CO2 batteries that store grid energy take off globally

Posted by rbanffy 12/21/2025

CO2 batteries that store grid energy take off globally(spectrum.ieee.org)

370 points | 311 commentspage 2

slfnflctd 12/22/2025|

People have been experimenting with compressed gas energy storage for a long time. This one may finally have legs.

First thing I thought of was a startup from years ago, mildly surprised no one has mentioned it:

https://en.wikipedia.org/wiki/LightSail_Energy

I was really excited about them and was disappointed to see the project fail.

It seems using pure CO2 and scaling up to a massive size are significant boosts to this type of technology (in addition to the heat mitigation along the way).

idiotsecant 12/22/2025||

We desperately need mass energy storage. Everyone gets excited about renewable generation, but it is counterproductive without investing 5x-10x what we spend on generation in improved transmission and storage. It would be better to build 1/10th the amount of solar we do and pair it with appropriate energy storage than it is to just build solar panels. This is a crisis that almost nobody seems to talk about but is blindingly obvious when you look at socal energy price maps. The physics simply doesn't work without storage!!

buckle8017 12/21/2025||

So it's a compressed air facility but it's using dry CO2 because it makes the process easier and CO2 is cheap.

Not a carbon sequestration thing, but will likely fool some people into thinking it is.

So the question is, how much does it cost? The article is completely silent on this, as expected.

to11mtm 12/21/2025||

> So the question is, how much does it cost? The article is completely silent on this, as expected.

Honestly considering the design overall, I feel like one could make a single use science project version of this on a desk (i.e. aside from the CO2 recharging part) for under 200 bucks. 12oz CO2 tank, some sort of generator and whatever you need to spin it that is sealed, tubing, and a reclamation bag for the used CO2.

And IMO using CO2 makes the rest of the design cheaper; Blow off valves are relatively cheap for this scenario, especially because CO2 gas system pressures are fairly low, and there's plenty of existing infrastructure around the safety margin. And I think even with blow off valves this could be a 'closed' system with minimal losses (although that would admittedly add to the cost...)

I guess I'm saying is the main unknown is how expensive this regeneration system is for the quoted efficiency gains.

thescriptkiddie 12/21/2025|||

The tanks to hold liquid CO2 will likely be a lot cheaper than compressed air tanks because the required pressure is much lower. But they are going to loose a lot of energy to cooling the gas and reheating the liquid. I would be surprised if the round-trip efficiency is higher than 25%.

alwa 12/21/2025|||

They claim 75% efficiency AC-AC [0], and they point out that there’s no degradation with time. What estimates are you using to arrive at the 25% figure?

[0] https://energydome.com/co2-battery/

thescriptkiddie 12/22/2025||

i didn't do any math tbh, i just took the 25% number from the wikipedia page for cryogenic energy storage. i assumed their efficiency would be lower of the smaller temperature differential, but maybe it will be higher because they are storing part of the energy as pressure rather than temperature

upofadown 12/21/2025||||

The energy used to liquefy the CO2 is the bulk of the energy stored. They don't throw it away afterwards. The the liquid-gas transition is why this works so much better than compressed air.

thescriptkiddie 12/22/2025||

of course they are not throwing the energy away. but by using a working fluid that changes phase they are trading away energy efficiency for power density, for the same reason that steam engines are less efficient than stirling engines.

kumarvvr 12/22/2025|||

Heat from compression is stored in a thermal energy storage system. Most likely something like a sand container.

riffraff 12/21/2025||

they do say

> Energy Dome expects its LDES solution to be 30 percent cheaper than lithium-ion.

buckle8017 12/22/2025||

That's hardly a number.

30% cheaper than batteries from when? today? two years ago?

huge difference, 30% cheaper than lithium batteries feels like a pitch deck number from years ago to me

jmward01 12/22/2025||

As always, diversity in the energy ecosystem is a huge plus. Time and time again we see that 'one size fits all' is simply not true so I'm a fan of alternative approaches that use completely different principles. This enables the energy ecosystem to keep exploring the space of possibilities efficiently. I hope this continues to be developed.

hn_throwaway_99 12/22/2025|

> Time and time again we see that 'one size fits all' is simply not true

Do we though? It feels like we're still in the stage where we're just trying to figure out what the best solution is for grid-scale storage, but once we do figure it out, the most efficient solution will win out over all the others. Yes, there may be some regional variation (e.g. TFA mentions how pumped hydro is great but only makes sense where geography supports it), but overall it feels like the world will eventually narrow things down to a very small number of solutions.

jmward01 12/22/2025||

The point I was making isn't that we are or aren't actually narrowing down our options, it is that diversity of options is important. We have artificially limited diversity in our energy ecosystem and the rapid adoption of solar/wind/etc shows that. We could have been here decades ago if we actually encouraged diversity and exploration of alternate energy instead of actively discouraging it. Now that it is impossible to hold wind/solar back they are dominating. We should learn from that and encourage exploring diverse options in storage. Luckily I don't think storage has nearly the pushback that generation has had so I think it will be easier for many options to enter and find their niche.

belviewreview 12/22/2025||

I seem to recall from an article I read about this technology a few years ago that it's efficient partly because when the gas is compressed, they are able to store the heat that is produced, and then later use the stored heat for expanding the gas.

andrewflnr 12/22/2025|

That seems important. I wish we knew how. I found an article that did mention the heat was "stored", with no further detail. The animation down on this page suggests it's stored in water somehow: https://energydome.com/co2-battery/

nashashmi 12/22/2025||

A better understanding of the science in the system: https://newatlas.com/energy/energy-dome-co2-sardinia/

Similar discussion: https://news.ycombinator.com/item?id=44685067 (162p/153c)

mark-r 12/21/2025||

They never mention what advantage CO2 has over any other gas, like plain air?

oneiric 12/22/2025|

The fluid in high pressure storage is a liquid, making the storage much cheaper. Liquid N2 (most of air) would require over 40 times more pressure or cold temperatures. Purifying out CO2 or any gas is generally a negligible cost.

nanomonkey 12/21/2025||

I'm curious if this method could be used along with super critical CO2 turbine generators. In other words after extracting the energy stored in compressed CO2, if you could then run it through a heat exchanger to bring it up to super critical temps and pressure and then utilize it as the working fluid in a turbine.

pjc50 12/22/2025|

It looks from the diagram that a turbine is the energy extraction mechanism? As you'd expect.

nanomonkey 12/22/2025||

Correct, going from cold compressed liquid co2 though. For supercritical CO2 one would then heat up the gas and use it as a working fluid to turn the turbines further.

If you could reuse the same turbine, one could store excess solar/wind energy in the compressed gas form, and then fire up a natural gas or biomass gasification reactor and then feed the heat into the system to produce more electricity on demand.

openasocket 12/22/2025||

I don’t know much about chemistry, but is there a reason why they are using CO2 as the gas medium instead of something else? I was thinking ambient air would be readily available, and you don’t have to worry about suffocating people if it ruptures. Is CO2 particularly efficient to compress?

GoToRO 12/23/2025|

Air is no good because it has moisture in it. When you decompress it, it becomes ice, blocking and breaking pipes.

standardUser 12/21/2025|

I've been waiting for large-scale molten salt/rock batteries to take off. They've existed at utility scale for years but are still niche. They're not especially responsive and I imagine a facility to handle a mass amount of molten salt is not the easiest/cheapest thing to build.

This sounds better in every way.

More comments...