Solar Thermal Energy System: Creates Steam from Sunlight – Green Energy
Solar thermal green energy systems concentrate the rays of the sun onto a reservoir holding a fluid, heating it to a very high temperature. The fluid, often molten salt, then circulates through pipes to transfer its heat to water, creating steam. High-pressure steam is next driven at the blades of a turbine which spins a rotor at very high speeds, typically between 1800–3600 rpm, generating electrical energy. Many electric power stations use steam, due to the higher rotations possible than with water or wind turbines, but these power stations generate their steam by burning fossil fuels or splitting atoms. A much cleaner green energy method is using a solar thermal energy system to create steam from sunlight.
There are three main types of solar thermal energy systems that create steam:
A parabolic trough collector has a long parabolic-shaped mirrored reflector that concentrates the sun’s rays on a fluid-holding pipe located at the focus of the parabola. The trough is motorized to tilt with the sun as it tracks from east to west during through the sky throughout the day to make sure that light is constantly focused on the receiver pipe. This design can concentrate light up to 100 times its normal intensity, bringing the temperature of the fluid used up to 750° F.
- Parabolic troughs are used in the longest operating solar thermal system facility in the world, which opened in 1984 – Solar Energy Generating Systems (SEGS) operated and partially owned by FPL Energy, supplying electricity to Southern California Edison. The Mojave Desert’s isolation and nearly constant sunshine have led to several expansions. Now SEGS’s nine solar power plants have a 354 MW installed capacity, making it the largest installation of solar thermal energy systems on the planet, using solar to generate electricity 90 percent of the time, a great source of green energy.
- Compact linear fresnel reflectors use thin, long parallel rows of lower-cost flat mirrors that rotate along a single axis. These modular reflectors focus rays of sunlight onto elevated receiving pipes filled with water. This design can concentrate light up to 30 times its normal intensity. The solar energy boils the water directly generating high-pressure steam to spin power generating turbines. CLFRs can be used in smaller installations because they don’t rely on costly fluid heat exchangers.
- Power towers rely on a central highly placed receiver to absorb the concentrated solar energy from an array of computer-controlled flat mirrors called heliostats that track the sun along two axes. Power towers are very efficient because energy losses are minimized by using a single receiver. Here the transfer fluid can be heated to over 1,000° F. The energy can be concentrated as much as 1,500 times that of the sunlight. Power towers are best for large installations.
Nearly all solar thermal energy systems use fossil fuel, typically natural gas, as backup when solar radiation alone is insufficient to generate enough electricity. Solar thermal energy systems that create steam from sunlight should be installed by more utilities. From the standpoint of stockholders, these systems make sense. Not only are they good for the environment, cutting pollution and combating global warming while generating green energy, but the electricity generated flows down the same grid already in place, keeping centrally distributed energy and billing in place for utility customers.
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