[HN Gopher] A company is building a giant compressed-air battery...
___________________________________________________________________
A company is building a giant compressed-air battery in the
Australian outback
Author : uncertainrhymes
Score : 135 points
Date : 2024-05-05 10:28 UTC (1 days ago)
(HTM) web link (www.wired.com)
(TXT) w3m dump (www.wired.com)
| greenbit wrote:
| I 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 wrote:
| A solution to deep water pumping is to lower the pump(s) into
| boreholes. Nobody has to go down there.
| willvarfar wrote:
| Yes 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 wrote:
| I'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 wrote:
| You 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 wrote:
| (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)
| JoeAltmaier wrote:
| Some designs might have no moving parts down there?
| Nothing to go wrong.
| willvarfar wrote:
| You made me more curious to find out about it.
|
| https://www.vvsbutiken.nu/product.html/ejektorer-
| grundfos?ca...
|
| Two normal plastic water pipes descend down to the bottom
| of the borehole. At the bottom is a brass u-shaped
| fitting with a inlet with a non-return valve.
| foota wrote:
| I think you can store energy here not just in the gravitational
| potential energy of the water, but also in the compression of
| the air. I _think_ this means that you can get away with a
| smaller cavern than you could for just pumped hydro.
|
| You might think that you'd need a large amount of water to make
| the energy release work, but I think it works like this. The
| force of the water on the air/water interface is dependent not
| on the reservoir volume, but on the weight of the water in the
| column (which depends only on the height of the shaft).
|
| By digging a very deep shaft, you can have a very large force
| of water on the interface, and moving that interface an equal
| distance hence releases more energy than it would with a
| shorter shaft.
|
| This way, you can store an arbitrary (up to your ability to
| compress air to a sufficient pressure, dig a deep shaft, and
| keep everything from blowing up) amount of energy.
|
| I think if you have a 1 square meter cross section of shaft,
| and the shaft is 1 kilometer deep, then at the bottom the force
| of the water above is the weight of 1 square meter * 1
| kilometer, or 1000 cubic meters of water, or 1 million kg.
|
| The force then is 9.8x10^6 newtons.
|
| Pressure is force/area, or 9.8x10^6 newtons/square meter here
| (since we have a unit area).
|
| There's a formula for the energy in compressed air, it's...
| involved. I downloaded an excel file from here:
| https://ehs.berkeley.edu/publications/calculating-stored-ene...
|
| It says under this pressure, a 1000 cubic meter tank of air at
| this pressure stores ~5000 KWh.
|
| The one planned in California is supposed to store 4000 MWh, so
| I guess they have a tank that is ~a million cubic meters.
|
| A water tank of the same size would store ~2700 MWh of energy
| (e.g., pumping that much water up a 1KM shaft requires that
| much energy), so it does seem to be more efficient.
|
| It may also be that hot air turbines are cheaper and easier to
| maintain than hydropower turbines, but I'm not certain.
| trenchgun wrote:
| >I think you can store energy here not just in the
| gravitational potential energy of the water, but also in the
| compression of the air. I _think_ this means that you can get
| away with a smaller cavern than you could for just pumped
| hydro.
|
| + they are storing the heat extracted from compressing the
| air.
| lucioperca wrote:
| isn't that used when decompressing the air, i.e. closed
| loop
| jagged-chisel wrote:
| You just pull that from the atmosphere.
|
| Compress to store [potential] energy, take the heat
| generated during compression and use it, decompress at
| time of need and let the [hot?] atmosphere supply energy
| to the decompressing gas.
|
| I wouldn't call it a closed loop, but maybe a lack of
| deficit.
| fanf2 wrote:
| I want to know how this heat storage works. It seems kind
| of important?
| logtempo wrote:
| also water tend to be scarse nowaday and valuable nowaday.
| 867-5309 wrote:
| they say, writing from an ocean planet
| droopyEyelids wrote:
| Salt water is a nightmare to include in any sort of
| mechanical system. It is super corrosive itself, enables
| galvanic corrosion, and is so "fertile" biologic fouling
| is a big issue.
| pjc50 wrote:
| > The force of the water on the air/water interface is
| dependent not on the reservoir volume, but on the weight of
| the water in the column (which depends only on the height of
| the shaft).
|
| Just wanted to highlight this, since it's the key insight
| which caused this to "click" for me.
|
| The difference between a 1km shaft and a 1km deep reservoir,
| when both are used for pumped hydro, is the amount of energy
| stored. Running a turbine at the bottom of the shaft (to
| where?!) would drain very quickly. But using air, which has
| very different properties, enables you to use the water as a
| "piston" to keep the air at a certain constant pressure
| underground. And you can store a larger volume of (more
| compressible) air in a space which is easier to access.
| westurner wrote:
| Is there any pump efficiency advantage to multiple pressure
| vessels instead of one large?
|
| You could probably move the compressed air in a GPE
| gravitational potential energy storage system, or haul it up
| on a winch and set it on a shelf; but would the lateral
| vectors due to thrust from predictable leakage change the
| safety liabilities?
