We don't need another few-hours storage technology. Batteries are going to clobber that. What we need is a storage technology with a duration of months. That would be truly complementary to these short term storage technologies.
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.
No mention of round-trip efficiencies, and claims are that it's 30% cheaper than Li-Ion. Which might give it an advantage for a while, but as Li-Ion has become 80% cheaper in the last decade that's not something which will necessarily continue.
Great if it can continue to be cheaper, of course. Fingers crossed that they can make it work at scale.
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.
Grid scale LFP with once daily cycling lasts 30 years before the cells are degraded enough to think about recycling.
And those are very low maintenance over that time.
You're probably mostly going to swap voltage regulators and their fans, perhaps bypass the occasional bad cell by turning the current to zero, unscrewing the links from the adjacent cells to the bad cell, and screwing in a fresh link with the connect length to bridge across.
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.
That is shockingly good. EIA reports existing grid scale battery round trip is like 82% which do not have moving parts.
...in 2019, the U.S. utility-scale battery fleet operated with an average monthly round-trip efficiency of 82%, and pumped-storage facilities operated with an average monthly round-trip efficiency of 79%....
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.
2021 total world energy production of approximately 172 PWh would require 27.5 billion metric tons of lithium metal at typical 0.16g/Wh of a modern LFP cell; meanwhile, we have approximately 230 billion metric tons of lithium for taking (e.g. as part of desalination plants producing many other elements at the same time from the pre-consecrated brine) from the oceans.
Note that we require only a fraction of a year's worth of energy to be stored, I think less than 5% if we accept energy intensive industry in high latitude to take winter breaks, or even more with further tactics like higher overproduction or larger interconnected grid areas.
And that's all without even the sodium batteries that do seem to be viable already.
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
I see this as complementary to other energy storage systems, including sodium ion batteries; each will have its own strengths and weaknesses. I expect energy storage density cost will be the critical parameter here, as this looks best suited to do diurnal storage for solar power systems near out-of-town predictable power consumers like data centers.
Maintenance of the system is my biggest question. Lot of mechanical complexity with ensuring your gas containment, compressors, turbines, etc are all up to spec. This also seems like a system where you want to install the biggest capacity containment you can afford at the onset.
All of that vs lithium/sodium where you can incrementally install batteries and let it operate without much concern. Maybe some heaters if they are installed in especially cold climates.
In fact, the limiting element for Li chemistries is generally the Nickel. Pretty much everything else that goes into these chemistries is highly available. Even something like Cobalt which is touted as unavailable is only that way because the industrial uses of cobalt is basically only li batteries. It's mined by hand not because that's the best way to get it, but because that's the cheapest way to get the small amount that's needed for batteries.
Sodium iron phosphate batteries, if Li prices don't continue to fall, will be some of the cheapest batteries out there. If they can be made solid state then you are looking at batteries that will dominate things like grid and home power storage.
> Even something like Cobalt which is touted as unavailable is only that way because the industrial uses of cobalt is basically only li batteries.
AFAIR Cobalt is also kinda toxic which is a concern.
But as far as that and
> In fact, the limiting element for Li chemistries is generally the Nickel
Isn't that part of why LiFePO was supposed to take off tho? Sure the energy density is a bit lower but theoretically they are cheaper to produce per kWh and don't have any of the toxicity/rarity issues of other lithium designs...
AFAIK, the brine pits are pretty economical, they just require ocean access.
What I'm somewhat surprised about is that we've not seen synergies with desalination and ocean mineral extraction. IDK why the brine from a desalination plant isn't seen as a prime first step in extraction lithium, magnesium, and other precious minerals from ocean water.
As I understand it (which is far from perfectly) it's still not using ocean water, because you can get so much higher lithium concentration in water from other sources. But it's a more environmentally friendly, and they argue cheaper, way to extract the lithium from water than just using the traditional giant evaporation pools.
Do you know how much magnesium you find with silicon and iron as olivine?
It's just the silicon that we haven't yet tamed for large scale mechanical usage that makes them uneconomical to electrolyze.
likely a matter of location. desal tends to be on the coast and near cities which tends to be pretty valuable land, making giant evaporation ponds a tough sell.
You don't use ponds, you run the desalination to as strong as practical and follow up with either electrolysis or distillation of the brine.
But once summer electricity becomes cheap enough due to solar production increasing to handle winter heating loads with the (worse) winter sun, we can afford a lot of electrowinning of "ore" which can be pretty much sea salt or generic rock at that point.
