> big yikes for something coming out of the Institute of Electrical and Electronics Engineers.

Besides the unit flub, there's an unpleasant smell of sales flyer to the whole piece. Hard data spread all over, but couldn't find efficiency figures. Casual smears such as "even the best new grid-scale storage systems on the market—mainly lithium-ion batteries—provide only about 4 to 8 hours of storage" (huh, what, why?). I could also have used an explanation of why CO2, instead of nitrogen.

Power plants are often described in terms of (max) power output, i.e., contribution to the grid. So, I can see how it might confuse a writer to then also talk about storage inadvertently.

But also, the second paragraph already describes the 100 MWh vs MW nuance.

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.

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.

I should have explained in my original comment why I think those sentences are wrong. I'll do so now.

> pumped hydro [...] can store thousands of megawatts for days.

You can't "store" a megawatt – because you can only store energy, not power.

But another interpretation is, if you actually store thousands of megawatts (i.e. gigawatts) for days, then at the very least, 1 GW × 1 day = 24 GW⋅h. If we take "a few" to mean 3, then 3 GW × 3 day = 216 GW⋅h. I'm not sure there exists a large enough pumped hydro plant in the world that stores 216 GW⋅h of energy. So I think the article meant to say, "store a few gigawatt-hours to be released over a period of a few days".

> Media reports show renderings of domes but give widely varying storage capacities—including 100 MW and 1,000 MW.

Once again, you can't store megawatts of power, full stop. You can store megawatt-hours of energy. The linked article at Bloomberg said that a project in China is building 600 MW of wind power, 400 MW of solar power, and 1 GW⋅h of energy storage – which is the correct unit.

I'm old enough to remember when IEEE Spectrum was a respected technical publication.

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.

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.

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.

I'm seeing round trip efficiencies around 75%.

That's not terrible.

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

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?

Different solutions for different needs.

It's good for engineers and planners to have multiple solutions available that provide better fit to their prerogatives and needs.

We don't need one solution to do it all. We need plural ones.

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.

I agree with you: the real test isn't whether it's 30% cheaper today, but whether it holds its economics over 20–30 years at scale

I think it is generally polite to flag when you are using an LLM to write your comment, some people tire of reading the same style of writing over and over - even if the content of your comment is interesting!

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).

> Because any pressurized gas energy storage is either including some advanced heat storage or is just venting the heat created during compression

    a thermal-energy-storage system cools the CO2 to an ambient temperature

I'm sort of thinking out loud here but could you have two batteries running simultaneously but on opposite cycles, so while one is cooling the other is heating? Obviously it wouldn't be 100% efficient but it might reduce some wasted energy.

If Google is colocating these with data centers, even low-grade heat that would otherwise be a loss could still be useful, or at least reduce how much active cooling the DC needs

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

To cite and expand on lambdaone below [1]:

> Clearly power capacity cost (scaling compressors/expanders and related kit) and energy storage cost (scaling gasbags and storage vessels) are decoupled from one another in this design

Lambdaone is differentiating between the costs to store energy (measured in kWh or Joules) and the costs to store energy per time (which is power, measured in Watts). If you want to store the whole excess energy that solar panels and wind turbines generate on a sunny, windy day, you need to have a lot of power storage capability (gigawatts of power generated during peak power generation). This can be profitable even if you only have a low energy storage capability, e.g. if you can only store a day worth of excess solar/wind energy, because you can sell this energy in the short term, for example in the next night, when the data centers are still running, but solar panels don't produce power. This is what batteries give you -- high power storage capabilities but low energy storage capacities.

Of course, you can always buy more batteries to increase the energy storage capacities, but they are very expensive per energy (kWh) stored. In contrast, these CO2 "batteries" are very cheap per energy (kWh) stored -- "just" build more high pressure tanks -- but expensive per power (Watts) stored, because to store more power, you need to build more expensive compressors, coolers etc. This ability to scale out the energy storage capability independently of the power storage capability is what Lambdaone was referring to with the decoupling.

For what is this useful? For shifting energy over a larger amount of time. Because energy storage costs of batteries are so high, they are a bad fit for storing excess energy in the summer (lots of solar) and releasing it in the winter (lots of heating). I'm not sure if these "CO2" batteries are good for such long time frames (maybe pressure loss is too high), but the claim most certainly is that they can shift energy over a longer time frame than is possible with batteries in an economically profitable fashion.

[1] https://news.ycombinator.com/item?id=46347251

Even if sodium-ion really gets to $10–20/kWh, you still have degradation, cycle limits, fire risk, and a practical lifetime that's maybe 10–15 years

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

> So what's the actual advantage of this ?

I would posit that they hope Wright's Law will take hold; the components can be optimised and the deployment standardised. Also it looks as if most of the stuff can be made within the US or EU, dodging tariffs.

[dead]

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.

The gotcha will be the “poor” round trip efficiency, in comparison to other storage technologies.

It’d be interesting to see if there’s any loss of efficiency with increasing storage duration too (relating to boil-off of the cryogenic side of the storage ?) because this would impact the economics of charging too.

I just get the feeling lithium/sodium ion for electricity and big piles of sand/dirt for heat are going to more-or-less win the energy storage race.

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.

The funniest part is that the "implicit cooling cycle" might be more valuable for grid alignment than raw efficiency

If you think this is simple, wait until you learn about oceans and forests do!

