AirBattery- Seems pretty dodgy to me. - Page 1
Forum section: electronics / general

author: Refrigerator
author_rank: Super Contributor
timestamp: December 31, 2021, 12:09:28 pm
content: Youtube decided to recommend me this vid about this new and revolutionary storage technology.Quick rundown of how it works:Bury sealed tank into the groundWater pump pushes water into tank so pressure goes upCompressing air makes it heat up but water absorbs this heatThey do it slowly so "no heat is generated" - wait what?When you need energy just release the waterPressurized air pushes water into turbines and generates electricity81% round trip efficiencyThe video includes the typical buzzwords like "patented technology" and highlights the "special polymers" used in the pressure tanks.And of course the obligatory CGI.But this all seems to be just a way to put a new twist on pumped water storage, yet they call it "air battery".To me this looks more like a grid-scale super soaker.

author: Ian.M
author_rank: Super Contributor
timestamp: December 31, 2021, 01:28:20 pm
content: Lovely shot ofSTEELtanks being lowered into the ground at 0:36. I'd give even odds they are reusing video of a filling station's fuel tanks being installed.Its just another take on near-isothermal compressed air energy storage. Wikipedia has a reasonable introduction:https://en.wikipedia.org/wiki/Compressed-air_energy_storage#Near-isothermal

author: tszaboo
author_rank: Super Contributor
timestamp: December 31, 2021, 01:44:30 pm
content: OK, a few things.1.) Composite tanks are way more expensive than steel tanks, only reason to make them is you can fit more liquid to a truck and stay below weight limit2.) If you bury an empty tank into the ground, ground water will push it out eventually. They were pouring concrete on it just to keep it in place. But why do it in the first place, when you can just put the tankaboveground.3.) Having many small tanks, because... why? The larger you can build something the more cost efficient it is, and the less material is used to make it. We are extremely good at making large tanks.4.) The idea would work, but I still think P2G is a better one. Compressed air stores about 100kJ/m3 while CNG is 22000000kJ/m3. And if you create if from carbon scrubbers, it is carbon negative.

author: madires
author_rank: Super Contributor
timestamp: December 31, 2021, 03:01:55 pm
content: AirBattery is a quite misleading term for compressed air energy storage. It doesn't give you electric power directly as a nomal battery does. BTW, the real air batteries are metal–air electrochemical cells. And especially the iron-air battery is a candidate for storage of power from PV and wind farms.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 31, 2021, 03:08:32 pm
content: Pushing water in the same tank as used for the air is a bit stupid. The energy storage is in the air part only, so much of the volume is wasted with water.For the larger to smaller tanks: It does no really save on the material using larger tanks. The wall thickness for a pressure vessel has to scale like the diameter. So the volume to wall ratio stays constant. There is still some saving in needing less corrosion protection.

author: Refrigerator
author_rank: Super Contributor
timestamp: December 31, 2021, 04:10:35 pm
content: Quote from: tszaboo on December 31, 2021, 01:44:30 pmFor a given pressure, increasing the tank size by 2x will require a wall thickness of 4x.Smaller tanks are also easier to make, transport, inspect.

author: Ian.M
author_rank: Super Contributor
timestamp: December 31, 2021, 04:17:30 pm
content: I think your maths is wrong. Although the cross section area and thus the total force to be resisted is proportional to the square of the linear dimensions, its distributed over a perimeter that's proportional to the linear dimensions, so the wall thickness only needs to increase linearly.

author: tszaboo
author_rank: Super Contributor
timestamp: December 31, 2021, 05:47:25 pm
content: Quote from: Refrigerator on December 31, 2021, 04:10:35 pmWith a quick play with this:https://www.engineersedge.com/calculators/shell_internal_pres_pop.htmwall thickness goes up linear with radius.

author: Refrigerator
author_rank: Super Contributor
timestamp: December 31, 2021, 06:24:10 pm
content: Quote from: tszaboo on December 31, 2021, 05:47:25 pmThen i stand corrected.

author: PlainName
author_rank: Super Contributor
timestamp: December 31, 2021, 06:30:45 pm
content: QuoteSeemed fairly obvious to me that shoving them underground means they use effectively no space. Once buried you can re-use the above-ground for solar panels (to provide the power you want storing), farming (as they show), roads, etc. Also, tubers like thunderfoot won't bang on about how much space they take vs a briefcase nuke or whatever.

author: tszaboo
author_rank: Super Contributor
timestamp: December 31, 2021, 06:35:08 pm
content: Quote from: dunkemhigh on December 31, 2021, 06:30:45 pmYou can put solar panels above the tanks, if you use small tanks. It's not like space is usually the issue. And what happens with your underground infrastructure, if you need repairs?

author: PlainName
author_rank: Super Contributor
timestamp: December 31, 2021, 06:41:40 pm
content: QuoteThat would likely be a problem, and no doubt why they go on about the special polymer coating.

author: Ian.M
author_rank: Super Contributor
timestamp: December 31, 2021, 07:27:15 pm
content: The prospect of acres of shallowly buried high pressure tanks filled with wet air is quite concerning. How far apart do the tanks need to be for there to be negligible risk of cascading failure if one ruptures, or a connection breaks loose?

author: PlainName
author_rank: Super Contributor
timestamp: December 31, 2021, 07:40:20 pm
content: That's an impressive video, but those bottle were all unconstrained. Tie them down and then knock the valve off - much less fun.I imagine the issue with a leak would be if it turned into an explosive breach.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 31, 2021, 07:48:04 pm
content: Pressure vessels for compressed air are normally made from a relatively mild steel so that they don't fail catastrophical, but in most cases more gradually with a leaking weld. They still require regular testing / inspection.So I don't think much space in between needed. More like some area for vertical loading from the top.Underground high pressure gas is not uncommon: long distance natural gas pipelines use quite some pressure ( AFAIR 70 bar in some cases).

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 31, 2021, 07:48:48 pm
content: Storing energy "mechanically" (rather than chemically) is nothing new, and is actually a seemingly promising approach for a number of use cases.It's being done using water (that you pump and release), heavy loads (that you lift and let fall), whatever. A number of variants. This one, I don't know how effective it actually is compared to what is claimed, but the basic idea is still the same.

author: AVGresponding
author_rank: Super Contributor
timestamp: January 01, 2022, 02:21:22 am
content: Underground compressed air tanks as a means of storing energy has been mooted about for decades, I remember reading about one using disused salt caverns in the New Scientist fifteen or so years ago. Exhausted oil wells have also been suggested iirc.The main reason for having them (in context of the OP) underground would be thermal stability, probably. Imagine having your tanks at full operating pressure, only to have the ambient temperature go up by 10oC or so...

author: Kim Christensen
author_rank: Super Contributor
timestamp: January 01, 2022, 05:53:07 am
content: QuoteThis is where the smelliest BS resides...

author: Ian.M
author_rank: Super Contributor
timestamp: January 01, 2022, 08:18:49 am
content: Yep. Compare with Dinorwig Power Station in Wales, which is a a pumped-storage hydroelectric system. It runs on average at 74% to 76% efficiency, with the benefit of an approximately constant head pressure due to the approx. 517 meters height difference between the upper and lower reservoirs, (varying only 34 meters between full and 'empty') and a 10 meters diameter tunnel and shaft feeding the turbines.AirBattery claims to do better than that with a water 'head pressure' that varies widely over its effective operating cycle, and with much narrower, far more twisty pipes.

author: gnuarm
author_rank: Super Contributor
timestamp: January 01, 2022, 04:43:13 pm
content: Quote from: Ian.M on December 31, 2021, 07:27:15 pmWhen I watched this video I clicked on a follow on video about how electricity flows in a wire. I noticed a response from Eevblog, seems Dave doesn't agree with the ideas in Veritasium's videoFunny how Dave has a 45 minute reply to a 15 minute video.

author: TimFox
author_rank: Super Contributor
timestamp: January 01, 2022, 04:47:04 pm
content: Early in the 20th century, there were locomotives powered by compressed air stored in an onboard tank, with mechanics resembling the far more common steam locomotive. They were used in munitions factories and other locations paranoid about fire. Even now, scale modelers of steam locomotives often fill the "boiler" with compressed air to avoid having to clean out the small boilers from combustion products.

author: gnuarm
author_rank: Super Contributor
timestamp: January 01, 2022, 04:47:57 pm
content: Quote from: Kleinstein on December 31, 2021, 07:48:04 pmThat would bedrycompressed air. With the combination of air and water under pressure, you are going to have a rather corrosive conditions that will damage steel tanks relatively quickly. That's why they are using composite materials.When they fill metal SCUBA tanks the air is DRY for this very reason. Let your tanks sit with just air in them for a year or two and that tank is crap.

author: gnuarm
author_rank: Super Contributor
timestamp: January 01, 2022, 05:12:28 pm
content: Quote from: Kim Christensen on January 01, 2022, 05:53:07 amWhy is 81% so unbelievable? I suppose it's because of the heat generated and lost when compressing the air? Thermo is not always an intuitive topic. I would need to look at the equations for isothermal compression... through the magic of television I've completed my research and it seems they are not full of bunk on the isothermal stuff. We are thinking the compression will produce heat which is dissipated into the water, tank and surroundings and that is true. But during the expansion the surroundings, tank and water allsupplyheat to the gas in the tank which maintains isothermal conditions for recovering the work as well. So no (or very small) round trip losses due to the heat of compression.

author: gnuarm
author_rank: Super Contributor
timestamp: January 01, 2022, 05:15:22 pm
content: Quote from: Ian.M on January 01, 2022, 08:18:49 amThe delta pressure for the AirBattery is not known by us. That is an operational factor that is controlled by them to optimize their operation.

author: Kim Christensen
author_rank: Super Contributor
timestamp: January 01, 2022, 08:25:44 pm
content: QuoteBecause even at 90% efficiency for both the motor (Running compressor) and generator (driven by impeller) we are at around 81%... And we haven't even considered other losses yet.

