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A company is building a giant compressed-air battery in the Australian outback
- ck2 2y agoWhy not lift super heavy but cheap objects like rocks or dirt and then let gravity be your battery?
- samcheng 2y agoThey definitely do that with water. It's called "pumped storage" and there are megawatt-scale installations all over the world.
- ninju 2y agohttps://en.m.wikipedia.org/wiki/Pumped-storage_hydroelectricity https://en.m.wikipedia.org/wiki/Pumped-storage_hydroelectric...
- time0ut 2y agoA company called Energy Vault[0] is (was?) working on this. I think it is relatively capital intensive compared to what the company in the article is doing. Of course storing underground requires particular geology. I also remember reading about a system that moved dirt/rock up a mountain on a train. Can’t find a link, but that also seems capital intensive and requires different geology. There is also pumped hydro storage that works via gravity. That’s been around a while. My dad worked as an engineer on one in the 80s [1]. [0] https://www.energyvault.com/ https://www.energyvault.com/ [1] https://en.m.wikipedia.org/wiki/Helms_Pumped_Storage_Plant https://en.m.wikipedia.org/wiki/Helms_Pumped_Storage_Plant
- greenbit 2y agoI must have missed something. Why not just use the water without the compressed air, i.e., pumped hydro? There must be some advantage, but they didn't seem to say. I'd guess maybe if your lower reservoir were underground, the water-only would require the generator systems to be down there, too, which would mean access for people as well, and being down a mine with a small lake's worth of water overhead seems pretty hazardous. Whereas by forcing air down to push water up, that whole below ground aspect can be almost entirely passive. Maybe?
- JoeAltmaier 2y agoA solution to deep water pumping is to lower the pump(s) into boreholes. Nobody has to go down there.
- willvarfar 2y agoYes this is normal even in normal residential wells. Boreholes are just a few inches across so obviously nobody ever goes down them! I have an injector pump that sits at the top of the borehole and has a pipe that pushes water down to pump water up through a second pipe, but it's more common to have a submersible pump down at the bottom of the bore.
- JoeAltmaier 2y agoI've wondered how well the inject-pump style works! Do you have experiences to relate? All the electronics are up top where you can get at them. Has the mechanism at the bottom ever needed to be serviced? Can it be retrieved easily?
- bluGill 2y agoYou can pull the parts out of the hole anytime you want to - special equipment is normally used, but a rope and a tripod to hold a pulley over the hole works (might not be safe). What is at the bottom of the hole is a "injector" which is basically a U shaped pipe and a small jet to push water back up. If the well water is only 25 feet below the ground a pump at the top along works. This jet system gets down to 60 feet. The pump down the hole gets to 600 feet (check the pump specs - many are rated to only 250). After that you need oil well type pumps where the motor is at the top of the hole but the pump is lowered down.
- willvarfar 2y ago(I can't find any English lit on it, but my Grundfos Ejektorpump (had to go out and look at it to see what it's called; perhaps the correct translation is ejector pump rather than injector pump?) is in a 85m deep borehole and works great. It's 40 years old, heavily used and never serviced and quite a puzzle how it's still going. I have no idea if they can pump from deeper than that)
- hackerlight 2y ago> The next project would be Willow Rock Energy Storage Center, located near Rosamond in Kern County, California, with a capacity of 500 megawatts and the ability to run at that level for eight hours. Their California battery will be 4GWh capacity with a $1.5 billion cost, which is $375/kWh. Their Australian one will be 1.6GWh for $415 million USD, working out to be $260/kWh. Both are more expensive than lithium ion, so I wonder what the case is for it.
- dhaavi 2y agoMy guesses: 1. no degradation 2. cheap to expand? - simply expand the cave
- lukan 2y ago"cheap to expand? - simply expand the cave" That is not cheap. And we have very high pressure here and not only cave and rock, but technic around it. And pushing air in and letting air out again will have degradation of that expensive equipment.