Form Energy is working on grid scale iron air batteries which use the same chemistry as would be used for (excess/spare) solar powered iron ore to iron metal refining.
AFAIK the coal powered traditional iron refining ovens are the largest individual machines humanity operates. (Because if you try to compare to large (ore/oil) ships, it's not very fair to count their passive cargo volume; and if comparing to offshore oil rigs, and including their ancillary appliances and crew berthing, you'd have to include a lot of surrounding infrastructure to the blast furnace itself.)
It will take coal becoming expensive for it's CO2 before we really stop coal fired iron blast furnaces. And before then it's hard to compete even at zero cost electricity when accounting for the duty cycle limitations of only taking curtailed summer peaks.
This seems almost too good to be true, and the equipment is so simple that it would seem that this is a panacea. Where are the gotchas with this technology?
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; are there any numbers publicly available for either?
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...
[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.
So… it’s a compressed air battery but with a better working fluid than air.
I remember wondering about using natural gas or propane for this a long time ago. Not burning the gas but using it as a compressed gas battery. It liquifies easier than air, etc., but would be a big fire risk if there were leaks while this is not.
> Not burning the gas but using it as a compressed gas battery. It liquifies easier than air, etc., but would be a big fire risk if there were leaks while this is not.
FWIW Back in the day, Ammonia was used for refrigeration because it had the right properties for that process; I mention that one because while it's not a fire risk it's definitely a health risk, also it's a bit more reactive (i.e. leaks are more likely to happen)
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.
I understand this, but it coincidentally uses CO2 and it's hard for me to understand why the technology would sound "too good to be true" without imagining such a purpose.
what happens if that large enclosure fails and the CO2 freely flows outside?
That enclosure has a huge volume - area the size of several football fields, and at least 15 stories high. The article says it holds 2k tons of co2, which is ~1,000,000 cubic meters in volume.
CO2 is denser than air will pool closer to the ground, and will suffocate anyone in the area.
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.
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.
Comparing it to X flights maybe correct from a greenhouse emissions standpoint, but extremely misleading from a safety perspective. A jet emits that co2 spread over tens of thousands of miles. The problem here is it all pooled in one location.
Also that statement of 70 meters seem very off, looking at the size of the building. What leads to suffocation is the inability to remove co2 from your body rather than lack of oxygen, and thus can be life threatening even at 4% concentration. It should impact a much much larger area.
Yep. When I had to fill CO2 tanks at a paintball shop yes there were times that I had to open a door (I mean we were talking a lot of fills in short time, btw fills had to start with draining the tank's existing volume so I could zero out the scale) but even indoors a door+fan was enough to keep even the nastiest of sale days OSHA compliant.
Also a 'puncture' is very different from the gasbag mysteriously vanishing from existence; My only other thought is that in cold regions (I saw wisconsin mentioned in the article) CO2 does not diffuse quite as fast and sometimes visibly so...
How did they calculate that evacuation distance? CO2 is heavy. That little house about 15m from the bubble needs to be acquired.
The topography matters. If the installation is in a valley, a dome rip could make air unbreathable, because the CO2 will settle at the bottom. People have been killed by CO2 fire extinguishing systems. It takes a reasonably high concentration, a few percent, but that can happen. They need alarms and handy oxygen masks.
Installations like this probably will be in valleys, because they will be attached to wind farms. The wind turbines go in the high spots and the energy storage goes in the low spots.
Good luck running 70m in a CO2 dense atmosphere. And CO2 hugs the ground it does not float away. It will persist in low areas for quite a while.
Anyone in the local vicinity would need to carry emergency oxygen at all times to be able to get to a safe distance in case of rupture. Otherwise it's a death sentence, and not a particularly pleasant one as CO2 is the signal that triggers the feeling of suffocation.
It's unlikely that the thing will burst and disperse all CO2 immediately. It's just slightly higher pressure than the outside (that's the whole principle). So you have a slow leak of CO2 to the outside. You don't have to run that fast (or run at all).
The way I understood the quote, the safety distance is when they have to do an emergency deflate (e.g. due to wind). The way they calculate the 70 m is probably based on the volume and how large of a area you cover until the height is low enough that you can still breath.
Generally, because it's leaking to the outside, where there is going to be wind it will not stick around for long time I suspect.
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.
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.
Yeah. Maybe this tech will have a place for week-long storage and be a good buffer for wind power but I hard to see the economics working for daily cycling.
