged electron, thus knocked loose from their atoms structure, gets transferred from the ‘valence band’ to the ‘conduction band’. Electrons in conduction band are free to flow through the material to produce electricity.
  4. The only condition for producing electricity in this p-n junction is that incident photons must have energy greater than the band gap of material. Majority of the photons reaching earth’s surface suffice this condition.
  5. When external load, such as a light bulb is connected across the p & n sides, free electrons on n-side flow through it via external wires to the p-side.

Thus an array of solar cells can convert solar energy into a usable amount of direct current (DC) electricity.

PV cells are wired together to form a module. A module of about 40 cells is enough to power a light bulb. For more power, PV modules are wired together into an array. PV arrays can produce enough power to meet the electrical needs of a home.

Applications of PV cells:

PV cells are commonly used today in calculators and watches. They also provide power to satellites, electric lights, and small electrical appliances such as radios and for water pumping, highway lighting, weather stations, and other electrical systems located away from power lines.

Environment Friendly:

PV cells are environmentally benign, ie. they do not release pollutants or toxic material to the air or water, there is no radioactive substance, and no catastrophic accidents.

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