Solar thermal tower plant (solar one)

Solar one, which operated from 1992 to 2000, was the world’s largest power tower plant. In that plant water was converted to steam in the receiver and used directly to power a conventional steam turbine. The project met most of its technical objectives by demonstrating (1) the feasibility of generating power with a power tower, (2) the ability to generate 10MWe for eight hours at summer solstice and four hours a day at winter solstice. During its final year of operation, Solar One’s availability during hours of sunshine was 96% and its annual efficiency was about 7%. (Annual efficiency was relatively low because of the plant’s small size.) The Solar One thermal storage system stored heat from solar-produced steam in a tank filled with rocks and sand using oil as a heat transfer fluid. The system extended the plant’s power capability at night and provided heat for keeping parts of the plant warm during off-hours and for morning start up.

Unfortunately, the storage system was complex and thermodynamically inefficient. While Solar One successfully demonstrated power tower technology, it also revealed the disadvantages of a water/steam system, such as the intermittent operation of the turbine due to clouds and lack of effective thermal storage.

To encourage the development of molten-salt towers, a consortium of utilities redesigned the Solar One plant to include a molten-salt heat transfer system. The goals of the redesigned plant, called Solar Two, are to validate nitrate salt technology, to reduce the technical and economic risk of power towers, and to stimulate commercialization of power tower technology. Solar Tower has produced 10 MW of electricity with enough thermal storage to continue to operate the turbine at full capacity for three hours after the sun has set. Long-term reliability is next to be proven. Solar Two was the first to be attached to a grid in early 2001.