By Kennedy Maize
Carbon dioxide, the simple and ubiquitous chemical that many see as the scourge of the earth driving global warming, may also be a salvation that turns intermittent wind and solar electricity into a round-the-clock asset.
Late last month (July 25), Google announced a deal with Energy Dome, a company based in Milan, Italy, with offices in Boston, for a novel CO2-powered long duration energy storage system. It is storage of potential energy that can be turned back into electricity, similar to compressed-air storage projects, which have never caught on.
If successful, the technology could overcome many of the problems of the current king of the battery hill: lithium-ion batteries, technology upscaled from tiny cell phone batteries to power electric vehicles and store excess power from solar and wind generation, rendering them able to be dispatched to follow load.
A note on that subject. Many in the electric industry, particular skeptics of renewables, make much of their lack of “dispatchability,” which is true. Even with lithium-ion technology, the ability to respond to loss of load is short term, although that can be very useful.
The critics usually cite as their favored “dispatchable” technologies coal, hydro, and nuclear. But nuclear is not “dispatchable.” It is dispatched, 24-7. Nuclear regulations do not, and should not, allow nuclear power plants to ramp up and own as load varies. That’s a significant distinction. While the industry brags of nuclear power’s high “capacity factors,” that’s an economic bug, not a feature.
Energy Dome says the technology is a “closed thermo-mechanical transformation.” It stores CO2 as a liquid, then evaporating and expanding it as a hot gas that runs “through a turbine and back into the gasholder.” The company says it can produce grid power for 8-24 hours. The technology uses power from renewable generation when the sun is shining or the wind blowing to compress the CO2 into a liquid.
The U.S. Department of Energy defines “long-duration energy storage systems” as “storage systems capable of delivering electricity for 10 or more hours in duration.
A 2022 article in MIT Technology Review described the CO2 process: “In Energy Dome’s designs, a flexible membrane holds the carbon dioxide in a huge dome at low pressure. When excess electricity is available, the gas goes through a compressor to reach high pressure. This process also generates heat, which is stored too.
“Then, when energy is needed, the stored heat is used to warm up the carbon dioxide, which decompresses and turns a turbine, generating electricity.”
Among the claimed advantages: it uses no expensive and fire-prone lithium; the needed materials are “water, steel, and CO2”; it avoids the high costs of the low temperatures of compressed-air storage as the liquid CO2 is stored at “ambient temperature”; zero CO2 emissions.
According to Google, “The technology has already proven successful, having injected electrons into the Italian grid for more than three years, thanks to their commercial demo facility, and now with their full-scale 20MW-200MWh commercial plant” on the Italian autonomous island of Sardinia.
Google has long been committed to eliminating CO2 emissions from its electricity supply. The company says, “In 2020, we set an ambitious new goal: to operate on carbon-free energy, 24 hours a day, 7 days a week, 365 days a year—all by 2030.”
No financial details of the Google deal are available. But there are some indications that CO2 technology may cost considerably less than lithium-ion batteries. In the MIT Technology Review article, Energy Dome CEO Caludio Spadacini claimed the early plants could come in at a bit under $200/kWh, compared to $300/kWh for lithium-ion, the current prices as of 2022.
Even with its inherent problems, lithium-ion technology has proven useful as renewable technology has boomed. Often, the legacy generation enamored by, among others, the Trump administration, has failed to prove its allegedly inherent dispatchability.
That was true in Winter Storm Uri in Texas in February 2021 and Winter Storm Elliott in the PJM Interconnection in December 2022. Coal piles freeze, pipelines fail, valves fail to open. In Texas, wind has often bailed out the state’s gas-centric power system in bad weather.
Most recently, Texas energy reporter Doug Lewin, proprietor of the Texas Energy & Power newsletter, wrote that during this summer’s heat dome on July 12, “There’s a new battery storage record in Texas: 6,300 megawatts. Gas and coal plant outages spiked as the sun was going down. It was another high demand day with renewables providing ~45% of the power most of the day.”
Lithium-ion technology isn’t doomed. The technology is getting better. Also, it is modular, easily scalable.
A family competitor, the sodium-ion battery, is showing some promising results, although sodium may not overcome the advantages of lithium. Lithium and sodium are cousins on the periodic table of the elements, numbers 1 and 2 on the list of alkali metals. Sodium is slightly heavier and somewhat less reactive and likely to catch on fire. Sodium is also far more abundant and cheaper than lithium and easier to operate, not needing active cooling systems.
Denver-based Peak Energy announced last week (July 30) that it had shipped the first grid-scale sodium-ion battery in the U.S., with few details other than as a “shared pilot with nine leading utility and independent power producer (IPP) customers.”
If the Energy Dome does the job, bringing competition to storing renewable power is likely to be worthwhile, as well as bolstering the case for renewables, which are considerably less costly than any of the administration-favored elderly technologies.
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