In principle, this effect is observable in solids, liquids, and gases, but it is mostly in the case of semi-conductors that significant conversion efficiencies have been achieved. Silicon is the most commonly used component of the solar semi-conductors.
Solar cells have already proved their usefulness in the space exploration programme in India as well as abroad. Solar cells successfully developed at the Bhabha Atomic Research Centre in Trombay, Bombay, have been tested in the satellite Bhaskara and have met part of the power requirement abroad (Gupta, 1981). Their potential for large-scale power generation to meet energy needs on earth is even greater.
This is produced from heat in the deep interior of the earth. The molten rock beneath the earth’s surface in some places has pushed up close to the earth’s crust. When underground water flows over these hot rocks, the hot water or steam rises through fissures in the earth’s crusts, producing geysers. This geothermal energy can be converted into electricity.