AFAIK cost here counts only the manufacturing side. While your conclusion that in the long run economies of scale will prevail, the lifetime costs are probably more than 30%. For example I expect recycling costs to be significantly worse for the Li-Ion.

Efficiency isn't that important if the input cost is low enough. Basically the utility is throwing it away (curtailment) so you probably can too. CAPEX is really the most important part of this.

I'm seeing round trip efficiencies around 75%.

That's not terrible.

These things would probably pair well with district heating and cooling.

It's cheaper, doesn't involve the use of scarce resources, and is expected to have an operational lifetime that is three times longer than lithium ion storage facility.

That's a significant difference.

Also sodium batteries are coming to the market at a fraction of the cost.

"We’re matching the performance of [lithium iron phosphate batteries] at roughly 30% lower total cost of ownership for the system." Mukesh Chatter, cofounder and CEO, Alsym Energy

Lithium supply is limited. So an alternative based on abundant materials is interesting for that reason I guess?

Batteries aren’t really suited for seasonal storage - they decay when fully charged.

And foreseeable future they provide such huge value for grid stability that it wouldn’t make sense economically either.

We need anything that scales quickly, safely, and cheap. Just getting us through the duck curve would be a tremendous win for energy. https://en.wikipedia.org/wiki/Duck_curve

We need every approach that's viable. Batteries are part of the solution, and will be in future. But I don't see why we we should assume they're better in every way than this approach

A few hours are sometimes enough to start generators when renewable energy supply decreases. Obviously, the more capacity the better, but costs will increase linearly with capacity in most cases.

Pumped-storage hydroelectricity - where it is feasible - is the only kind of energy storage close to "months".

Had heard a lot about flow batteries few years back. I am guessing they are slowly taking off as well, the trial and error that explains their feasibility , need and ability to pay for themselves in a market like ERCOT is the key.

This is one place where I think by 2030 a clear no of options will be established.

I don't know numbers but I at least remember my paintball physics;

As far as the storage vessel, CO2 has much lower pressure demands than something like, say, hydrogen. On something like a paintball marker the burst disc (i.e. emergency blow off valve) for a CO2 tank is in the range of of 1500-1800PSI [0].

A compressed air tank that has a 62cubic inch, 3000PSI capacity, will have a circumference of 29cm and a length close to 32.7cm, compared to a 20oz CO2 tank that has a circumfrence of 25.5cm and a length of around 26.5cm [1]. The 20oz tank also weighs about as much 'filled' as the Compressed air tank does empty (although compressed air doesn't weigh much, just being through here).

And FWIW, that 62/3000 compressed air vs 20oz CO2 comparison... the 20oz of CO2 will almost certainly give you more 'work' for a full tank. When I was in the sport you needed more like a 68/4500 tank to get the same amount of use between fills.

Due to CO2's lower pressures and overall behavior, it's way cheaper and easier to handle parts of this; I'm willing to bet the blowoff valve setup could in fact even direct back to the 'bag' in this case, since the bag can be designed pessimistically for the pressure of CO2 under the thermal conditions. [2]

I think the biggest 'losses' will be in the energy around re-liquifying the CO2, but if the system is closed loop that's not gonna be that bad IMO. CO2's honestly a relatively easy and as long as working in open area or with a fume hood relatively safe gas to work with, so long as you understand thermal rules around liquid state [also 2] and use proper safety equipment (i.e. BOVs/burst discs/etc.)

[0] - I know there are 3k PSI burst discs out there but I've never seen one that high on a paintball CO2 tank...

[1] - I used the chart on this page as a reference: https://www.hkarmy.com/products/20oz-aluminum-co2-paintball-...

[2] - Liquid CO2 does not like rapid thermal changes or sustained extreme heat; This is when burst discs tend to go off. But it also does not work nearly as well in cold weather, especially below freezing. Where this becomes an issue is when for one reason or another liquid CO2 gets into the system. This can be handled in an industrial scenario with proper design I think tho.

Thermal energy storage is one gotcha. It will eventually leak away, even if the CO2 stays in the container indefinitely, and then you have no energy to extract.

The 75% round-trip efficiency (for shorter time periods) quoted in other threads here is surprisingly high though.

Well, it isn't going to sink enough CO2 to move the needle:

> If the worst happens and the dome is punctured, 2,000 tonnes of CO2 will enter the atmosphere. That’s equivalent to the emissions of about 15 round-trip flights between New York and London on a Boeing 777. “It’s negligible compared to the emissions of a coal plant,” Spadacini says. People will also need to stay back 70 meters or more until the air clears, he says.

So it's really just about enabling solar etc.

CO2 is in general less dangerous than inert gases, because we have a hypercapnic response - it's a very reliable way to induce people to leave the area, quite uncomfortable, and is actually one of the ways used to induce a panic attack in experimental settings.

If it were, say, argon, it would be much more likely to suffocate people, because you don't notice hypoxia the way you do hypercapnia. It can pool in basements and kill everyone who enters.

That being said it is an enormous volume of CO2, so the hypercapnic response in this case may not be sufficient if there's nowhere to flee to, as sadly happened in the Lake Nyos disaster you cited.

The last section of TFA is called "What happens if the dome is punctured?". The answer: a release of CO2 equal to about 15 transatlantic flights. People have to stand back 70m until it clears.

It would not be good, but it wouldn't be Bhopal. And there are still plenty of factories making pesticides.

Yeah, I was also immediately thinking about the Lake Nyos disaster. But that one released something like 200k tons of CO2 in an instant, whereas this facility has 2k tons, which would more likely be released more gradually.

> People will also need to stay back 70 meters or more until the air clears, he says.

I wonder whether it'd be possible to augment the CO2 with something that would make it more detectable visually and aromatically, like we do natural gas.

Natural gas is naturally odorless and colorless. Therefore, by default, it can accumulate to dangerous levels without anyone noticing until too late. We make natural gas safer by making stink, and we make it stink by adding trace amounts of "odorizers" like thiophane to it.

I wonder whether we could do something similar for CO2 working fluid this facility uses --- make it visible and/or "smell-able" so that if a leak does happen, it's easier to react immediately and before the threshold of suffocation is reached. Odorizers are also dirt cheap. Natural gas industry goes through tons of the stuff.

Aren’t CATL already producing sodium-ion batteries for about 60% the cost of lithium-ion for equivalent capacity?

Very unlikely. All the technologies involved work best at scale; for example, the area-to-volume ratio of the liquid gas storage vessel is a critical parameter to keep energy losses low.

> 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.

they do say

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

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%.

And I suppose the whole thing is a closed system? Which means, none of the CO2 would be released to the outside?

These days CO2 is actually quite commonly used in air-conditioners as a refrigerant, R-744. Fluorinated gases like Freon are being phased out due to being even worse for global warming.

It's easy to liquefy, so it has a density advantage over air, and would be bad if released but not super bad.

It's pretty cheap to acquire a boatload of and, assuming you don't get it directly from burning fossil fuels, there's really no environmental harms of it leaking into the atmosphere. [1]

[1] https://en.wikipedia.org/wiki/Carbon_capture_and_storage