Storing oversized large scale PV with molten salt storage


Linking oversized large scale PV with molten salt storage tanks is claimed to be a workable technical solution for regions with high energy consumption, according to recent research from Israeli and French scientists.

In the study Providing large-scale electricity demand with photovoltaics and molten-salt storage, published in Renewable and Sustainable Energy Reviews, the researchers presented a model to integrate solar power generation from utility scale facilities with high-temperature molten-salt storage in regions with low direct solar beam radiation and high levels of global solar radiation.

The PV-plus-thermal-storage (PV-TS) solution proposed by the academics, which is claimed to be “ready for immediate implementation,” due to the “unusually favorable economics” provided by PV technology, represents an alternative to CSP molten salt towers in areas where CSP technology is not considered viable because concentrators cannot exploit diffuse solar radiation. “Rather than aiming for precise answers for specific locations, the objective here is to see if the magnitudes for PV system size, storage capacity, grid penetration levels and cost estimates are feasible,” the academics explained.

In the PV-TS unit, a significant part of the generated solar power would be used to resistively heat molten-salt thermal storage to temperatures over 565 degrees Celsius, and the stored thermal energy would be in turn used to drive high-efficiency superheated steam turbines for power generation.

The simulations conducted by the Israeli-French group showed that in certain areas PV can see its grid penetration rate increase from around 30%, when no thermal storage is used, to around 80% with just 12 hours of thermal storage. “Furthermore, with only a 25% increase in solar input, 90% grid penetration can be attained,” the group further explained. “For the higher-insolation locations, where proportionality can be maintained up to approximately 90%, an extra 25% of solar input can raise grid penetration to about 95%.”

In this kind of project, the PV plant should not be sized as a common facility that needs to meet a particular peak daytime demand and most of the generated electricity should be used for heat storage in the molten salt tanks. “And that stored heat would satisfy the power demand not only at night, but also during daytime periods of sub-peak insolation,” the researchers specified, adding that an average land area of approximately 0.64km2 would be necessary for a terawatt-hour of annual power generation.

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According to them, the “unconventional” solution proposed in the study may also be integrated with rooftop PV arrays and large steam turbines already operating in fossil fuel and nuclear power plants that are being decommissioned in several countries.

The findings of the research relate only to the U.S. territory but they could be extended to all regions with similar climatic conditions and utility demand profiles. “For regions with average insolation that is higher than the U.S. – some of which also happen to have electricity demand profiles that are better correlated with solar availability – the PV and storage requirements per terrawatt-hour of electricity consumption will be lower,” the paper notes. “Furthermore, the transition to all-electric vehicles may increase the fraction of electricity demand during daytime hours, when much of the battery charging will be performed.”

Russia, the former Soviet republics, Japan, northern Asia, and mid-to-northern Europe are pointed out as the most suitable areas, along with the United States, for the deployment of PV-TS projects.

The research team is composed of scientists from Israel's Ben-Gurion University of the Negev, France's Aix-Marseille University and Promes, which is the French national R&D laboratory on solar concentrating systems.

*The article was updated on January 26 to add an additional paragraph on the PV-TS  system configuration.

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