Solar Thermal Elec.

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Solar Thermal Electric Generation

Background

Note that this topic is limited to solar energy as a source of electric power generation. Solar energy used to provide hot water to end-users is discussed in the topic "Solar Water Heating."

The intense energy of the sun has long been used to heat liquids. The sun's heat can be used in two ways with homes and businesses. The sun is used to heat water for domestic hot water systems, or the sun's light can be concentrated and water temperatures increased to make steam and electricity.

This thermal energy from the sun can also generate electricity. While solar photovoltaics (PV) are better known, the largest central solar power station in the world are the 360 MW from the solar thermal power plants located in California’s Mojave Desert. These solar thermal power plants rely upon curved mirrored troughs that concentrate sunlight. The sun heats a liquid that creates steam to turn a traditional turbine.

There are four main types of solar thermal electric systems.

		Parabolic Trough Collectors	These collectors combine a curved mirror, shaped like a parabola to maximize the amount of sunlight collected, with an absorber tube embedded along the center of the mirror. The absorber tube is filled with oil or another fluid that can easily be heated. When sunlight hits these collectors, the mirrors focus it on the tube, heating the fluid inside. This hot fluid is then used to boil water and produce steam in a connected device and the steam is transferred to a generator that can produce electricity. A large array of connected parabolic trough collectors is needed to provide enough power for a generator.
		Dish/Engine Systems	These systems use an array of mirrors, arranged in the shape of a dish, to concentrate sunlight onto a receiver placed at the focal point of the dish. The heat produced by these systems is transferred to a heat engine which converts the heat into mechanical energy. This energy then drives a generator to produce electricity.
		Power Towers	Power tower systems use a circular array of mirrors that track the sunlight and concentrate it on a receiver, placed at the top of a central tower at the focal point of the array. In much the same way as parabolic trough collectors, heat produced by the receiver is used to create steam which then powers a generator.
		Hybrid Systems	Hybrid systems combine power towers with natural gas generators, creating a system that can continuously generate electricity, even when the sun isn't shining. This technology is still in development and experimental systems have been connected to several utilities in the Southwest.

Solar PV panels register efficiencies ranging from 9 to 15 percent. The solar thermal trough rankine cycle facilities are approximately 22 percent. Stirling solar dishes have been measured at efficiencies as high as 30 percent.

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References, Sources, and Other Useful Data

California Energy Commission, “Solar Thermal Electricity”
http://www.consumerenergycenter.org/renewables/solarthermal/index.html

A general discussion of the technology. Also discusses funding available in California for solar-thermal electricity systems.

Massachusetts Technology Collaborative (MTC), “Solar Thermal Electric (Concentrating Solar) Technologies”
http://www.masstech.org/cleanenergy/solar_info/thermal.htm

The Massachusetts Technology Collaborative is the state’s development agency for renewable energy and the innovation economy. This website provides information on the four main types of solar thermal electric systems: parabolic trough collectors, dish/engine systems, power towers, and hybrid systems.

U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, “Concentrating Solar Power”
http://www.eere.energy.gov/solar/csp.html

DOE researches and develops concentrating solar power (CSP) technology, focusing on three types of CSP technologies: trough systems, dish/engine systems, and power towers.

Western Area Power Administration, “Renewable Resources Program”
http://www.wapa.gov/es/renewables/default.htm

Western has a long and fruitful history of promoting and implementing solar energy – including solar thermal and photovoltaic systems – on both agency and power customer facilities. Western offers Federal customers two renewable resource products and facilitates customer access to renewable energy developers. The goal of the program is to identify customers that desire renewable resources in their generation mix and provide the technical and marketing assistance required for them to fully evaluate the option.

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Website prepared for the Edison Electric Institute and the Electric Power Industry Climate Initiative		Prepared by Twenty-First Strategies, LLC. Copyright © 2009. All rights reserved. Last revised: Dec. 11, 2009.