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

Here total power , P = 8 kW = 8,000 W
Let the area needed to supply this power `A m^(2)`
Energy incidence per unit area = 200 W
Energy incidence on area A = 200 A W
Energy converted into useful electric energy = 20 % of 200 A
` = 20/100 xx 200 A W `
` = 40 A W `
As 40 AW = 8 kW
40 AW = `8 xx1000 W`
(b) This area is comparable to a roof of largee sized house of dimensions `(14xx14)` m