Super Hot Salt: A Super Cool Solar Energy Storage Technology Innovation

Policymakers and energy industry experts often talk about clean energy as though it isn’t reliable. In fact, while an MIT study recently found the existing grid would probably be up to the challenge of absorbing clean energy, intermittency does present a real challenge that renewables must address to get to high levels of penetration.

But BrightSource Energy, a major player in the market for concentrating solar power, or CSP, recently announced the installation of new thermal energy storage technology at three of its planned power plants in California. This thermal energy storage technology will go a long way toward solving the intermittency problem for concentrating solar power. BrightSource’s announcement demonstrates that we can in fact get reliable baseload power from the sun [or, even better, load-following power].

The thermal energy storage system, built using SolarPLUS technology, works by using hundreds of flat glass mirrors — called heliostats — to concentrate the rays of the sun, heating molten salts to several hundred degrees above the boiling point of water. The superheated salt is then stored in a giant insulated container. When the power plant needs to add additional output, it can use the heat stored in the molten salt to boil water to create steam to drive its turbines.

The added storage capacity will allow BrightSource’s new concentrating solar thermal power plants to continue producing electricity up to two hours after the sun stops shining. It will also enable the power plants to produce electricity at a steady and predictable rate throughout the day and will smooth out fluctuations that make managing solar power tricky for grid operators. Even better, the new thermal storage systems will allow the CSP plants to produce twice the electricity on the same amount of land as could be produced by traditional photovoltaic panels. This advance is yet another step toward the near future when solar energy can replace rather than simply supplement energy produced by fossil fuel power plants.


Adding this storage capacity to three existing plants will increase production by 4 million megawatt-hours, according to BrightSource. The company had originally planned to build seven plants at its location in California, but by applying storage technology, it discovered it could decrease the number of plants while producing more energy. The new plants are slated for completion over the next five years.

The deal is awaiting approval from the California Public Utilities Commission, or CPUC, which tentatively gave the green light to Pacific Gas and Electric to make a power purchase agreement with the Mojave Solar Project amid objections that the agreement would be too costly. But the CPUC has little to worry about with BrightSource and Southern California Edison. The technology BrightSource employs, which consists of mirrors and a water boiler, is cheaper and more cost-efficient than the older CSP technology that the Mojave Solar Project utilizes, and since the plants are air-cooled, they consume low amounts of precious desert water resources. By increasing storage capacity, BrightSource estimates it will actually lower costs for customers.

Additionally, the CPUC should approve the contracts because the deal is a natural consequence of a 2010 California bill, AB 2514, imploring the CPUC to determine good commercial targets for improved energy storage. The bill would hold the commission responsible for identifying cost-effective storage targets for power producers and then creating the appropriate regulations and incentives for storage deployment. BrightSource’s announcement of thermal storage technology shows the company is remaining a step ahead of the game.

Some environmentalist opponents object to the impact that the solar plants will have on Mojave ecosystems. But the storage technology will allow BrightSource to produce as much power with six plants as it otherwise would have with seven. The decision to scrap the seventh plant will translate to even more price cuts for consumers, as well as 1,280 acres of desert spared from development.

In what looks like a win-win for BrightSource, Southern California Edison, the environment, and consumers, solar storage is evolving from a distant dream to the reality of the present. Altogether the Ivanpah project will lead to 1,400 union construction jobs at peak construction, $650 million in worker wages over the life of the project, and avoid 13.5 million tons of carbon dioxide emissions. Said BrightSource Chief Executive John Woolard, “We came out very strongly with what I believe is the largest solar storage deal in the world.” If the CPUC approves the landmark contracts, the rest of the nation could also come out very strongly, as the region and the nation reaps the economic and environmental benefits of this new and dynamic industry.


Lauren Simenauer is a former intern with Science Progress, and Sean Pool is Assistant Editor of Science Progress. This piece was originally published at Science Progress.

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