Concentrated Solar Power: Now and Tomorrow

August 3, 2017

Concentrated solar power (CSP) differs from photovoltaic (PV) solar power generation, but both are common methods of harnessing solar energy. CSP is a less popular method in the age of modern technology, though it had been predominately used before photovoltaic cells were invented.

The idea behind CSP is simple: water (or another heat transfer fluid) is heated using solar energy to become steam, which is used to run a turbine, or other heat engine, which generates electricity. However, the amount of solar energy needed to reach such temperatures for a body of water simply exposed to sunlight is too great; this is where concentration of solar power comes into play. Using mirrors, solar energy is reflected from a wide area and focused onto one location to concentrate solar energy on the working fluid. The range of technologies available for solar energy reflection is dazzling; technologies include parabolic reflectors, solar tracking mirror arrays and Fresnel reflectors.

Currently, CSP plants worldwide generate about 4.4 GW of energy per year. The country with the most renewable energy capacity in the form of CSP is Spain, followed by the United States and India, which have both added capacity recently. However, when compared to PV methods that produce nearly 177 GW globally, the output of CSP seems minuscule.

Cost

The cost of solar PV electricity generation has dropped drastically over the years, such that the technology is nearly cost competitive with coal-generated electricity. If CSP harnesses the same energy source and doesn’t rely on advanced processing with rare earth elements, why is not as widely adopted as photovoltaics? The answer is varied.

PV cells are infinitely scalable. Energy will be produced at the same efficiency whether an array is a square centimeter or a square mile. CSP, on the other hand, is much more akin to conventional energy plants. Instead of burning coal to heat water for steam, directed sunlight is used to heat the water. Otherwise, all plant components are identical to conventional electricity generation, including the steam turbine and electricity distribution. Thus, CSP is only cost effective at utility-level Scales.

Solar power efficiency: CSP or PV- or both?

Currently, CSP plants are slightly less efficient than PV plants, requiring 10 acres to generate one MW, whereas PV only requires eight acres per MW. Since CSP relies on a steam turbine for energy conversion, it is limited by thermodynamics. PV has increased in efficiency by leaps and bounds, primarily through new PV cell materials. However, CSP is behind PV as a utility-Scale technology. Cost efficiency may increase for CSP as manufacturing for plant components Scales up.

On the other hand, PV cell utilization is limited by a lack of battery technology that can integrate with distribution systems. CSP is able to circumvent this issue by storing heat energy prior to electricity generation. Whereas batteries to distribution Scale systems do not yet exist, thermal energy storage (TES) technologies such as the use of molten salt to store excess heat can extend CSP plant efficiencies. With further improvements to TES technologies, CSP may become more attractive. Additionally, CSP with TES can be used in conjunction with solar PV (or wind turbines) to store energy during periods of intermittent energy availability. Technologies working in combination, instead of in competition, may prove to be the most efficient solution yet.

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