A solar cell is a device which converts solar energy directly into electricity. Since solar energy is also known as light energy, so we can also say that "solar cell is a device which coverts light energy into electrical energy." About one hundred years ago it was discovered that when sunlight falls on a thin layer of selenium element, then electricity is produced. It was also found that only 0.6 per cent of the solar energy (or light energy) falling on the selenium layer got converted into electricity (which was very low). Since the efficiency of such a solar cell was very low, therefore, no serious efforts were made to use this phenomenon for producing electricity. Before we discuss solar cells further, we should know the meaning of semi-conductors. This is given below.
How Solar Cells are Made :
These days solar cells are usually made from semi-conductor materials like silicon and gallium. To make a solar cell, the wafers (thin layers) of semi-conductor materials containing impurities are arranged in such a way that when light falls on them, then a potential difference is produced between the two regions of the semi-conductor wafers. And this potential difference then produces electric current. The potential difference produced by a single solar cell of 4 square centimetre size is about 4 volt to 0.5 volt and generates a current of 60 milliamperes (60mA). In addition to silicon and gallium elements, the other elements which can be used to fabricate a solar cell are : selenium and germanium.
Solar Cell Panel :
A lot of electric energy (or electric power) is required for the working of various devices like artificial satellites; water pumps; street lighting and for radio and television sets in the remote areas. No single solar cell can provide so much electricity. But by joining a large number of solar cells in a particular way, we can obtain any amount of electrical energy at any desired voltage. This group of solar cells is called a solar cell panel.
A solar cell panel contains a large number of solar cells joined together in a definite pattern (see Figure 4). A solar cell panel can provide much more electric power than a single solar cell. The electric power required for the working of artificial satellites stationed in outer space; street lighting in remote areas and running of irrigation water pumps in far-off areas is obtained with the help of solar cell panels (and not any single solar cell alone).
Uses of Solar Cells :
The use of solar cells has been very effective in providing electric power to remote, inaccessible and isolated places. The important uses of solar cells are given below :
(i) Solar cells are used for providing electricity in artificial satellites and space-probes. In fact, all the artificial satellites and space-probes depend mainly on the electricity generated by solar panels.
(ii) In India, solar cells are being used for street-lighting; for operating water-pumps and for running radio and television sets in remote areas.
(iii) Solar cells are used for providing electricity to "light houses" situated in the sea and to the off-shore oil drilling rig platforms,
(iv) Solar cells are used for operating electronic watches and calculators.
The solar cells have gained too much importance in the last few decades because solar cells are being used increasingly for providing electricity to artificial satellites and space-probes; for providing electricity to remote areas and for operating modern instruments like electronic watches and calculators. The greatest advantage of solar cells is that they make use of "everlasting solar energy" and their use does not produce any environmental pollution.