Monday, March 9, 2009

Solar Thermal Energy

Solar: Solar Thermal: Making Electricity From The Sun's Heat

  • Solar thermal electric power plant generates heat by using lenses and reflectors to concentrate the sun's energy. Because the heat can be stored, these plants are unique because they can generate power when it is needed, day or night, rain or shine.

  • Solar thermal electric systems operating in the US today [Solar Parabolic Troughs] meet the needs of over 350,000 people (equal to the population of the city of Fresno, CA or Miami, FL) and displace the equivalent of 2.3 million barrels of oil annually.

  • Solar thermal power plants create two and one-half times as many skilled, high paying jobs as do conventional power plants that use fossil fuels.

  • A CEC (California Energy Commission) study shows that even with existing tax credits, a solar thermal electric plant pays about 1.7 times more in federal, state, and local taxes than an equivalent natural gas combined cycle plant. If the plants paid the same level of taxes, their cost of electricity would be roughly the same.

  • Solar Two, a "power tower" electricity generating plant in California, is a 10-megawatt prototype for large-scale commercial power plants. It stores the sun's energy in molten salt at 1050 degrees F, which allows the plant to generate power day and night, rain or shine. Construction was completed in March 1996, and it is now in its three year operating and testing phase. (source: Southern California Edison)

  • Over 700 megawatts of solar thermal electric systems should be deployed by the year 2003 in the U.S. and internationally. The market for these systems should exceed 5,000 megawatts by 2010, enough to serve the residential needs of 7 million people (larger than the state of Georgia) which will save the energy equivalent of 46 million barrels of oil per year.

  • Utilizing only 1% of the earth's deserts to produce clean solar electric energy would provide more electricity than is currently being produced on the entire planet by fossil fuels.

  • The sun's heat can be collected in a variety of different ways: Solar Parabolic Troughs consist of curved mirrors which form troughs that focus the sun's energy on a pipe. A fluid, typically oil, is circulated through the pipes which is used to drive a conventional generator to create electricity. Solar Parabolic Dish systems consist of a parabolic-shaped concentrator (similar in shape to a satellite dish) that reflects solar radiation onto a receiver mounted at the focal point at the center. The collected heat is utilized directly by a heat engine mounted on the receiver which generates electricity. Solar Central Receivers or "Power Towers" consist of a tower surrounded by a large array of heliostats. Heliostats are mirrors that track the sun and reflect its rays onto the receiver, which absorbs the heat energy that is then utilized in driving a turbine electric generator.

  • Why Solar Thermal Energy?

  • The myth about baseload power is always used to attack solar electricity, which of course is only available during daylight hours. This myth is based on misconceptions.

    Firstly, not all forms of electricity generation are required to supply baseload and there is a very valuable place for technologies that can supply power during the day when the demand for electricity is greater than overnight.

    Secondly, the rapid advancement in solar thermal electricity generation, producing steam to drive a turbine and generator, can be easily combined with geothermal energy (hot rocks) which can produce steam day and night.

    Australia, USA, Spain, South Africa, Israel and other countries are very well placed to deploy these technologies because they have many locations where power grids run through very sunny inland where geothermal energy exists. Australia is a particularly good example of this.

    Thirdly, should it be considered necessary for solar energy to be available overnight, there are now very good prospects for the commercialisation of several different energy storage technologies that will make this possible.

    These include vanadium redox and inc-bromine batteries, both of which are being developed in Australia and elsewhere. And sometimes as is the case with Australia there is government financial support for demonstration installations.

    In summary, an electricity system that uses a mix of different renewable technologies such as geothermal, wind and wave power along with some energy storage and a good geographical dispersion of solar thermal energy generation, will have just as much ability to supply reliable baseload power as the current coal based generation system.

    One should just remember, in less than an hour every day the sun produces more energy than we all need globally in a year. We just need to capture some of it. 1% will more than suffice to meet our current and future world needs.

Stirling Energy Systems, Inc. (SES)/Boeing, 25 kW Dish Stirling system at sunset.

Stirling Energy Systems, Inc. (SES)/Boeing, 25 kW Dish Stirling system at sunset.

Source: National Renewable Energy Laboratory, Photographic Information Exchange.

Solar thermal devices use direct heat from the sun, concentrating it in some manner to produce heat at useful temperatures. The modern solar industry began with the oil embargo of 1973-1974 and was strengthened with the second embargo in 1979. The growth of the solar industry during this period of fuel shortages and high prices (1974-1984) soared from 45 solar collector manufacturing firms to 225 firms.The solar market was helped during this period by government assistance, both Federal and State. Currently, solar thermal devices do everything from heating swimming pools to creating steam for electricity generation.

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