Themis opened in 1983 as an experimental power plant - the sun's power was directed, via the mirrors (called heliostats), to the top of the "power tower", where it heated a boiler and the thermal energy powered an electic turbine. It was only used like this until 1986, when, due to a lack of political and finincial commitment the plant was closed for more than 20 years. According to wikipedia, there is now a plan to redevelop the plant as a research center into solar power - although there was not a lot happening when I visited. If you look closely at the top of the tower (where there seem to be quite a few families of birds living) - you can see a couple of big burn marks where it looks like someone didnt quite aim the mirrors properly.