July 23, 2017 – Over 10,000 tracking heliostats focus solar energy at the receiver on the 640 foot power tower at the Crescent Dunes Solar Thermal Facility, owned by SolarReserve. The facility, built with US sourced steel, glass and technology, provides more than 500,000 megawatt hours of electricity per year, available day or night through molten salt storage. (Photo by Dennis Schroeder / NREL)

Many power plants today use fossil fuels as a heat source to boil water. The steam from the boiling water rotates a large turbine, which activates a generator that produces electricity. However, a new generation of power plants, with concentrating solar power systems, uses the sun as a heat source. There are three main types of concentrating solar power systems: power tower, parabolic-trough, and dish/engine

A power tower system (see lead image) uses a large field of mirrors to concentrate sunlight onto the top of a tower, where a receiver sits. This heats molten salt flowing through the receiver. Then, the salt’s heat is used to generate electricity through a conventional steam generator. Molten salt retains heat efficiently, so it can be stored for days before being converted into electricity. That means electricity can be produced on cloudy days or even several hours after sunset.

January 19, 2012- . Crews work around the clock installing mirrored parabolic trough collectors, built on site, that will cover 3 square miles at Abengoa’s Solana Plant. Solana a 280 megawatt utility scale solar power plant (CSP) under construction in Gila Bend, Arizona, USA. When finished it will generate 280 MW ‘s of clean, sustainable power serving over 70, 000 Arizona homes. (Photo by Dennis Schroeder / NREL

Parabolic-trough systems concentrate the sun’s energy through long rectangular, curved (U-shaped) mirrors. The mirrors are tilted toward the sun, focusing sunlight on a pipe that runs down the center of the trough. This heats the oil flowing through the pipe. The hot oil then is used to boil water in a conventional steam generator to produce electricity.

A dish/engine system uses a mirrored dish (similar to a very large satellite dish). The dish-shaped surface collects and concentrates the sun’s heat onto a receiver, which absorbs the heat and transfers it to fluid within the engine. The heat causes the fluid to expand against a piston or turbine to produce mechanical power. The mechanical power is then used to run a generator or alternator to produce electricity. This technology is rarely used today.


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Concentrating Solar Power content for this section provided in part by the National Renewable Energy Laboratory and the Department of Energy.