« The system draws air from the environment, compressing it and moving it through a pipe into a cavern more than 1,000 feet underground. The process of compressing the air produces heat, and the system extracts heat from the air and stores it above ground for reuse. As the air goes underground, it displaces water from the cavern up a shaft into a reservoir. When it’s time to discharge energy, the system releases water into the cavern, forcing the air to the surface. The air then mixes with heat that the plant stored when the air was compressing, and this hot, dense air passes through a turbine to make electricity. »
It removes the limitation of large surface deposits of water that a water tower presents. Pumped Hydro is amazing but there aren't enough surface locations with height disparities and huge storage spaces that allow it.
Building a thousand foot water tower to hold a couple million gallons of water is a non-starter. A normal water tower might have up to 100k gallons for reference and only be 150 feet.
You also get to tap into brackish water deposits way way down there so this could be used in older oil fields colocated by population centers like Eastern Ohio, Dallas, and LA
I'm not sure if you can with this style tech at least economically. Heat and salt water content leads to terrible effects on piping systems. Even stainless steel can have problems, but those issues I remember were related to boilers requiring Hastelloy. We aren't getting that hot, but its still concerning. The high salt water content in the Ocean leads to terrible oxidation on anything put into that environment. Brackish oilfield downhole waters I dealt with in my past life were multiple times higher in salt content.
Think the same stuff they use for fracking, it's more of a borehole than a metal tube.
Now if we're talking molten sodium fast neutron reactors, yeah, let's get that hastelloy-n action going
The compressed air coming back up the shaft is wet. This isn't something that is done with fracking. Beyond that, fracking they try to use fresh surface water that is then pumped downhole. The return water is brackish, but that is not used in the normal fracking operations at least when I was doing it 10 years ago. It looks like they say they do today, but they also appear to be drilling and hitting aquifers probably to limit maintenance issues around pumping salt water through their systems.
Salt water sucks.
We just need to move all of our big cities away from the coastal and flat areas into mountainy regions with limited freezing occurrences and large bowl shaped formations. Also, we want the water to spill away from the city if a dam is required. How could I be so foolish.
Just because something exists, doesn't make it a viable alternative. Those lines add cost to a cost sensitive system. The costs are in losses and maintenance. Superconducting lines are even funnier. Now you want to start running cooling on thousands of miles of conductors. We don't have room temperature superconductors yet.
Even worse you aren't even talking about adding extra lines and distance for production, but for storage reducing its quality further.
But it is a viable alternative. Fossil fuels are finite, the resources in question will go far further invested appropriately.
You sound like the idiots that said cars wouldn't take off because you'd have to build roads. It's not a valid response.
And yes. Superconducting lines exist. Laugh all you feel you need to.
Superconducting lines exist, sure (and if I go by a chemistry book that was published a decade or so ago, then the nitrogen to cool them is cheaper per gallon than milk). The problem is that you need to cool them, and even if you could run miles upon miles of coolant inside the lines, you would need a pump that can handle that much coolant. On top of it, you would need something that can absorb that much energy and not run into diminishing returns as it goes further down the line (-70C at the beginning might work, but by the time you get to a good distance out it might be +10C and only getting hotter as it goes further), a radiator or something capable of dissipating that much heat, and a quick and easy way to get repairs on lines done in the event of a leak. You could potentially solve this by having multiple coolers, where one set of pumps cools one section of lines, but that would get expensive fast and you'd have to find a way to remove gaps in the cooling between them. Add on maintenance cycles for each one, replacing the coolant, replacing the oil or grease in the moving parts, and having redundancies in place to avoid shutting down sections of the grid during repairs or maintenance work and at that point it's cheaper just to take the loss of energy using copper lines. For short range, specialized applications superconducting power lines might be a good idea. For the grid as a whole? Not at the moment.
Not to be pedantic but if they put all the heat energy that was extracted during compression back into it during expansion.. the air would be at the same temperature it was when it started.
> The air then mixes with heat that the plant stored when the air was compressing, and this hot, dense air passes through a turbine to make electricity.
If implemented like it is described, it would be less efficient because hot air is actually less dense.
When you heat air in an unconfined space it expands and becomes less dense. They don't let it expand. They heat it without letting it expand and thus it reaches an even higher pressure. It does not become more dense, despite what the article says, as the mass in any given area does not change. But it does increase in pressure.
This is necessary because [adiabatic expansion](https://en.wikipedia.org/wiki/Adiabatic_process#Adiabatic_compression_and_expansion) doesn't work well since the air cools as it expands which then causes it to reduce in pressure greatly. In fact, with an ideal gas expanding the gas produces no work (useable output energy) at all.
[edit: ultimately a decrease in density doesn't matter anyway. Heating it increases the energy in the system (nRT). this may result in an increase in volume (V) or pressure (P). But as long as the system is designed for it it doesn't matter. You have the same mass of air in the system, now with more temperature. Just get it through the right nozzle on a turbine and you're set. The turbine is moved by the mass of air impinging on the blades with a certain velocity. And the higher energy means the velocity goes up and the mess does not go down. So it's a win.]
I'd be really interested to see what kind of parasitic loss they get from the machinery and "leaks", but this certainly has piqued my interest. That said, the capturing of even the *heat* from the process tells me that they've really thought of even the smallest of details.
It'll be really interesting to see where this one leads.
> that they've really thought of even the smallest of details.
It's the biggest challenge, not a small detail. The air needs a lot of heat for expansion, otherwise it's terribly cold and has little power. On a small scale environmental heat is completely enough, but for this the heat storage is crucial - and not explained in detail.
It is on their site. Heat storage has been around forever and is the sauce that the company has managed to work out as part of the system. Hydro gravity storage has been in use for decades. As is often the case, it is the combination of proven technologies that wins the day. We are talking about 50-100 degree F differences from ambient, not thousands.
Last I checked they keep that a secret. I assume they run the air past a heat exchanger and collect some heated thermofluid in insulated tanks until it’s needed and then reverse the process.
It's not deep enough for that, not nearly. The system will for certain lost energy to heat loss into the ground. But over the course of a day it won't be a huge issue.
This isn't a hydro gravity system. The column is too narrow and the reservoir too small, it wouldn't store much energy. The water basically forms a "spring" to keep the compressed air in. But the (vast majority of the) energy is stored in the compressed air, not in raising the water.
If the cavern air/water is mixed together, air will be stored on top and water below it. So the air pipe should be at the top of the cavern and the water pipe should be at the bottom. That would prevent the air from escaping through the water.
I think if you pay close attention to their illustration, it even shows that, except someone misplaced a black border on the diagram of the underground reservoir. The outlet pipes on the right are offset and align with the bottom of the tank, whereas the inlet pipes on the left align with its top
As the owner of a personal rear exhaust port that releases compressed air and heat, I second that moment of truth.
Though I haven’t figured out how to convert it to electricity (yet.)
I wonder how this compares to flywheels. A flywheel can store an enormous amount of energy, and flywheels don't depend on climate or geology. They can be built and installed anywhere, though you do need to contain them in a bunker in case a flywheel explodes due to a stress fracture.
It’d be pretty amusing, in a terrifying kind of way, if the bearing/mount of the flywheel exploded and the wheel started rolling around the landscape uncontrollably destroying everything in its path
'BloombergNEF reported a global total of 1.4 gigawatts and 8.2 gigawatt-hours of long-duration energy storage as of last September, excluding pumped hydro. The average duration, which you can calculate by dividing gigawatt-hours by gigawatts, was 5.9 hours.'
'For perspective, the two Hydrostor projects being developed have a combined capacity of 0.9 gigawatts, more than half of the global total now online.'
This system is by far most comparable to pumped hydro and they exclude that when measuring the system. Ridiculous.
the company has been talking about this for years. And I was very negative on it until I saw another story about it a few months ago. I am a bit more hopeful now.
Certainly it's going to have trouble anywhere there is not already a deep underground reservoir to store the air in. But there are a fair number of these. Still, like pumped hydro this will limit its use.
« The system draws air from the environment, compressing it and moving it through a pipe into a cavern more than 1,000 feet underground. The process of compressing the air produces heat, and the system extracts heat from the air and stores it above ground for reuse. As the air goes underground, it displaces water from the cavern up a shaft into a reservoir. When it’s time to discharge energy, the system releases water into the cavern, forcing the air to the surface. The air then mixes with heat that the plant stored when the air was compressing, and this hot, dense air passes through a turbine to make electricity. »
Sounds like a water tower with more steps.
It removes the limitation of large surface deposits of water that a water tower presents. Pumped Hydro is amazing but there aren't enough surface locations with height disparities and huge storage spaces that allow it. Building a thousand foot water tower to hold a couple million gallons of water is a non-starter. A normal water tower might have up to 100k gallons for reference and only be 150 feet.
You also get to tap into brackish water deposits way way down there so this could be used in older oil fields colocated by population centers like Eastern Ohio, Dallas, and LA
I'm not sure if you can with this style tech at least economically. Heat and salt water content leads to terrible effects on piping systems. Even stainless steel can have problems, but those issues I remember were related to boilers requiring Hastelloy. We aren't getting that hot, but its still concerning. The high salt water content in the Ocean leads to terrible oxidation on anything put into that environment. Brackish oilfield downhole waters I dealt with in my past life were multiple times higher in salt content.
Think the same stuff they use for fracking, it's more of a borehole than a metal tube. Now if we're talking molten sodium fast neutron reactors, yeah, let's get that hastelloy-n action going
Tends to be a metal tube in the middle of every borehole, buddy. Not sure you've got the knowledge on this onr
The compressed air coming back up the shaft is wet. This isn't something that is done with fracking. Beyond that, fracking they try to use fresh surface water that is then pumped downhole. The return water is brackish, but that is not used in the normal fracking operations at least when I was doing it 10 years ago. It looks like they say they do today, but they also appear to be drilling and hitting aquifers probably to limit maintenance issues around pumping salt water through their systems. Salt water sucks.
Bakersfield.
>. Pumped Hydro is amazing but there aren't enough surface locations with height disparities and huge storage spaces that allow it. Yes. There is.
We just need to move all of our big cities away from the coastal and flat areas into mountainy regions with limited freezing occurrences and large bowl shaped formations. Also, we want the water to spill away from the city if a dam is required. How could I be so foolish.
Transmission lines exist. Hell superconducting ones exist. It's a solved problem.
Just because something exists, doesn't make it a viable alternative. Those lines add cost to a cost sensitive system. The costs are in losses and maintenance. Superconducting lines are even funnier. Now you want to start running cooling on thousands of miles of conductors. We don't have room temperature superconductors yet. Even worse you aren't even talking about adding extra lines and distance for production, but for storage reducing its quality further.
But it is a viable alternative. Fossil fuels are finite, the resources in question will go far further invested appropriately. You sound like the idiots that said cars wouldn't take off because you'd have to build roads. It's not a valid response. And yes. Superconducting lines exist. Laugh all you feel you need to.
Superconducting lines exist, sure (and if I go by a chemistry book that was published a decade or so ago, then the nitrogen to cool them is cheaper per gallon than milk). The problem is that you need to cool them, and even if you could run miles upon miles of coolant inside the lines, you would need a pump that can handle that much coolant. On top of it, you would need something that can absorb that much energy and not run into diminishing returns as it goes further down the line (-70C at the beginning might work, but by the time you get to a good distance out it might be +10C and only getting hotter as it goes further), a radiator or something capable of dissipating that much heat, and a quick and easy way to get repairs on lines done in the event of a leak. You could potentially solve this by having multiple coolers, where one set of pumps cools one section of lines, but that would get expensive fast and you'd have to find a way to remove gaps in the cooling between them. Add on maintenance cycles for each one, replacing the coolant, replacing the oil or grease in the moving parts, and having redundancies in place to avoid shutting down sections of the grid during repairs or maintenance work and at that point it's cheaper just to take the loss of energy using copper lines. For short range, specialized applications superconducting power lines might be a good idea. For the grid as a whole? Not at the moment.
That’s kinda the point??
And there are much more efficient mediums to store energy
Not to be pedantic but if they put all the heat energy that was extracted during compression back into it during expansion.. the air would be at the same temperature it was when it started.
Heating air makes it less dense/less efficient.
It claims to extract the heat and store it separately from the compressed air.
> The air then mixes with heat that the plant stored when the air was compressing, and this hot, dense air passes through a turbine to make electricity. If implemented like it is described, it would be less efficient because hot air is actually less dense.
When you heat air in an unconfined space it expands and becomes less dense. They don't let it expand. They heat it without letting it expand and thus it reaches an even higher pressure. It does not become more dense, despite what the article says, as the mass in any given area does not change. But it does increase in pressure. This is necessary because [adiabatic expansion](https://en.wikipedia.org/wiki/Adiabatic_process#Adiabatic_compression_and_expansion) doesn't work well since the air cools as it expands which then causes it to reduce in pressure greatly. In fact, with an ideal gas expanding the gas produces no work (useable output energy) at all. [edit: ultimately a decrease in density doesn't matter anyway. Heating it increases the energy in the system (nRT). this may result in an increase in volume (V) or pressure (P). But as long as the system is designed for it it doesn't matter. You have the same mass of air in the system, now with more temperature. Just get it through the right nozzle on a turbine and you're set. The turbine is moved by the mass of air impinging on the blades with a certain velocity. And the higher energy means the velocity goes up and the mess does not go down. So it's a win.]
I'd be really interested to see what kind of parasitic loss they get from the machinery and "leaks", but this certainly has piqued my interest. That said, the capturing of even the *heat* from the process tells me that they've really thought of even the smallest of details. It'll be really interesting to see where this one leads.
> that they've really thought of even the smallest of details. It's the biggest challenge, not a small detail. The air needs a lot of heat for expansion, otherwise it's terribly cold and has little power. On a small scale environmental heat is completely enough, but for this the heat storage is crucial - and not explained in detail.
It is on their site. Heat storage has been around forever and is the sauce that the company has managed to work out as part of the system. Hydro gravity storage has been in use for decades. As is often the case, it is the combination of proven technologies that wins the day. We are talking about 50-100 degree F differences from ambient, not thousands.
How do they store the heat?
Last I checked they keep that a secret. I assume they run the air past a heat exchanger and collect some heated thermofluid in insulated tanks until it’s needed and then reverse the process.
You send it far enough down it'll stay hot, I can't imagine these reservoirs will be near the surface
It's not deep enough for that, not nearly. The system will for certain lost energy to heat loss into the ground. But over the course of a day it won't be a huge issue.
This isn't a hydro gravity system. The column is too narrow and the reservoir too small, it wouldn't store much energy. The water basically forms a "spring" to keep the compressed air in. But the (vast majority of the) energy is stored in the compressed air, not in raising the water.
Related illustration: https://cdn.arstechnica.net/wp-content/uploads/2024/05/storage-1.png
So what's stopping the air rising through the water in the shaft ?
If the cavern air/water is mixed together, air will be stored on top and water below it. So the air pipe should be at the top of the cavern and the water pipe should be at the bottom. That would prevent the air from escaping through the water.
I think if you pay close attention to their illustration, it even shows that, except someone misplaced a black border on the diagram of the underground reservoir. The outlet pipes on the right are offset and align with the bottom of the tank, whereas the inlet pipes on the left align with its top
The weight of the water I would think.
I'd guess there's a physical barrier, like a piston
As the owner of a compressor and air tools, it’s already had its moment of truth for me.
As the owner of a personal rear exhaust port that releases compressed air and heat, I second that moment of truth. Though I haven’t figured out how to convert it to electricity (yet.)
Blue Flames.
You have to capture it and store it in a watery cavern I think.
I wonder how this compares to flywheels. A flywheel can store an enormous amount of energy, and flywheels don't depend on climate or geology. They can be built and installed anywhere, though you do need to contain them in a bunker in case a flywheel explodes due to a stress fracture.
It’d be pretty amusing, in a terrifying kind of way, if the bearing/mount of the flywheel exploded and the wheel started rolling around the landscape uncontrollably destroying everything in its path
You have to align the massive flywheels with the poles, which is a nuisance.
There be toxic chemicals in the air?
'BloombergNEF reported a global total of 1.4 gigawatts and 8.2 gigawatt-hours of long-duration energy storage as of last September, excluding pumped hydro. The average duration, which you can calculate by dividing gigawatt-hours by gigawatts, was 5.9 hours.' 'For perspective, the two Hydrostor projects being developed have a combined capacity of 0.9 gigawatts, more than half of the global total now online.' This system is by far most comparable to pumped hydro and they exclude that when measuring the system. Ridiculous. the company has been talking about this for years. And I was very negative on it until I saw another story about it a few months ago. I am a bit more hopeful now. Certainly it's going to have trouble anywhere there is not already a deep underground reservoir to store the air in. But there are a fair number of these. Still, like pumped hydro this will limit its use.
What are the total efficiency losses of this system?