Concentrated Solar Thermal SystemsCST power plants (often referred to as CSP) produce heat from sunlight, which is subsequently converted into electricity. A number of technologies have been developed to concentrate and collect sunlight. The collected sunlight creates heat, which in turn is used to drive a turbine and generator as in a conventional power station. |
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Stand-Alone Solar Rankine SystemPrincipleIn a stand-alone configuration, a heat transfer fluid is heated as it circulates through the receivers in the collectors. It runs trhough a heat exchange to generate high-pressure heated steam. The steam is then fed into a separate circle to drive a conventional steam turbine. The spent steam from the turbine is condensed into liquid ready to be re-heated in the steam generator to complete the circle.Storage TankThe system becomes more 'despatchable" with the addition of a storage tank.
Most CST power plants operate according to the Rankine cycle, a thermodynamic cycle that uses steam as a working fluid at temperatures up to 655°C. Required cooling comes usually from water. The exception is the parabolic dish. |
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Hybrid SystemFossil Fuel BackupThough CST plants can operate at their full rated electric power for up to 12 hours a day in clear and sunny locations, most CST plants include a fossil-fuelled backup capability that can be used to supplement the solar output during periods of low solar readiation. Power plants in California have been connected to the grid for years, and use up to 25% natural gas in order to cover sunless periods. |
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Integrated Solar Combined Cycle System (ISCC)
Combined Cycle SystemThe gas turbine in a combined cycle system operates at an input temperature range from 900°C - 1,400°C while the output ranges from 450°C to 650°C. This high output temperature makes the combination with a Rankine cycle as the second cycle very appealing. To achieve this, the heat from the gas turbine is fed into the waste heat recover system, which produces high-pressure steam (420°C - 580°C) for the steam cycle.Integration of CSTTo increase the power output from the second cycle, solar heat is used either to produce high-pressure steam fed into the waste heat recovery system or to produce additional low-pressure steam for the Rankine turbine.The ISCC design is particularly promising, as many combined-cycle plants will be built regardless, though their efficiency can be greatly augmented by the use of solar thermal heat. ProjectThe first such project is being built in Algeria with a total plant capacity of 150MW, 20MW of which will be supplied by a solar thermal trough system. It will have 180,000m² of solar collectors. |