Africa Defense Forum
ADF is a professional military magazine published quarterly by U.S. Africa Command to provide an international forum for African security professionals. ADF covers topics such as counter terrorism strategies, security and defense operations, transnational crime, and all other issues affecting peace, stability, and good governance on the African continent.

South Africa Moves Into Solar Age

West of the town of Upington, South Africa, is mostly desert. But nearby a tower looms on the horizon.

It stands 5 kilometers down a bumpy dirt road, a 200-meter cylinder stretching to the sky, surrounded by more than 4,000 large, wall-like solar mirrors. It may look like the set of a science fiction film, but this is Khi Solar One, Africa’s first concentrated solar power project.

The 140-hectare plant will produce 50 megawatts (MW) of energy and reduce South Africa’s carbon dioxide emissions by 138,000 metric tons a year.

Khi Solar One forms part of the Department of Energy’s bid to bring 1,400 MW of wind- and solar-based energy online by 2016. It is part of the South African government’s larger strategy to generate 17,800 MW from renewable energy by 2030.

The energy produced will be sold to channel it to the national grid. Kurt Drewes, Khi Solar One’s general manager, said it will serve South Africans in the evenings, when energy use is at its peak.

Concentrated solar power gets its name from using mirrors to concentrate sunlight, creating temperatures high enough to drive steam turbines or engines that in turn create electricity. At the heart of the Khi Solar One plant is the hollowed-out superheated steam solar tower. Stretching 205 meters, the tower is surrounded by 4,200 concave solar mirror panels. These are tilted at an angle that reflects the sun’s rays onto the top of the tower. Each panel has an autonomous computerized control system with a GPS signal that tells it the exact time of day. It determines the sun’s angle and adjusts for light to be reflected to the top of the tower.

The tower is filled with boiling tubes, painted black to absorb heat from the reflection. These contain high-pressure water pumped from the Orange River. When the sun’s rays are reflected onto the tubes, the water heats until it becomes steam. The steam is heated further, to 500 degrees Celsius, to create enough pressure to turn the turbine and produce electricity.

The tower has a dry-cooling system, an innovation in concentrated solar power. The walls, Drewes said, have openings to allow in air, making it both a heating and cooling tower when required.

Concentrated solar power is the only renewable energy technology that can effectively store power. Khi Solar One has two hours of steam storage capacity — the longest in the world. Although this may seem short, the advantage of concentrated solar power is that supply can be adjusted to meet the demand. If capacity needs to be increased, they do not have to make the tower bigger. They would simply increase the surface of the mirrors, which Drewes said is easy to do.

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