The world's largest solar thermal power plant has been in operation for 2 decades in the California Mojave desert. Nine plants with a total capacity of 350 MWe providing enough electricity to meet the residential needs of a city with 250,000 people (implying an availability of the power plant at full-load equivalent of approximately 2,500 hours).
Solar thermal power generation is promising, since it complements well other forms of ambient generation - for example, wind power generation peaks in winter, while solar thermal peaks in summer. And during poor hydroelectric periods, solar power is naturally higher. And through thermal energy storage, generation can be semi-dispatchable. Learning effects have reduced generation cost, and further major cost reductions are possible.
Despite this, no new solar thermal power plant has been constructed in the USA for 20 years, but a (symbolic) new 1 MW plant has just started operation in Arizona.
A planned 500 MW project may become the next biggest facility in the coming decade.