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 01, 2022, 08:38:53 pm
content: Quote from: tszaboo on December 31, 2021, 01:44:30 pmPerhaps to use the ground as a blast shield in case of an explosive failure?

author: AVGresponding
author_rank: Super Contributor
timestamp: January 01, 2022, 08:46:20 pm
content: Quote from: gnuarm on January 01, 2022, 05:12:28 pmIt's bullshit because the tank and its contents will tend towards ambient temperature. This means you don't preserve and then use the heat, you just lose it. That's why it's an efficiency "loss".This will happen whether the tank is underground, above ground, in space, or anywhere else.

author: bdunham7
author_rank: Super Contributor
timestamp: January 01, 2022, 09:32:39 pm
content: Quote from: gnuarm on January 01, 2022, 05:12:28 pmBecause previous air-storage schemes, including one that used a water/air heat exchanger to 'separate the heat energy from the pressure energy and then recombine them for recovery' have claimed much lower numbers and then failed to even meet those. A combined motor/pump efficiency of 90% would be truly remarkable and at the limits of what is achievable at any scale under ideal conditions, the same goes for the impeller/generator combo. And as previously stated, that alone gets you down to 81%. Now you add in the pressure delta--if start with X pressure and fill the tank halfway with water, you have 2X pressure--so while we may not have the spec, we can assume it isn't small. And finally the requirement that the process be real-time isothermic can probably be approached on the compression end by spraying the water in, but that takes energy. And then for recovery, you would need some other magic method. They mention 'going slowly', so at least they are acknowledging these issues. Good luck to them meeting their stated goals.

author: tszaboo
author_rank: Super Contributor
timestamp: January 01, 2022, 11:13:27 pm
content: Quote from: gnuarm on January 01, 2022, 05:12:28 pmIt's probably up to 81% theoretical max limit calculated on whiteboard for adiabatic compression, frictionless pipes and ballpark estimate for a turbine. A turbine that they looked up on wikipedia and which is not even sized for them.

author: SiliconWizard
author_rank: Super Contributor
timestamp: January 01, 2022, 11:16:45 pm
content: Here is the website:https://www.aug-wind.com/Typical greenish-carbon-neutral-energy-startupy thing.

author: PlainName
author_rank: Super Contributor
timestamp: January 02, 2022, 12:49:49 am
content: They claim to have installed units. Unidentified, of course, due to customer confidentiality.

author: gnuarm
author_rank: Super Contributor
timestamp: January 02, 2022, 03:31:22 am
content: Quote from: Kim Christensen on January 01, 2022, 08:25:44 pmMotors and generators can exceed 90% efficiency. Pumped hydro storage exceeds 80% efficiency. That's essentially what this is only the work is done by compressed air rather than gravity.

author: gnuarm
author_rank: Super Contributor
timestamp: January 02, 2022, 04:17:41 am
content: Quote from: AVGresponding on January 01, 2022, 08:46:20 pmYou don't seem to understand. On storing energy the air would become hot if not done slowly. The process is slow enough so the heat is continually lost into the surroundings, particularly the water, making the compression isothermal. On recovering the energy in the compressed air it expands lowering its temperature if not doneslowly. Again it is done slowly enough so as it expandsheat is absorbedfrom the surroundings making the expansion isothermal. An isothermal cycle recovers all the heat put in without requiring insulation of the medium.If you were to insulate the tank and provide some means of the water not exchanging heat with the air, you would have an adiabatic cycle which could also provide high efficiency. However even with insulation the higher temperature of the compressed air would not last and that heat energy would be irrecoverably lost. When recovering the stored energy as the gas expands the temperature drops along with the pressure and you don't recover all the energy that was stored in the gas. So you lose energy on both parts of the cycle. I expect this is the process you are thinking of.

author: gnuarm
author_rank: Super Contributor
timestamp: January 02, 2022, 04:27:48 am
content: Quote from: bdunham7 on January 01, 2022, 09:32:39 pmI think you are being overly pessimistic. I would give you the assignment to figure out how to make it work rather than proving it won't work. But I'm sure you would quit the job and storm off, so I'll explain how it works.First, your numbers seem to be shooting from the hip. If you look up the efficiency of pumped hydro you will find very similar figures. They are doing everything this system is doing, just using gravity rather than air to provide the storage.I'm not sure what pressure delta you are referring to. The isothermal issues are easy to manage. The system is designed to store and supply energy over long periods of time. If all the tanks are used in parallel, no tank has to supply large quantities of water, so it is easy to keep them isothermal. The spraying you saw in the video was nothing that takes a lot of energy. Once the pressure rises in the tank the tiny pressure behind those nozzles are a tiny part of the equation. I'm not even sure they are needed or useful, but I have to trust they wouldn't be there if they weren't.On the recovery side I'm concerned that it all seems to be from the top while it should be from the bottom. I guess I don't see all the details.

author: bdunham7
author_rank: Super Contributor
timestamp: January 02, 2022, 04:55:12 am
content: Quote from: gnuarm on January 02, 2022, 03:31:22 amWe know that, which is why I referred to the motor/pump combination for the input and the impeller/generator for the output.QuoteExample or citation? AFAIK, 80% would be best-case and under specific conditions. Many do worse.QuoteThe tank has an initial pressure before any water is pumped in. If you fill it 2/3 of the way with water, the pressure will now be 3X the original. The pressure delta is the difference between the initial pressure and the final pressure. This is critical because if you browse the web looking for examples of extremely efficient pumps and impellers, the will all reach those efficiencies within specific, narrow operating parameters, not a 3X or 4X or whatever pressure, power or flow difference. To use a very small pressure delta would require a very low power density--huge tanks with little energy storage.

author: gnuarm
author_rank: Super Contributor
timestamp: January 02, 2022, 09:23:58 am
content: Quote from: bdunham7 on January 02, 2022, 04:55:12 amI really hate discussing things with people who cite numbers without even looking at data. Why would you cite anything other than hydro storage? But you don't actually cite anything, no reference at all, but you insist that I provide references. Ok... Now show me yours.QuoteShow us your data to support that then. Here's a few of mine.https://www.ge.com/renewableenergy/hydro-power/hydro-pumped-storagehttps://iopscience.iop.org/article/10.1088/2516-1083/abeb5bLots of details, search on "round-trip efficiency of about 80%".https://atb.nrel.gov/electricity/2021/pumped-storage_hydropowerThis one gives a range of 70% to 87% showing that 80% is in no way stressing the technology or is a lab queen.QuoteAgain, you are making a claim about a field you don't show any expertise in and no indication that you have even looked for references. You are focusing on pressure delta, but you don't actually know that is an issue for turbines or pumps. I know someone who designed large pumps for a living. I'll ask him about the pumps. I know they have a spot in the curve where the efficiency goes to hell. Apparently there is a bit of a knife edge between the pump casing body and the discharge shoot. There is a condition where an oscillation sets in because of interactions at that knife edge that messes with efficiency. Otherwise he talked as if the efficiency varied slightly. They did tune the pumps for the application, but as long as they avoided the oscillation they always worked well even if slightly off the peak efficiency.Bottom line is pumped hydro also works with varying pressure and you have numbers for that above. If you want to continue to dispute the info, then you need to find some references that shows this is wrong.

author: IanB
author_rank: Super Contributor
timestamp: January 02, 2022, 09:56:21 am
content: I'm not quite following what the dispute is here, but for sure there is a big difference between pumped hydro storage and compressed air storage when it comes to energy efficiency.With pumped hydro, water is an incompressible liquid, which means all the input power to the pump is used to increase the potential energy of the water when raising it to a higher elevation, less electrical, mechanical and hydraulic losses in the system. With careful design it is possible to keep the losses down and get the efficiency quite high.With compressed air, thermodynamics becomes your enemy, because compressing a gas is inherently inefficient. Some of the work of compression gets turned into heat, which is dissipated and lost.You can hypothesize about "slow" compression and getting close to isothermal conditions, but in reality the air has to go through a compressor to get to the storage tanks, and any compressor will have a limit on its energy efficiency, in terms of being able to recover the work of compression. Thermodynamics says that if you compress a gas it will get hotter, and to achieve an isothermal process you have to remove the heat as it is generated. That very act of removing the heat of compression is stealing energy from the system that you are putting in through the compressor. So even with isothermal compression, you lose.There are only two ways I can think of to make compressed gas energy storage systems efficient: (1) Keep the gas hot after compression, and don't let it cool down; (2) Minimize the pressure change in the gas (large volume, low pressure rise).The first method is impractical, and the second method is used, for example, in undersea tethered balloon storage systems. (Edit: it seems there may be ways to recover and re-use the heat of compression to improve the round-trip efficiency in the first case.)In conclusion, compressed air storage is doomed by thermodynamics to be inefficient, and there is no technology that can overcome that. There are three things that are certain in life: death, taxes, and the laws of thermodynamics.

author: IanB
author_rank: Super Contributor
timestamp: January 02, 2022, 10:13:45 am
content: This page has a high level summary of what I described above:https://energystorage.org/why-energy-storage/technologies/compressed-air-energy-storage-caes/It indicates a power-to-power efficiency for compressed air storage being about 42% unless special arrangements are made to recover and re-use the waste heat. But even then it is not likely to get much above 55%, with 70% being a theoretical upper limit (not sure if that's on paper or actually achieved).In contrast, pumped hydro systems can have a power-to-power efficiency up to 85%.

author: bdunham7
author_rank: Super Contributor
timestamp: January 02, 2022, 03:19:20 pm
content: Quote from: IanB on January 02, 2022, 09:56:21 amIn this system, they pump the water not the air. The water absorbs the heat and then releases it again when the process reverses. Presumably the heat capacity of the water is so much higher than the air that the water temperature won't go up much and everything stays near ambient.

author: bdunham7
author_rank: Super Contributor
timestamp: January 02, 2022, 03:59:25 pm
content: Quote from: gnuarm on January 02, 2022, 09:23:58 amI said 'AFAIK'. There are numerous pumped hydro stations here in CA, such as the Castaic/Pyramid Lake complex. I recall reading about them years ago and they had RTEs of 67-75% or so. I don't have a cite for that and couldn't find one easily, but I have found stuff saying 'up to 80%' and occasionally '80% or more'. Your data seems to say the same thing, despite one source saying that the range was 'up to 87%' without supplying a specific example. From one of your sources:The efficiency of generation is about 90%. This means that 10% of the energy stored in an upper reservoir is lost when the water passes through the turbine to produce electricity. In a complete PHES cycle, water is pumped from a lower to an upper reservoir and at a later time returns to the lower reservoir, with a round-trip efficiency of about 80%. In other words, about 20% of the electricity is lost in a complete pumping/generation cycle.So if you want to agree on 80% as a reasonable number for a modern system, fine. If you think it is more than that, just show me one actual example, not some white paper that casually tosses out an unsupported number.QuoteWell, go ahead and ask. But keep in mind that you have a motor and pump, so even if the pump remains efficient over a pressure change of 3X--which it might--the torque on the motor will be varying by a factor of 3. If you get that 90% one-way efficiency with a 93% efficient pump and a 97% efficient motor (very good numbers), your motor would have to maintain that efficiency over a torque range of 1X to 3X or more. I only have limited experience with smaller pumps, so I can't say if that is possible or not, just that it would certainly be a challenge. And I haven't considered variable speed systems.QuoteI don't see what you mean--what numbers? Francis turbines can be made to work with a range of head pressures, but again AFAIK, they are engineered and manufactured with a specific installation in mind. I don't know of any pumped hydro systems that have large variances in the head pressures to the turbines. Some impounded water generation systems, like Oroville, do see a significant change in head pressure--but I don't know that those systems have efficiency as a priority since electricity generation is a secondary purpose.Anyway, I don't need to win an argument. If you are convinced that they can do what they say, go ahead an click on their "Investors" page.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 02, 2022, 04:37:29 pm
content: The 81% efficiency number looks like (90%)² and may be a reasonable first approximation for a first start before actually doing the design and details.The big problem I see with this system is that it would be simply quite expensive. The steel vessels would be about as efficient as some water in lake some 40 m up, so maybe 1 kwh for 1 m³. Chances are the costs for the vessels alone would be higher than batteries and there is little chance to get lower prices from large quantities: steel is already made in quantities.

author: gnuarm
author_rank: Super Contributor
timestamp: January 02, 2022, 04:51:28 pm
content: Quote from: IanB on January 02, 2022, 09:56:21 amYes, you aren't following and no, there is not a big difference in efficiency in this case because it isisothermal. I've made two posts that explain this clearly. If you still don't understand it there's nothing more I can say. Read a thermodynamics text. Not trying to be rude, I'm serious. This is one of the more simple concepts of thermo, but you have to understand what is involved.QuoteTrueQuoteNot correct. This is an oversimplification because you areignoringthe return of that heat during the expansion.QuoteNot hypothetical, very real. You can't see past the heat leaving in an isothermal compression and see the heatreturningin an isothermal expansion.QuoteWhat you write is wrong because you don't actually understand the thermodynamics of isothermal processes.

