Solar Energy Faces Problems In Drought-Stricken California

  • Date: 05/02/14
  • Kevin Bullis, MIT Technology Review

Reducing water consumption at solar thermal plants raises costs and decreases power production.

The drought is already forcing solar thermal power plant developers to use alternative cooling approaches to reduce water consumption. This will both raise costs and decrease electricity production, especially in the summer months when demand for electricity is high. Several research groups across the country are developing ways to reduce those costs and avoid reductions in power output.

Solar thermal power plants use large fields of mirrors to concentrate sunlight and heat water, producing steam that spins power-plant turbines. Utilities like them because their power output is much less variable than power from banks of solar panels (see “BrightSource Pushes Ahead on Another Massive Solar Thermal Plant” and “Sharper Computer Models Clear the Way for More Wind Power”).

The drawbacks are that solar thermal plants generate large amounts of waste heat, and they consume a lot of water for cooling, which is usually done by evaporating water. Solar thermal plants can consume twice as much water as fossil fuel power plants, and one recently proposed solar thermal project would have consumed about 500 million gallons of water a year.

A technology called dry cooling, which has started appearing in power plants in the last 10 years or so, can cut that water consumption by 90 percent. Instead of evaporating water to cool the plant, the technology keeps the water contained in a closed system. As it cools the power plant, the water heats up and is then circulated through huge, eight-story cooling towers that work much like the radiator in a car.

Dry cooling technology costs from two and a half to five times more than conventional evaporative cooling systems. And it doesn’t work well on hot days, sometimes forcing power plant operators to cut back on power production. In the summer, this can decrease power production by 10 to 15 percent, says Jessica Shi, a technical program manager at the Electric Power Research Institute. On extremely hot days, power production might be reduced even more than that.

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