CO2 batteries that store grid energy take off globally • Hacker News Board

Re: CO2 batteries that store grid energy take off globally

#261

Post by hamdingers » Mon, Dec 22, 2025, 4:26 PM UTC

Waterluvian wrote: post #117

nayuki wrote: post #109

> The tried-and-true grid-scale storage option—pumped hydro [--> https://spectrum.ieee.org/a-big-hydro-project-in-big-sky-cou... ], in which water is pumped between reservoirs at different elevations—lasts for decades and can store thousands of megawatts for days. > Media reports show renderings of domes but give widely varying storage capacities [--> https://www.bloominglobal.com/media/detail/worlds-largest-co... ]—…

If 1 watt is 1 joule per second then, honestly, what are we doing with watt-hours? Why can’t battery capacity be described in joules? And then charge and discharge being a function of voltage and current, could be represented in joules per unit time. Instead its watt-hours for capacity, watts for flow rate. Watt-hours… that’s joules / seconds * hours? This is cursed.

Of course it can be. Nobody does it in practice because it's inconvenient.

Watts = volts * amps and the people working with batteries are already thinking in terms of voltage and amperage. It'd be painful to introduce a totally new unit and remember 1 watt for an hour is 3.6kj instead of... 1 watt-hour.

Re: CO2 batteries that store grid energy take off globally

#262

Post by adrianN » Mon, Dec 22, 2025, 4:34 PM UTC

kumarvvr wrote: post #133

pfdietz wrote: post #129

Earlier quoted context omitted.

Utility-scale Li-ion batteries are good for an order of magnitude more than that. "LFP chemistry offers a considerably longer cycle life than other lithium-ion chemistries. Under most conditions, it supports more than 3,000 cycles; under optimal conditions, more than 10,000 cycles." https://en.wikipedia.org/wiki/Lithium_iron_phosphate_battery...

https://iopscience.iop.org/article/10.1149/1945-7111/abae37/... This is the paper that claims 10,000 cycles under optimal conditions. But if you read it, they measure Equivalent Full Cycles, and it seems that implies 10000 cycles at partial discharge, not full discharge. The paper calculates everything at nominal discharge upto 80%. Meaning, the installed capacity has to be 25% more than paper value, leading to incre…

You can buy batteries for your home solar systems with ten year warranties.

Re: CO2 batteries that store grid energy take off globally

#263

Post by adrianN » Mon, Dec 22, 2025, 4:42 PM UTC

usrusr wrote: post #224

PunchyHamster wrote: post #199

Earlier quoted context omitted.

lithium yearly discharge is in single digit %, what a nonsense argument.

GP wasn't talking about discharge, losing a little energy, they were talking about wear and tear, as in the batteries aging fast while in a highly charged state. Battery recycling still hasn't really left the "we can do it in a lab" stage.

The supply side for battery recycling hasn’t really taken off yet. Wait another ten or twenty years until large numbers of electric cars reach eol.

Re: CO2 batteries that store grid energy take off globally

#264

Post by yoan9224 » Mon, Dec 22, 2025, 4:43 PM UTC

The round-trip efficiency comparison (60-75% vs lithium-ion's ~90%) is interesting but somewhat misleading without context. For grid-scale storage, the relevant question isn't efficiency in isolation - it's lifecycle economics including capex, degradation, and replacement cycles.

Lithium-ion has superior efficiency but degrades significantly after 5,000-7,000 cycles, typically reaching 80% capacity in 7-10 years. If CO2 batteries can maintain performance for 20+ years with minimal degradation (which the article suggests), the lower efficiency becomes less relevant. You're trading 15-25% energy loss for potentially 2-3x longer operational life and no lithium supply chain dependencies.

The real breakthrough is duration-flexible storage. Lithium-ion economics break down beyond 4-hour discharge rates because you're paying for both energy capacity and power capacity. CO2 systems decouple these - the turbine size determines power output, the storage tank size determines duration. That makes them ideal for seasonal storage patterns where you might charge for days during high renewable production and discharge slowly over weeks during winter lulls.

What's missing from the article: what's the round-trip efficiency at different discharge rates? Does efficiency drop significantly when discharging over 12 hours vs 4 hours? That would determine whether these make sense for daily solar smoothing vs weekly wind intermittency vs seasonal storage.

Re: CO2 batteries that store grid energy take off globally

#265

Post by nine_k » Mon, Dec 22, 2025, 4:53 PM UTC

yoan9224 wrote: post #264

The round-trip efficiency comparison (60-75% vs lithium-ion's ~90%) is interesting but somewhat misleading without context. For grid-scale storage, the relevant question isn't efficiency in isolation - it's lifecycle economics including capex, degradation, and replacement cycles. Lithium-ion has superior efficiency but degrades significantly after 5,000-7,000 cycles, typically reaching 80% capacity in 7-10 years. If…

The system actually sort of uses the atmosphere as an ambient heat sink (when compressing) or heat source (when expanding).

