[katieHaylor (OP)]

Meesam asks:

Can we use a concave mirror to focus sunlight?

What do you think?

[Bored chemist]

Yes.
A parabola does it best. A spherical one more or less works, and is easier to make.

[evan_au]

Can we use a concave mirror to focus sunlight?

Yes, But....  There is a limit to the extent you can focus the sunlight.

The Sun is about half a degree across in the sky. The image of the Sun will also be about half a degree across on the target.

This limits the intensity you can achieve, so you can't produce temperatures hotter than the surface of the Sun.

This is sort of implied by the laws of thermodynamics: If you could focus light from the Sun to produce a temperature hotter than the surface of the Sun, you could (in principle) use the surface of the Sun as the "cold" end of a heat engine, and produce energy for nothing in a closed system.

Nevertheless, those molten-salt thermal solar plants look pretty impressive!
https://en.wikipedia.org/wiki/Solar_power_tower