- affgrff2 2y agoThese are the costs of installation, but what about maintenance and replacement costs?
- aplummer 2y agoSurely to prove and improve the technology? Being able reuse gas technology as the article says, in Australia would be a boon - there’s an enormous CSG industry
- dzhiurgis 2y ago> Both are more expensive than lithium ion Are you comparing battery cell cost vs battery pack + structures + electronics + lines + land + installation + different continent + N other things I have no idea about?
- zidel 2y ago
- foreigner 2y agoHow does the air "push the water up"? What mechanism prevents the air from simply bubbling up through the water column? I'm assuming some kind of valve or piston, but would be interested to see what it looks like.
- liftm 2y agoI'll assume the inlet is below water level / at the bottom of the tank…
- ulrikrasmussen 2y agoI wondered the same thing. I guess it would work if the water shaft was actually U-shaped, but that would mean drilling three shafts instead of one.
- ajb 2y agoWhy three? Their diagram shows two (plus the cavern, which must already exist)
- ulrikrasmussen 2y agoTo build a trap, the pipe would have to go almost all the way up to the reservoir, then down, and then up again to connect to the reservoir: https://en.wikipedia.org/wiki/Trap_(plumbing) https://en.wikipedia.org/wiki/Trap_(plumbing) But there might another way to avoid bubbling which I have missed. Maybe the compressed air is under so much pressure that it becomes denser than the water?
- ajb 2y agoIt doesn't need to be denser than the water because the incoming air is always above the water. Imagine an cavern shaped like the great pyramid of Giza, full of water. They dig two pipes, an air entry pipe to the point at the top, and a water exit pipe to one of the corners at the base. Air pumped in at the top pipe will almost evacuate the cavern, before the water level drops to the point where air could get to the exit pipe. What this means is that depending on the shape of the cavern, they may not be able to utilise its whole volume. In the worst case, if its roof were entirely flat, they would not be able to use any. They can use the volume of a section, bounded by horizontal planes, from the air entry pipe either down as far as the exit pipe, or (if the roof dips down between the two) down as far as the lowest point on the highest possible path between the two. That's assuming totally vertical pipes. I know they can curve them a bit, but I don't know if they can curve them enough to enter a cavern from below. If they could, then they can utilise the entire volume, as long as they can identify the lowest and highest points
- tromp 2y ago> the system extracts heat from the air and stores it above ground for reuse. As the air goes underground, it displaces water from the cavern up a shaft into a reservoir. > When it’s time to discharge energy, the system releases water into the cavern, forcing the air to the surface. The air then mixes with heat that the plant stored when the air was compressing, and this hot, dense air passes through a turbine to make electricity. By "releases water into the cavern", do they mean simply opening the air valve to let the air (pressured by the water) come back out?
- ajb 2y agoYes, the diagram shows that the same water is used
- usrusr 2y agoThey don't really release water into the cavern, they release air out (through the turbine stages). The water is never really held back. It's a floating counterbalance for keeping the air pressure constant (or mostly constant, considering surface reservoir level differences which would never exceed a tiny fraction of the total water head, unless the facility runs into extreme water shortage)
- mikewarot 2y agoI always wondered why compressed air storage systems work against ambient pressure instead of having two tanks at high and higher pressures. This would greatly increase the density of the gas, as well as lowering the temperature differential. It would take a long time to get it up to initial pressure, as there would be a lot of heat to dissipate, but then it differential mode, the gradient would be much better.
- ssl-3 2y agoSuppose we are driving a turbine. Does having an increase in the density of gas present an advantage over having a higher pressure delta by dumping to ambient for a given volume of compressed-gas storage? Why would I want one tank at "high" pressure, and another tank at "higher" pressure, when I could just have one tank of "higher" pressure to begin with? Or, better: Two tanks of "higher" pressure in even less space than one of "high" and one of "higher" pressure? (If the answer is "Because turbines work better with higher densities," then: Do they work more-betterer-enough to make up for the size and complexity?)
