An array of heliostats continuously concentrates sunlight onto the receiver at the top of the tower.

Central tower solar power plants belong to the category of concentrating solar power (CSP) systems. They concentrate direct solar radiation collected over a large area onto a receiver at the top of a tower. To achieve this, they use sun-tracking mirrors called heliostats, which are distributed around the tower. A computer continually calculates the Sun’s position in the sky and adjusts the heliostats to ensure that the reflected sunlight remains aimed at the receiver at the top of the tower.

In the receiver, a heat-transfer medium is heated and, in some systems, part of the thermal energy is stored in molten-salt storage tanks for later use.

The solar receiver is located at the top of the central tower, while the power-generation equipment is generally located at ground level. Due to the high concentration of solar energy, temperatures in the receiver can exceed 500 °C. These high temperatures improve the efficiency of converting thermal energy into electricity.

Diagram of a central tower solar power plant.

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The first central tower solar power plants were built in the 1980s. One of the most important early projects was the 10 MW Solar One pilot plant in California’s Mojave Desert (map). It used water/steam as the heat-transfer medium and an oil-and-rock thermal energy storage system. In the mid-1990s, Solar One was converted into Solar Two to demonstrate molten-salt heat transfer and thermal energy storage. A later Spanish project originally known as Solar Tres was developed into the Gemasolar power tower plant (map), which entered operation in 2011 with an electrical capacity of about 20 MW and molten-salt thermal energy storage. Other important Spanish power tower plants include PS10 (map) and PS20 (map), with installed capacities of 11 MW and 20 MW respectively.