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Google Launches CO2 Battery Plants for Long-Duration Storage of Renewable Energy (ieee.org) 75

Posted by EditorDavid from the power-plays dept.
In July Google promised to scale the CO2 batteries of "Energy Dome" as a long-duration energy storage solution. Now IEEE Spectrum visits its first plant in Sardinia, where 2,000 tonnes of carbon dioxide power a turbine generating 20 MW over 10 hours — storing "large amounts of excess renewable energy until it's needed..."

"Google likes the concept so much that it plans to rapidly deploy the facilities in all of its key data-center locations in Europe, the United States, and the Asia-Pacific region." Developed by the Milan-based company Energy Dome, the bubble and its surrounding machinery demonstrate a first-of-its-kind "CO2 Battery," as the company calls it... And in 2026, replicas of this plant will start popping up across the globe. We mean that literally. It takes just half a day to inflate the bubble. The rest of the facility takes less than two years to build and can be done just about anywhere there's 5 hectares of flat land.

The first to build one outside of Sardinia will be one of India's largest power companies, NTPC Limited. The company expects to complete its CO2 Battery sometime in 2026 at the Kudgi power plant in Karnataka, in India. In Wisconsin, meanwhile, the public utility Alliant Energy received the all clear from authorities to begin construction of one in 2026 to supply power to 18,000 homes... The idea is to provide electricity-guzzling data centers with round-the-clock clean energy, even when the sun isn't shining or the wind isn't blowing. The partnership with Energy Dome, announced in July, marked Google's first investment in long-duration energy storage...

CO2 Batteries check a lot of boxes that other approaches don't. They don't need special topography like pumped-hydro reservoirs do. They don't need critical minerals like electrochemical and other batteries do. They use components for which supply chains already exist. Their expected lifetime stretches nearly three times as long as lithium-ion batteries. And adding size and storage capacity to them significantly decreases cost per kilowatt-hour. Energy Dome expects its LDES solution to be 30 percent cheaper than lithium-ion.

China has taken note. China Huadian Corp. and Dongfang Electric Corp. are reportedly building a CO2-based energy-storage facility in the Xinjiang region of northwest China.
Google's senior lead for energy storage says they like how Energy Dome's solution can work in any region. "They can really plug and play this."

And they expect Google to help the technology "reach a massive commercial stage."
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Google Launches CO2 Battery Plants for Long-Duration Storage of Renewable Energy More

Google Launches CO2 Battery Plants for Long-Duration Storage of Renewable Energy

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  • Why not just compress air? (Score:1)

    by Anonymous Coward

    To extract Co2 from the air to fill this oversized balloon also uses up a significant amount of energy while it puts it back in the air when running the turbine.
    This all sounds like some nasty greenwashing where Google can claim they are CO2 neutral based on some messed up logic.

    • Re:Why not just compress air? (Score:5, Informative)

      by bartoku ( 922448 ) on Sunday December 21, 2025 @10:08PM (#65873823)

      CO2 liquifies at Room Temperature, air does not. CO2 has higher energy density. CO2 has a higher round trip efficiency.

      CO2 can be turned into a liquid at roughly 30C (86F) when under pressure (about 70 bar). To turn air into a liquid, you must cool it to extreme cryogenic temperatures (around -196C). Liquid CO2 is roughly 400 times denser than gaseous CO2 at atmospheric pressure. Because it stays liquid at "ambient" (normal) temperatures, it can be stored in standard steel tanks without the need for massive refrigeration systems. CO2 transitions between gas and liquid so easily at moderate pressures, the system loses very little energy during the phase change. In a typical air-based system, much of the energy is lost as "waste heat" during compression. In the CO2 battery, that heat is captured and stored in "thermal bricks" and then used later to turn the liquid CO2 back into gas, making the cycle highly efficient.

      • Thank you, Bartoku, that is a very helpful explanation.
        • If the CO2 is somehow released, it will not be possible to drive away from the accident because car engines require oxygen to burn fuel.

          • The CO2 should have to escape through whatever opening is created, and ripstop is pretty standard for this sort of thing, keeping openings small. A venting liquid CO2 tank would be limited by evaporation.
            The danger zone would depend on the size of the hole, but like old CO2 fire extinguishers, CO2 tends to disburse fast, and the lethal range for it is drastically higher than things like carbon monoxide, ammonia, and such.
            Plus, think of the future! An EV would operate just fine, and a couple minutes would

            • The venting of a CO2 tank is limited by evaporation until the remaining liquid freezes solid. Then the venting is limited by the melting of the solid CO2, which is much slower.

