The Energy Blog has an interesting post about solar towers, a method of solar power generation. The tower is surrounded by mirrors which reflect sunlight onto a receiver at the top of the tower (the mirrors move to track the sun). Fluids are pumped through pipes in the receiver for heat exchange, and the fluids are then used in steam generators.
The post contains a link to a previous post with more details about the types of fluids used for heat exchange: it's a salt mixture which is able to retain heat for power generation at night or in cloudy weather.
The process is said to be over 40% effective in converting thermal energy into electricity.