Solar Cell or Photogalvanic Cell

SOLAR CELL (or) PHOTOGALVANIC CELL

Definition

Solar cell (or) Photogalvanic cell is the one, which converts the solar energy (energy obtained from the sun) directly into electrical energy.

Principle

The basic principle involved in the solar cells is based on the photovoltaic (PV) effect. When the solar rays fall on a two layer of semi-conductor devices, a potential difference between the two layer is produced. This potential difference causes flow of electrons and produces electricity.

Construction

Solar cells consist of a p-type semiconductor (such as Si doped with B) and n-type semiconductor (such as Si doped with P). They are in close contact with each other.

Fig. 7.7 Solar cell

Working

When the solar rays fall on the top layer of p-type semiconductor, the electrons from the valence band get promoted to the conduction band and cross the p-n junction into n-type semiconductor. There by potential difference between two layers is created, which causes flow of electrons (ie., an electric current). Thus, when the p and n layers are connected to an external circuit, electrons flow from n-layer to p-layer, and hence current is generated.

The potential difference and hence current increases as more solar rays falls on the surface of the top layer.

1. Applications of solar cells

1. Lighting purpose

Solar cells can be used for lighting purpose. Now a days electrical street lights are replaced by solar street lights.

Fig. 7.8 Solar light

2. Solar pumps run by solar battery

When a large number of solar cells are connected in series it form a solar battery. Solar battery produces more electricity which is enough to run, water pump, street-light,

Fig. 7.9 Solar pump run by solar cells (Battery)

etc., They are also used in remote areas where conventional electricity supply is a problem.

3. Solar cells are used in calculators, electronic watches, radios and TVs.

4. Solar cells are superior to other type of cells, because these are non-polluting and eco-friendly.

5. Solar energy can be stored in Ni-Cd batteries and lead-acid batteries.

6. Solar cells can be used to drive vehicles.

7. Solar cells, made of silicon, are used as a source of electricity in space craft and satellites.

2. Advantages and Disadvantages of solar cells

Advantages (or) Merits

1. Solar cells can be used in remote and isolated areas, forests and hilly regions.

2. Maintenance cost is low.

3. Solar cells are noise and pollution free.

4. Their lifetime is long.

5. They operate at ambient temperature.

6. They need not be recharged.

Disadvantages (or) Demerits

1. Capital cost is higher.

2. Storage of solar energy is not possible.

3. It produces only DC voltage.

4. Solar energy is not available throughout day and night.