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.
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 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?
"First, a compressor pressurizes the gas from 1 bar (100,000 pascals) to about 55 bar (5,500,000 pa). Next, a thermal-energy-storage system cools the CO2 to an ambient temperature. Then a condenser reduces it into a liquid that is stored in a few dozen pressure vessels, each about the size of a school bus. The whole process takes about 10 hours, and at the end of it, the battery is considered charged.
To discharge the battery, the process reverses. The liquid CO2 is evaporated and heated. It then enters a gas-expander turbine, which is like a medium-pressure steam turbine. This drives a synchronous generator, which converts mechanical energy into electrical energy for the grid. After that, the gas is exhausted at ambient pressure back into the dome, filling it up to await the next charging phase."
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 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]
> CCS could have a critical but limited role in reducing greenhouse gas emissions.[6] However, other emission-reduction options such as solar and wind energy, electrification, and public transit are less expensive than CCS and are much more effective at reducing air pollution. Given its cost and limitations, CCS is envisioned to be most useful in specific niches. These niches include heavy industry and plant retrofits.[8]: 21–24
> The cost of CCS varies greatly by CO2 source. If the facility produces a gas mixture with a high concentration of CO2, as is the case for natural gas processing, it can be captured and compressed for USD 15–25/tonne.[66] Power plants, cement plants, and iron and steel plants produce more dilute gas streams, for which the cost of capture and compression is USD 40–120/tonne CO2.[66]
... And then for this usage, presumably you'd have to separate the CO2 from the rest of the gas.
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.
Pumped-storage hydroelectricity - where it is feasible - is the only kind of energy storage close to "months".
This is one place where I think by 2030 a clear no of options will be established.
Great if it can continue to be cheaper, of course. Fingers crossed that they can make it work at scale.
And those are very low maintenance over that time.
You're probably mostly going to swap voltage regulators and their fans, perhaps bypass the occasional bad cell by turning the current to zero, unscrewing the links from the adjacent cells to the bad cell, and screwing in a fresh link with the connect length to bridge across.
That's not terrible.
These things would probably pair well with district heating and cooling.
A few percent here of there is not that important if the input energy is cheap enough.
That's a significant difference.
Note that we require only a fraction of a year's worth of energy to be stored, I think less than 5% if we accept energy intensive industry in high latitude to take winter breaks, or even more with further tactics like higher overproduction or larger interconnected grid areas.
And that's all without even the sodium batteries that do seem to be viable already.
"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
All of that vs lithium/sodium where you can incrementally install batteries and let it operate without much concern. Maybe some heaters if they are installed in especially cold climates.
And foreseeable future they provide such huge value for grid stability that it wouldn’t make sense economically either.
And if you want an alternative, sodium batteries are already coming online.
Sodium iron phosphate batteries, if Li prices don't continue to fall, will be some of the cheapest batteries out there. If they can be made solid state then you are looking at batteries that will dominate things like grid and home power storage.
AFAIR Cobalt is also kinda toxic which is a concern.
But as far as that and
> In fact, the limiting element for Li chemistries is generally the Nickel
Isn't that part of why LiFePO was supposed to take off tho? Sure the energy density is a bit lower but theoretically they are cheaper to produce per kWh and don't have any of the toxicity/rarity issues of other lithium designs...
It's the exact reason LFPs are taking off, especially in grid storage scenarios.
The high cycle life combined with the fact that all the materials are easy to acquire and dirt cheap.
There are plenty more, but they're explored only when there's a price hike.
What I'm somewhat surprised about is that we've not seen synergies with desalination and ocean mineral extraction. IDK why the brine from a desalination plant isn't seen as a prime first step in extraction lithium, magnesium, and other precious minerals from ocean water.
I think these guys are basically using desalination tech to make lithium extraction cheaper: https://energyx.com/lithium/#direct-lithium-extraction
As I understand it (which is far from perfectly) it's still not using ocean water, because you can get so much higher lithium concentration in water from other sources. But it's a more environmentally friendly, and they argue cheaper, way to extract the lithium from water than just using the traditional giant evaporation pools.
But once summer electricity becomes cheap enough due to solar production increasing to handle winter heating loads with the (worse) winter sun, we can afford a lot of electrowinning of "ore" which can be pretty much sea salt or generic rock at that point.
Form Energy is working on grid scale iron air batteries which use the same chemistry as would be used for (excess/spare) solar powered iron ore to iron metal refining.
AFAIK the coal powered traditional iron refining ovens are the largest individual machines humanity operates. (Because if you try to compare to large (ore/oil) ships, it's not very fair to count their passive cargo volume; and if comparing to offshore oil rigs, and including their ancillary appliances and crew berthing, you'd have to include a lot of surrounding infrastructure to the blast furnace itself.)
It will take coal becoming expensive for it's CO2 before we really stop coal fired iron blast furnaces. And before then it's hard to compete even at zero cost electricity when accounting for the duty cycle limitations of only taking curtailed summer peaks.
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; are there any numbers publicly available for either?
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.
I remember wondering about using natural gas or propane for this a long time ago. Not burning the gas but using it as a compressed gas battery. It liquifies easier than air, etc., but would be a big fire risk if there were leaks while this is not.
Seems neat.
FWIW Back in the day, Ammonia was used for refrigeration because it had the right properties for that process; I mention that one because while it's not a fire risk it's definitely a health risk, also it's a bit more reactive (i.e. leaks are more likely to happen)
> Seems neat.
Agreed!
With compressed air, you just release the air back to the atmosphere.
The 75% round-trip efficiency (for shorter time periods) quoted in other threads here is surprisingly high though.
> 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.
That enclosure has a huge volume - area the size of several football fields, and at least 15 stories high. The article says it holds 2k tons of co2, which is ~1,000,000 cubic meters in volume.
CO2 is denser than air will pool closer to the ground, and will suffocate anyone in the area.
See https://en.wikipedia.org/wiki/Lake_Nyos_disaster
Edit: It holds 2k tons, not 20K tons.
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.
It would not be good, but it wouldn't be Bhopal. And there are still plenty of factories making pesticides.
Also that statement of 70 meters seem very off, looking at the size of the building. What leads to suffocation is the inability to remove co2 from your body rather than lack of oxygen, and thus can be life threatening even at 4% concentration. It should impact a much much larger area.
Also a 'puncture' is very different from the gasbag mysteriously vanishing from existence; My only other thought is that in cold regions (I saw wisconsin mentioned in the article) CO2 does not diffuse quite as fast and sometimes visibly so...
I don't know the safety limits for this quantity, I hope the "70 meters" claim was by someone who modelled it carefully rather than a gut check.
How did they calculate that evacuation distance? CO2 is heavy. That little house about 15m from the bubble needs to be acquired.
The topography matters. If the installation is in a valley, a dome rip could make air unbreathable, because the CO2 will settle at the bottom. People have been killed by CO2 fire extinguishing systems. It takes a reasonably high concentration, a few percent, but that can happen. They need alarms and handy oxygen masks.
Installations like this probably will be in valleys, because they will be attached to wind farms. The wind turbines go in the high spots and the energy storage goes in the low spots.
Anyone in the local vicinity would need to carry emergency oxygen at all times to be able to get to a safe distance in case of rupture. Otherwise it's a death sentence, and not a particularly pleasant one as CO2 is the signal that triggers the feeling of suffocation.
The way I understood the quote, the safety distance is when they have to do an emergency deflate (e.g. due to wind). The way they calculate the 70 m is probably based on the volume and how large of a area you cover until the height is low enough that you can still breath.
Generally, because it's leaking to the outside, where there is going to be wind it will not stick around for long time I suspect.
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.
Can see how this could scale up for longer storage fairly cheaply but on current trends batteries will have caught up in cost in 2-3 years.
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.
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.
[0] https://energydome.com/co2-battery/
To discharge the battery, the process reverses. The liquid CO2 is evaporated and heated. It then enters a gas-expander turbine, which is like a medium-pressure steam turbine. This drives a synchronous generator, which converts mechanical energy into electrical energy for the grid. After that, the gas is exhausted at ambient pressure back into the dome, filling it up to await the next charging phase."
How much energy us used to purify and maintain the CO2?
[1] https://en.wikipedia.org/wiki/Carbon_capture_and_storage
> The cost of CCS varies greatly by CO2 source. If the facility produces a gas mixture with a high concentration of CO2, as is the case for natural gas processing, it can be captured and compressed for USD 15–25/tonne.[66] Power plants, cement plants, and iron and steel plants produce more dilute gas streams, for which the cost of capture and compression is USD 40–120/tonne CO2.[66]
... And then for this usage, presumably you'd have to separate the CO2 from the rest of the gas.
This sounds better in every way.