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WIREs Energy Environ.
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Thermal energy storage for solar power production

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Solar energy is the most abundant persistent energy resource. It is also an intermittent one available for only a fraction of each day while the demand for electric power never ceases. To produce a significant amount of power at the utility scale, electricity generated from solar energy must be dispatchable and able to be supplied in response to variations in demand. This requires energy storage that serves to decouple the intermittent solar resource from the load and enables around‐the‐clock power production from solar energy. Practically, solar energy storage technologies must be efficient as any energy loss results in an increase in the amount of required collection hardware, the largest cost in a solar electric power system. Storing solar energy as heat has been shown to be an efficient, scalable, and relatively low‐cost approach to providing dispatchable solar electricity. Concentrating solar power systems that include thermal energy storage (TES) use mirrors to focus sunlight onto a heat exchanger where it is converted to thermal energy that is carried away by a heat transfer fluid and used to drive a conventional thermal power cycle (e.g., steam power plant), or stored for later use. Several approaches to TES have been developed and can generally be categorized as either thermophysical (wherein energy is stored in a hot fluid or solid medium or by causing a phase change that can later be reversed to release heat) or thermochemical (in which energy is stored in chemical bonds requiring two or more reversible chemical reactions).

This article is categorized under:

  • Concentrating Solar Power > Science and Materials
  • Concentrating Solar Power > Systems and Infrastructure
The global distribution of solar energy expressed as an annual averaged sum of direct normal insolation (DNI)2. This represents the amount of solar energy that could be intercepted by a collector tracking the sun in two axes, such as a parabolic dish. Source: DLR (www.dlr.de).
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A schematic of a thermochemical transport and storage system that could be used in conjunction with a parabolic dish or central receiver collection system, enabling more efficient solar collection for high‐temperature power conversion processes such as those based on the Stirling or Brayton cycles. Reaction products may be placed in storage at a fairly low temperature, enabling long‐term storage are relatively high efficiency.
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A parabolic trough power plant with thermal energy storage (TES). This is an illustration of an indirect TES configuration that would likely use a synthetic oil heat transfer fluid in the collector field and a nitrate salt media in the storage system. A heat exchanger is used to move heat between the two fluids. This configuration is currently in use at Andasol I and II in Spain. Source: NREL.
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Operating temperature limit and energy storage density for thermophysical (sensible and latent) and thermochemical energy storage media. In this chart, the energy storage density for sensible energy media is constrained by the temperature range over which energy is stored. This was fixed at 350°C. In addition, sensible energy storage is not included in either the thermochemical or latent energy storage media calculations.
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A central receiver power plant with two tank molten nitrate salt thermal energy storage (TES). This configuration is identical to that demonstrated at the Solar Two project sited in Barstow, CA. This is an example of direct TES wherein the heat transfer fluid and thermal storage media are identical. Source: SolarReserve.
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Estimated thermal conversion efficiency (heat to mechanical work) for power cycles either in use or under consideration for concentrating solar power (CSP) systems. The operating temperature range for the three main CSP platforms is highlighted.
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An illustration of a typical utility load curve compared with the power output from a solar energy plant operating either with or without thermal energy storage.
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The global distribution of solar energy resources that could be developed for power production. This map has been ‘filtered’ relative to Figure and shows only those geographic areas that satisfy a number of criteria related to land use, topography, infrastructure, and other issues impacting development2. Source: DLR (www.dlr.de).
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