This giant bubble on Sardinia contains 2,000 tons of carbon dioxide. But the gas is not captured from factory emissions, nor is it drawn from the air. It came from a gas supplier, and lives permanently within the dome system to serve an environmentally friendly purpose: storing large amounts of excess renewable energy until it is needed.
It was developed by a Milan-based company Energy domeThe bubble and surrounding machinery showcase a first-of-its-kind “CO2 battery,” as the company calls it. The facility compresses and expands carbon dioxide2 Every day in its closed system, it runs a turbine that generates 200 megawatt-hours of electricity, or 20 megawatts in 10 hours. In 2026, replicas of this plant will begin to appear all over the world.
And we mean that literally. It only takes half a day to blow a bubble. The rest of the facility will take less than two years to build and can be done almost anywhere with 5 hectares of flat land.
The first to build one outside Sardinia will be one of India’s largest energy companies, NTPC LIMITED. The company expects to complete the CO2 battery sometime in 2026 at the Kudji Power Plant in Karnataka, India. In Wisconsin, meanwhile, public utilities Allied energy It has received approval from authorities to start building one in 2026 to power 18,000 homes.
And Google Loves this concept So much so that it plans to quickly deploy the facilities across all of its major data center locations in Europe, the US and the Asia-Pacific region. The idea is to supply data centers that consume large amounts of electricity with clean energy around the clock, even when the sun is not shining or the wind is not blowing. The partnership with Energy Dome, announced in July, marks Google’s first investment in long-term energy storage.
“We scanned the world for different solutions,” he says. They appointed yourGoogle’s chief energy strategy officer, in Paris. The challenge for the tech giant was not only finding a long-term storage option, but also one that worked with each region’s unique specifications. “So standardization is really important, and that’s one of the aspects we really like” about the Energy Dome, she says. “They can really plug this in and run it.”
Anda says Google will prioritize placing energy dome facilities where they will have the greatest impact on decarbonization and grid reliability, and where there is plenty of renewable energy to store. The facilities can be located next to Google’s data centers or elsewhere within the same network. The companies did not disclose the terms of the deal.
Anda says Google expects to help the technology “reach a huge commercial scale.”
Innovation in long-term energy storage
All this excitement builds on Energy Dome’s single, grid-connected, full-scale plant in Otana, Sardinia, which was completed in July. It’s designed to help solve one of the biggest challenges facing the energy transition: the need for grid-scale storage that can provide power for more than 8 hours at a time. This concept is called long-duration energy storage, or LDES in industry parlance, and is key to maximizing the value of renewable energy.
When sun and wind are abundant, solar and wind farms tend to produce more electricity than the grid needs. So storing surpluses for use when these resources are scarce makes sense. LDES also makes the grid more reliable by providing backup and supplementary power.
The problem is that even the best new grid-scale storage systems on the market — especially lithium-ion batteries — only provide about 4 to 8 hours of storage. That’s not long enough to provide power for an entire night, several cloudy, windy days, or the hottest week of the year, when power demand peaks.
After the carbon dioxide leaves the dome, it is compressed, cooled, turned into a liquid and stored in pressure vessels. To release energy, the process is reversed: the liquid is vaporized, heated, expanded, and then fed through a turbine that generates electricity. Luigi Avantagiato
Lithium-ion battery systems can be scaled up to store more and last longer, but systems of this size are usually not economically viable. Other grid-scale battery chemistries and approaches are in development, such as sodium-iron-air-vanadium-based redox flow batteries. But energy intensity, costs, degradation, and financing complexities have presented a challenge to developers of these alternatives.
Researchers have also experimented with storing energy by compressing air, heating blocks or sand, using hydrogen or methanol, pressurizing water deep underground, and even suspending and dropping heavy objects in the air. (The creativity dedicated to LDES is impressive.) But geological constraints, economic feasibility, efficiency, and scalability have hampered the commercialization of these strategies.
A tried-and-true grid-scale storage option — pumped hydro, where water is pumped between reservoirs at different heights — lasts for decades and can store thousands of megawatts for days. But these systems require specific terrain, a lot of land, and can take up to a decade to build.