|
| Air with extra CO2 is less of an accelerant, but at what
| concentration of CO2 does the facility need air tanks for
| hazard procedures?
|
| FWIU, you can also get energy from a CO2 gradient: "Proof-of-
| concept nanogenerator turns CO2 into sustainable power"
| (2024) https://news.ycombinator.com/item?id=40079784
|
| And, CO2 + Lignin => Better than plastic; "CO2 and Lignin-
| Based Sustainable Polymers with Closed-Loop Chemical
| Recycling" (2024)
| https://news.ycombinator.com/item?id=40079540
|
| From "Oxxcu, converting CO2 into fuels, chemicals and
| plastics" https://news.ycombinator.com/item?id=39111825 :
|
| > _" Solar energy can now be stored for up to 18 years [with
| the Szilard-Chalmers MOST process], say scientists"_
|
| > [...] _Though, you could do CAES with captured CO2 and it
| would be less of an accelerant than standard compressed air.
| How many CO2 fire extinguishers can be filled and shipped
| off-site per day?_
|
| > _Can CO2 can be made into QA 'd [graphene] air filters for
| [onsite] [flue] capture?_
|
| "Geothermal may beat batteries for energy storage" (2022)
| https://news.ycombinator.com/item?id=33288586 :
|
| > _FWIU China has the first 100MW CAES plant; and it uses
| some external energy - not a trompe or geothermal (?) - to
| help compress air on a FWIU currently ~one-floor facility._
| eastbound wrote:
| Did you mean 5000KWh (air) and 2700KWh (water), or MWh for
| the second?
|
| Also, 1000m3 in air is just a cube of 10m. It seems like a
| good illustration of the convenience of air vs water.
| foota wrote:
| The same size here is a million cubic meters, what I figure
| the size of the planned California plant must be in order
| to store 4000MWH.
| jusssi wrote:
| You need to get replacement air to the cavern when you pump the
| water up, and let the air to make room for the water when it's
| going down. So you need a separate shaft for airflow anyway. I
| assume the rest is just economics, it's probably a lot cheaper
| to have all the moving parts easily accessible on the surface.
|
| Edit: Also the fact, that if the pump was at the very bottom
| and it failed, you'd need to have an alternative way to clear
| the cavern of water in order to go down and fix the pump.
| mywittyname wrote:
| Edit: Also the fact, that if the pump was at the very bottom
| and it failed, you'd need to have an alternative way to clear
| the cavern of water in order to go down and fix the pump.
|
| Put the pump on a chain and hoist it up with a crane, like
| they do with pumps in lift stations.
| audunw wrote:
| I suspect the maximum stored energy for the compressed air
| solution is significantly higher.
|
| Not only can you store the energy required to lift the water to
| the surface, but after all the water is lifted you can keep
| compressing the air in the closed reservoir to store even more
| energy.
|
| If you only used water you could of course build an open
| reservoir with more storage capacity instead. But maybe these
| will be built in areas where that's not feasible. It'd take
| much more space on the surface, and you need to deal with
| evaporation.
| usrusr wrote:
| I do wonder, regarding the hydrostor approach, if the stored
| energy (theoretical best, excluding all losses) is 2x the
| amount that would be stored if it was just the water head
| (mass x height), with air displacement served by an open
| connection to the surface, or if there can be more to it:
|
| Constant volume CAES would store energy without any water
| lift involved, and with water mediated constant pressure CAES
| the lifted water is added to the amount of energy contained
| in the "air spring". But that's balanced at equal force in
| the force x surface area x underground reservoir level
| system. My bird's eye view understanding suggests that it
| would come down to 2x the amount of energy stored in either
| (minus losses, of course) due to the balance. Is that the
| maximum energy a water-column mediated constant pressure
| A-CAES could hold, per water displacement volume x head
| height, or am I missing something? That 2x would surely be an
| improvement over conventional mineshaft pumped hydro, but it
| would also define a somewhat sobering limit to the amount of
| theoretical best case capacity.
|
| Minor but perhaps very relevant detail: afaik, or rather as
| far as I _don 't_ know, hydrostore aims at a shaft depth
| equivalent to a pressure either right below of where pure CO2
| would liquefy, or right above where that happens (no idea
| about the boiling points of N2, O2 and all those other main
| components of ambient air). I think the target depth is not
| quite that deep, as in carefully avoiding the "transliquid"
| range (as in transonic).
| hydrox24 wrote:
| The short answer is that pumped hydro is mature technology with
| a pretty wide range of places it can be implemented (at least
| in Australia[0], which has a mountain range going down the east
| coast where everyone lives). A-CAES has three advantages, which
| are in my opinion aren't very fundamental:
|
| 1. It takes up less space on the surface than most PHES.
| This... is almost always a marginal benefit.
|
| 2. It doesn't require building a reservoir or dam. These are
| very well regulated in Australia and elsewhere, and the
| downsides are known so they are quite slow to get approval.
