In the past, how was solar energy concentrated to produce heat?

ماضی میں ، گرمی پیدا کرنے کے لئے شمسی توانائی کس طرح مرکوز تھی؟

Using electric motors

Using spherical mirrors and lenses

Using coal and gas

None of these

Concave mirrors or lenses were used to focus sunlight onto a single point.

This focused sunlight generated high temperatures for cooking or heating.