Over at Treehugger, they have a clip of a BBC show, in which they use a solar oven made out of mirrors to melt a rock.

The solar oven uses concave mirrors to concentrate sunlight. Stand-out features, beside the melting rock, include the nervous scientist trying to keep the BBC reporter from sticking his hand into the oven, and the reporter's priceless delivery of 'oh my life' when the oven sets fire to a piece of wood.