U.S. Department of Energy - Energy Efficiency and Renewable Energy

Solar Energy Technologies Program

Power Tower Systems

Power tower systems are one of the three types of concentrating solar power (CSP) technologies in use today. Here you will learn about the basic operation of power tower systems.

In this CSP technology, numerous large, flat, sun-tracking mirrors, known as heliostats, focus sunlight onto a receiver at the top of a 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.

Illustration of a power tower power plant. Sunlight is shown reflecting off a series of heliostats surrounding the tower and onto the receiver at the top of the tower. The hot heat-transfer fluid (shown as red) exiting from the receiver flows down the tower, into a feedwater reheater, then into a turbine, generating electricity that is fed into the power grid. The cool heat-transfer fluid (shown as blue) exiting the turbine flows into a steam condenser to be cooled and sent back up the tower to the receiver.

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, 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 for 24 hours a day for almost seven consecutive days before cloudy weather interrupted operation.

Currently, Spain has several power tower systems operating or under construction. 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.

Power towers also offer good longer-term prospects because of the high solar-to-electrical conversion efficiency. Additionally, costs will likely drop as the technology matures.

Learn more about DOE's power tower R&D.