          • Re: (Score:2)

            by Jeremi ( 14640 )

            If the CO2 is somehow released, it will not be possible to drive away from the accident because car engines require oxygen to burn fuel.

            Well, that, and because humans require oxygen to remain conscious. If there's so little oxygen in the air that your car won't start, your car won't be the worst of your problems.

            OTOH your self-driving EV could perhaps evacuate your unconscious body from the area :)

          • Re: (Score:1)

            by kig8472 ( 915313 )
            Air gets "dangerous" to breathe at about 4% CO2. At that level an ICE car will probably run just fine, because there's still plenty of O2 left. EVs won't care anyway.

      • Thanks for all the details!
        Something learned today.

        Still, only the (re)compression all the CO2 will set you back a $22 per metric ton every time.
        And turbines aren't that efficient either.
        I wonder how much will be left when taking all the costs and inefficiencies into account.

        • Re: (Score:1)

          by Anonymous Coward

          One source I found says Lithium batteries return 90% of the energy stored while CO2 returns about 80%, but at half the cost of Lithium batteries per Watt stored, they appear to be a cheaper option that doesn't degrade each cycle.

          • Re: (Score:2)

            by bn-7bc ( 909819 )
            Allso CO2 is noy somthing that has most of it's deposits in politically unstable places as opposed to lithium. This might be a rather large advantage and worth th slightly less eficient energu capture

      • Re: (Score:2)

        by mattr ( 78516 )

        It seems so elegant, wonder why it didn't arrive earlier. Google says Energy Dome (Italian co.) actually invented it in 2019 with a test in 2022 so I guess it is pretty new but still it seems so simple compared to stacks of lithium or whatever. Though gravity batteries are even simpler it seems.

        • Re: (Score:2)

          by tragedy ( 27079 )

          Though gravity batteries are even simpler it seems.

          By gravity batteries I hope you mean pumped hydro storage. If you mean raising weights up towers or even disused mine shafts, I've never seen a plan for one that didn't fail back of envelope math for actual utility and cost effectiveness that it was impossible not to consider it to be a scam.

    • Re: (Score:2)

      by shilly ( 142940 )

      CO2 can operate at ambient temperatures vs cryogenic requirements for liquid air. That’s a major advantage

    • I'm curious about the "thermal bricks." I can't think of a material with a higher specific heat than water, and the diagrams show water in the heat-exchanger areas. How much water is needed to store the latent heat of phase change? And how well insulated does that heat-storage mechanism need to be? The water is closed-loop, so consumption in operation will be small, but if a large amount is needed for installation, that could constrain locations. If not water, what material is used for "thermal bricks"?

      • I'm curious about the "thermal bricks." I can't think of a material with a higher specific heat than water, and the diagrams show water in the heat-exchanger areas.

        I'm curious about this too. I don't understand the properties of CO2 but if you're compressing the gas, it heats up (PV=nRT). But you don't want to waste that heat, that's the energy you're trying to store. IIRC, condensing a gas to a liquid also releases heat so I don't understand the energy flows.

        • The problem is, when you discharge you get a lot of cold. So your turbine efficiency drops unless you can get heat from somewhere. Thermal stores keep cold from discharge and heat from charge to offset against the next cycle.

          • The problem is, when you discharge you get a lot of cold. So your turbine efficiency drops unless you can get heat from somewhere. Thermal stores keep cold from discharge and heat from charge to offset against the next cycle.

            Right. I wonder though: how much energy is stored in the compressed gas versus in the thermal store?

            If we were talking air, I'd expect that liquified air is a net energy sink, not a store. There must be some interesting physics going on with CO2 that I don't understand.

    • Closed cycle (Score:4, Informative)

      by Firethorn ( 177587 ) on Monday December 22, 2025 @12:03AM (#65873945) Homepage Journal

      Reading the site page, it is closed cycle. The big gas dome holds more or less atmosphere temperature and pressure CO2. There are one or more tanks holding relatively non-cryogenic liquid CO2.
      When there is excess power, pumps liquify CO2 into the tanks. When power is demanded, evaporating CO2 goes through a turbine to produce power, then into the dome.
      Water is used, most likely to cool the freshly compressed CO2, and warm expanded CO2 after the turbine.

