Archimedes is said to have used it to torch the sales of invading Roman galleons.  In the early middle ages, it was used in Italy to melt lead.  Leonardo da Vinci designed machines to “automate” the polishing of curved solar reflectors.  And kids still focus the sun’s rays on un-suspecting ants.

“It’s only when you look closely at an ant
through a magnifying glass on a sunny day
that you realize how often
they burst into flames”
                                            Harry Hill

Concentrating solar technology is still very much alive & well.  Very large concentrating solar arrays of varying designs are being used in the U.S. and in other parts of the world to generate steam which in turn is used to generate electricity.  The fuel is free, and so is the pollution (pollution-free that is).

For more information download Concentrating Solar Power Technology