Concentrating Solar Thermal Power

Concentrating solar power is relatively low cost and have the ability to deliver power during periods of peak demand-when and where it is needed-means that it can be a major contributor to the world’s future needs of energy. Concentrating solar plats differ from traditional photovoltaic technologies
The international Energy Agency claimed that up to 11% of world’s electricity could come via concentrating solar power by 2050. In a Concentrating Solar power plant (CSP) mirror configurations focuses the sun’s energy, heating a fluid which eventually produces steam that drives a generator. The CSP plant consists of two parts, one that collects solar energy and converts in into heat and another that converts heat energy to electricity.        

Concentrating solar power technology utilizes three alternative technology approaches.

Concentrating solar power by newphysicist[/caption] CSP technology utilizes focused sunlight. CSP plants generate electric power by using mirrors to concentrate (focus) the sun’s energy and convert it into high-temperature heat. That heat is then channeled through a conventional generator. The plants consist of two parts: one that collects solar energy and converts it to heat, and another that converts the heat energy to electricity. A brief video showing how concentrating solar power works (using a parabolic trough system as an example) is available from the Department of Energy Solar Energy Technologies Web site.  

Linear Concentrator System

Linear concentrator systems collect the sun’s energy using long rectangular, curved (U-shaped) mirrors. The mirrors are tilted toward the sun, focusing sunlight on tubes (or receivers) that run the length of the mirrors. The reflected sunlight heats a fluid flowing through the tubes. The hot fluid then is used to boil water in a conventional steam-turbine generator to produce electricity. There are two major types of linear concentrator systems: parabolic trough systems, where receiver tubes are positioned along the focal line of each parabolic mirror; and linear Fresnel reflector systems, where one receiver tube is positioned above several mirrors to allow the mirrors greater mobility in tracking the sun.        

Dish/Engine Systems

A dish/engine system uses a mirrored dish similar to a very large satellite dish, although to minimize costs, the mirrored dish is usually composed of many smaller flat mirrors formed into a dish shape. The dish-shaped surface directs and concentrates sunlight onto a thermal receiver, which absorbs and collects the heat and transfers it to the engine generator. The most common type of heat engine used today in dish/engine systems is the Stirling engine. This system uses the fluid heated by the receiver to move pistons and create mechanical power. The engine has thin tubes containing hydrogen or helium gas that run along the outside of the engine’s four piston cylinders and open into the cylinders. As concentrated sunlight falls on the receiver, it heats the gas in the tubes to very high temperatures, which causes hot gas to expand inside the cylinders. The expanding gas drives the pistons. The pistons turn a crankshaft, the mechanical power is then used to run a generator or alternator to produce electricity.    

Power Tower systems

A power tower system uses a large field of flat, sun-tracking mirrors known as heliostats to focus and concentrate sunlight onto a receiver on the top of a tower. A heat-transfer fluid heated in the receiver is used to generate steam, which, in turn, is used in a conventional turbine generator to produce electricity. Some power towers use water/steam as the heat-transfer fluid. Other advanced designs are experimenting with molten nitrate salt because of its superior heat-transfer and energy-storage capabilities. The energy-storage capability, or thermal storage, allows the system to continue to dispatch electricity during cloudy weather or at night. Molten salt retains heat efficiently, so it can be stored for days before being converted into electricity. That means electricity can be produced during periods of peak need on cloudy days or even several hours after sunset.

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