The solar furnaces are simply a form of solar collectors constructed as huge buildings that are used for one purpose – to concentrate the rays of the sun by use of parabolic mirrors or heliostatic mirror arrays (mirrors that follow the sun as it track across the sky) into a relatively small (about a foot square) point of light. That point of light usually culminates in a building away from the mirrors, in a special environmental room that captures the heat produced by the light. The furnaces can achieve a temperature of 4,000 degrees Celsius (well over 7,000 degrees Fahrenheit) at the point of light. The temperature can easily be controlled by controlling the focus of the light. (Invention of this type of solar concentration is generally attributed to Wolfgang Scheffler, although this is hard to confirm or deny.)
The concentrated heat from these solar collectors is then used to generate power of some kind. Some examples would be to heat water to turn it to steam, then use the steam to power engines. The heat can also be used to power Stirling engines to generate electricity. In at least one solar furnace, the heat is used directly to melt metal to produce nanomaterials. In another plant currently under construction in India, the government hopes to use the furnace as a crematorium. In this case, the solar furnace can prevent the burning of up to 300 kilograms of wood per cremation.
Solar furnaces are not used extensively around the world, although their use may become more popular as the positive results from the current installations are discovered. There are currently solar furnaces generating electricity in France and Russia.