I wonder if that heat could be stored in a more sensible way, e.g. as heated water in a tank near the bubble. This could improve the efficiency figures at short repeating patterns (charding at high noon, discharging through the night).

Re: CO2 batteries that store grid energy take off globally

#266

Post by woeirua » Mon, Dec 22, 2025, 4:53 PM UTC

PunchyHamster wrote: post #192

Jean-Papoulos wrote: post #178

>The company uses pure, purpose-made CO2 instead of sourcing it from emissions or the air, because those sources come with impurities and moisture that degrade the steel in the machinery. So no environmental advantages. It's supposedly 30% cheaper than lithium-ion, but BYD cars have sodium-based based batteries on the road right now which CATL says will end up being 10-20$/kwh (10x cheaper than current batteries). So…

If it is barely cheaper than lithium, it's much more expensive than traditional pumped storage. Yeah, it's expensive to build, but then cheap to run for decades. It's nice that we explore alternatives but this just seems like investor bait

Pumped hydro is not viable in most areas of the world. This is.

Re: CO2 batteries that store grid energy take off globally

#267

Post by usrusr » Mon, Dec 22, 2025, 5:01 PM UTC

gosub100 wrote: post #246

scoot wrote: post #230

Earlier quoted context omitted.

Isn't this effectively neutral over time? Heat generated during compression, lost during decompression, so basically using the air as a heat storage medium?

I think what he's saying is you can boost efficiency if you compress a cooler gas. So if you could capture the "cold" that you get from discharging the device, and use it to pre-cool the air for the next cycle (or use it for the data centers cooling system) , it would be much more efficient.

Cooling is rarely done in any other way than compressing a gas, allowing the heat to dissipate and then allowing it to decompress again. You don't want to compress a gas to cool another gas about to be compressed. What reasonably advanced compressed gas storage systems do is capture and store the heat that gets created during compression and feed it back during decompression. This gives the same efficiency difference as compressing some magically pre-cooled gas would do, only on the discharge side.

So far so good, just the old thermodynamics. It gets interesting when you have a cooling use case anyways: then you can skip on some of the decompression recovery and use the "cold" from decompression directly, to cool down something that needs cooling, without going the extra way of converting back to electricity and then sending the electricity recovered into a compressor setup for "creating cold". Bonus points if you also have a use case for the heat you did not use in reconversion to electricity, but chances are between losses during storage and heating some the gas back some amount beyond neutral you won't have much spare heat anyways.

Re: CO2 batteries that store grid energy take off globally

#268

Post by nine_k » Mon, Dec 22, 2025, 5:08 PM UTC

jakewins wrote: post #220

alextingle wrote: post #162

Earlier quoted context omitted.

It ought to be cheaper at scale. Batteries' cost scales linearly with storage capacity. Cost for a plant like this scales linearly with the storage rate - the compressor and turbine are the expensive part, while the pressure vessels and gas bags are relatively cheap. The bigger you build it, the less it costs per MWh of storage.

> Energy Dome expects its LDES solution to be 30 percent cheaper than lithium-ion. Grid scale lithium is dropping in cost about 10-20% per year, so with a construction time of 2 years per the article lithium will be cheaper by the time the next plant is completed

Li-ion and even LFP batteries degrade; given a daily discharge cycle, they'll be at 80% capacity in 3 years. Gas pumps and tanks won't lose any capacity.

Re: CO2 batteries that store grid energy take off globally

#269

Post by anotherpaul » Mon, Dec 22, 2025, 5:09 PM UTC

nine_k wrote: post #265

yoan9224 wrote: post #264

The round-trip efficiency comparison (60-75% vs lithium-ion's ~90%) is interesting but somewhat misleading without context. For grid-scale storage, the relevant question isn't efficiency in isolation - it's lifecycle economics including capex, degradation, and replacement cycles. Lithium-ion has superior efficiency but degrades significantly after 5,000-7,000 cycles, typically reaching 80% capacity in 7-10 years. If…

The system actually sort of uses the atmosphere as an ambient heat sink (when compressing) or heat source (when expanding). I wonder if that heat could be stored in a more sensible way, e.g. as heated water in a tank near the bubble. This could improve the efficiency figures at short repeating patterns (charding at high noon, discharging through the night).

As far as I understand they do try to keep the heat around for the next decompression. As of course they need it. But I could not find what type of heat storage they use. Ultimately they "only" seem to need to store it for 12h, right?

Re: CO2 batteries that store grid energy take off globally

#270

Post by while_true_ » Mon, Dec 22, 2025, 5:10 PM UTC

nayuki wrote: post #109

> The tried-and-true grid-scale storage option—pumped hydro [--> https://spectrum.ieee.org/a-big-hydro-project-in-big-sky-cou... ], in which water is pumped between reservoirs at different elevations—lasts for decades and can store thousands of megawatts for days. > Media reports show renderings of domes but give widely varying storage capacities [--> https://www.bloominglobal.com/media/detail/worlds-largest-co... ]—…

California found out pumped hydro isn't so "tried and true" when it was shut down during a drought due to lack of water behind the dam.