Inside Clean Energy: Here’s How Compressed Air Can Provide Long-Duration Energy Storage

A grid that runs mostly on wind and solar, part of the future that clean energy advocates are working toward, will need lots of long-duration energy storage to get through the dark of night and cloudy or windless days.

Hydrostor, a Canadian company, has filed applications in the last week with California regulators to build two plants to meet some of that need using “compressed air energy storage.” The plants would pump compressed air into underground caverns and later release the air to turn a turbine and produce electricity.

The stored energy would be able to generate hundreds of megawatts of electric power for up to eight hours at a time, with no fossil fuels and no greenhouse gas emissions. Long-duration storage includes systems that can discharge electricity for eight hours or more, as opposed to lithium-ion battery storage, which typically runs for up to four hours.

This project and technology have potentially huge implications for the push to develop long-duration energy storage. But the key word is “potentially,” because there are many companies and technologies vying for a foothold in this rapidly growing part of the energy economy, and the results so far have been little more than research findings and hype.

“Their technology is not overly complicated,” said Mike Gravely, a manager of energy systems research for the California Energy Commission, speaking in general about CAES. “Compressed air is a very simple concept.”

The main challenge, as with so many clean energy technologies, is to get the costs low enough to justify building many of the plants.

Hydrostor, founded in 2010 and based in Toronto, has completed two small plants in the Toronto area, including a 1.75-megawatt storage plant that can run for about six hours at a time.

The company’s system begins with an industrial scale air compressor that runs on electricity and sucks in air from the environment. The compression of air produces heat, which the system removes and stores in a thermal storage vessel.

Meanwhile, the compressed air flows through a pipe into a cavern more than 1,000 feet below the surface. The cavern would be excavated for the project, as opposed to natural caves providing the storage.

To discharge the energy, the system releases water into the cavern, which forces the air to the surface, where it mixes with the heat that had been stored. The heated air then flows through turbines to produce electricity.

Hydrostor filed an application last week for a plant, called Pecho Energy Storage Center, that would be located in San Luis Obispo County and cost $800 million. It would have a generating capacity of 400 megawatts, with a duration of up to eight hours.

The company then filed an application on Wednesday for the second plant, called Gem Energy Storage Center, that would be located just east of the Pecho plant in Kern County and cost $975 million. It would have a generating capacity of 500 megawatts, with a duration of up to eight hours.

The projects, both of which could be built as soon as 2026, would help the region replace some of the electricity that now comes from Diablo Canyon nuclear power plant in San Luis Obispo County, which is scheduled to close by 2025.

“Long-duration energy storage is one of the cornerstone solutions to a carbon-free renewable energy future,” Hydrostor said.

The Bakersfield Californian reported in April that the Gem plant’s customers would include the Los Angeles Department of Water and Power and the operator of the state’s power grid.

But Hydrostor does not list a buyer for the electricity from the Pecho plant. This is a key detail that will help determine whether the project is financially viable. Asked about potential customers, a Hydrostor spokesman referred to a recent interview with the company’s president, Jon Norman, who said that talks are ongoing with potential buyers and that the company hopes to announce details “in the near term.”

Hydrostor also is developing a 200-megawatt plant in Australia.

Compressed air energy storage is not a new concept. A 290-megawatt compressed air storage plant went online in 1978 in Huntorf, Germany, and remains in operation today. Another went online in 1991 in McIntosh, Alabama, with a capacity of 110 megawatts. Both plants use a version of the technology that relies on natural gas to produce electricity.

For decades, researchers have seen the promise of compressed air storage and tried to develop a way to do it without fossil fuels. The results were disappointing, with projects that were announced but never completed, including one by the California utility PG&E in the early 2010s. PG&E said in a 2018 report that it found the technology to be promising, but couldn’t find the right partner to build the project at an acceptable price.

The difference today is that companies say they have learned how to build more efficient systems.

“They’re getting better because they’re making smarter designs,” said Gravely, of the energy commission, whose job gives him a close-up view of the evolution of storage technologies.

