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State the principle and working of photovoltaic cell used for solar energy.
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Solar Energy:

  • Solar energy is radiant light and heat from the Sun. Solar energy is an inexhaustible source of energy and the best replacement to other non-renewable energies.
  • It is environment friendly, it does not release CO2 and other gases which pollute the air while used.
  • Solar cells use photovoltaics to convert sunlight directly into electricity by converting photons (light particles) into electrons (negatively charged particles).
  • Solar cells are made of semiconductors and silicon, mixed with other material.

Principle:

  • It is based on principle of solid-state physics of semiconductors.
  • It is a device made of semiconductor materials that produce electric energy under light (photon) energy. This conversion does not involve any chemical reactions.
  • Silicon is a popular material for solar PV cells because it is a semiconductor material, technology is well developed to make silicon for an elctric cell or battery.
  • Silicon is abundant in supply and relatively inexpensive in production.

     

Conversion of solar energy directly on to electrical energy in a solar cell:

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Photovoltaic Cells :

"Photovoltaic cells or Solar cells" are the semiconductor devices which coverts sunlight into direct current electricity on illumination.

                 The Solar cells or Photovoltaic cells are made out of semiconductors which have the capacity to absorb light. When n-type and p-type semiconductor are brought together a semiconductor diode is formed. The semiconductor diode separates and collects the carriers and conducts the generated electric current preferentially in a specific direction.

                  A typical silicon photovoltaic cell is composed of a thin wafer consisting of an ultra thin layer of phosphorus doped. (n-type) silicon on top of boron doped (p-type) silicon. Hence a p-n junction is formed. A metallic grid forms one of the electrical current contacts of the diode and allows light to fall on the semiconductor between the grid lines. An antireflective layer between the grid lines increases the amount of light transmitted to the semiconductor. The cell`s other electrical contacts is formed by a metallic layer on the back of the solar cell.

                  When light radiation falls on the p-n junction diode, electron hole pairs are generated by the absorption of the radiation. The electrons are drifted to and collected at the n-type end and the holes are drifted to p-type end. When these two ends are electrically connected through a conductor, there is a flow of current between the two ends through the external circuit. Thus photoelectric current is produced.

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Importance of Photovoltaic cells :

  1. The conventional energy exhaustible and depleting. Whereas Solar energy being ultimate, inexhaustible and renewable energy. There the photovoltaic cells are important means to utilize this continuous energy source.
  2. The Photovoltaic cells can serve for both off-grid and on-grid applications. It can be used for off-grid professional devices and supply systems such as telecommunication equipment, solar home systems, etc.
  3. The Photovoltaic energy conversion environmental friendly as there is no harmful emission of pollutants. Use of or production of solar energy doesn`t produce noise pollution.
  4. The electricity obtained from solar energy is useful in minimizing global warming due to carbon dioxide.
  5. Photovoltaics can be used as roof integrated systems, providing power and also serving as optical shading elements for the space below and preventing overheating in the summer.
  6. Photovoltaic cells provide power for spacecraft and satellites.
  7. Developments in the field of photovoltaic cells will boost the semiconductor industry and storage battery industries.
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