Electricity companies are coming out with plans to build large solar-thermal power plants in the deserts of the Southwest United States. Solar thermal technology promises lower construction costs and higher thermodynamic efficiency compared with the more familiar photovoltaic panels, and also offers the possibility for storage and hybrid operation with natural gas. There is only one catch which some developers are finding: water. It takes water to cool the plants, billions of gallons of it per year, in a place where there is already fierce competition for water resources.
Most thermal power plants, whether solar, coal, nuclear, gas, or geothermal, utilize wet cooling. Evaporating water carries the waste heat away from the plant in an extremely efficient manner and allows the temperature of the plant's heat sink to be lower than the ambient air temperature, especially in dry desert regions. In a water-starved area, however, sending all of this pristine water into the sky is not an option.
Dry cooling towers use mechanical draft (electrically-driven fans) to blow air over a heat exchanger carrying the hot water from the condenser. The problem is that the temperature to which the condenser can be cooled is limited to the ambient air temperature (which in the desert reaches above 100°F during prime power production periods), and requires electricity to drive the fans. The lower temperature difference between the boiler and heat sink results in an efficiency hit as does the need to send electricity to the cooling fans instead of the grid. Lower thermodynamic efficiency increases the economic cost of electricity production.
It is a serious setback, and another example of the interconnection of ecological issues and how technology has limits. Shop-till-ya'-Drop throwaway culture isn't going to find its salvation in renewable energy or any form of energy production for that matter, including $8000/kW nuclear power plants for those free market capitalists pushing nuclear energy and its "affordability". The same goes for IGCC coal with front groups (e.g. America's Power) putting the "Affordable Clean Coal" fossil fuel techno-fix in our faces with little idea of how much it will really cost.
Solar photovoltaic systems do not require water at all (besides for periodic panel washing), and may have an advantage in desert areas despite the higher cost and lower efficiency. Where water is available, the thermal option is superior. Solar thermal on homes and other buildings to replace electric water heating should also be highly promoted in national and state energy policies.