author: gnuarm
author_rank: Super Contributor
timestamp: January 02, 2022, 04:58:30 pm
content: Quote from: IanB on January 02, 2022, 10:13:45 amThey are talking about an adiabatic compression followed by a removal of the added heat throwing it away basically. Yes, that will always be rather inefficient. The process we are talking about uses an isothermal process to allow that heat to be recovered. The environment is used as a heat sink. On compression the heat moves to the environment. On expansion instead of the gas cooling down heat is recovered from the environment to maintain the temperature recovering nearly all the energy used.Given the slow use of the total energy in the entire installation this is very practical and is a very workable idea.

author: IanB
author_rank: Super Contributor
timestamp: January 02, 2022, 05:01:46 pm
content: Quote from: bdunham7 on January 02, 2022, 03:19:20 pmThat doesn't really change anything. It is still the air that is being compressed and storing the energy.Water doesn't inherently get hot when you pump it, so there is no heat to absorb at the pump. However, when the water is pumped into the chambers, it compresses the air inside them, and this air will get hotter as it is compressed. This is now the worst possible situation as there is no means to recover that heat. It will dissipate into the surrounding ground and get lost.It is true that when you try to recover the energy from the system, the surrounding ground will provide some heat back into the expanding air, but I'm not sure it will be enough to make much of a difference. It depends on the effectiveness of the heat transfer between the compressed air and the surrounding ground.

author: gnuarm
author_rank: Super Contributor
timestamp: January 02, 2022, 05:13:35 pm
content: Quote from: bdunham7 on January 02, 2022, 03:59:25 pmHow about you get off your high horse and consider the context. I never said anything about this system being higher than 81% efficient. Several were talking about this being a bogus number and I provided information showing it is a realistic number. Whether they do or don't achieve exactly this number in reality, it can be close as this is what other pumped hydro systems achieve.QuoteI'll talk to him later today.QuoteWhen a pumped hydro facility uses the water the head changes. Underground systems use much lower differences in level, so much higher differences in pressure. In this system no one knows the details so claiming large variations in pressure and efficiency is not supportable.QuoteMostly people here don't understand what is being done. That's fine, but making claims in contradiction to facts is silly.

author: IanB
author_rank: Super Contributor
timestamp: January 02, 2022, 05:22:21 pm
content: Quote from: gnuarm on January 02, 2022, 04:58:30 pmThat is a valid process, and it is true that storage and recovery of the heat will improve the cycle efficiency.QuoteFair enough. If the system operates close to thermal equilibrium at all times, then it could approach an ideal reversible process, and might make sense.Quote from: gnuarm on January 02, 2022, 04:51:28 pmThere's no need to be rude. I am a thermodynamicist.QuoteI understand.QuoteYes, I can see that. It was an element I overlooked when I was writing before.QuoteI do understand. I missed an aspect of this when I was writing before that I see more clearly now.

author: gnuarm
author_rank: Super Contributor
timestamp: January 02, 2022, 05:25:37 pm
content: Quote from: IanB on January 02, 2022, 05:22:21 pmOk, I had made a reply to another of your posts which I have since deleted after reading this post. I'm glad the light bulb has come on. Maybe you can help others see the light now.

author: bdunham7
author_rank: Super Contributor
timestamp: January 02, 2022, 05:35:35 pm
content: Quote from: IanB on January 02, 2022, 05:01:46 pmPresumably the heat capacity of the water is so much higher than the air that the water temperature won't go up much and everything stays near ambient.The water is sprayed into the air chamber so why wouldn't it absorb the heat? The efficiency of this process will depend on how closely they can maintain an ideal isotherm. If there is a nearby source of waste heat, they might even be able to improve it further by warming the water after the compression is complete.

author: IanB
author_rank: Super Contributor
timestamp: January 02, 2022, 05:49:52 pm
content: Quote from: bdunham7 on January 02, 2022, 05:35:35 pmI had an incomplete picture of the system before, that I have now appreciated.Broadly speaking, when you put energy into the system by pumping the water and compressing the air, you want to be able to get as much as possible of this energy back again when you reverse the process. This is called the power-to-power efficiency, and you want to get as close to 100% as you can achieve.Now, the energy put into the system gets distributed into two places: (1) pressure energy of the compressed air, and (2) thermal energy (heat) resulting from compressing the gas. If you don't do anything to recover it, the heat part is energy that would be permanently lost.Apparently, in this system the heat of compression is to be absorbed by the surrounding ground, and when the system reverses the surrounding ground puts the heat back into the air as it cools down on expansion. In traditional compressed air systems extra heat has to be provided to compensate for the air cooling down, but here they are avoiding the need for that by using the ground heat to do it. (There is some analogy with ground storage heat pump systems.)So, conceptually, the system can work. Can it work in practice? That would seem to be an engineering design problem, and I cannot say. I do know that ground storage heat pump systems use a system of buried pipes to improve the heat transfer.

author: Kim Christensen
author_rank: Super Contributor
timestamp: January 02, 2022, 07:02:09 pm
content: Not my area of expertise, but someone may find this PDF about "Isothermal Compression" to be of interest:

author: tszaboo
author_rank: Super Contributor
timestamp: January 02, 2022, 07:58:02 pm
content: Honestly, efficiency of the energy storage system doesn't matter. Really, it is a bold claim, but I have reasons to say that.What matters is the investment cost of (solar generation+ wind generation+ energy storage) / stored energyIf you have a system, that only has 60% storage efficiency (compared to a 90% system), you can easily offset the losses by installing 50% more solar/wind. Solar and wind is cheap, so what you need is cheap storage. Cheap way to store energy means large energy density, like natural gas. We can store months worth of natural gas for entire countries. Plus one way of the conversion can happen in existing infrastructure, as you can just feed it into the pipelines and burn it in the existing power plant. Or someone house boiler for heating.Plus you don't need to retrofit houses to use electricity for heating the radiators, boilers.Power to gas has just so many benefits...

author: SiliconWizard
author_rank: Super Contributor
timestamp: January 02, 2022, 10:34:58 pm
content: I agree with the storage efficiency not mattering all that much, as long as it still provides more net energy than without. (Since it's made to store energy that we otherwise would "lose".)Now, a relatively low efficiency would be OK - the bad thing is bold and false claims, that doesn't bode well for the company promoting this. And, of course, we have to consider the cost of maintenance. If it happens to be on the high side, then it could eventually be a net loss over the whole operating life.

author: gnuarm
author_rank: Super Contributor
timestamp: January 03, 2022, 01:28:11 am
content: Quote from: IanB on January 02, 2022, 05:49:52 pmNot quiet correct. The heat is removed intentionally. This way the PV curve is isothermal. If you don't remove the heat as it is generated the PV curve is different. A larger portion of the work input will go into the compression. If you leave the temperature high during compression, ultimately the pressure drops as the temperature drops and you lose work stored in the PV curve.QuoteSurrounding ground, water, whatever. The point is the universe is a heat sink and the heat of compression is removed during compression yielding an isothermal PV curve.What is important as well is that the expansion be isothermal which happens with the heat sinkprovidingenergy which ends up compensating perfectly with the heat lost in the isothermal compression curve.If the compression is adiabatic, you end up at a lower pressure (after cooling) than in the isothermal case and the resulting work recovered is less.QuoteI find it amusing that there is still much doubt. The system is amazingly simple once it is understood. I can't find any practicalities that would make it a problem. I'm assuming they have the material issues well in hand. Considering man has been burying tanks in the ground for a very large number of years I expect there won't be any surprises in that. The rest of the system is not new technology unless they decide to use some new turbine or pump to get another two percent efficiency improvement.A ground source heat pump is nothing like this in that it uses a one way flow of heat and simply uses the ground as a heat sink. There is no cycle of heat input and output, so not really relevant. The advantage in the ground source heat pump over using an air heat sink is simply that it uses less energy to transfer the heat (lower thermal resistance) and the ground temperature is much more stable. An air system gets a double blow from temperature extremes in that more heat is required to be moved and more work is required to move that heat against a larger temperature differential.

author: PlainName
author_rank: Super Contributor
timestamp: January 03, 2022, 01:41:20 am
content: QuoteSlightly off topic, but... can't the ground source heat pump wear out? That is, the ground gets colder and colder as the heat is sucked out? With an air source, there's always a bit more air around the corner even if the temperature varies a bit (usually, what goes up must come down).

author: gnuarm
author_rank: Super Contributor
timestamp: January 03, 2022, 01:57:22 am
content: Quote from: SiliconWizard on January 02, 2022, 10:34:58 pmEfficiencydoesmatter, the only question is to what extent. To compensate for a 10% loss in the storage, the entire system must be 10% larger, generation and storage, to achieve a given amount of energy to be delivered when needed. So clearly this efficiency is not unimportant. It just has diminishing returns as 100% is approached. Running a storage system with 50% energy efficiency would require double the capital and land, etc as a system very close to 100% efficient. 90% is a very good number, 80% is acceptable. Even batteries are not much better than 80%.I'm still surprised there are questions of efficiency or maintenance costs. This is not really different from pumped hydro storage. The only question I've seen is about the efficiency over the operating pressure range. We don't know what that range is so it's hard to evaluate efficiency over the range even if we had perfect knowledge of the electrical and mechanical components.It would be interesting to see more details on this system.

author: gnuarm
author_rank: Super Contributor
timestamp: January 03, 2022, 02:09:44 am
content: Quote from: dunkemhigh on January 03, 2022, 01:41:20 am"Wear out" is an odd term for this, but not if it is sized correctly. Heat flows in the ground just like anywhere else. The ground immediately by the coils will be the major impedance to heat flow, but as you radiate out from the coils the flow spreads out effectively reducing the impedance. So the amount of heat that can be sunk this way is quite large and is more a matter of flow rate than a total quantity.I believe it was here that someone discussed a storage system that collected solar directly as heat and stored it in the ground using vertical pipes. I can't remember any details really, but it was in a housing community with the collectors on the garages to maintain an appearance to the street and a community storage facility. The idea was to supplement the home heating system by providing warm air/water to the house rather than having to deal with the temperature outside. This was in a northern clime so cooling was less important, Canada I believe. The analysis of this system showed how the heat was conducted very well within the arrangement of pipes. Hmmm, I may be arguing with myself. They were storing the heat in the ground, so at some point it became an insulator. I think this was because the area was large enough that the losses around the periphery were not so large compared to the heat stored in the bulk. This thing stored energy through most of the winter! I would also point out that water/air based heat systems are pretty effective and inexpensive. That's the reason why this system was practical.

author: bdunham7
author_rank: Super Contributor
timestamp: January 03, 2022, 02:24:36 am
content: Quote from: gnuarm on January 03, 2022, 01:28:11 amWell, we were only discussing efficiency, but since you asked, practicalities would include energy density and capital cost. Unless I screwed up the calculations, if you assume an tank pressurized with air at 10 bar and then pumped up with water to 3X or 30 bar, you get an energy density of about 3 kWh/m3. So you need to build a corrosion-proof (interior and exterior) tank with a working pressure of 450psi--how much do those cost per cubic meter? So you have your tanks, lets say they are a bit over meter in diameter and 30 meters long, which is a good way to build a high-pressure tank. You can now store about as much energy as an EV battery. Maybe I goofed somewhere.

