Question

why are concave mirrors used in solar devices?

Answer 1

it is it because of converging nature of concave mirror it focus the heat or sun rays to one point to generate more heat

Answer 2

(1) When rays of light coming from a distant object or source such as the sun and parallel to the principal axis are incident on a single point (focus). Thus, a concave mirror is a focusing mirror.

(2) This result is concentration of heat of the sunlight at that point. Hence, concave mirrors are used in solar devices.