Question

State three ways by which you can enhance the collection of solar energy.

Answer 1

Following are the three ways by which we can enhance the collection of solar energy:
(i) Use of black painted surface: Black surfaces are good absorbers as well as good radiators of radiant heat. Thus the surfaces of the objects which are to collect radiant heat are painted black so that their temperature rises rapidly. But after some time, an equilibrium state is reached when the solar energy absorbed by a blackened object is equal to radiant heat radiating out from its surface. To overcome this difficulty, some means should be provided to that the rate of radiant heat from its surface is reduced or stopped altogether.
(ii) Use of insulated box with glass cover: The objects painted black, should be placed in a well insulated box provided with glass cover. The insulated box will prevent heat losses due to conduction, convection, and radiation. The glass cover will allow solar energy to pass through it as it is transparent to the radiant heat of smaller wavelengths. However, when the object with a blackened surface gets hot within the box and radiates out radiant heat, the glass will not allow these radiations to pass through, as they are of longer wavelength. Thus, the heat radiations are trapped within the insulated box, thereby raising the temperature of objects with blackened surface.
(iii) Use of reflectors: As mentioned earlier, the amount of solar energy per square meter per second is too small to do any useful work. Thus, if solar energy is directly allowed to enter a solar heating device, it does not raise its temperature sufficiently. However, if solar energy is collected from a sufficiently large area and then reflected into the small area of a solar heating device, its temperature rises sufficiently to do some useful work. It is here that reflectors are useful for solar heating devices.

The figure shows the use of a plane mirror as a reflector. In the diagram, it is clearly shown that a part of solar energy enters directly into a solar heating device and a part is reflected in it by the plane mirror. As the solar heating device receives more energy per unit time, its temperature rises quickly.