- bluGill 2y agoBecause with the tanks are not infinite size. That means as you release pressure the differential between the two tanks equalizes in the middle. Mean while in the current system the low pressure vessel is effectively infinite and so you have more usable volume to work with. Plus of course you can use both vessels to store energy instead of one.
- amluto 2y agoSeveral reasons. The first is fundamental: density is not really helpful for this sort of application. The work done in expanding material (including gas) at a given pressure is P dV, and the work done in moving material across a pressure difference is V dP. Notably, mass doesn’t appear at all here, so adding more mass or density doesn’t add energy storage capacity in and of itself. You can compute this more explicitly, and, for an ideal gas, the useful energy extractable from a tank of gas at pressure P (under ideal, isothermal conditions) is proportional to the change in log P. So it’s actually rather more important to achieve low pressure than high pressure. On top of this, there’s a practical consideration: the atmosphere is an effectively infinite source of gas at 1 atm. If you are working between high and higher pressure, you need two reservoirs. All you’re gaining is less temperature change per unit pressure change, but it’s probably the same amount of heat for any practical purpose, so you still need an intercooler of some sort for good efficiency.
- masteruvpuppetz 2y agoI found another technique quite fascinating.. When electricity is surplus, spin large disk-shaped rocks levitated by magnets in a vacuumed enclosure. Use this spinning motion to create electricity when required.
- okl 2y agoExists, just not with rocks. I think the modern versions use heavy metal blocks embedded in carbon fibre. https://en.m.wikipedia.org/wiki/Flywheel_storage_power_system https://en.m.wikipedia.org/wiki/Flywheel_storage_power_syste...
- jimnotgym 2y agoWhat stops the air from just bubbling up the water pipe?
- ourmandave 2y agoWell this changes the whole look and feel of future Bartertown entirely. They probably won't even have a Thunderdome. =(
- hinkley 2y agoOh they'd still have Thunderdome. The population of pigs might be a bit lower, however.
- littlestymaar 2y agoHow do they work around the ”heat problem” with compressed air storage. When you compress the air, it heats up, and actually there's a big part of the energy that get stored in the form of heat, not pressure. When you want the energy out the pressured air cools down during depressurization. If you were able to keep the air hot the whole time the process is almost symmetrical so that's not an issue, the “heat problem” as I call it is how do you store this heat for an extended period of time? At scale, it's much harder to keep than just the pressurized air. The prototypes I've seen in the past were not storing the heat, but relied on industrial fatal heat (that was lost anyway) but this also has scale problem as you don't have that much available power except near very specific industries (NPP are an option, as are other heavy industries, but the supply is necessarily limited)
- bluGill 2y agoIf the energy input is free/renewable they can ignore this to some extent. Yes they lose a lot of energy, but who cares if the wind is blowing/sun is shining making more energy than you need right now - the other option is turning those systems off - either way they cost the same $$$.
- littlestymaar 2y agoThe problem is that you need this energy when you want to provide electricity from the storage, which isn't the moment where energy in general is cheap. The positive aspect of such a system is that the thermal energy you need is not subject to Carnot's law, so the temperature of the heat source doesn't matter unlike most use of thermal energy (and that's why you can use waste thermal energy in the first place) but you still need a way to get that energy.
- bluGill 2y agoThe air still is there whes you need it. The thermal energy is lost but the pressure isn't.
- 2y ago
- gcanyon 2y agoNo mention of how efficient the energy cycle is? Without checking sources, I think I've read that batteries and pumped hydro end up in the 80-90% range round trip? Without knowing what this method produces it's almost pointless to consider. One advantage this has (I assume) is almost limitless cycle lifespan.
- Pxtl 2y agoCompressed air energy-storage is notoriously low-efficiency compared to the alternatives. The idea is that this is a hedge: if it turns out that solar/wind become "too cheap to meter"? Then "efficiency" is meaningless and what matters is cost-per-unit-storage and the hope is that compressed-air will be able to store and output more joules-per-dollar than any other storage method (regardless of how many more joules you had to put in first).
