Solar power plant

Pages: 5 (1095 mots) Publié le: 1 février 2011
| Solar Power PlantSolar Trough SystemTrough systems predominate among today’s commercial solar power plants. Trough systems convert the heat from the sun into electricity. Because of their parabolic shape, troughs can focus the sun at 30 to 60 times its normal intensity on a receiver pipe located along the focal line of the trough. Synthetic oil captures this heat as the oil circulatesthrough the pipe, reaching temperatures as high as 390°C (735ºF). The hot oil is pumped to a generating station and routed through a heat exchanger to produce steam. Finally, electricity is produced in a conventional steam turbine.Composition of the reflectorsThe reflectors are composed of individual concentrator modules that are a consist of a steel support structure with a mirror mounted on it. Development efforts are aimed at reducing the thickness of the mirror, improving the reliability of the glass to metal seal, surface coatings on the mirrors to improve their performance and development of a composite concentrator modules with lightweight, front-surface mirrors instead of heavy (4 mm) glass mirrors that were used on the original SEGS plantsHow does it work?The fluid going throughthe receiver pipe is routed through a thermal storage system which permits the plant to keep operating for several hours after sunset while the electrical demand is still relatively high.  The thermal storage system (to be used in Spain) is a two tank system in which the HTF flows through the solar field and then through a heat exchanger where it gives up a portion of its heat to heat a nitratesalt solution that is stored in a hot salt tank.  The slightly cooled HTF continues on to the power generation system.  At night the hot salt solution flows through the same heat exchanger heating up the HTF for generating power.  The cooler oil flows from the heat exchanger to the cold storage tank where it stays until daytime when it is reheated and returned to the hot storage tank.Solar Power TowersThese systems produce electricity on a large scale. They are unique among solar technologies because they can store energy efficiently and cost effectively. They can operate whenever the customer needs power, even after dark or during cloudy weather. Power towers operate by focusing a field of thousands of mirrors onto a receiver located at the top of a centrally located tower.The receiver collects the sun's heat in a heat-transfer fluid, which is used to generate steam for a conventional steam turbine located at the foot of the tower for production of electricity. Early power towers use steam as the heat transfer fluid. Current power towers use molten nitrate salt. Nitrate salt is used because of its superior heat transfer and energy storage capabilities.Advantages ofUsing Molten Salt A variety of fluids was tested to transport the sun's heat, including water, air, oil, and sodium, before molten salt was selected as best. Molten salt is used in solar power tower systems because it is liquid at atmosphere pressure, it provides an efficient, low-cost medium in which to store thermal energy, its operating temperatures are compatible with todays high-pressure andhigh-temperature steam turbines, and it is non-flammable and nontoxic. In addition, molten salt is used in the chemical and metals industries as a heat-transport fluid, so experience with molten-salt systems exists for non-solar applications.The Salt Mixture A mixture of 60 percent sodium nitrate and 40 percent potassium nitrate is employed as the salt storage medium. This salt melts at 220ºC andis maintained in a molten state of 290ºC in the ‘cold’ storage tank. It is then traveled through the receiver where it is heated to 565ºC and then on to a ‘hot’ tank for storage.Hot salt is pumped to a steam generating system when power is needed from the plant. These hot salts produce superheated steam for a conventional Rankine-cycle turbine generator system. From the steam generator, the salt...
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