### Q.23:- A family uses 8 kW of power. (a) Direct solar energy is incident on the horizontal surface at an average rate of 200 W per square meter. If 20% of this energy can be converted to useful electrical energy, how large an area is needed to supply 8 kW? (b) Compare this area to that of the roof of a typical house.

**Answer:-**(a)** **Power used by the family, *P* = 8 kW = 8 × 10^{3} W

Solar energy received per square metre = 200 W

Efficiency of conversion from solar to electricity energy = 20 %

Area required to generate the desired electricity = *A*

As per the information given in the question, we have:

8 × 10^{3} = 20% × (*A* × 200)

= (20 /100) × *A* × 200

∴ *A* = 8 × 10^{3} / 40 = 200 m^{2}

(b)** **The area of a solar plate required to generate 8 kW of electricity is almost equivalent to the area of the roof of a building having dimensions 14 m × 14 m. (≈ √200).