…concentrated solar power (CSP) makes electricity by making steam that drives a turbine, like combustion of coal or natural gas does.
Except that instead of creating heat by removing mountains to dig up coal or fracking up groundwater to get at natural gas, CSP boils a heat transfer fluid using just reflected sunlight for clean energy.
In power tower CSP, thousands of mirrors concentrate multiple ‘suns’ on one spot; the receiver in the tower. The solar flux heats what’s in the receiver (water for Ivanpah; molten salt for Crescent Dunes) to ultimately make the steam.
It was designed by BrightSource Energy to use more than 170,000 mirrors to focus sunlight onto boilers positioned atop three towers, which reach nearly 500 feet (150 meters) into the dry desert air. The reflected sunlight heats water in the boilers to make steam, which turns turbines to generate electricity—enough to power more than 140,000 homes.
Parabolic trough systems use curved mirrors to focus the sun’s energy onto a receiver tube that runs down the center of a trough.
Compact Linear Fresnel Reflector uses the principles of curved-mirror trough systems, but with long parallel rows of lower-cost flat mirrors. These modular reflectors focus the sun’s energy onto elevated receivers, which consist of a system of tubes through which water flows.
Power tower systems use a central receiver system, which allows for higher operating temperatures and thus greater efficiencies. Computer-controlled flat mirrors (called heliostats) track the sun along two axes and focus solar energy on a receiver at the top of a high tower.
Mirrors are distributed over a parabolic dish surface to concentrate sunlight on a receiver fixed at the focal point. In contrast to other CSP technologies that employ steam to create electricity via a turbine, a dish-engine system uses a working fluid such as hydrogen that is heated up to 1,200° F in the receiver to drive an engine such as the Stirling engine. Each dish rotates along two axes to track the sun.
*Photo courtesy of Jack Freer May 2015*