    • Re: (Score:2)

      by pz ( 113803 )

      I know of at least one company that was trying to do exactly that: have long tubes into which you pump air to some ridiculous pressure to store energy, and then run turbines from that compressed air when you want to draw back that energy.

    • Yup, just another example of the Carbon Capture Perpetual Motion Machine Scam. The thermodynamic uphill problem with atmospheric capture is so extreme that if you had enough free energy sitting around to make it worthwhile, you wouldn't need to do any of this.

      • And I have to wonder what the net efficiency of the process is -- i.e., if you're getting 200MWh of energy out of a fully-charged system, how much more than 200MWh did you have to put in to charge it?

        • Here's a video by Matt Farrell https://www.youtube.com/watch?v=GSzh8D8Of0k that explains the technology.
          Efficiency is projected to be 75-80%, so you put in 250-267 MWh of energy, and get 200 MWh back out.

  • Renewable energy at scale requires a mix of generation types, of storage types, of locations, of temporal phasing, etc etc. And that’s what we’re getting: for storage, we are getting short, medium and long term storage solutions using thermal, chemical, kinetic, gravitational and other mechanisms. This heterogenous approach lowers risks associated with single points of failure such as materials supply chain crunches or inability to meet demand spikes. It means a higher initial cost per kWh becau

  • I've seen work on this (Score:2, Informative)

    by Luckyo ( 1726890 )

    I've had some inside access to this tech in recent past. The main problem is efficiency. It's horrendous. You lose tremendous amounts of energy doing this, and you need quite a bit of energy to maintain the compressed state. We're nowhere near mainline chemical batteries in terms of efficiency numbers, and whatever numbers they're claiming on their website are likely specifically negating some critical losses. I've seen efficiency numbers as low as 20-25%, through they can really struggle to push into upper

    • Quoting from the Google blog post linked in the summary,

      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.

      By supporting multiple commercial deployments of Energy Dome's technology globally, and making an investment in the company, we aim to bring this technology to scale faster and at lower costs.

      I'm going to go out on a limb and say that if Google is investing in them, they've probably done their due diligence and found it's real.

      • Re: (Score:1)

        by Luckyo ( 1726890 )

        There have been successful prototypes of gas compression capacitors "injecting electrons into the grid" for much longer than that.

        What matters isn't "injecting electrons in the grid". What matters is doing this efficiently at low cost.

        My entire point is that none of these sources, including this blog have a single word to say on the issue that matters. Instead they all focus on various language trick and creative wording to divert attention from thing that matters to things that don't.

        You know, like "inject

        • It isn't hard to find their given efficiency claims, as you can also find compressed air stats, but of which are in commercial prototype phase. CO2 is better than air but you need to keep the CO2 around.

      • I'm going to go out on a limb and say that if Google is investing in them, they've probably done their due diligence and found it's real.

        That is a silly appeal to authority. There are many reasons why this is real, including that it is simple, physics are known and used in other industries, and that the logic is technically sound.

        But Google's due diligence is not any sound reasoning. You remember Google right? The company that has already bought future fusion power which doesn't exist: https://edition.cnn.com/2025/0... [cnn.com], has signed purchase power agreements for small modular reactors which don't exist yeat (and all projects to date have faile

    • Hmm, Luckyo, have you ever tried secret sauce? I think here it's in the "thermal bricks". Or maybe it's not all that secret. Humans commonly store co2 in liquid form in steel tanks. Or am I missing something?

      • Re: (Score:1)

        by Luckyo ( 1726890 )

        Yes. We store is in steel tanks by cryogenically cooling it prior to compression so it doesn't go supercritical during compression. After compression is done, we just need to maintain subcritical temperature and pressure.

        Basic physics time: do you remember that when you compress something, it heats up? So what happens to a gas that goes supercritical at around 30 celsius if you attempt to rapidly compress it into a liquid without doing extreme cooling on it before compressing it?

        Important part of the batter

        • They have a big tank of water. That keeps the gas below 30C for compression and warm during expansion. They have been doing this for three years. How that works in summer in Sardegna, I don't know. I guess a bit of insulation and some evaporative cooling.

          • Re: (Score:1)

            by Luckyo ( 1726890 )

            Big tank isn't going to cut it. You'll need to pump everything through high surface high throughput heat exchangers. It's going to cause significant additional energy losses.

