CSP - A Dispatchable Renewable Energy Source
Combined with integrated storage, solarthermal solutions can provide dispatchable solar power at an industrial scale, to take advantage of higher prices at times of peak demand.
How it works
A concentrated solar power (CSP) plant works much like any thermal power plant. The difference is that it uses solar energy to produce steam to drive a turbine and generator. A CSP plant needs the right location: one that has lots of flat open space (for putting up mirrors) and lots of sun (like Southern Europe and the arid regions of Northern Africa and North America).
In Europe, plans for commercial CSP plants are focusing mostly on sites in Spain, which offers both solar intensity and the necessary infrastructure. CSP plants need a nearby source of water (for the steam turbine) and a nearby transmission line (to move the power to where it will be consumed).
Parabolic-trough power plants
Parabolic troughs reflect sunlight onto a tube, called an absorber, which is filled with a liquid. The concentrated sunlight produces enough heat to bring the liquid to a boil, creating steam which drives a turbine. Parabolic troughs can be mounted in rows several hundred meters long. Some of the heat produced in the steam-making process is stored so that the plant can run for up to six hours without sunlight. The world's largest research center for high-temperature solar technology, the Plataforma Solar de Almeria in Spain, has been developing this technology since 1981. Nine parabolic-trough power plants with an aggregate generating capacity of about 350 megawatts are in operation in the United States. Their energy-conversion efficiency is roughly 14 percent.
Fresnel collectors operate according to the same principle but concentrate sunlight using flat mirrors instead of parabolic mirrors. The advantage of this system is that it incorporates many standardized, competitively priced, and easily sourced components. E.ON is involved in research projects in this technology, as well.
Solar-tower power plants
Solar-tower power plants use hundreds of mirrors (called heliostats) that track the sun and concentrate its light onto an absorber at the top of the tower. The concentrated sunlight can generate temperatures of up to 1,000 degrees Centigrade (1,832 degrees Fahrenheit). This heat is used to create steam to drive a turbine. Heliostats represent about half the construction costs of such facilities, the largest of which is a 10-megawatt facility in California. Scientists and technicians are working to improve heliostats' optical performance and to make them last longer. The trend is towards larger heliostats with a surface area of up to 200 square meters (2,150 square feet).
Dish Stirling units
Dish Stirling units use a parabolic dish that tracks the sun and concentrates its light onto a collector that heats an absorber (helium or hydrogen) that drives a Stirling engine. A generator transforms the engine's rotational energy into electric energy. Dish Stirling units are relatively small and are thus suitable in micropower applications. Prototypes with a dish diameter of 8 to 10 meters (26 to 32 feet) have a generating capacity of up to 50 kilowatts.