A family uses 8kW of power. (a) Direct solar energy is incident on the horizontal surface at an average rate of 200 W per square metre. If `20%` of this energy can be converted to useful electrical energy, how large an area is needed to supply 8kW? (a) Compare this area to that of the roof of a typical house.

Explanation

Let the area be A square metre.
`:.` Total power `=200A`.
Useful electrical energy produced `//` sec `=(20)/(100)(200A)=40A=8000(2wat t)`
Therefore, `A=(8000)/(40)=200sq. m`
This area is comparable to the roof of a large house of 250sq. metre.