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Concentrated Solar Thermal Power Generation


Of all the renewable power generation technologies being developed, concentrated solar thermal is probably the most promising due to it's low cost and it's potential for energy storage so that power can be generated even if the sun is not shining. It is called "concentrated" because mirrors are used to concentrate the sun's energy providing higher temperatures for steam generation.

There are two basic solar thermal techniques being investigated:
  • Trough Mirror
    The most tested technology consists of an array of long so-called "trough" mirrors. Each mirror reflects sunlight onto a long tube at its focal line that is filled with liquid (usually an oil). The tube is encased in a glass "thermos" tube for insulation. The oil circulates constantly, carrying heat to a central steam turbine or to a storage tank. The trough mirrors track the sun in only one dimension (vertically). Their length eliminates the need for more complex tracking
  • Power Tower
    The most promising economically is the "power tower" centrally located in a circular array of simple mirrors which track the sun accurately both vertically and horizontally. They aim sunlight at the top of the tower where a collector provides very high temperatures for generating steam for turbines. Excess super-heated liquid can be stored.
The power tower design requires less complex mirrors and less plumbing and oil circulation. It doesn't need the miles of evacuated glass insulating tubes as well. This more than compensates economically for the more complex tracking.

Here's a paper on the Ausra companies website that gives a good explanation of various types of solar thermal technology.