author: IanB
author_rank: Super Contributor
timestamp: January 03, 2022, 02:28:00 am
content: Quote from: gnuarm on January 03, 2022, 01:28:11 amI'm not sure what part you think is not correct here. To maintain isothermal conditions, heat has to flow from the gas into the surroundings (tank walls, soil, water, whatever). Whether intentional or unintentional, the heat still flows.Now if we treat air as an ideal gas (which under these conditions it practically is), then the enthalpy of the gas is independent of the pressure. That means the heat that flows into the surroundings did not come from the gas itself, it came from the work of compression. Some of the work done pumping water into the system is lost as heat into the surroundings. Isothermal compression (and expansion) can only be achieved by heat transfer.The interesting bit for a complete compression/decompression cycle is if you can get that heat back again. Because when a gas expands it cools down, and to maintain isothermal expansion you have to put heat back into it. Which is the next paragraph...QuoteTrue, but the parallel problem occurs with adiabatic expansion too, and we need an isothermal process both ways.Here is where we go beyond thermodynamics and into heat transfer. To maintain isothermal conditions in the gas during compression and expansion, there has to be very effective heat transfer between the air and the surroundings. Very effective means large surface area or high heat transfer coefficient. Static air contained inside a walled vessel may not exhibit a high enough heat transfer rate to maintain the isothermal conditions that are desired. This is where the engineering comes into it.QuoteThe relevance of the ground source heat pump is that it needs good heat transfer between the working fluid and the surrounding ground. If our system being considered here is to operate isothermally, it also needs good heat transfer. Nothing in the video talks about that. I know it is a marketing thing and doesn't have much technical content, but still the matter must be considered.

author: gnuarm
author_rank: Super Contributor
timestamp: January 03, 2022, 03:45:14 am
content: Quote from: bdunham7 on January 03, 2022, 02:24:36 amWhy do you want to debate made up numbers? An EV like battery is not a cheap device. They are running around $125 per kWh so 100 kWh would be $12,500, not installed, plus the conversion electronics, so say $25,000 as a wild guess. Do you expect the 30 meter tank would be significantly different? I have no idea. Installing 100 of these may end up fairly inexpensive from a factory that does 1,000 such builds a year.It's hard to find prices on such tanks, but the prices I found were in the ballpark of the lithium battery without the electronics. The price goes down considerably with quantity. I expect in the end the cost is as much installation as the tank. I bet in these are very price competitive with batteries. Batteries may come down in price with time, but that's some years away.Vanadium flow batteries are the likely grid storage device if you want to stay electrical. They are still new, but the first installations are being done now. They have the property of storing electrolyte to be run through the battery not entirely unlike a fuel cell, but reversible. So the storage capacity is not determined by the actual cell, rather the size of the tank. I wonder if vanadium is a difficult to mine mineral?

author: gnuarm
author_rank: Super Contributor
timestamp: January 03, 2022, 04:03:36 am
content: Quote from: IanB on January 03, 2022, 02:28:00 amThis...QuoteWe are intentionally tossing this heat in order to optimize the energy going into the PV of the gas.QuoteOk.QuoteIf you say so.QuoteYou can say you are "getting that heat back", but the reality is you aren't. You are getting heat from the isothermal expansion and the surroundings. It's not the heat you lost in the isothermal compression, it's just heat from the environment.QuoteTrue, but the parallel problem occurs with adiabatic expansion too, and we need an isothermal process both ways.Yes, that's what I said, no?QuoteHumpty Dumpty said, a word "means just what I choose it to mean—neither more nor less." "Effective" depends on the context and in this context we don't need large surface areas or radiators or high thermally conductive materials because the rate of heat generation is limited. The tanks aren't filling in 10 minutes. They are filling in a work day or maybe a full day or maybe a week. So how hard is it to allow the heat produced or absorbed to be exchanged in 8 hours or more?QuoteI believe that is a fallacy, the comparison between the two systems. A heat pump has to exchange the full heat flow into the ground or air. This system has to exchange the heat from compression/expansion which is only a part of the total energy flow. Also, you seem to only seeAtank. The system is composed of many tanks with each one handling a small part of the total power flow. So each very large tank only needs to handle a small heat flow. An earlier estimate per tank was 100 kWh. Over an 8 hour day that would be 12.5 kW. I think the air in a 30m3tank can exchange the level of heat produced without a significant temperature rise.

author: Kim Christensen
author_rank: Super Contributor
timestamp: January 03, 2022, 04:27:39 am
content: Quote from: gnuarm on January 03, 2022, 01:28:11 amWell, it is simply more efficient to have doubt than belief.When you think of how many times we are bombarded with false claims of new battery technology, cold fusion, and other miracle solutions, is it any wonder that people are skeptical?

author: bdunham7
author_rank: Super Contributor
timestamp: January 03, 2022, 04:33:36 am
content: Quote from: gnuarm on January 03, 2022, 03:45:14 amWell I do have a bit of experience with tanks, so a 100-foot long tank with a working pressure of 450psi, so a test pressure of at least 600psi. Corrosion resistant, safety certified (it's a BIG bang when something like that fails) and suitable for underground. Hmmm. Would that cost more than $12,500? Hmmmm. Yeah, I'm pretty sure it would. Just the postage might be more than that, actually. But feel free to shop around. Or just click 'Investors' if you're sold. I'm sure they will respond. Maybe they'll even give you some more details!Here's a 200 cubic meter tank on AliBaba for propane (about half the pressure, above-ground and won't tolerate water) for $80K. Perhaps there's a volume discount, although I doubt they have free shipping.https://m.alibaba.com/product/62415230410/ASME-200000l-propane-gas-tank-200.html?__detailProductImg=https%3A%2F%2Fs.alicdn.com%2F%40sc04%2Fkf%2FH41f306ee0add40f29d0b4f9b3902d343Q.jpg_200x200.jpg

author: gnuarm
author_rank: Super Contributor
timestamp: January 03, 2022, 04:38:10 am
content: Quote from: Kim Christensen on January 03, 2022, 04:27:39 amSkepticism is good when you don't understand or are not given the information to consider something new properly, but so far there is little about this that is not clear and actually well established principles. There's no rocket science involved, no dark matter, no new technology really. It is existing knowledge, technology and principles that we simply need to understand.The economics are not known for this system. But I can't see anything to even suspect without gathering some information. It's not like pressure tanks aren't already very commonly produced, installed and operated over decades.They are presently building systems. If the idea is not so good, we will find out soon enough.Someone once told me that increasing the production quantity of a thing ten fold cuts the cost in half. I'm not sure this is an absolute rule, but if these things take off I expect to see "gigafactories" producing them at very affordable prices. I really like the fact that they are low tech. Every problem doesn't require high tech.

author: gnuarm
author_rank: Super Contributor
timestamp: January 03, 2022, 04:53:07 am
content: Quote from: bdunham7 on January 03, 2022, 04:33:36 amWhy would you look at a tank that isn't suitable for the application when you don't even know details of the application??? I found tanks at much lower prices that aren't in Mozambique. Not sure why you are looking at 200m3when we were talking about 30m3. Given that this tank would be equivalent to 7-100 kWh batteries, $80,000 is not bad at all. The one new thing in this system is the tank actually. Well, it's not metal anyway. They don't give specifics, but its "polymer" based.I suppose there's no point in discussing this further. We've uncovered all the information available and people are inventing information. There's also the call for me to invest, so essentially "ad hominem". Are we all good? Or is there something else factual to discuss?

author: Kim Christensen
author_rank: Super Contributor
timestamp: January 03, 2022, 05:11:05 am
content: Quote from: bdunham7 on January 03, 2022, 04:33:36 amIt looks like they are using inflatable polymer tanks which are placed in a hole, surrounded by rebar, and covered with concrete. Claimed pressure is 40bar. (580 psi)PV magazine article.

author: IanB
author_rank: Super Contributor
timestamp: January 03, 2022, 05:24:54 am
content: Look, I'm not trying to prove anyone right or wrong here, I'm just pointing out certain details that have to be considered in the design of such a system.Quote from: gnuarm on January 03, 2022, 04:03:36 amThat is a problem. Because for an ideal gas, increasing the pressure isothermally does not increase the energy stored in the gas. For an ideal gas, both internal energy and enthalpy are a function only of temperature. Reference here, but you can find others:https://www.ecourses.ou.edu/cgi-bin/ebook.cgi?doc=&topic=th&chap_sec=03.4&page=theoryFurthermore, this has an interesting consequence for isothermal compression.All of the work done compressing the gaswill be lost as heat to the surroundings. If you pump 100 kWh into your storage system isothermally, 100 kWh of heat will flow through the walls of the tank and into the ground. This comes from the thermodynamic relation that dU = Q + W, and if dU = 0, then Q = -W. Reference here:https://en.wikipedia.org/wiki/Isothermal_process#:~:text=It%20is%20also,of%20ideal%20gases.QuoteSee below.QuoteThis is true, but it is also a matter of accounting. If I lend you $100 today, and you pay me back $100 tomorrow, is it the same $100? Is it important?If I store 100 kWh into my system and 100 kWh disappears as heat lost to the surroundings, then if I have any hope of getting some of my 100 kWh back again, I need to get at least some of that heat back. Is it the same 100 kWh? Yes, from an accounting point of view it is, or the books won't balance.QuoteSee, I don't know. Maybe yes, maybe no. Without doing some engineering calculations and running some numbers, I couldn't say. However, I can say it is something to be considered in the system design.QuoteIt's not a matter of doubt. Clearly the system can work with some level of efficiency. I don't think any of us know the actual numbers, though.QuoteI really don't know without doing some calculations. Aren't you doing what you complained about with others, taking some numbers and supposing results without supporting analysis? Do keep in mind that for heat transfer to occur, there has to be a temperature difference. If the temperature does not rise in the tank there can be no heat exchange with the surroundings. So the temperature must rise at least somewhat.

author: PlainName
author_rank: Super Contributor
timestamp: January 03, 2022, 08:02:59 am
content: QuoteIf the alternative is 0 storage then being only 50% efficient isn't that bad, is it? And on the plus side, there is plenty of scope for improved versions later on.

author: Haenk
author_rank: Super Contributor
timestamp: January 03, 2022, 10:29:30 am
content: Funny thing about their business model:They quote a typical deal size of 250-350k USD. For an industrial installation, that sounds almost like "free". (For comparison, that would be the same cost as a small flat (50m2) in a low-medium attractive city in some larger building complex in Germany. I don't think building costs will be cheaper in Israel...)

author: gnuarm
author_rank: Super Contributor
timestamp: January 03, 2022, 02:03:22 pm
content: Quote from: dunkemhigh on January 03, 2022, 08:02:59 amZero storage is not the alternative. There are many forms of energy storage available today.That's also not the way engineers and businessmen would look at it. The spec would be X kWh of energy to be delivered at Y kW rate. With a 50% efficiency you would need twice the size of everything making the project cost twice as much including both the storage since you need a fixed amount of energy output and the generation since you lose half of this in storage so you must make twice as much to start with. As a result the system costs twice as much and the energy costs twice as much per kWh. This is a major issue for converting to renewables. They need to be priced in the ball park with fossil fuels for many to accept them.If your car got half the fuel mileage, would you think that was ok? You'd be shopping for a new car. No?

author: gnuarm
author_rank: Super Contributor
timestamp: January 03, 2022, 02:44:55 pm
content: Quote from: Haenk on January 03, 2022, 10:29:30 amI don't get your point? I didn't see the quote you mention, but it makes sense they would start out with fairly small installations as they are a new company and no one is going to give them a $100,000,000 contract to start. Where did you see these numbers? Ah, I found it. That is for the Airsmart system which is a different product for storing compressed air in a factory. So yeah, that's not going to be as large a system as grid storage. Under the Airbattery they list Typical deal size: $18M-$22MDoes that suit you better?https://www.google.com/search?client=firefox-b-d&q=250+site%3Aaug-wind.com

author: Kleinstein
author_rank: Super Contributor
timestamp: January 03, 2022, 03:06:37 pm
content: The cost for a tank are quite substantial. A common pressure for compressed air is some 10 bar. This would give around 1 kWh/m³, maybe a bit less if part of the volume is occupied with water and maybe 90% efficiency for the conversion back. I somewhat doubt one could get a 10 m³ tank for less than $1500, which would be about the price for Li Cells. The costs for the tank would not significant change with scaling to a different size or pressure. For the isothermal concept to work, one may even have to keep the diameter small, so more like a stretch of gas pipeline than a conventional tank as a comparison. Even than it would be isothermal only when used slow.Efficiency is a factor, but not that dramatic when for longer time storrage and if the costs per kwh are low. After long time storrage the energy put into the system is only a part and maybe a smaller part of the costs. It is like getting the energy when the price is lowest and using the energy when the price is highest. Currently the ratio between the highest and lowest costs is quite large, even if no counting the short time extremes. So 50% efficiency could still be OK if the storrage itself is cheap.A more expensive system for more short time storrage should be reasonable efficient to use it more on a daily bases, whith less difference in the price.In the end the available storrage systems would set that ratio.

author: bdunham7
author_rank: Super Contributor
timestamp: January 03, 2022, 03:43:13 pm
content: Quote from: Kim Christensen on January 03, 2022, 05:11:05 amThat's a more interesting article and it looks like their primary expertise is compressed air. Their tanks are interesting too and they've solved the corrosion problem, but they still look fairly expensive to construct. It looks like their niche is combined systems for facilities that use a lot of compressed air, where recovering and saving power is an issue of big money. That makes sense. I guess we'll see if they can successfully branch out into straight-up energy storage.

author: IanB
author_rank: Super Contributor
timestamp: January 03, 2022, 05:20:42 pm
content: That article is indeed illuminating, but it contains some interesting contradictions.It contains lots of discussion about heat dissipation and heat absorption in the water, and in the concrete surroundings, which I would expect, but it also contains contradictory statements about "generates minimal heat", "minimal heat produced in the isothermal compression process", and "compress the air without generating any heat", which are thermodynamically inaccurate.These statements are contradictory because of Boyle's Law of gases. The pressure energy stored in compressed air is approximately equal to pressure times volume, and Boyle's Law for isothermal compression states that pressure times volume is constant (P1v1=P2v2). This effectively says that you do not store "pressure energy" in air by compressing it isothermally. Instead, if you pump 10 MWh of energy into the system isothermally, the 10 MWh of electrical energy gets turned into heat. This is not "minimal heat" in my book, it is "maximal heat", sinceallthe supplied electricity becomes heat in the system.(Thermodynamically, you have the first law of thermodynamics which says that ΔU=Q−W, where ΔUis the change in internal energy of the system,Qis the heat added to the system, andWis the work done by the system. Since ΔUis zero for an isothermal change in an ideal gas, it follows that compression work is exactly balanced by heat generation.)When you want to get your energy back out of your battery, you have to turn that 10 MWh of heat back into mechanical energy to turn the turbine. This effectively turns the whole system into a heat engine, and there are well known thermodynamic principles that apply to heat engines which likely have relevance here. (In particular, there is the Carnot efficiency, which is the maximum theoretical efficiency of any heat engine, given by \$\eta = 1 - \sqrt{T_c / T_h}\$ . If the hot and cold temperatures are close to each other, as would be implied by an isothermal system, then the maximum efficiency would approach 0%. That would not be encouraging, and really has me thinking.)Overall, I think it is fair to be skeptical about the system. The company may have expertise in compressed air storage, but does it have sufficient expertise in energy storage?

author: PlainName
author_rank: Super Contributor
timestamp: January 03, 2022, 05:51:27 pm
content: QuoteHalf mileage of what? A better question is whether the cost of the fuel is more bearable than the time taken to walk, or the danger and messiness of cycling. If I already have a car andthensomeone brings out one with better economy, I might well look at it (but still think the exchange of mileage vs gadgets not worth it).So, for this airbattery it's pointless to go on about efficiency because there is not alternative similar system to compare it against. The efficiency here is what it is - you want an air battery, that's what you have to pay.Instead, you should be asking whether the costs of the airbattery are better or worse than, say, a Lion stack, a hydrogen generator, whatever kind of storage might be an alternative. But then you also have to factor in that this is underground and you can then use the surface for other projects, which you couldn't do with many alternatives.I think you have succumbed to that complaint of running numbers without considering what they meanEdit: forgot to mention that one big alternative, which was already stated as a reason for having this setup, was lack of storage space so 100% loss of energy when the sun or wind goes down.

author: IanB
author_rank: Super Contributor
timestamp: January 03, 2022, 06:40:43 pm
content: Quote from: dunkemhigh on January 03, 2022, 05:51:27 pmBut there is, though:https://energystorage.org/why-energy-storage/technologies/compressed-air-energy-storage-caes/

author: bdunham7
author_rank: Super Contributor
timestamp: January 03, 2022, 07:18:25 pm
content: Quote from: gnuarm on January 03, 2022, 04:53:07 amEither a math or explanation error on my part. If you fill the tank with water to compress the air, the final air volume is some fraction of the actual volume of the tank. I think I had calculated that tank would have about 100kWh, given it's lower pressure limits. And why not Mozambique? I'm sure they need energy too.Now that I've read more, I see that they do have a niche product that probably appeals to facilities that use a lot of compressed air. The system appears to be more complicated than just filling individual tanks in parallel. It looks like they use the water a piston to actually provide compressed air for more than energy storage. With two tanks, you can pump the water into one and then the other in succession to work as a very slow two-cylinder almost-isothermal compressor, provided you mind the water temperature. Whether this can be adapted to compete in the pure energy-storage arena is another matter.

author: PlainName
author_rank: Super Contributor
timestamp: January 03, 2022, 08:22:26 pm
content: Isn't that the same thing? Just without the flash investor flytrap.

author: IanB
author_rank: Super Contributor
timestamp: January 03, 2022, 08:43:10 pm
content: Not, it's not quite the same thing. One thing is storing compressed air, the other thing is storing energy.It's counter-intuitive, but compressed air itself doesn't actually store any energy. You can see this a bit from the link I provided above:https://energystorage.org/why-energy-storage/technologies/compressed-air-energy-storage-caes/Here is a quote, with an important part in red:QuoteIt is essentially saying that power you feed in becomes heat, and to get power back out you need put heat back in. If you don't manage your heat, you don't get back the energy you expect from the system.The thermodynamics of the system doesn't change whether you use traditional compressors, or whether you pump water into underground tanks. You can't use words like "isothermal" and use that to somehow change the laws of physics. If you are compressing air for energy storage, you have to manage your heat.

author: PlainName
author_rank: Super Contributor
timestamp: January 03, 2022, 09:40:17 pm
content: I think we might be heading for an angels-on-a-pin back-and-forth. Either it's a comparable alternative or it's not, and it looks like it's not really (the only similar aspect is air being compressed). But that doesn't actually matter since the efficiency is going to be worse, isn't it? So whatever the airbattery efficiency is, this isn't going to make it better and might cost more to boot.

author: IanB
author_rank: Super Contributor
timestamp: January 03, 2022, 09:58:26 pm
content: I'm seeking illumination and enlightenment here, and I am leaning towards a conclusion that the AirBattery thing might be a very inefficient method of energy storage. If so, you would be correct, it will not do better than traditional compressed air energy storage systems, and might do considerably worse. It might be no alternative at all, and the company promoting it might fail to to deliver on their promises.

author: tszaboo
author_rank: Super Contributor
timestamp: January 04, 2022, 10:58:38 am
content: Quote from: Kleinstein on January 03, 2022, 03:06:37 pmA common 40 foot steel intermodal tank goes for about 80K USD new. Their internal is about 40 cubic m. These are not pressurized, they are only good for about 4 bars. Composite tanks are more expensive. High pressure tanks are more expensive probably. For fixed installation, maybe it is cheaper, because they don't need the frame for the cranes, but I don't think that's the expensive part.

author: gnuarm
author_rank: Super Contributor
timestamp: January 04, 2022, 11:35:22 am
content: Quote from: IanB on January 03, 2022, 08:43:10 pmI don't know what is going on with you. You seem to understand the concept of an isothermal cycle, but then you say stuff like this. It is clear that you literally do not understand the laws of physics. Or maybe you are not saying what you seem to be saying. After all, "manage your heat" is not a very technical description.An isothermal cycle requires the heat of compression to be released into a heat sink, i.e. virtually no temperature change. The expansion part of the cycle then recovers heat from the heat sink so that the full energy added to the system is recovered in the cycle.Is there anything about this that requires further "management" of the heat?

author: Kleinstein
author_rank: Super Contributor
timestamp: January 04, 2022, 12:51:27 pm
content: To get the heat exchange from the air to the thermal storage needs time or small dimensions. So you can't compress the air fast in large tank. With not much pressure the water (e.g. 1/2 filled with water) in tank would be OK to take up the heat with not too much loss in efficiency, but it take time for the air to heat up the water. This would mean a more slow operation, with a limited power to charge or dischrage if there are no special means (e.g. fans) to accelerate the heat exchange. So isothermal operation comes at a price, especially with larger tanks. Even if only a few degrees of temperature rise some if the heat may get lost to the environment.Compressed air in steel tanks is already non competative as storrage - half filled with water the costs about double, though it can slightly improve the efficiency.

author: Ian.M
author_rank: Super Contributor
timestamp: January 04, 2022, 01:32:16 pm
content: A small correction: "So you can't compressor expandthe air fast in large tank."Its therefore just as difficult to get energy back out quickly without loss of efficiency.

author: madires
author_rank: Super Contributor
timestamp: January 04, 2022, 02:00:24 pm
content: Maybe I'm wrong but I'd think that the compressed air is expanded in the turbine generator.

author: Ian.M
author_rank: Super Contributor
timestamp: January 04, 2022, 02:10:31 pm
content: Then you'd need to add a lot of heat at the turbine, which, as discussed above, leads to poor efficiency . . .Its also mechanically difficult to add heat efficiently in-between spinning blades unless you resort to burning fuel in the turbine.

author: IanB
author_rank: Super Contributor
timestamp: January 04, 2022, 03:48:37 pm
content: Other points of note about the heat transfer: There is a system of connected tanks so that one tank fills with water and displaces the air through a pipe into a separate air tank. So there is limited contact between the air and the water. They also mention the tanks are made from a polymer material (a thermal insulator), and surrounded by concrete (also a thermal insulator).What I would expect to read in their blurb is some description of "how we arrange for the heat sink to work and how we arrange for the heat flow to be sufficient to support the power requirements". This is what I have not seen, therefore it remains an open question.It is not safe to make broad statements like "the process is slow enough for thermal equilibrium to be achieved" without doing some kind of engineering calculations on heat transfer areas, heat transfer coefficients, and required rates of heat transfer. Engineering is all about the numbers. Maybe AirBattery have the numbers, but if so they are not visible to us.

author: bdunham7
author_rank: Super Contributor
timestamp: January 04, 2022, 04:02:34 pm
content: Quote from: gnuarm on January 04, 2022, 11:35:22 amJust the understanding that heat transfer requires a temperature differential. The claims made here are basically based on 1) matching large state-of-the-art pumping and generation systems at a much smaller scale and 2) having vanishingly small losses in the 'isothermal' compression and expansion processes. If you look at their process vs regular air compressors, I think it is quite plausible that it is much more efficient for producing compressed air, given the tremendous inefficiencies in more conventional compressed air systems. However, if you need to reduce the losses to 1 or 2 percent, you have to rely on very small temperature differentials. Perhaps they have some extra trick up their sleeve that they aren't telling us about.

author: gnuarm
author_rank: Super Contributor
timestamp: January 04, 2022, 05:15:50 pm
content: Quote from: Kleinstein on January 04, 2022, 12:51:27 pmThere is no rush to fill any one tank. This is for grid storage and the time scales would be significant, set by the application details. Solar would need to charge during half the day and supply power the other half. Or possibly they would want to charge during the peak four or five hours and discharge during the late afternoon peak, hours. With wind power the time scale would be on the order of days!No one is interested in storage that only provides power for 15 minutes. The emphasis is not on power, but on capacity. No rush to fill the tanks. So with the many tanks, all filling and emptying in parallel, the tanks would fill slowly.I don't get why people keep talking about this aspect? The rate of pressurizing and depressurizing is NOT an issue for grid storage. The primary issue is capacity per unit dollar.There's also no reason to "half fill" the tanks with water. I think you are trying to raise the pressure to improve the PV curve, but that can be done by pressurizing the tank with more than 1 atm of air pressure without half filling with water.Also, why are you talking about steel tanks???

author: gnuarm
author_rank: Super Contributor
timestamp: January 04, 2022, 05:23:58 pm
content: Quote from: madires on January 04, 2022, 02:00:24 pmCorrect, if you are talking about the Airbattery, you are wrong. That's why there is no air compressor. Water is the medium that transfers the pressure to the fluid turbine.The Airbattery is pumped hydro storage. Little different from pumping uphill to store energy with a recovery when the water flows downhill. The difference is by using pressurized tanks the land requirements are reduced and simplified (no elevation requirements) and the same land can be used for other purposes such as farming.The big issue with pumped hydro is it either requires a particular geography to obtain the storage requirements and elevation as well as the water. The Airbattery seems like a win-win-win to me.

author: gnuarm
author_rank: Super Contributor
timestamp: January 04, 2022, 06:18:22 pm
content: Quote from: IanB on January 04, 2022, 03:48:37 pmYeah, this does seem to be a disconnect. If they are pressurizing many air tanks (something I had not seen in the video before) the heat is generated in all the air tanks. This is still not a deal-breaker. The other tanks can get rid of the heat through the tank walls. Or perhaps they also contain water to absorb the heat. The insulating properties of concrete are not as significant as you seem to claim with a rather low R value. In fact concrete has a high thermal capacity making it a good heat sink which may be why they bother to use it rather than fill dirt. Also, keep in mind that heat is being generated in many tanks so they all disperse the heat in parallel.I can't say I fully understand their video. They show 16 tanks that fill with water, which I would think would define the storage capacity. They also show what appears to be a variable number of air tanks which they appear to claim defines the system capacity. Perhaps they are showing just the air tanks in the video while the number of hydro tanks also changes for capacity. Nope, they specifically claim they increase capacity by adding air tanks alone. I don't get this.This explains why the system they show being constructed has one tank perpendicular to several tanks aligned in parallel, 1 water tank and the rest air tanks. The illustrations in the video show 16 water tanks for a much larger number of air tanks, so I have to assume they are deployed in a fixed ratio. The purpose of the air tanks is to diminish the variation in pressure as the system is charged and discharged making the pumps and turbines more efficient.QuoteHave you asked? This is the sort of information that would not be understood by most people involved in the purchase decision and not of concern to those would would understand. Why? The same reason I don't care about the details of angles and RPM for the variable valve timing in a car I am looking at buying. I want to know the mileage and power, the aspects that directly affect me. For the Airbattery it comes down to storage capacity per dollar and the power rating per dollar, installation time, land occupied and of course, reliability.Expecting the company to provide details of the thermal properties of the container and concrete is a bit much. They have built these, so obviously they have the data, likely both calculated and measured.

author: gnuarm
author_rank: Super Contributor
timestamp: January 04, 2022, 06:25:34 pm
content: Quote from: bdunham7 on January 04, 2022, 04:02:34 pmThey don't need tricks. They simply fill the tanks slowly. Yes, it's that simple.I expect they would lose some efficiency in a small system where it would likely be needed to fill more rapidly. For most applications the need is for capacity that lasts over a significant period of time, not short term, high power.

author: IanB
author_rank: Super Contributor
timestamp: January 04, 2022, 06:42:13 pm
content: Quote from: gnuarm on January 04, 2022, 06:18:22 pmOne would hope so. We know they have built compressed air storage facilities. I'm less clear whether they have built operational grid electrical storage facilities.There is a legitimate reason for asking questions. If the battery is being discharged, and supplying 1 MW of power to the grid (for example), then the battery has to provide 1 MW or more of heat input to sustain that output. That heat could either be stored inside the battery, or it could be supplied from outside (from the surroundings). Is it feasible that the required heat rate can be achieved with the design illustrated? That is all that is being debated here.Since they have committed to deliver a working system to at least one major customer, let's hope they have done the engineering calculations correctly and they are not going to be hugely embarrassed.Quote from: gnuarm on January 04, 2022, 05:23:58 pmIt's really a huge difference. With pumped hydro storage, electrical energy is converted to gravitational potential energy. With AirBattery, electrical energy is converted to thermal energy (heat). For AirBattery to make sense, there does need to be an understandable thermal model of the system.(It's slightly unintuitive, but compressed air itself is not a good energy store. One ton of air at 1 atm and 60°F contains about the same amount of energy as 1 ton of air at 20 atm and 60°F.)

author: gnuarm
author_rank: Super Contributor
timestamp: January 04, 2022, 09:48:33 pm
content: Quote from: IanB on January 04, 2022, 06:42:13 pmBut there are so many parts of this that people don't understand. Your statement above is not correct, so how can you possibly estimate if the system is feasible. It does not take 1 MW of heat to produce 1 MW of power at the output of the system. You repeatedly make mistakes like this in the basic thermodynamics of the system.QuoteYeah, I suppose they are going off half cocked without even building a prototype. I'm sure the system in the video is just a highly realistic CGI and they actually don't even know how to pour concrete.Your concerns seem to me to be at the far end of reasonable. I don't doubt they have done the basic design calculations correctly. Then there is the fact that this is really just another form of a pumped hydro facility. My only concern is that I don't understand their statement of being able to add capacity by adding air tanks but not hydro tanks. I'm missing something about that.QuoteYou still don't understand the thermodynamics of the design. I don't know what to tell you. I'm tried of trying to explain it. The Airbattery does have an understandable thermodynamic model. That doesn't mean everyone will understand it. You have to understand thermodynamics before you will understand this system.QuoteAgain, wrong. The problem with compressed air is that it is normally created in a high volume air compressor which creates too much heat, too quickly for the process to be isothermal, rather it is adiabatic. This turns more of the input energy into heat which is lost irrecoverably without special techniques. In long term storage this heat is always lost.Your analysis of the "energy" in air at different pressures and the same temperature is pointless. What is significant is the difference in energy vs. the difficultly in producing that difference in energy. By "difficulty" I mean the complexity and cost of the system. In other words, the amount of energy storage vs. the cost.BTW, what makes up the "energy" of your air in this comparison? Obviously it is something other than PV.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 04, 2022, 10:45:39 pm
content: Quote from: gnuarm on January 04, 2022, 05:15:50 pmThe speed depends on the size, the larger the tank (vertical dimension) the slower the filling needs to be. Depending on the size 4 hours may not be slow enough. With the high price such a system would only be usefull for very frequent use, like daily fill and empty and this would need rather fast fill and discharge to also cover the short time. With more than 1 hour needed this would limit the use.Thermal diffusivity of air is 19 mm²/s at normal pressure, going down with increasing pressure and thus more like 2 mm²/s at 10 bar.So 2 mm distance would need some 1 second time scale. Going up like the square the distance. 20 cm would thus be a time scale of some 3 hours.So to no suffer from reduced efficiency the distance in air should be less than some 20 cm to get a 3 hour charge time. With 1 m diameter this would be more like a few days for nearly isothermal charge / discharge.I took steel tanks as the comparison, as for compressed air steel tanks are still the current mature technology and typical choice. Chances are alternatives would not be much cheaper, as they are not in large scale use, except caverns in salt.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 04, 2022, 10:49:08 pm
content: Quote from: gnuarm on January 04, 2022, 09:48:33 pmYou are correct : it does not take 1 MW of heat transfer. Air is not an ideal gas and compression generates a little (AFAIR some 10%) more heat. The 1:1 ration is still a good approximation.

author: PlainName
author_rank: Super Contributor
timestamp: January 04, 2022, 11:43:57 pm
content: QuoteWould it be the same for a horizontal change? If it depends on surface area then surely a longer tank would be better than a taller one.

author: IanB
author_rank: Super Contributor
timestamp: January 04, 2022, 11:46:41 pm
content: Quote from: gnuarm on January 04, 2022, 09:48:33 pmThis is correct, of course. It takes more than 1 MW since no system can be 100% efficient. I'm just using round numbers for the sake of discussion.QuoteYou have to explain it using appropriate equations and thermodynamic laws, as I have done above.We have the First Law of Thermodynamics, which is fundamental. It states that:ΔU = Q − Wwhere ΔU is the change in internal energy of the system, Q is the heat added to the system, and W is the work done by the system.Since ΔU is zero for an isothermal change in an ideal gas, it follows that compression or expansion work is exactly balanced by heat generation or absorption.For every unit of work you want to get out of the system, you have to put the equivalent amount of heat into the system.Air behaves very closely to an ideal gas at room temperature and pressures up to 50 atm and beyond.QuoteThermodynamics is not affected by the speed at which things happen. The fundamental laws apply at any rate, fast or slow.The heat generated in an air compressor does not happen because the air is being compressed at a fast rate, it happens simply because the air is being compressed. You can compress air as slow as you like, the same heat will be generated.(Adiabatic means exchanging no heat with the surroundings, isothermal means exchanging enough heat with the surroundings to keep the temperature the same. Processes can be fast and adiabatic or slow and adiabatic. They can be fast and isothermal, or they can be slow and isothermal.)QuoteIf you want the energy to be PV, or pressure times volume, then the appropriate law is Boyle's Law of gases.If you change the pressure of an ideal gas isothermally, the PV product is constant. If you double the pressure, you halve the volume, the product of pressure times volume does not change, and there is no increase in "pressure energy" of the gas.If you wish to store energy in a system like this, you have to change its temperature. If you keep it isothermal, you have shot yourself in the foot and you have not stored any energy.Make it real: If I use 1 MWh to compress a volume of air without letting the temperature change, then by definition I have removed 1 MWh of heat from the system (see the first law of thermodynamics above). I have stored no energy at all. My energy storage efficiency has become 0%.The question we are all asking in this thread is, if the "battery" stores 0% of the energy fed into it, how does it work?(Sure, it can store some little bit of energy, in some limited way, but this is meant to be a storage battery for the electrical grid. It has to store many MWh of energy and provide most of it back again.)

author: gnuarm
author_rank: Super Contributor
timestamp: January 05, 2022, 03:28:18 am
content: Quote from: Kleinstein on January 04, 2022, 10:45:39 pmYou mean it would limit the use to the uses that the system is designed for? Yes, that is a true statement.QuoteWhy are you picking a 3 hour charge time? What is your definition of "nearly isothermal"? Why are you not taking into account the turbulence of the air?QuoteThe devil is in the details. It may well be that for this application the polymer tanks are cheaper. Are you considering that the tanks are nearly encased in concrete? Only the upper portion needs to be fully capable of the full system pressure... which we don't know the value of.

author: gnuarm
author_rank: Super Contributor
timestamp: January 05, 2022, 03:29:33 am
content: Quote from: Kleinstein on January 04, 2022, 10:49:08 pmIt has nothing to do with air not being an ideal gas. In your ratio, what is each 1?

author: gnuarm
author_rank: Super Contributor
timestamp: January 05, 2022, 03:45:02 am
content: You seem to be applying the right equations the wrong way. Here's a thought experiment. Tell me what I am doing wrong.If you compress a volume of air with 1 MWh of energy input and you produce 1 MHh of heat in the process, that would imply there is no additional energy added to the gas.The gas is at a higher pressure and a smaller volume than at the start and can be expanded to produce work. If the expansion is adiabatic, no heat flows into the expansion process so this energy must have all been in the gas. If 1 MWh of heat was already released from the compression and more energy is released by the expansion, we have created energy from nothing. Which thermodynamic law does that break? I believe that is the first, no?What's more, the expansion produces a temperature differential to the environment which can be harnessed to produced more work (energy) in a useful form.The 1 MWh heat number from compression is bogus according to the 1st law of thermodynamics. Which one were you applying again?

author: IanB
author_rank: Super Contributor
timestamp: January 05, 2022, 05:07:00 am
content: Quote from: gnuarm on January 05, 2022, 03:45:02 amSeems unlikely, given my area of expertise, but let's continue.QuoteThis is a good start.QuoteYes, this actually is correct. For an ideal gas it is exactly correct, and for a real gas it is approximately correct.The reason that for an ideal gas the internal energy of the gas (the inherent energy it contains) is a function only of temperature. Verify with any reference, such as this one:https://www.futurelearn.com/info/courses/thermodynamics/0/steps/25358QuoteThis is true.QuoteThis is true, also. The gas started out with some energy before we compressed it, due to its temperature. The internal energy of an ideal gas is a function only of temperature, and if the gas started out at some temperature such as 300 K (about 25°C, or 60°F), then it had an internal energy at the start corresponding to this temperature.QuoteNo, we have extracted some of the energy which the gas already had.If we do this, and perform an adiabatic expansion, then we will follow a line of constant entropy on a thermodynamic diagram such as the ones shown here:https://www.oreilly.com/library/view/chemical-engineering-fluid/9781498724449/xhtml/29_Appendix04.xhtml(To read this diagram,his enthalpy (a measure of energy change),sis entropy, and ρ is density.)As the gas expands the temperature will rapidly drop, and before long no more expansion will be possible. Compressing the gas made it possible to get at some of the energy it started with, but at none of the energy we used to compress it. Furthermore, to get any of that energy back into the gas and repeat a cycle, we have to heat it up again.You can do the calculations to verify this, if you are able.QuoteIt breaks no laws. Thermodynamic laws cannot be broken.QuoteIf you used the low temperature of the gas as a cold sink to let heat flow from the surroundings, then yes, you could convert some of that heat into work. But this is not breaking any accounting laws, as you are making use of external heat from outside the original system.QuoteThis sentence doesn't make any sense, so there is no way to respond to it.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 05, 2022, 09:39:27 am
content: Compressed air gives storrage of free energy (as Gibs free energy), but for an ideal gas no actual energy is storred, as the internal energy only depends on the temperature, not on the pressure. The free energy part is the more inportant one, as heat at envirinmental temperature is essentially for free - though it still needs some effort to get the heat in and out.So a compressor that consumes 1 kW of power also produces around 1 kW of heat. The efficiency of the compressor mainly effects the volume of compressed air, but hardly the heat. The way air deviates from an ideal gas is that there is a little extra heat release when compressing the air. So heat is even a little bit higher then the electricity consumed. Another small contribut is condensation of water vapor, that also produces extra heat.Quote from: gnuarm on January 05, 2022, 03:28:18 am3 hours are about 10000 seconds. The calculation is only for the order of magnitude. 1-3 hours would be about the relevant time scale needed for a daily use storrage.Turbulance is difficult to calculate and only works well with higher temperature differences. The closer one is at isothermal the less efficient natural turbulent heat exchange works. The point is that you can't take isothermal for granted, just because there is a liquid plunger and not solid one. It would likely need extra effort, like fans to get closer to isothermal. With the main heat sink / source (water) at the bottom natural convection would not be very effective.Near isothermal would be in a way that only a small part (e.g. 10%) of the heat stays in the gas, so that one is still relatively close to the isothermal efficiency. A full heat transfer would not be possible, as even the water has a limited heat capacity.

author: IanB
author_rank: Super Contributor
timestamp: January 05, 2022, 05:23:56 pm
content: Quote from: Kleinstein on January 05, 2022, 09:39:27 amYes. The free energy of the gas is a measure of its capacity to do work. Increasing the pressure makes it more possible to use some of its internal energy to make it do useful work.For the ideal gas under isothermal conditions, the change in free energy is given by:ΔF= −TΔSAnd the change in entropy is:ΔS= −Rln(P2/P1)IfP2>P1then ΔSis negative and the entropy decreases. Correspondingly, the free energy increases according to the first equation.Workers like Josiah Willard Gibbs did a huge amount in the 19th century to figure these things out and put them on a rigorous mathematical footing.

author: tszaboo
author_rank: Super Contributor
timestamp: January 05, 2022, 06:07:24 pm
content: OK, so something else, the price efficiency of the system again. I've looked at a frame of the video, and it was claiming 10MWh energy storage for about 90 tanks. Let's say these are 40 foot tanks.My low estimate would be 90*80K ~ 7MUSD for the storage, just the tanks. An equivalent battery would be about 1.2MUSD.So it would need a projected lifetime maybe 5x of a battery system to be worth it. I dont know about you, but in my experience, moving parts always break faster than electronics. Also batteries are getting cheaper by the year.LNG stores 16 KWh/Kg, so it would be a 625Kg or about 1600 liter, or 1/25th of the same tank, let's call that negligible, even though LNG tanks are more expensive. So for an P2G LNG system, you can install 7MW extra solar capacity from the same initial investment to offset any inefficiencies.IMHO. This system doesn't make any financial sense. Only to someone who grew up with physics lessons from Looney Tunes.

author: PlainName
author_rank: Super Contributor
timestamp: January 05, 2022, 06:41:06 pm
content: QuoteWikipedia suggest <40% efficiency for P2G2P. And maintenance hassle.

author: bdunham7
author_rank: Super Contributor
timestamp: January 05, 2022, 06:46:36 pm
content: Quote from: dunkemhigh on January 05, 2022, 06:41:06 pmEfficiency isn't as critical if you aren't trying to arbitrage power that you don't produce yourself. If I can trade a 80% efficient storage system for one of 40% but save enough to install double the generation capacity, I'm ahead of the game.

author: gnuarm
author_rank: Super Contributor
timestamp: January 05, 2022, 07:03:30 pm
content: Quote from: tszaboo on January 05, 2022, 06:07:24 pmYou mean your estimates don't make any sense. We have no idea how much your estimates are like the Airbattery systems.

author: gnuarm
author_rank: Super Contributor
timestamp: January 05, 2022, 07:05:15 pm
content: Quote from: dunkemhigh on January 05, 2022, 06:41:06 pmIs this system anything remotely like the Airbattery??? We have already discussed that compressed air storage typically involves an adiabatic cycle which has significant losses as implemented.

author: gnuarm
author_rank: Super Contributor
timestamp: January 05, 2022, 07:10:24 pm
content: Quote from: bdunham7 on January 05, 2022, 06:46:36 pmHuh? What you described requires twice the amount of input power. Unless that power is very, very inexpensive, it is cost prohibitive to do this unless youaredoing arbitrage where you can sell it for more than double the price you pay. That is one use for energy storage.While many installations are justified for stabilizing the grid, they reap financial rewards by using part of the capacity for energy arbitrage. Systems can typically pay for themselves in just a few years. However, that doesn't justify installing a highly inefficient system when much more efficient systems are available.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 05, 2022, 07:29:10 pm
content: Quote from: gnuarm on January 05, 2022, 07:03:30 pmThe cost estimate for the compressed air system make some sense and are more like a lower end estimate. I would expect quite a bit less energy in a 40 foot tank, especially with part of the tanke wasted to water.AFAIK P2G usually make methan gas and this is more storred as pressurized gas. LNG would be only at the very large scale as this adds more effort. The Tanks than are completely different. As compressed methane this would be something like 1 tank. Storage of natural gas is nothing new and known to work for quite some time.

author: bdunham7
author_rank: Super Contributor
timestamp: January 05, 2022, 08:06:06 pm
content: Quote from: gnuarm on January 05, 2022, 07:10:24 pmIf the power is generated by an additional resource--say solar--that you were able to buy with the savings from installing the lower efficiency storage system, then it is indeed very inexpensive. Negative cost, actually.

author: PlainName
author_rank: Super Contributor
timestamp: January 05, 2022, 08:38:03 pm
content: Quote from: gnuarm on January 05, 2022, 07:05:15 pmTo answer properly you'd need to determine what solutions the airbattery is providing, and whether the alternative covers those at least as well. AFAICS, the main features are underground installation (which presumably also implies low maintenance), long life and, er, perhaps cost. Does the P2G2P match that? Looks reasonable except for the low maintenance.Not sure how adiabatic cycles apply to P2G2P. Surely the crunch is TCO per power unit, however that's achieved.

author: tszaboo
author_rank: Super Contributor
timestamp: January 05, 2022, 09:50:01 pm
content: Quote from: dunkemhigh on January 05, 2022, 06:41:06 pmThere are systems in Germany, operating with 70% efficiency.Quote from: bdunham7 on January 05, 2022, 08:06:06 pmThere are some exceptional times, when electricity price is negative in some countries in Europe. The more solar installation we do, the more like these times there is.Also, just think about long term storage, like 6 months. Storing the summer to be used in the winter. Or having your solar farm halfway across the globe and ship the LNG.Quote from: gnuarm on January 05, 2022, 07:10:24 pmSo what? It is cheaper, you spend the extra money to buy solar panels. I cannot make this more ELI5 than this.

author: PlainName
author_rank: Super Contributor
timestamp: January 05, 2022, 11:41:42 pm
content: QuoteIs that there and back, or just one way.Wikipediasays a tad over 70% for P2G, but < 40% for P2G2P - did you perhaps misread my comment or is the wiki - gasp, horror - wrong?

author: tszaboo
author_rank: Super Contributor
timestamp: January 05, 2022, 11:55:49 pm
content: Quote from: dunkemhigh on January 05, 2022, 11:41:42 pmI believe it is only one way, as the utilization happens with existing infrastructure, so the conversion back is not counted.I would argue, that someone heating their house with the gas created during the summer could be better efficiency than P2G2P.So your 40% could be for P2G2P and I was wrong. And I still think that it doesn't matter.Try heating your house during an entire winter with compressed air or batteries and we quickly realize that the climate goals are not achievable without this.

author: gnuarm
author_rank: Super Contributor
timestamp: January 06, 2022, 04:00:43 am
content: Quote from: bdunham7 on January 05, 2022, 08:06:06 pmStorage isn't that expensive now. But yeah, what is important is the total cost. That's why I pointed out for a 40% system compared to an 80% system, you need twice the amount of generation which isn't so cheap. Of course, this also has to factor in the details of generation since the same system provides different energy levels in different locations.For now virtually all storage systems make money with the high ratio of buying cost and selling price of off peak and on peak times. At some point in the future, as storage becomes much more common, that price difference will be diminishing small.

author: gnuarm
author_rank: Super Contributor
timestamp: January 06, 2022, 04:05:31 am
content: Quote from: dunkemhigh on January 05, 2022, 08:38:03 pmWhen you pump gas it is done at a rate that does not allow the escape of the heat generated as the heat is formed. Rather the temperature builds up and the compression happens on a different curve than isothermal which results in lower efficiencies.By pumping the water and letting it flow into many tanks, the temperature rise of the gas is minimized and a near isothermal cycle is achieved allowing higher efficiencies.

author: gnuarm
author_rank: Super Contributor
timestamp: January 06, 2022, 04:10:15 am
content: Quote from: tszaboo on January 05, 2022, 09:50:01 pmYou are assuming you save enough money to pay for the extra generation. Why don't you do something to show this assumption might be, in some way, valid?ELI5 indeed.

author: gnuarm
author_rank: Super Contributor
timestamp: January 06, 2022, 04:12:38 am
content: Quote from: tszaboo on January 05, 2022, 11:55:49 pmI wish I could remember the name of the system that stored heat in the ground anddidstore enough heat to manage a winter, or most of it. This heat was supporting other heating means rather than being the only source of heat. It lowered heating bills rather than replacing them.

author: tszaboo
author_rank: Super Contributor
timestamp: January 06, 2022, 08:54:10 am
content: Quote from: gnuarm on January 06, 2022, 04:10:15 amI did.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 06, 2022, 09:56:47 am
content: Quote from: gnuarm on January 06, 2022, 04:05:31 amThere is no real difference between the water or use of a solid plunger or compressor. If the heat from the compressed air is not kept at constant temperature the efficiency is going down. Using the water plunger has the advantage of adding heat capacity, but it comes at the price of filling up expensive tank capacity with water.Quote from: gnuarm on January 06, 2022, 04:00:43 amThe difference between the times with high and low electricity price would ideally reflect the costs of the storage. Even if the become more common they don't get much cheaper. One of the main ways (and lowest costs) for storrage is pumped hydroelectric power and this is in many regions limited by the available places. So new installations will become more expensive than the existing ones. Flexible power stations (e.g. gas) also take over the role of stabilizing the price, but on the long run in a CO2 emission free world this would be less available. There will be more demand for storrage, and higher cost solutions may have to be used. So I would more expect the variablity in electricity price (whole sale - normal consumers usually see a fixed rate) will more like go up. Things can be different between countries / regions: those with lots of hydro-power would be less effected.For the efficiency it depends on the time scale: for the smaller inter day variations the effciency matters. For the seasonal storrage the costs for the energy send in are often only a minor part and efficiency is less important. If the capacity is cheap even 30% efficiency would be OK. This does not mean it would take 3 times the production capacity, as only a relatively small part of the energy goes through long term storage. Much of the energy is still consumed in time or only needs short time storage. For seasonal storrage it's the cost per capacity that needs to be low as there are not that many cycles to go around - with only some 20 cycles batteries are just too expensive.

author: gnuarm
author_rank: Super Contributor
timestamp: January 11, 2022, 02:13:04 pm
content: Quote from: Kleinstein on January 06, 2022, 09:56:47 amInteresting, at first you say there is no difference, but then you go on to explain the difference.QuoteThe cost and the availability. Right now there is little of such storage. In the future there will be greater demand.QuoteThat is a self contradiction. Most technologies fit a price demand structure where a ten fold increase in volume provides a halving of cost.QuoteAgain, that does not follow since the cost of storage can be mitigated by increased quantity.QuoteYour logic is flawed, so your conclusion is invalid. By definition storage will smooth demand vs. supply easing price fluctuations. If it were not so, storage would simply not be financially prudent.While some countries take carbon emissions seriously, most pay only lip service and will not require rate increases to deal with the issue.QuoteYou would need to define terms like "cheap". There's no forecast of any energy source becoming cheap enough that wasting 70% of it would be economical other than ICE autos and those only because it was that way from day one with few alternatives until now. Such inefficiency would produce huge price differences between direct use and storage and would likely not be acceptable.Since this likelihood is based on a false premise, that 30% efficiency is useful in some way, it will never happen. Instead we will be able to use much more economical storage of energy.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 11, 2022, 06:56:38 pm
content: Quote from: gnuarm on January 11, 2022, 02:13:04 pmNot everything gets cheaper when needed in larger numbers / quantities. Some things like computer chips do, but other things that are rare (e.g. oil, gold or antiques) the price goes up when the demand rises. For things like the pressurized tanks a main part of the price is just plain steel and even when they build more tanks the steel won't get much cheaper. Similar with concrete to build dams that is already made in quantities. Labor costs can go down, but the raw materials usually not.The awailable technology with the lowest cost would ideally set the price. Because of limited availablity pumped hydro may not be that in many areas (e.g. Australia). So it would be the next best technology.For seasonal storage the costs for the energy used (in times of excess power, e.g in summer) can be very low (e.g. 1-2 cents / kWh), well below the year round average for the production. So efficiency does not really matter. Things are different for the storage on a daily basis - here the price on some days can be substantial and much less money earned from the energy released. So far my best guess is batteries for the daily cylce and hydrogen gas (maybe with the extra step to CH4) for the long term part. Where available pumped hydro can be used and may be cheaper then hydrogen, but where not enough it would not set the price.The proposed compessed air does not look like it can compete with the existng batteries. Not for the costs and not for the effciency. For seasonabl storage it is hopeless from the start because of the costs. There is no chance to get a 1 m³ tank for costs in the sub $10 range - the scap value for the steel tends to be higher and it does not get better when larger.

author: bdunham7
author_rank: Super Contributor
timestamp: January 11, 2022, 07:06:49 pm
content: Quote from: gnuarm on January 11, 2022, 02:13:04 pmNo need for a forecast, we can just consider things already known to occur. When energy prices turn negative (and they do at times) then wasting even 100% becomes economical. Leaving that aside, if you match storage with your own solar or wind or hydro generation and then use that system to sell peak-time power, again wasting 70% would not be a problem if the peak-time price were commensurately higher.

author: gnuarm
author_rank: Super Contributor
timestamp: January 12, 2022, 12:14:02 am
content: Quote from: Kleinstein on January 11, 2022, 06:56:38 pmRaw materials can be very pricey in small quantities. It is only when utilized in larger quantities that mass production techniques can be used to lower the price. What you are talking about is using materials to the point of scarcity and the short term response to rising demand. In any industry a stable rise in demand will be met with more production lowering the cost of production and the selling price.In production, this cost/quantity relation is a very common guideline. You keep talking about steel when the tanks are not made of steel. Materials may get somewhat cheaper, but the savings mostly comes from advances in the production process which includes finding ways to reduce the material quantities. Every industry goes through optimizations early on. This design is no different and is in the very early days.QuoteNot sure why you are talking about that.QuoteI've never seen any real numbers talking about even 2 cents per kWh for solar or wind much less 1 cent. The fuel cost is more than that much for fossil fuels.QuoteOf course it matters. More than doubling your costs is a hard thing to sweep under the carpet.QuoteWhat do you do with hydrogen exactly? Where/how is it made? I've never seen any plan for hydrogen that was economically feasible.QuoteExcept that you don't have any information to compare the two... and you keep talking about steel.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 12, 2022, 09:36:39 am
content: Quote from: gnuarm on January 12, 2022, 12:14:02 amSteel and concrete are already produced in quanteties and they don't get cheaper if you need 20% mode. It is more that both need quite some energy that the costs there are expected to go up.For the compressed air tanks I take steel as the baseline, as this is the industry standard and it would be odd if there is something much cheaper and not used instead. The numbers for the air battery are so poor that even a factor of 10 reduction in the price would hardly make them really competative (a factor 100 may). Assuming multiple new technologies with unrealistic improvement on existing state of the art is a common thing for doggy technology scums.Quote from: gnuarm on January 12, 2022, 12:14:02 amNew large scale PV and wind installations reach costs of some 5 cents (sometimes 3 cent's at a good location) for the year round average. This is comparable to fossile fuel costs - so what. The problem with large scale use is that lack of storrage and thus not a fixed year round value. In times of high demand they get a higher price (e.g. up to 50 cents) and in times of excess supply they have to give it away essentially for free (at lest well below the average costs) unless there are government subsedies. In Germany the whole sale electricity price occasionally even gets negative, because there is not enough storage capacity to use it and small scale PV usually does not turn off because they get paid a fixed rate (subsedies).They don't need to install extra PV to provide electricity just for storrage. The PV installation would still make most of there money in times when no storrage, or only the daily cycle is needed. The long term storrage would use the surplus in times of excess.Storage lives from the variations and it will work against variations in the price. However with a reduction in fossile power plants there are also factors to make the supply more variable and thus cause more variations. There will be a balance somewhere, when the price variations are so to make extra storrage about profitable. For most of the part the prices would adapt and the lowest cost storrage will have a chance, even if that means getting the excess energy for free or very high rates in the peak times.

author: IanB
author_rank: Super Contributor
timestamp: January 12, 2022, 03:25:15 pm
content: Quote from: Kleinstein on January 12, 2022, 09:36:39 amTheir literature and publicity material says they use some form of polymer construction. So the discussion should try to reference what they actually tell about their system.

author: gnuarm
author_rank: Super Contributor
timestamp: January 16, 2022, 02:58:14 pm
content: Quote from: Kleinstein on January 12, 2022, 09:36:39 amYou will need to take that up with the manufacturer. Explain to them how they are wrong and should be using steel.QuoteSorry, what numbers are you talking about???QuoteYeah, that's a problem with management and not an issue inherent to renewable energy itself. Anyone can screw things up and it's hard to not screw things up temporarily.QuoteHmmm... I think what you just said is that they have already installed the PV required to utilize storage. But that still doesn't justify inefficient storage when efficient storage is just as available.QuoteI don't fully understand what you are saying, but it sounds like you think there is free energy on the market and that somehow justifies inefficient storage. I guess we will find out. I suspect the flaw in your argument is that once the storage is built and utilizing the "free" energy, it won't be free anymore and the lower cost, low efficiency storage will no longer be economical.Don't confuse temporary market conditions with a stable, functional energy economy.