Hawaii's Energy Future - Concentrated Solar Power

Renewable

Energy Sources

Concentrated Solar Power

Concentrating solar technologies utilize concentrated sunlight to produce electricity directly (photovoltaics) or by capturing heat (solar thermal electric). Concentrating photovoltaic and solar thermal electric technologies (parabolic trough, parabolic dish, central receiver, and solar chimney) are in various stages of development.

Parabolic trough systems focus the sun's energy through long rectangular, curved mirrors. The mirrors follow the sun, focusing sunlight on a pipe that runs down the center of the trough. This heats an oil flowing through the pipe. The hot oil can be used to produce electricity, air conditioning or drinking water from sea water. Parabolic trough systems have been reliably operating in the U.S. for over 22 years.
Concentrating photovoltaic systems use lenses to concentrate sunlight on high efficiency photovoltaic cells to produce electricity. By concentrating sunlight, higher efficiencies can be achieved and less photovoltaic material is required. Concentrating photovoltaic systems are currently undergoing research and demonstration to further improve performance, increase reliability, and reduce costs.
Parabolic dish systems use parabolic reflectors arranged in a dish-type pattern to focus concentrated sunlight onto a receiver (e.g., Stirling engine) located at the focal point of the dish. The sunlight heats a working fluid (e.g, hydrogen or helium) in a reciprocating Stirling engine to produce mechanical power which is then converted to electricity by an electric generator. Another application is to use the focused sunlight on photovoltaic cells mounted on the receiver to produce electricity.
Central receiver systems, or power towers, use hundreds of mirrors called heliostats to track the sun and focus concentrated solar energy on a tower-mounted heat exchanger. The concentrated solar radiation heats water, or a molten salt that transfers heat to water, to produce steam for a conventional steam turbine cycle. Two central receiver systems were operated in the U.S. in the late 1980s and 1990s.
Solar chimneys do not use a thermal heat cycle to produce power, but instead generate and collect hot air in a large greenhouse. The hot air rises and enters a tall chimney located at the center of the greenhouse. A wind current is produced from the natural updraft of the hot air. This air movement turns a series of air turbines to generate electricity. The first solar chimney is currently under development in Australia.