Central Tower Solar Power Plants

An array of heliostats continuously concentrates the sunlight to the flat absorber at the top of the tower. (Source: © Darren Baker / stock.adobe.com)

An array of heliostats continuously concentrates the sunlight to the flat absorber at the top of the tower.

Central tower solar power plants fall into the category of concentrated solar systems. They concentrate solar radiation from a huge area into a very small space on top of a tower. To achieve that, they use flat mirrors, called heliostats, which are distributed around the tower with the absorber. A computer continually calculates the Sun’s position in the sky and adjusts the heliostats every few seconds to track it, to ensure the reflected light stays aimed at the top of the tower.

In the absorber, a heat-transfer medium is heated up and in some cases a part of the energy goes into molten salt-based thermal accumulators.

All the energy conversion technology is located in the central tower. Due to the high concentration of energy, relatively high temperatures are reached in the absorber, commonly exceeding 500 °C. This improves the heat-to-electricity conversion efficiency.

Diagram of central tower solar power plant

Diagram of central tower solar power plant

The first central tower solar power plants were built in the eighties. The most important was the pilot project Solar One power plant located in the Mohave Desert, California (map). It had an installed capacity of 10 MW, water as the heat transfer medium and an oil-rock thermal accumulator. In the mid-nineties, Solar One was redesigned to test the molten salt thermal energy storage technology and renamed Solar Two. Based on the success of the Solar Project, a similar plant was built in Spain, the Solar Tres Power Tower (map), which has an installed capacity of 15 MW. The Spanish central tower solar power plants PS 10 (map) and PS 20 (map) with their 11 and 20 MW of installed capacity respectively are also among the more powerful plants of this type.

A view of the PS 10 and PS 20 central tower solar power plant near Seville, in Andalusia, Spain. (Source: © SHD / stock.adobe.com)
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A central tower solar power plant with a circular absorber, which allows for the heliostats to be positioned evenly around the central tower. (Source: © paulrommer / stock.adobe.com)
The towers of the PS 10 and PS 20 solar power plants in Andalusia (Spain) awaiting the sun to rise. (Source: © Darren Baker / stock.adobe.com)
A field of mirrors — heliostats ready to reflect the first sunbeams of the day at the top of the tower. (Source: © Darren Baker / stock.adobe.com)
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