February 16, 2009 | 29 comments
By Matthew L. Wald
In solar-thermal, a trough-shaped mirror that tracks the sun over the course of the day focuses light to heat an oil- or water-based fluid in a black pipe. The pipe snakes over miles to a heat exchanger, which makes steam to drive a turbine. The system can be built as an adjunct to a natural gas–fired plant, so that gas can make steam during cloudy periods or after sunset. Future models may substitute molten sodium as the working fluid, which would allow higher temperatures without requiring higher pressures.
A variant is a “power tower,” which looks a bit like a water tower but is filled with molten sodium and heated by a vast array of mirrors, some at a distance of a kilometer. The sodium can be connected to an insulated tank and can store enough heat to run around the clock or at least well into high-demand times.
March
Adapting to the Freshwater CrisisForward-thinking experts are getting a better handle on the growing global water shortage and coming up with innovative approaches to ensuring the security, safety and sustainability of this resource
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