The sun has been radiating an enormous amount of energy at the present rate for nearly 5 billion years and will continue radiating at that rate for about 5 billion years more. Only a small part of solar energy reaches the outer layers of the earth atmosphere. Nearly half of its absorbed value passing through the atmosphere and the rest reaches the earth surface.
A black surface absorbs more heat as compared to a white or a reflecting surface under identical condtions. Solar cooker and solar heater uses this property in their working.
But these devices are useful only at certain times during the day. This limitation of using solar energy is overcome by using solar cells that convert solar energy to electrical energy. A typical cell develpos a voltage of 0.5 - 1 Volt and can produce about 0.7 watt of electricity when exposed to the sun. A large number of solar cells are combined in arrangement called solar panel that can deliver eough electricity for practical use.
The main advantage associated with the solar cells are that they have no moving parts, require little maintanence and work quite satisfactorily without the use of any focussing device. Another advantage is that they can be set up in remote and inaccessible hamlets of very sparsly inhabited areas. As in These places power transmission line may be expensive and not commercially viable.
Silicon is used for making solar cells. It is abundant in nature but availability of special grade silicon for making solar cells is limited. The entire process of manufacture is very expensive, silver used for interconnection of the cells in the panel further adds to the cost. In spite of the high cost and low efficiency, solar cells are used for many scientific and technological applications. Artificial satellites and space probes like Mars orbiters use solar cells as the main source if energy. Radio or wireless transmission systems or TV relay station in remote locations use solar cell panels. Traffic signals, claculators and many toys are fitted with solar cells. The solar cell panels are mounted on specially designed inclined roof tops so that more solar ebergy is incident over it. The domestic use of solar cells is limited ude to its high cost.