Trees are literally CO2 based solar batteries: they take CO2 + solar energy and store it as hydrocarbons and carbohydrates for later use. Every time you're sitting by a campfire you're feeling heat from solar energy. How much better does it get that free energy storage combined with CO2 scrubbing from the atmosphere!

When you look at the ocean, it's able to absorb 20-30% of all human caused CO2 emissions all with no effort on our behalf.

Unfortunately, these two solution are, apparently, "too good to be true" because we're increasingly reducing the ability of both to remove carbon. Parts of the Amazon are not net emitters of CO2 [0] and the ocean has limits to how much CO2 it can absorb before it starts reach its limit and become dangerously too acidic for ocean life.

0. https://www.theguardian.com/environment/2021/jul/14/amazon-r...

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.

Company says safe limit is 70 meters, about 200 feet.

Easy to build infra and other stuff that far away, especially in locations where this is meant to be used.

There are many aspects of safety

1. If the puncture is due to hurricanes, etc, the danger is non existent. The hurricane will blow away the co2 in no time.

2. If the puncture is due to wear and tear, then the leak will be concentrated and localized. It could naturally diffuse.

CO2 meters can be installed around the unit for indication.

Oxygen masks can be placed around the facility for emergency use.

The dangers are very much mitigatable.

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.

So .. significantly less dangerous than a corresponding volume of natural gas, which is also unbreathable but also flammable/explosive?

> 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.

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

There are way cheaper options than the Anker Solix 3800. Here are some options, in no particular order:

- $3,300: 10 kWh with 2x EG4 WallMount Indoor 100Ah.

- $3,110: 14 kWh with 1x WallMount Indoor 280Ah.

- $2,690: 10 kWh with 1x Deye RW F10.2 B

- Will Prowse's YouTube channel has reviewed several battery builds that are >10 kWh and near $2,000, but they're DIY assembly.

The YouTuber Will Prowse has an excellent site where he tracks his most recommended batteries (and other equipment like inverters) at any time. The prices are always changing, and there are new products all the time so check on the his list any time you are looking to buy:

https://www.mobile-solarpower.com

Like the other commenter said, batteries are a lot cheaper if you are willing to shop around. His top recommended budget battery today is a 4x your Anker Solix's capacity, and around 1/4th the price. You can find many 5kWh server rack batteries for under $1000 now.

Here's a quote I got for a solar install in the Philippines this week:

51.2v 314ah cells (15kwh battery) 16x 580-590w solar panel

Installed for 310k PHP = $5,275

I've also specced out 15-16kwh batteries using the Yxiang design for around the price of your Solix. The problem in the US is regulatory and a particularly predatory tradesman market at the moment.

Western storage options are very expensive.

We are starting to see Chinese options pop up but not sure if I would install them yet.

https://www.docanpower.com/eu-stock/zz-48kwh-50kwh-51-2v-942...

Wait that Anker Solix 3800 costs more than my 84kwh battery containing _car_ (3.8 kwh x 22 batteries)? Something not right.

The batteries in MWh range cost around 160 EUR/kWh all in. Including grid connection and BOP.

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.

> What we need is a storage technology with a duration of months

Actually, having expandable, highly re-usable tech like this is much better when the capacities are in terms of hours.

This storage, combined with say 2.5x solar panel installation, could essentially provide power at 1x day and night.

Hell, even week will do a lot, you can start importing energy from areas that have currently better renewables conditions over night, even preemptively for a period of bad weather

I don't understand. Why is a duration of months preferable? What is the benefit above storing energy beyond say peak-to-peak? I suppose you can flatten out seasonal variation, but that's not nearly as big of a problem.

> 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.

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%.

they do say

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

> 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.

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/

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.

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

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

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

Probably extremely poorly, as that's basically pumped hydro on _tiny_ scale. The amount of mass/water that fits into storage lakes is insane

The article does address that.

...and even dangling heavy objects in the air and dropping them. (The creativity devoted to LDES is impressive.) But geologic constraints, economic viability, efficiency, and scalability have hindered the commercialization of these strategies.

The article mentions > 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: 70 meters

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.

The turbines would have to spin at very high speeds at those sizes to be efficient.

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

Sure, some people have proposed that, but if you calculate how much has to be lifted to get 20 MW stored (or so), it gets pretty ridiculous pretty quickly. Like "Lift the largest aircraft carrier 20 meters" silly. You have some pretty severe size/mass issues.

It makes more sense to use water + a dam, but then again, we like to use water for things besides energy storage, and we're talking about a _lot_ of water.

This gas bag is effectively the same as water+dam, except the pressure is from the tanks and the compressor creates it, vs pumping uphill to create pressure.

It could be made much less vulnerable by dividing the gas storage balloon structures into a set of multiple smaller structures, ideally with some further internal partitioning so a single punctured surface does not release all the gas in that structure. Everything else is as 'hard' or 'soft' as any other piece of industrial plant, and can be hardened further by putting it inside a reinforced building or set of buildings, internal redundancy etc.

No reason this couldn't be put underground, except cost.

Customers will evaluate the risks. Thermal power plants are an easy target too, and oil and gas pipelines. And the oil tankers, according to the news of the last weeks. By the way, nobody cares about oil spills anymore. I guess all those ships were sailing empty /s

https://energydome.com/co2-battery/ states 75% efficient.

After the five years of planning approvals and grid connection approvals, of course.