The big difference between Hydrostor’s proposals and the compressed air plants in Germany and Alabama is the way heat is stored for reuse, which is more efficient than allowing the heat to escape into the atmosphere as waste. In contrast, the older plants release much of their heat and then burn natural gas to produce additional heat later in the process.

Edward Barbour, of Loughborough University in the United Kingdom, has written about the push to develop “adiabatic” CAES, the term for the approach to heat management that Hydrostor is using.

Barbour said it’s a positive sign that Hydrostor is announcing the projects, but he’s also mindful of the history of companies like the now-defunct Lightsail Energy that announced plans for systems that were never built.

“I’m crossing my fingers that this will be different,” he said.

One difference today is the strength of demand for long-duration storage, with California officials and others recognizing the great need for energy resources to fill in the gaps of a grid that relies heavily on wind and solar.

In June, the California Public Utilities Commission approved a plan to require utilities to develop or buy 11,500 megawatts of new electricity resources that would come online from 2023 to 2026, including 1,000 megawatts of long-duration storage.

This requirement, along with California’s previous support for energy storage research, has made the state a proving ground for storage technologies.

“We probably have the most diverse portfolios of anybody in the world right now, particularly long-duration storage,” said Gravely.

The Energy Storage Association has a good rundown of the technologies being developed, such as long-duration batteries; mechanical storage systems—a category that includes compressed air storage—and systems that use electricity to produce hydrogen for storage and later use.

The new, long-duration storage systems would be in addition to a resource that is already well-established: pumped hydroelectric storage: systems that charge by pumping water to a high elevation and then discharge by releasing the water through turbines. There are 21.9 gigawatts of pumped hydro storage in the United States, and California leads all other states with 3.7 gigawatts.

“It’s a very exciting time now,” Gravely said. “I get calls weekly from companies looking to come to California from all over the world, because they know that’s where the market is, and they want to come here and demonstrate and go back to wherever they came from and sell more.”

Other stories about the energy transition to take note of this week:

Global Renewables Market is Accelerating, with China Poised to Be the Leader: The International Energy Agency issued a report Wednesday about the global market for renewable energy, showing that the world is on track to add a record 290 gigawatts of renewables this year. The report shows that China is on track to be the leader in renewable energy installations for the next few years, followed by Europe, the United States and India, as Anmar Frangoul reports for CNBC. The forecast includes revisions from last year that show an acceleration in IEA’s view of the pace of growth of renewables. The prices of some renewable energy components have risen this year, but this has not been enough to slow momentum.

New York Faces Big Challenges to Get to 100 Percent Clean Energy: New York has some of the most ambitious climate and clean energy goals of any state, but to meet them it will need to overcome some major challenges in the way electricity gets delivered within the state. Much of the electricity used in New York is produced in rural parts of the state or in other states and then transported to the New York City metro area by transmission lines. To increase the state’s use of renewable energy, the state will need to build many more lines, something that is politically challenging because communities tend to oppose the projects, according to Anne Barnard and Grace Ashford of The New York Times. 

China’s Wind Turbine Makers Look to Expand in Global Markets: Chinese wind turbine manufacturers dominate the large market in their home country, but they have not been nearly as active in the rest of the world. That may be changing because China’s Goldwind and others are planning to expand in ways that would challenge turbine manufacturers like General Electric and Vestas, Bloomberg News reports. Goldwind has said it will be able to “run shoulder by shoulder” with its major overseas competitors, starting next year.

Norilsk in the Russian Arctic is Severely Polluted as It Shifts to Provide Metals for the Clean Energy Economy: Norilsk, Russia, is one of the most polluted places on Earth following generations of damage by a metal smelting company. Now, the company has the potential to grow because of demand for nickel and other metals used in lithium-ion batteries and other products that are part of the clean energy economy, as my colleague Marianne Lavelle reports. But the processes used in the production of metals in Norilsk are still immensely harmful for the air and water in a sensitive ecosystem, and the company and government are doing little to reduce the damage.

Inside Clean Energy is ICN’s weekly bulletin of news and analysis about the energy transition. Send news tips and questions to [email protected].