CO2 batteries check a lot of boxes that other methods don’t. They do not require special terrain like pumped water reservoirs. They do not require important metals like electrochemical and other batteries. They use components for which supply chains already exist. Its expected life span is approximately three times that of lithium-ion batteries. Adding size and storage capacity to it significantly reduces the cost per kilowatt-hour. Energy Dome expects its LDES solution to be 30 percent cheaper than lithium-ion.
China has taken note of this. China Huadian Corp and Dongfang Electric Corp are said to be building the CO22An energy storage facility in the Xinjiang region of northwest China. Media reports Show renderings Of the domes but give Storage capacities vary widely– Of which 100 megawatts and 1000 megawatts. Chinese companies did not respond IEEE SpectrumRequests for information.
“What I can say is that they are developing something very similar [to Energy Dome’s CO2 Battery] “But it is very large in size,” he says. Claudio Spadasinifounder and CEO of Energy Dome. Chinese companies, he says, “are good, they’re very fast, and they have a lot of money.”
Why is Google investing in CO2 batteries?
When I visited the Energy Dome’s Sardinia facility in October, the CO2 It had just been pumped out of the dome, so I was able to peek inside. It was huge, monochromatic, and largely empty. The inner membrane, which held uncompressed carbon dioxide2It collapsed all over the floor. A few pockets of gas remained, causing the yellowish-white layer to swell in some spots.
Meanwhile, the translucent outer dome allowed some daylight through, creating a creamy glow that blanketed the vast space. With no structural frame, the only thing keeping the dome upright is the slight difference in pressure between the inside and outside air.
“This is unbelievable,” I said to my guide, Mario TorchioDirector of Global Marketing and Communications at Energy Dome.
“It is,” he said. “But it’s physics.”
Outside the dome, a series of machines connected by undulating tubes transport carbon dioxide2 Outside the dome for pressure and condensation. First, the compressor compresses the gas from 1 bar (100,000 Pa) to about 55 bar (5,500,000 Pa). The thermal energy storage system then cools the carbon dioxide2 to ambient temperature. The condenser then turns it into a liquid that is stored in a few dozen pressure vessels, each about the size of a school bus. The whole process takes about 10 hours, at the end of which the battery is considered charged.
To discharge the battery, the process is reversed. Liquid CO2 It is vaporized and heated. It then enters a gas expander turbine, which is similar to a medium pressure steam turbine. This turns on a synchronous generator, which converts mechanical energy into electrical energy for the grid. The gas is then exhausted at ambient pressure and returns to the dome, filling it to await the next charging stage.
Energy Dome engineers inspect the desiccant system, which keeps the dome’s gaseous carbon dioxide at optimal dryness levels at all times.Luigi Avantagiato
It’s not rocket science. However, someone had to be the first to put this idea together and figure out how to do it in a cost-effective way, something Spadasini says his company has accomplished and patented. “The way we close the turbomachinery, how we store the heat in the thermal energy storage, how we store the heat after condensation… can actually reduce costs and increase efficiency,” he says.
The company uses pure, designated carbon dioxide for this purpose2 Instead of getting it from emissions or air, because these sources come with impurities and moisture that deteriorate the steel in machines.
What happens if the dome is punctured?
On the downside, the Energy Dome facility occupies about twice as much floor space as a lithium-ion battery of similar capacity. And the domes themselves, roughly the height of a sports field at their top, and perhaps taller, might stand out against the landscape and attract some NIMBY opposition.
What if a hurricane comes? Spadasini says the dome can withstand winds of up to 160 kilometers per hour. If the Energy Dome could get a half-day warning of severe weather, the company could just compress and store the carbon dioxide2 In the tanks and then empty the outer dome, he says.
If the worst happens and the dome is punctured, 2,000 tons of carbon dioxide will be produced2 It will enter the atmosphere and that is equivalent to the emissions of about 15 round-trip flights between New York and London on a Boeing 777. “They are negligible compared to the emissions from a coal plant,” says Spadasini. He says people will also need to stay 70 meters or more apart until the air clears.
Worth the risk? The companies lining up to build these systems seem to think so.
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