|Fig. 1: The trough, dish and central receiver (tower) concentrating solar panel systems. (Source: Wikimedia Commons)|
Heat from the sun is a unique and essential energy source that we have not yet taken full advantage of. These concentrating solar power (CSP) systems are not mature enough to compete with non-renewable energy generation but with their technological progress this seems reachable in a couple of decades.  The suns natural heat energy can be concentrated using mirrors and turned into electricity, distinct to solar (photovoltaic) cells, which use the light from the sun to produce energy.  These CSP systems can support the nation's electricity grid during all hours of the day without the need for expensive battery systems.  Thus far only a few electric utility companies have created these concentrated solar power systems, they are most common in the Southwest of the U.S. 
The most common form of CSP, the trough system, uses mirrored parabolic troughs to focus the Sun's energy to a receiver tube that is carrying oil. [1,2] The receiver tube is insulated in an evacuated glass envelope and the system moves in tandem with the sun as it crosses the sky (see Fig.1).  As the synthetic oil in the tube heats up it goes through a conventional steam generator, which generates about 80 MW of electricity.  There has so far been no or little thermal storage capabilities in these systems. 
Dish systems use either a singular dish-shaped parabolic mirror or multiple parabolic disc mirrors to reflect, concentrate and focus the Sun's rays onto a receiver directly above the dish (see Fig.1).  As the receiver absorbs the Sun's energy, the engine inside it turns it into heat. This system works by compressing the fluid as it hits the receiver, heating it and then expanding it through a turbine or with a piston to produce mechanical power. The mechanical power is converted to 5-50kW of electrical power.  This CSP, like the trough system, is able to move in tandem with the sun so to reap all of the day's energy. 
Heliostats are small individual sun-tracking mirrors that reflect solar energy.  A central receiver system uses thousands of these heliostats to reflect large amounts of the Sun's energy onto a receiver located on top of a tall tower (see Fig.1).  Once the molten salt, inside the storage tanks below the receiver, is heated, it combines with cold molten salt to make steam that generates electricity in a steam generator.  Unlike the other two systems, this central receiver system has many more components and it is less expensive to use thermal storage. Thermal storage adds an additional benefit of saving electricity for when it is actually needed, increasing the efficiency of the system. [1,3]
© Fran Tew. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 "Technology Roadmap Concentrating Solar Power," International Energy Agency, 2010.
 "Concentrating Solar Power: Energy From Mirrors," U.S. Office of Energy Efficiency and Renewable Energy, DOE/GO-102001-1147, March 2001.
 S. Pool and J. D. P. Coggin, "Fulfilling the Promise of Concentrating Solar Power," Center for American Progress, June 2013.