In power tower concentrating solar power systems, numerous large, flat, sun-tracking mirrors, known as heliostats, focus sunlight onto a receiver at the top of a tall tower. A heat-transfer fluid heated in the receiver is used to generate steam, which, in turn, is used in a conventional turbine generator to produce electricity. Some power towers use water/steam as the heat-transfer fluid. Other advanced designs are experimenting with molten nitrate salt because of its superior heat-transfer and energy-storage capabilities. Individual commercial plants can be sized to produce up to 200 megawatts of electricity.
|A power tower power plant.|
Two large-scale power tower demonstration projects have been deployed in the United States. During its operation from 1982 to 1988, the 10-megawatt Solar One plant near Barstow, California, demonstrated the viability of power towers by producing more than 38 million kilowatt-hours of electricity.
The Solar Two plant was a retrofit of Solar One to demonstrate the advantages of molten salt for heat transfer and thermal storage. Using its highly efficient molten-salt energy storage system, Solar Two successfully demonstrated efficient collection of solar energy and dispatch of electricity. It also demonstrated the ability to routinely produce electricity during cloudy weather and at night. In one demonstration, Solar Two delivered power to the grid 24 hours a day for almost 7 consecutive days before cloudy weather interrupted operation.
Spain has several power tower systems. Planta Solar 10 and Planta Solar 20 are water/steam systems with capacities of 11 and 20 megawatts, respectively. Solar Tres will produce some 15 megawatts of electricity and have the capacity for molten-salt thermal storage.
To learn about other types of concentrating solar power systems, see: