There's probably a much greater amount of energy lost from conversion to liquid form and stored and converted back into usable electricity from steam generators. I believe the article mentions it but it likely has better long term storage than batteries as well. The equipment required for the 'air' battery would have a longer lifespan and be cheaper to repair then a massive battery bank. On top of that batteries aren't exactly the most 'green' thing to produce, so from a carbon footprint perspective, I imagine the air battery is much more efficient.
Compressed air storage seems like a really appealing method, especially considering the low carbon footprint and massively longer lifetime than lithium batteries. This post covers it quite well https://solar.lowtechmagazine.com/2018/05/ditch-the-batterie... , I’d be really keen to see if compressed air can also be successful for independent households looking to go off grid or reduce dependence on the grid.
It has its own issues, not the least of which is safety. There is lots of energy in compressed air, that's the point. I would look heavily into the risks of structural fatigue. A lithium ion battery might catch fire, but an "air battery" can go boom.
Isn’t this the issue with any large battery? Water in large volumes can cause a lot of damage too. I suspect it’s hard to find a large battery that isn’t scary when mishandled.
TBF I'm pretty comfortable with a proper steel tank.
But, nowadays I'd be afraid to use any of the fiber wrapped ones. I remember in the middle of the 2000s when a lot of new companies jumped into the Fiber-wrapped tank market... and shortly thereafter there were a notable number of recalls in/around the bonding between the fiber and metal layers of the tanks.
And, mind you, this was all in the paintball industry, which was a field where many did not have an understanding of the dangers of a piece of fiberglass with 800-5000PSI pushing it somewhere.
Happened more than once:
phone rings
Boss working at field nearby: "Hey, someone might be coming across the street to try to fill a tank that we refused to fill because it was (damaged/out of hydro)"
Me: "Yeah, I turned them away 5 minutes ago."
Customer walks in
Customer: "Hey the field said they were out of air but otherwise they would fill this."
Joules are joules. A "grid scale" compressed air tank going pop is going to do a lot more damage in the immediate vicinity but won't do anything 50mi away. You can't say the same thing about a dam burst.
Just because it's dangerous in a way you're not used to doesn't mean it's more dangerous.
When talking about battery failure how quickly the energy is released is important.
>A "grid scale" compressed air tank going pop is going to do a lot more damage in the immediate vicinity but won't do anything 50mi away. You can't say the same thing about a dam burst.
If your comparing it to an entire dam, then your looking at underground storage of compressed gas in caverns. For that I agree both are dangerous in different ways.
But the context I was talking about was compressed air tanks which are more comparable to chemical batteries and gravity storage. Catastrophic failure of compressed air tanks is generally going to be more destructive than many other similar alternatives.
>Just because it's dangerous in a way you're not used to doesn't mean it's more dangerous.
A large lithium battery is much less likely to level several buildings than an air tank storing a similar amount of energy. I'm not saying that the dangers of compressed air can't be engineered around, but by almost any reasonable, objective metric you could come up with, compressed air is more dangerous.
Given that anything that contains energy can go boom, I think of all of them this one doesn't sound too bad. Probably local casualties but no risk of cancer for the next century, or ground pollution for the next decades.
Literally anything you store energy in is going to have the same safety issue. You can muck around with space efficiency and peak wattage but at the end of the day you've got the same amount of joules that want out and if they get out in an uncontrolled manner it will be bad.
While it is appealing compared to many alternatives and is more portable for smaller settings, when used on an industrial scale like this giant battery, I wonder how it compares in overall utility to gravity batteries [0].
The nice thing about gravity batteries is that they can form a closed loop with water supply, too, pumping reclaimed water back up into reservoirs when there's excess power. I'd expect compressed air to have much higher energy density, but it would be interesting to see if anyone has the numbers.
In my country, there are economic challenges: water isn't available everywhere, diverting water is not cheap, and it messes with water sharing agreements, which are a political issue in themselves.
Rocks and hills are equally geographically limited.
Cranes would work, but I think you’re ignoring the massive difference in mass between what the biggest cranes in the world can lift and even the smallest reservoir.
Still pretty small compared to pumped storage - they give a value of 20 megawatt-hours, the Cruachan pumped storage scheme (which isn't particularly large) stores 7.1 gigawatt hours:
Those methods are actually quite similar, they're all ultimately related (limited by) tensile strength of materials. So costs and specific energy densities (per construction material unit) are similar. An important figure is cost/tensile strenght I guess.
(Compressed air: limited by container tensile strength; gravity batteries: limited by strength of cables)
I suspect even the constants involved are the same (given the materials are almost uniformly under nominal load), although I don't have time to investigate right now (a good curiosity research topic!).
Indeed! In this case it's the integrity and friction of the soil (of the hill) that's keeping the potential energy contained, and this hill soil is "free".
I mistakenly interpreted the headline as a battery with some kind of liquid electrolyte and outside air as a reactant. Kind of like a https://en.wikipedia.org/wiki/Zinc%E2%80%93air_battery . But nope, it's just the liquefaction of air, no chemical reactions involved.
Yep. A lot of people call pumped storage "water batteries" or the like[0]. It baffles me as well, but now that language is evolving to redefine a battery as pretty much anything that generates electrical power than can be recharged with electrical power, I guess that's the world we're walking into and I should get used to that.
Have you seen where "battery" comes from? Electrical batteries are called that since they were made of sets of electrical cells working together, analogously to a battery of artillery.
Yes I'm aware of that - good point. I could have included that in my post above to highlight that this word itself has gone through plenty of language change already, from meaning "a number of pieces of artillery used together" to "electrochemical energy storage" to "energy storage." While it keeps most of those original definitions as well - including "to strike" etc. The only definition I don't think has really survived to the current day that I see when looking at its etymology is "metal articles wrought by hammering." Wonderful word.
Likewise, I was expecting some kind of redox flow battery. Compressed air is heinously inefficient due to thermal losses (and pumping losses to a lesser extent) but I guess if the energy is literally free (eg. solar or wind overproduction) then that matters less than the cost per kWh stored.
>The new liquid air battery, being developed by Highview Power, is due to be operational in 2022 and will be able to power up to 200,000 homes for five hours, and store power for many weeks.
Is it just they're expecting many leaks in the system? I don't see why they couldn't just store things for years basically.
Liquid air is cryogenic - they'll have to either bleed off or spend energy to keep it cooled. The "many weeks" measurements is probably some measurement of bleed off rate assuming no top offs (but I'm just guessing - the company website https://www.highviewpower.com/technology/ doesn't seem to call it out clearly).
If the tanks are strong enough, is cooling required? My understanding is that you'd only need to cool the liquid if the structure holding it wasn't sufficiently strong enough to handle the pressures.
Approximating air as nitrogen... nitrogen cannot exist as liquid phase at room temperature - it can exist as a supercritical fluid though at 5MPa (so 50 atm). At that point it has a density of roughly 56 kg/m^3. At ~1 atm, nitrogen becomes liquid at -194C and has a density of roughly 800 kg/m^3. So your mass density of the system is like 14 times better with liquid nitrogen, and the pressure loading requirements are stupidly lower.
Making the tanks strong enough to handle the pressure if the liquid turns to gas is very expensive. It is much cheaper to make a tank that just holds a liquid.
It's not cost effective to store for a very long time. If you stored for a year, and the tanks last 30 years, you only get 30 tanks worth of electricity for the price of the tank. If you store for a few hours, you get 30*365 tanks worth of electricity for the price of the tank, but you need to factor in the cost of the compressor and generator. Presumably there's some balance when you're getting best value out of the compressor and generator, but don't need an excessive number of tanks.
Wondered what they were doing with the thermal energy from the process. The manufacturer has a video here that helps explain the technology a little bit: https://www.youtube.com/watch?v=kDvlh_aG7iA
That's not increasing the efficiency of the storage, though. It's just using otherwise wasted heat from a different process (which could probably be otherwise used for cogeneration or something).
In hot countries it might be efficient if the chilled exhaust is used for air conditioning or something, I guess.
The "air" gets stored in liquid form... but what I don't understand is what parts of the air? The gasses in air mix as gasses, no so much when liquid. Will the tanks include a layer of liquid oxygen? What prevents those layers vaporize selectively as the tank temperature is raised again? That would seem very dangerous. Or am I misreading this and they are only liquefying nitrogen and aren't playing around with liquid O2?
I am guessing they pump the liquid air and then “boil” it, so there is no risk of selective vapourisation as they are not boiling the bulk liquid within the tank.
Dry ice is actually a precious commodity among algae growers - another alternative energy source - algae diesel. Or any frozen food dealers - and sometimes they run into shortages: https://www.marken.com/alerts/dry-ice-shortage/
Not just alge but ag in general. CO2 makes plants grow fast, farmers would buy it for greenhouses if it was produced on a large scale, although finding a way to stop it going back into the atmosphere would be better.
They aren't going to be handling large enough volumes of air to make this worthwhile. Co2 is such a small part of air that direct air capture of it requires massive fan farms.
Why wouldn't they stay mixed as a liquid? They're highly miscible, if you leave liquid N2 out it can actually enrich with oxygen with time as oxygen dissolves into it. You need to distill them to separate oxygen and nitrogen cryogenically. That happens in the boiling off part, but as another commenter mentioned you could pump out what you want to boil to avoid boiling the bulk liquid and causing the remaining liquid to be enriched in oxygen.
It doesn't sound like they are doing much separation though maybe they should for a secondary income stream. I wonder how the scale of this compares to traditional cryogenic ASUs.
“IMechE says this process is only 25% efficient but it is massively improved by co-siting the cryo-generator next to an industrial plant or power station producing low-grade heat.“
“More energy is saved by taking the waste cool air when the air has finished chilling, and passing it through three tanks containing gravel“ as a thermal store.
“their kits could be up to 70% efficient, and IMechE agrees this figure is realistic.”
Plus ublock origin says it blocked 30% of requests. I'm all up for paying for good journalism but part of me wonders their paid customers aren't getting a great experience either.
The technology sounds fantastic. The synergy with heat power plants is particularly cool (heh). The same goes for desalination: waste heat can be reduced by recycling heat between the processes, increasing the overall efficiency of the system.
Now for the rant: reputable news organizations need to stop enabling "creates x jobs" propaganda through repetition. It doesn't create 200 jobs, it briefly employs 200 to build the thing. Maybe 5-10 full-time jobs will be "created" to maintain a giant mechanical battery. This lie is particularly popular around pipeline projects. "You don't think we should spend billions of dollars on this pipeline? Do you want tens of thousands of imaginary people to lose their imaginary jobs?"
I wonder in an era where clean energy costs fall more than 10x whether it is possible to channel surplus energy into desalination and pumping water into deserts near the coasts. Like a slow geo engineering project. Combined with future developments in vertical farming, it may make sustainable cities possible in places like Middle east, parts of South Asia and Africa
I recall reading about a proposed solution to global warming that included digging a channel from the Atlantic into the Sahara. Big sections are below sea level. So we'd create a new ocean/sea effectively, cool the local climate, and significantly reduce hurricanes on the East coat of America.
The Amazon rainforest relies on annual global sandstorms transporting nutrient-rich (phosphorus) sand from the Sahara to South America. If you flood significant parts of this desert, you'll disrupt this process.
I think the "creates 200 jobs" usage is completely fair here. The thing is due to be operational in 2022, so that's two years of work for 200 people, and the ongoing operation jobs will be "a few dozen", not 5-10. The article makes all this clear.
More broadly, infrastructure jobs are still jobs, even if they only last a few years instead of indefinitely. The average tenure of a software engineer at a big tech company is less than that; is it fair to say they don't have jobs? It's not like we're ever going to run out of projects to improve the world, so these 200 workers will hopefully finish this job and move onto the next "job-creating project".
==The average tenure of a software engineer at a big tech company is less than that; is it fair to say they don't have jobs?==
I don’t follow, after a software engineer leaves the big tech firm, the job still exists. They hire someone else to do it. In this instance the job doesn’t exist after 2 years. It’s also probably not 2 full years for those jobs as they are typically brought in with teams to perform their function (dig, foundation, build, framing, electrical/water/gas, finishing) then move on.
Hiring a software engineer as a full-time employee for a temporary software project, then firing them, is a poor use of company resources.
If you are talking about a contract software engineer, then you are correct that the worker rolls off. We typically don't see those considered "full-time jobs created" because they have a well-defined term and are never employees of the company.
At first, I thought this was interesting. And then I read the part about the battery only lasting for a few weeks, before it must be recharged. This sounds terribly inefficient.
I recall reading about a spring type of battery made of diamond nano fibers a few weeks ago. They were saying this was even more efficient than lithium ions, since it was a physical process of releasing its energy, instead of a chemical process. It behaves like a child’s wind up toy, but at the molecular level.
Would it be better instead to have a physical battery, instead of a chemical battery?
Perhaps something like a big wind up spring can be built. Then it can hold its charge indefinitely. And you stack thousands of these together, and they can just sit there for a long time, until they are needed.
Or even that idea to use large cement blocks stacked into skyscrapers. Each block holds potential energy, and when released, it can glide down a magnetic track and generate electrical energy. This is also a concept of a physical battery.
Even a hydroelectric dam is physical energy. You’re moving the water uphill.
> will use spare green energy to compress air into a liquid and store it.
Is that really right? It's not just green energy sources that benefit from energy-storage. Fossil-fuel plants and nuclear plants prefer to run at a constant output, but demand varies depending on the time of day.
This seems like useless pedantry on the word "green", no? The electric field is not coloured, you can't really attribute grid power to a specific source sensibly.
Coal is almost entirely gone from the UK. Nuclear does indeed prefer to run at constant output, but almost all the remaining fossil generation in the UK is CCGT which can ramp up and down fairly quickly.
Cool. Technology like liquid air, compressed air, electrolysed hydrogen etc. has a very different use case to lithium ion batteries.
Batteries are good for short cycle times, if you need to balance your grid and even to some extent if you need to correct for diurnal patterns, you want batteries. The high capital cost is compensated for by the high round-trip efficiency.
For seasonal storage or even inter-year storage, batteries do not work. You spend a fortune on them and then cycle the system once a year or less.
The advantage of these other systems is you can decouple three elements:
The conversion in
The storage
The conversion out
and match the capacity of each to what you need. For long term storage of hydrogen for instance, you want relatively small electrolysers with fast response times so that you can use excess electricity during sunny windy periods, a massive geological storage that can hold a year+ of production, and modestly sized fuel cells to turn it back into electricity in the winter (in Europe anyway) with good heat recovery.
In the case of this technology, you can again size the charging, discharging, and storage separately. The scaling for tanks is much cheaper than batteries.
Flow batteries use a similar idea by separating out the charging/discharging membrane and the electrolyte tanks but I don't think anyone has gotten satisfactory performance from them yet.
You can't build a lithium ion battery where you specify the storage capacity separately from the charge and discharge rates with anything like that kind of freedom. You can adjust the battery chemistry of course but nothing like the same.
Pumped hydro using existing dams is brilliant and should be maximally exploited but we already have dams on all the really good sites. We can improve by adding the pump-up stage to many of them but there is simply no scope for massive expansion in total reservoir / energy storage capacity.
The question is, would it be possible to use large scale liquid air storage to speed up removing CO2 from atmosphere?
I have no idea if removing CO2 is easier in liquid form but if it is feasible then ff we already had huge infrastructure to store energy that requires pumping astronomical amounts of air back and forth, it might make sense make sense to add a bit to it to remove CO2 while in liquid form.
Hmm. This actually has legs - CO2 can't be present in liquid air, because it freezes at only about -80 rather than the -200ish for air. So at some point CO2 "snow" will collect in the system. Unfortunately it's ~0.04% of the air, so this will take a long time to collect much. But if it's removed anyway, sure. Then you have to work out where to put it.
The energy required to liquefy air is probably too large. Say we have 400pm CO2 in air - that's ~630mg of CO2 per kilogram of air.
Given that the specific heat of air sits at around 1kJ/kg[0], you'd have to spend over 125kJ of heat energy to get just one gram of CO2 - that's 35Wh.
If you used wind power(14g CO2/kWh) and a heat pump with a coefficient of performance of 1 (not sure how possible at these gradients) you'd "emit" 0.5g of CO2 in the process.
Well, you missed the fact that the plan is already to liquefy the air. So the air will already be in liquid form.
Also I don't think they are going to cool it but rather compress it. Cooling would require constant expenditure of energy to keep it cool whereas you can compress it and leave it in the vessel at room temperature. It takes 33 atmospheres to liquefy nitrogen and 50 for oxygen.
The power cycle used here is quite an interesting one.
The heat from the compression cycle and cold from the expansion cycle are stored separately and re-used which substantially increases storage efficiency.
Waste heat from co-located industrial plants is used to further boost expansion performance. A lot of "low grade" industrial heat is available but when you're re-heating from cryogenic temperatures, 100 C is actually high grade heat.
I suspect that the time over which it's efficient to store is limited by losses from the temperature stores.
That's not "greenwashing" because it's obvious. Thermal input in industrial processes is essentially all fossil fuel, high temperature input is 100% fossil fuel. To the extent that we need these processes, we may as well get as much bang for our CO2e buck as we can. Even if and when these processes can be driven using hydrogen combustion or other heat sources, there will still be low grade waste heat to use.
It's greenwashing because it's not obvious, and the wording is deliberately deceptive. An accurate description would give readers the relevant facts, not assume they can figure out the hidden catch.
I was looking into this briefly when I was investigating molten salt batteries. Can anyone who has expertise in this field tell me a bit about why molten salt batteries aren't more common? From what I can tell, the materials used are more renewable than Lithium Ion batteries, and with comparable (potentially higher) density. I can see why molten salt isn't as common in the more portable form factor, but it seems like it would be a great fit for large energy reservoir/grid type applications.
Stationary batteries in general aren't common. We don't have enough transient power generation for them to be very lucrative. (What, is very obviously going to change in the near future.)
Added to that, for molten salt batteries, there are old designs with bad cost and density properties and new ones with dangerous materials and patent minefields. I don't think anybody was ever able to sell a Na-S design without being destroyed in some court.
100 comments
[ 3.3 ms ] story [ 121 ms ] threadIt really depends on what you perceive to be efficiency.
TBF I'm pretty comfortable with a proper steel tank.
But, nowadays I'd be afraid to use any of the fiber wrapped ones. I remember in the middle of the 2000s when a lot of new companies jumped into the Fiber-wrapped tank market... and shortly thereafter there were a notable number of recalls in/around the bonding between the fiber and metal layers of the tanks.
And, mind you, this was all in the paintball industry, which was a field where many did not have an understanding of the dangers of a piece of fiberglass with 800-5000PSI pushing it somewhere.
Happened more than once:
phone rings
Boss working at field nearby: "Hey, someone might be coming across the street to try to fill a tank that we refused to fill because it was (damaged/out of hydro)"
Me: "Yeah, I turned them away 5 minutes ago."
Customer walks in
Customer: "Hey the field said they were out of air but otherwise they would fill this."
Just because it's dangerous in a way you're not used to doesn't mean it's more dangerous.
When talking about battery failure how quickly the energy is released is important.
>A "grid scale" compressed air tank going pop is going to do a lot more damage in the immediate vicinity but won't do anything 50mi away. You can't say the same thing about a dam burst.
If your comparing it to an entire dam, then your looking at underground storage of compressed gas in caverns. For that I agree both are dangerous in different ways.
But the context I was talking about was compressed air tanks which are more comparable to chemical batteries and gravity storage. Catastrophic failure of compressed air tanks is generally going to be more destructive than many other similar alternatives.
>Just because it's dangerous in a way you're not used to doesn't mean it's more dangerous.
A large lithium battery is much less likely to level several buildings than an air tank storing a similar amount of energy. I'm not saying that the dangers of compressed air can't be engineered around, but by almost any reasonable, objective metric you could come up with, compressed air is more dangerous.
The nice thing about gravity batteries is that they can form a closed loop with water supply, too, pumping reclaimed water back up into reservoirs when there's excess power. I'd expect compressed air to have much higher energy density, but it would be interesting to see if anyone has the numbers.
[0] https://en.wikipedia.org/wiki/Gravity_battery
Cranes would work, but I think you’re ignoring the massive difference in mass between what the biggest cranes in the world can lift and even the smallest reservoir.
https://qz.com/1355672/stacking-concrete-blocks-is-a-surpris...
I believe there's a beta test facility under construction now.
https://en.wikipedia.org/wiki/Cruachan_Power_Station
(Compressed air: limited by container tensile strength; gravity batteries: limited by strength of cables)
I suspect even the constants involved are the same (given the materials are almost uniformly under nominal load), although I don't have time to investigate right now (a good curiosity research topic!).
https://en.wikipedia.org/wiki/Energy_return_on_investment#ES...
according to the wiki, pumped hydroelectric storage has a ratio of 704 where as compressed air energy storage has a ratio of 792.
[0] https://www.hydropower.org/sites/default/files/publications-...
Is it just they're expecting many leaks in the system? I don't see why they couldn't just store things for years basically.
In hot countries it might be efficient if the chilled exhaust is used for air conditioning or something, I guess.
I am guessing they pump the liquid air and then “boil” it, so there is no risk of selective vapourisation as they are not boiling the bulk liquid within the tank.
https://newatlas.com/energy-vault-concrete-tower-battery/571...
(It stores energy by stacking rocks.)
https://www.bbc.com/news/science-environment-19785689
“IMechE says this process is only 25% efficient but it is massively improved by co-siting the cryo-generator next to an industrial plant or power station producing low-grade heat.“
“More energy is saved by taking the waste cool air when the air has finished chilling, and passing it through three tanks containing gravel“ as a thermal store.
“their kits could be up to 70% efficient, and IMechE agrees this figure is realistic.”
With adblocker: https://imgur.com/a/fWuoJEi
Without adblocker: https://imgur.com/a/cvmu3dm
Plus ublock origin says it blocked 30% of requests. I'm all up for paying for good journalism but part of me wonders their paid customers aren't getting a great experience either.
Help me understand the thermodynamics, are they storing the heat too?
Now for the rant: reputable news organizations need to stop enabling "creates x jobs" propaganda through repetition. It doesn't create 200 jobs, it briefly employs 200 to build the thing. Maybe 5-10 full-time jobs will be "created" to maintain a giant mechanical battery. This lie is particularly popular around pipeline projects. "You don't think we should spend billions of dollars on this pipeline? Do you want tens of thousands of imaginary people to lose their imaginary jobs?"
End rant.
A source: https://www.nasa.gov/content/goddard/nasa-satellite-reveals-...
More broadly, infrastructure jobs are still jobs, even if they only last a few years instead of indefinitely. The average tenure of a software engineer at a big tech company is less than that; is it fair to say they don't have jobs? It's not like we're ever going to run out of projects to improve the world, so these 200 workers will hopefully finish this job and move onto the next "job-creating project".
I don’t follow, after a software engineer leaves the big tech firm, the job still exists. They hire someone else to do it. In this instance the job doesn’t exist after 2 years. It’s also probably not 2 full years for those jobs as they are typically brought in with teams to perform their function (dig, foundation, build, framing, electrical/water/gas, finishing) then move on.
If you are talking about a contract software engineer, then you are correct that the worker rolls off. We typically don't see those considered "full-time jobs created" because they have a well-defined term and are never employees of the company.
I recall reading about a spring type of battery made of diamond nano fibers a few weeks ago. They were saying this was even more efficient than lithium ions, since it was a physical process of releasing its energy, instead of a chemical process. It behaves like a child’s wind up toy, but at the molecular level.
Would it be better instead to have a physical battery, instead of a chemical battery?
Perhaps something like a big wind up spring can be built. Then it can hold its charge indefinitely. And you stack thousands of these together, and they can just sit there for a long time, until they are needed.
Or even that idea to use large cement blocks stacked into skyscrapers. Each block holds potential energy, and when released, it can glide down a magnetic track and generate electrical energy. This is also a concept of a physical battery.
Even a hydroelectric dam is physical energy. You’re moving the water uphill.
Is that really right? It's not just green energy sources that benefit from energy-storage. Fossil-fuel plants and nuclear plants prefer to run at a constant output, but demand varies depending on the time of day.
See the 'Duck curve' https://en.wikipedia.org/wiki/Duck_curve
Coal is almost entirely gone from the UK. Nuclear does indeed prefer to run at constant output, but almost all the remaining fossil generation in the UK is CCGT which can ramp up and down fairly quickly.
Batteries are good for short cycle times, if you need to balance your grid and even to some extent if you need to correct for diurnal patterns, you want batteries. The high capital cost is compensated for by the high round-trip efficiency.
For seasonal storage or even inter-year storage, batteries do not work. You spend a fortune on them and then cycle the system once a year or less.
The advantage of these other systems is you can decouple three elements:
The conversion in
The storage
The conversion out
and match the capacity of each to what you need. For long term storage of hydrogen for instance, you want relatively small electrolysers with fast response times so that you can use excess electricity during sunny windy periods, a massive geological storage that can hold a year+ of production, and modestly sized fuel cells to turn it back into electricity in the winter (in Europe anyway) with good heat recovery.
In the case of this technology, you can again size the charging, discharging, and storage separately. The scaling for tanks is much cheaper than batteries.
Flow batteries use a similar idea by separating out the charging/discharging membrane and the electrolyte tanks but I don't think anyone has gotten satisfactory performance from them yet.
You can't build a lithium ion battery where you specify the storage capacity separately from the charge and discharge rates with anything like that kind of freedom. You can adjust the battery chemistry of course but nothing like the same.
Phase locking human activity, including economic to the energy cycle would obviate the need for many technical solutions. We should just hibernate.
I have no idea if removing CO2 is easier in liquid form but if it is feasible then ff we already had huge infrastructure to store energy that requires pumping astronomical amounts of air back and forth, it might make sense make sense to add a bit to it to remove CO2 while in liquid form.
Given that the specific heat of air sits at around 1kJ/kg[0], you'd have to spend over 125kJ of heat energy to get just one gram of CO2 - that's 35Wh.
If you used wind power(14g CO2/kWh) and a heat pump with a coefficient of performance of 1 (not sure how possible at these gradients) you'd "emit" 0.5g of CO2 in the process.
[0] https://www.ohio.edu/mechanical/thermo/property_tables/air/a...
Also I don't think they are going to cool it but rather compress it. Cooling would require constant expenditure of energy to keep it cool whereas you can compress it and leave it in the vessel at room temperature. It takes 33 atmospheres to liquefy nitrogen and 50 for oxygen.
The heat from the compression cycle and cold from the expansion cycle are stored separately and re-used which substantially increases storage efficiency.
Waste heat from co-located industrial plants is used to further boost expansion performance. A lot of "low grade" industrial heat is available but when you're re-heating from cryogenic temperatures, 100 C is actually high grade heat.
I suspect that the time over which it's efficient to store is limited by losses from the temperature stores.
Let's not greenwash this. The "waste heat" is fossil fueled.
The heat is essentially "free" which makes the molten salt heat retention properties perfect for storing energy overnight.
Added to that, for molten salt batteries, there are old designs with bad cost and density properties and new ones with dangerous materials and patent minefields. I don't think anybody was ever able to sell a Na-S design without being destroyed in some court.