- usrusr 2y agoCompressed air is notoriously low-efficiency when you do it like in ye olden days, by venting the compression heat to the environment. A-CAES means capturing that heat, storing it separately and transferring it back into the decompression stream in discharge. Yes, this means that there will be some trickle discharge loss when using the storage scheme for long duration, but heat storage is a happy square-cube law thing, at a certain scale it even become viable for seasonal storage. A-CAES usually claim about 70% round trip efficiency. But you are right in that this number really isn't all that important in the renewables age: when we are anywhere close to getting to 100% renewables on a point of median supply and median demand, production capacity (conversion capacity from sunshine and air movement) at times when sun coincides with wind will so far outpace demand that any energy sink will do that can still pay a positive rate. We're a long way from fully renewable were I live, and some days I see two thirds of turbines stopped in nice wind. It's really all about capex per W and per Wh. Admittedly, A-CAES isn't necessarily excellent in this right now, but it might scale quite nicely with routine. Recently there was a gravity storage scheme linked here on hn about lowering mining refuse back into old mines to discharge, and digging it back up to charge, which comes with the curious property that it never really reaches a point of saturated capacity: in theory you could keep digging new tunnels forever when energy surplus keeps coming in.
- watershawl 2y agoThis is a good solution (storing in rock) to get around the heat and corrosion (from water) that above-ground tanks go through when storing compressed air.
- pfdietz 2y agoFrom a thermodynamic point of view, it should be noted that compressed air does not actually store energy! The internal energy of a compressed gas is from the kinetic energy of its molecules, and this is a function only of temperature(*). What a compressed gas represents is not stored energy, but stored (negative) entropy. It is a resource that allows low grade heat to be converted to work at high efficiency. This is what's to happen in this facility: the heat of compression is separated out and stored, then used to reheat the compressed air at discharge time. The energy is actually being stored in that thermal store. But there are other ways to do this that don't involve compressed air storage. Instead, after the heat of compression is removed and stored the compressed air could be reexpanded, recovering some of the work. This would leave the gas much colder than when it started. This cold could be stored (heating the gas back to its initial temperature) and the gas sent around again. To discharge, the temperature difference between the hot and cold stores could be exploited. This is called "pumped thermal storage". I believe Google/Alphabet has/had a group looking at this (called Malta). It has no geographical limitations. (*) Highly compressed air will store some energy because the molecules become so crowded some energy is stored in intermolecular repulsion, but that should be a small effect in this system.
- danhau 2y agoInsightful, thanks!
- pfdietz 2y agoI should add that there's also some energy stored lifting water. So this is not entirely a thermal store. I didn't run the numbers, but I guess the thermal store stores > energy than is stored lifting water.
- foobarian 2y agoI'm trying to reconcile how a consumer-grade compressor fits into this. Clearly such a device can compress a few gallons of gas, which could be allowed to cool to room temperature, and then used to spin a small dynamo. This action clearly converts some amount of energy, but where does it come from? Perhaps the problem is we're not looking at a closed system at that point.
- Pxtl 2y agoI couldn't see in the article - is this using natural caverns or did they excavate? I know the pilot versions of this tech generally use old salt-caverns, like the one in Germany. I'm actually pretty excited about this tech - it seems like solar and wind are getting cheap faster than batteries will be able to meet the needs for grid-scale energy storage, so a cheap-but-inefficient energy storage tech is an exciting prospect. Massively overbuild the solar/wind and use these things to defer the overflow.
- psadri 2y agoWhile at it… they could try to extract some atmospheric CO2 from the more concentrated air.
- coryfklein 2y agoWhat happens when you get a leak in a random seal in the chamber deep under ground, does all the compressed air escape? How do you ensure such a large reservoir stays air-tight for 20 years?
- 0xE1337DAD 2y agoTotho, has graduated from snap bows.