A Canadian company called Hydrostor has a new compressed air energy storage system that the company says costs half that of grid-scale batteries and is comparable to adding a new natural gas power plant to a grid.
The system, called Hydrostor Terra, uses electricity when it is abundant to compress air and send it underground in a specially constructed tank. As the system compresses the air, it also takes the heat generated by the compressors and stores it in a thermal management system. Then, if there is a shortage of electricity, the Terra system returns that compressed air from underground and heats the airstream at the surface using the heat captured during the compression process. The heated air moves a turbo-expander connected to a generator, which generates electricity.
Hydrostor’s method of capturing heat from the compression process sets the Terra project apart from other compressed air energy systems (or CAES systems). Traditionally, CAES systems burn natural gas to heat compressed air as it is brought to the surface to make electricity. But burning natural gas detracts from the overall efficiency of the system and creates greenhouse gases. Hydrostor says Terra will not burn natural gas in its adiabatic system, that is, a system in which heat does not dissipate. (Note that a search of Ars Technica returns five pages of results including the word “adiabatic,” all of which relate to quantum computing. Well, until today. Today we’re talking about energy.)
According to the Energy Storage Association, adiabatic compressed air systems can be up to 70 percent efficient, and a video from Hydrostor suggests the system has an efficiency of about 60 percent. Diabatic systems, which burn natural gas to reheat the compressed air, are usually only 42 to 54 percent efficient.
According to a Hydrostor spokesperson, the company owns and operates the world’s only adiabatic compressed air energy storage system (A-CAES). That system has been running on Toronto Island in Canada since 2015 and has a capacity of 0.7 MW. Because this system uses several submersible balloons to store the compressed air, it is currently being expanded to provide several megawatt hours of energy storage. Hydrostor also has a 1.75 MW, 7 MWh A-CAES system under construction in Goderich, Ontario, Canada and is contracted to build another 1 MW, 6 MWh system in Aruba.
The Terra system also differs from previous CAES systems in that Hydrostor and its partner engineering company, Aecom, build special underground tanks for the compressed air and pipes in water from an outside source to move the compressed air. This helps maintain a constant pressure in the tank, reducing the risk of damage while the system is being charged and discharged. Earlier systems generally tried to make use of existing geological caves underground or had to build artificial caves in salt deposits. According to Hydrostor’s press release, “The Terra system, on the other hand, can be deployed at any location near a body of water, including inner-city and urban areas.”
While exact pricing details depend on the project, UtilityDive noted in January that Hydrostor’s systems cost between $1,000 and $2,000 per kilowatt to build, and the company’s spokesperson confirmed that, adding that the price is a “fully installed system including warranty. “Many other technologies, including batteries, are usually not listed on a fully installed basis,” the spokesperson said. As of 2014, new natural gas plants cost about $1,488 per kilowatt to build, according to the U.S. Energy Information Administration (EIA).
Hydrostor president and CEO Curtis VanWalleghem noted in the company’s press release that it is “partnering with several utilities around the world to deploy systems of hundreds of megawatts, delivering gigawatt-hours of storage with durations ranging from four hours to multiple hours. to dawn.” The Hydrostor spokesperson told Ars that the company could not provide details about those partnerships at this time, but hoped to announce larger projects in the coming months.
In January of this year, Canada’s Globe and Mail reported that Hydrostor was seeking contracts from U.S.-based utilities that purchased energy from closed or soon-to-be-closed peak plants (that is, plants that only come on when electricity demand is greatest). The company apparently targeted dozens of largely coal-powered facilities with a capacity of at least 100 megawatts in the US that closed in 2016 or will close this year. Globe and Mail wrote.
Frame image by Hydrostor