Solar thermal uses the heat in sunlight to generate energy, rathern than using photons striking a photovoltaic panel. It is a much older technology, and in my opinion one that holds a lot of promise.

This is an interesting article about the resurgence of solar thermal research from the magazine Popular Mechanics. An excerpt follows:

“The heat is used to run a Stirling engine, an elegant 192-year-old technology that creates mechanical energy from an external heat source, as opposed to the internal fuel combustion that powers most auto­mobile engines. Hydrogen gas in a Stirling engine’s four 95 cc cylinders expands and contracts as it is heated and cooled, driving pistons to turn a small electric generator. The configuration of the dish and engine represent the fruit of more than a decade of steady improvements, developed in collaboration with Arizona-based Stirling Energy Systems.”