            • Yes, of course there is a heat exchanger. It's all very well known and widely available technology. Their claimed efficiency is 70% over 12 hours, so that is enough to make solar function all day, at half the unit price of lithium.

              Of course, these figures might not pan out, they might not be able to scale up, or battery prices might drop fast enough that their lower cost might disappear. Or their dome might be too weather sensitive or, or, or. For now, though, they appear to have an early stage product that

    • I don't know anything at all about this technology, I'd not heard about it before. I came to the comments to find out if it was relying on liquification of CO2, which I assumed, or was something else.

      First point to note, 80 bar isn't high pressure in an industrial setting and 30C is low enough that there's large parts of Europe where you can assume that ambient air temperature almost never exceeds it. Therefore passive cooling is possible and in many cases, forced air cooling will be is sufficient. (I liqui

    • Re: (Score:3)

      by Whibla ( 210729 )

      I've had some inside access to this tech in recent past. The main problem is efficiency. It's horrendous. You lose tremendous amounts of energy doing this, and you need quite a bit of energy to maintain the compressed state. We're nowhere near mainline chemical batteries in terms of efficiency numbers, and whatever numbers they're claiming on their website are likely specifically negating some critical losses. I've seen efficiency numbers as low as 20-25%, through they can really struggle to push into upper 30s for long term storage, and can probably get above 50 for very short term (i.e. minimal compressed state maintenance costs). Still nowhere near the required efficiency numbers to competitive with chemical batteries of current gen. These people claim 75%. Odd.

      Well, they're the ones who have been running a pilot plant. Presumably their efficiency figures come from their real world electrical power requirements / production. However, I must confess I share your scepticism. If we look at each component of the plant individually alongside their typical efficiencies (Compressor: 70% - 90%; Turbine: 40% - 95%; Electric Motor: 75% - 95%; Electrical Generator: 85% - 98%; Thermal Insulation: 80% - 98%) and factor in frictional / pressure losses in the pipe network (tbf w

    • You might be right, but at the same time CO2 storage doesn't seem to be an issue when I order a soda.

    • When you pressurize the gas, it heats up. A lot

      And when you depressurize it, it cools down, a lot. So in theory, the heat from pressurization is something you only have to worry about the first time.

  • Hmm (Score:3)

    by dskoll ( 99328 ) on Sunday December 21, 2025 @10:58PM (#65873887) Homepage

    2000t generating 20MW over 10h... that's 2 milliion kg generating 720GJ. Equivalent to lifting that 2000t by 36km.

    Color me very, very skeptical.

    • This isn't gravity storage. It liquifies the CO2 by pressurizing it.

      • Re: (Score:2)

        by dskoll ( 99328 )

        According to Wikipedia, 2000t of CO2 can store 100MWh [wikipedia.org] which is 360GJ, half of the 720GJ I calculated above. So that would be 20MW for 5h, not 10h.

        So I guess I was right to be a bit skeptical, but am still surprised by how much energy can be stored.

    • 2000t generating 20MW over 10h... that's 2 milliion kg generating 720GJ. Equivalent to lifting that 2000t by 36km.

      Color me very, very skeptical.

      Everyone should be skeptical of things they don't understand, however a very basic university level physics undergrad wouldn't be skeptical about those numbers. There is an amazing difference in overcoming the potential energy of gravity and deriving energy from decompression. People completely underestimate just how powerful this can be, especially when it involves a phase change.

      If you want to compare energy required for things that may sound similar but are wildly different think about making some tea:
      It

  • Aren't these operations only considered efficient if the liquid COâ is a byproduct of another, much more expensive, operation?

    Do we think they're doing this because there's some flaw in an existing California law where they can get credit for using a former Linde facility as a 'battery'?

    • It is a closed loop system. Smallish tanks for the liquid co2, great big football field or larger dome for gaseous CO2. Website does not have dimensions, I'd guess the dome varies in size based on total energy desired.
      As such, it is like worrying about the inner loop water in a nuclear reactor. Since you theoretically only need that initial charge, it rounds to zero per unit of energy over time.

    • They buy the CO2 commercially. Very little should be lost. CO2 isn't hard to source in industrial quantities.

  • Because of the viscosity, normal breathing gases (nitrogen, oxygen, and trace gasses, like c02) would be more efficient--unless they are proposing it because of ulterior motives.

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