Concentrating Solar Power
There are two main types of concentrating solar power: concentrating photovoltaics and concentrating solar thermal. Both applications require very sunny sites that offer expansive, flat, and wide-open spaces. These technologies are currently developed for utility-scale applications.
Concentrating Photovoltaics Systems
Concentrating photovoltaic systems use lenses or mirrors to concentrate sunlight onto high-efficiency PV cells. Concentrating the sunlight greatly reduces the size of the solar cells needed, especially compared to those used in conventional PV panels. Most concentrating photovoltaic systems are mounted on tracking devices and are usually mounted on the ground. Concentrating photovoltaic systems are more expensive than conventional photovoltaics. Concentrating photovoltaics uses no water.
Concentrating Solar Thermal
Concentrating solar thermal uses mirrors to reflect and concentrate sunlight onto receivers that collect solar energy and convert it to heat energy. The thermal energy then generates electricity via a steam turbine or heat engine. Concentrating solar thermal systems include parabolic trough, dish/engine, and power towers.
Parabolic Trough Systems
Parabolic trough systems use curved mirrors shaped like a giant “U” to focus the sun’s energy onto a receiver tube that runs down the center of a trough. In the receiver tube a high-temperature heat transfer fluid absorbs the sun’s energy and passes it through a heat exchanger to heat water and produce steam. The steam powers a turbine to generate electricity.
Dish/Engine Systems
Dish/engine systems use a mirrored dish similar to a very large satellite dish. The dish-shaped surface directs and concentrates sunlight onto a thermal receiver that absorbs and collects the heat. The receiver transfers the heat energy to an engine generator. The most common type of heat engine used today in dish/engine systems is the Stirling engine. The Stirling engine uses the fluid heated by the receiver to move pistons, which create mechanical energy. The mechanical energy runs a generator or alternator to produce electricity. Dish/engine systems are attractive because they use no water.
Power Towers
Power towers use computer-controlled flat mirrors called heliostats to track the sun and focus its energy on a receiver at the top of a high tower. The focused energy heats a transfer fluid to produce steam and power a central generator. Power towers’ thermal storage capability allows the system to continue to generate electricity during cloudy weather or at night.
New Concentrating Solar Power Technology
New concentrating solar power technology includes a relatively new technology that is highly modular, scalable, and suitable for distributed generation between 250 kW and 20 MW. It utilizes the same technological concepts as the large utility-scale concentrating solar power systems; however, the smaller scale systems allow for deployment in areas where much less land is available. A smaller-scale parabolic trough collector has modules mounted into an array that tracks the sun and circulates the heat transfer fluid. These arrays are suitable for installations ranging in size from a single rooftop to a large solar farm.