Solar thermal power plants can use twice as much water as fossil fuel plants and are generally in deserts. The problem is obvious, water is pumped from aquifers. The primary advantage solar thermal has over solar photovoltaic (which uses practically no water) is energy can be stored for later use. Solar thermal reflects the heat of the sun to a central tower to power steam turbines. Excess heat can be stored in molten salt and used to create power when the sun isn’t shining. This makes power production steadier and more reliable.
Newer solar thermal plants use dry cooling rather than evaporation. However, it is costlier and doesn’t work efficiently on hot days, forcing cutbacks in production precisely when it is needed the most.
One approach to solving this problem is to oversize the cooling system so that it can deliver enough cooling even on hot days. That’s the approach taken by the developers of California’s new Ivanpah solar thermal plant, which is about to start production. But it adds to the cost of an already expensive system.
However, the extra cost is generally about 5% of the total construction cost and reduces water use by 90% over traditional methods.