METHODS OF ENHANCING THE COLLECTION OF SOLAR ENERGY.

• As we know that Earth receives 0.64 kJ of heat energy per second per square meter on an average. Furthermore, this energy is quiet diffused and as such it is too small to do any useful work.

FOLLOWING ARE METHODS OF COLLECTING SOLAR ENERGY & INCREASING ITS INTENSITY PER SQUARE METER• Use of black painted surface :- black surfaces are good

absorbers as well as good radiators of radiant heat. Thus, the objects which are to collect radiant heat are painted black, so that their temperature rises rapidly. But this is not enough because the amount of energy received, the same amount is radiated out so there is a equilibrium state reached when no more solar energy is absorbed. Hence the temperature of the object stops rising and it cannot collect more solar energy. To overcome this difficulty some means should be taken to reduce the rate of radiant heat or stop it all together.

Incoming heat radiation

Out going radiant heat

• Use of insulated box with glass cover :- the objects painted black, should be placed in well insulated box provided with glass cover. The insulated box will prevent heat looses due to conduction, convection & radiation. The glass allows the solar radiation to enter being transparent to smaller wavelengths, but does not allow the radiated heat from the black painted surface to move out as it acts as a barrier to the longer wavelengths. Hence, increasing the temperature of the objects with blackened surface.

Smaller wavelengths

Long wavelengths

Reflected back

• Use of reflectors:- as mentioned earlier, the of solar energy per square meter per second is too small to do any useful work. Thus, if the solar energy is directly allowed to enter a solar heating device, it does not raise the temperature sufficiently. So the energy is collected from a large area and reflected into the solar device. Hence, the temperature increases which could do sufficient work.

reflection

• Solar cooker

is used for cooking dal & pulses . The temperature reaches 140 degree C, which is sufficient to cook food in 2 to 3 hours.

• Solar water heater

is used in bog hotels , hospitals & industries which need hot water for various purposes.

APPLICATIONS

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