Concentrating Solar Power: Energy from Mirrors
Mirror mirror on the wall, what's the greatest energy source of all? The sun. Enough energy from the sun falls on the Earth everyday to power our homes and businesses for almost 30 years. Yet we've only just begun to tap its potential. You may have heard about solar electric power to light homes or solar thermal power used to heat water, but did you know there is such a thing as solar thermal-electric power? Electric utility companies are using mirrors to concentrate heat from the sun to produce environmentally friendly electricity for cities, especially in the southwestern United States.
DOE/GO-102001-1147 FS 128 March 2001
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sume no fuel other than sunlight. About the only impact concentrating solar power plants have on the environment is land use. Although the amount of land a concentrating solar power plant occupies is larger than that of a fossil fuel plant, both types of plants use about the same amount of land because fossil fuel plants use additional land for mining and exploration as well as road building to reach the mines. Other benefits of concentrating solar power plants include low operating costs, and the ability to produce power during high-demand energy periods and to help increase our energy security—our country's independence from foreign oil imports. Because they store energy, they can operate in cloudy weather and after sunset. When combined with fossil fuels as a hybrid system, they can operate around the clock regardless of weather. Concentrating solar power plants also create two and a half times as many skilled jobs as traditional plants.
cations, ranging from remote power systems as small as a few kilowatts (kW) up to grid-connected applications of 200-350 megawatts (MW) or more. A concentrating solar power system that produces 350 MW of electricity displaces the energy equivalent of 2.3 million barrels of oil.
Individual trough systems currently can generate about 80 MW of electricity.
Fig. 1 A parabolic trough
Types of Systems
Unlike solar (photovoltaic) cells, which use light to produce electricity, concentrating solar power systems generate electricity with heat. Concentrating solar collectors use mirrors and lenses to concentrate and focus sunlight onto a thermal receiver, similar to a boiler tube. The receiver absorbs and converts sunlight into heat. The heat is then transported to a steam generator or engine where it is converted into electricity. There are three main types of concentrating solar power systems: parabolic troughs, dish/engine systems, and centralreceiver systems. These technologies can be used to generate electricity for a variety of appli-
These solar collectors use mirrored parabolic troughs to focus the sun's energy to a fluid-carrying receiver tube located at the focal point of a parabolically curved trough reflector (see Fig.1 above). The energy from the sun sent to the tube heats oil flowing through the tube, and the heat energy is then used to generate electricity in a conventional steam generator. Many troughs placed in parallel rows are called a "collector field." The troughs in the field are all aligned along a northsouth axis so they can track the sun from east to west during the day, ensuring that the sun is continuously focused on the receiver pipes. Individual trough systems...