|
| 3. It's a bit quicker at 2.5 - 3.5 years as opposed to 3-7
| years.[1] This is a bigger advantage than it looks if you have
| some tricky renewable energy targets to hit by 2030 (see our
| 42% emissions reductions target as well as an 82% renewable
| energy target)
|
| I can't see this gaining traction outside of a few locations in
| Australia, at least. I wouldn't be surprised if A-CAES is only
| briefly viable as a result of subsidies and cheap government
| financing.
|
| [0]:
| https://re100.anu.edu.au/#share=g-fa5a20c9c63f6ed6343a7e7573...
|
| [1]: https://www.csiro.au/-/media/Do-
| Business/Files/Futures/23-00...
| usrusr wrote:
| > with a pretty wide range of places it can be implemented
|
| How so? Yes, if you dammed up most valleys you could build a
| lot more capacity than humanity currently has, but that's
| because we don't really have that much. A factor of two or so
| might be well within range. But the total amount reasonably
| buildable simply isn't enough, except for some very local
| scopes where demand is low in both energy and in other use
| for the landscape that would be taken over by reservoirs. And
| that's before you start considering the geological realities
| required for actually building a dam, you don't just need the
| geometric shape of a valley, you need the bedrock to brace
| the dam against and the impermeability of the ground required
| to not have leakage wash out pathways for ever increasing
| leakage. Viable sites for pumped hydro are extremely rare and
| quite a few have actually been given up decades after
| building the dam, because the geology wasn't quite as
| cooperative as hoped.
|
| The promise of deep site water head CAES is that you can just
| throw money at the problem (excavation) and get as much
| capacity as you want to buy. The price per capacity is higher
| than that of a low hanging fruit pumped hydro site, but many
| of those buildable have already been built.
| gregoryl wrote:
| Let's not forget the extreme environmental impact a dam
| has.
| pfdietz wrote:
| Those are for dams on rivers. PHES doesn't have to be on
| rivers.
| olau wrote:
| The sources I've seen point out plenty of places. They may
| be overoptimistic. But excavation is really expensive, and
| in a competitive market, you cannot just throw money at the
| problem. It's the same reason nuclear fission is dead in
| many markets.
| Intermernet wrote:
| Australia loves excavation. If you could double up mining
| with pumped hydro you'd be the belle of the ball.
| globalise83 wrote:
| It could make a nice option for huge abandoned open cast
| mines - build a dam across the pit, flood it and then
| pump water from one side to the other using solar-
| generated electricity, allowing it to flow back to
| generate electricity as and when needed.
|
| For example:
| https://www.news.com.au/technology/environment/abandoned-
| min...
| rtkwe wrote:
| A big problem is those mines usually leave behind pretty
| toxic remains so the water you're pumping around is
| extremely hostile to the people and equipment you're
| thinking of putting it through/near. Then there's the
| chance of a dam collapse releasing that toxic water
| outside the mine.
| taneq wrote:
| I've thought for a while that old open-cut iron ore pits
| could be prime spots for 'inside-out' pumped hydro, like
| that system that some German researchers were working
| which pumped water out of submerged concrete spheres
| instead of up a mountain.
| psd1 wrote:
| If you have abandoned deep shafts, they may be smaller in
| volume than an open pit, but they have several hundred
| metres of head, so every kilogram of water is much more
| effective than in schemes with less head.
| bryanlarsen wrote:
| Most viable hydro sites are gone, yes. But you don't need a
| viable hydro site for pumped hydro. What you need is water
| at the bottom of a hill. That's common.
| jefftk wrote:
| If you just have water at the bottom of the hill you'll
| need to build a giant tank on the top of the hill. The
| best spots for pumped hydro have a natural depression
| elevated above a water source, so you can use that
| instead.
|
| (I agree that this is different from traditional hydro
| locations, and so there are many good spots still
| available)
| bryanlarsen wrote:
| The best spots already have a reservoir up top, or most
| of one. Pumped hydro is so much cheaper than other long
| term storage options you can spend a little extra on the
| reservoir and still come out ahead of competitors.
|
| 50 year old example: https://en.wikipedia.org/wiki/Luding
| ton_Pumped_Storage_Power...
| pfdietz wrote:
| Most _primary_ hydro sites are gone. Pumped hydro can
| work in a much wider variety of places, including in
| deserts.
|
| https://www.whitepinepumpedstorage.com/
| denton-scratch wrote:
| Pumped hydro won't work unless you have a suitable mountain
| to hand. Compressed air can be built in flat country.
| verelo wrote:
| I'd expand on your point (2) with these points.
|
| 1. Dams require water. Australia has suffered water supply
| challenges as long as I've been alive.
|
| 2. Dams can be environmental disasters. Both building,
| maintaining and one day destroying these has a lot of
| challenges and expenses that we're not great at measuring.
| rtkwe wrote:
| Not having to build and maintain a dam and find an
| appropriate area to flood is a pretty large upside. Big
| thing in the US is that we already have a lot of dammed
| lakes in mountains in some places so we're really talking
| about making the water level more variable and adding some
| infrastructure instead of building net new lakes.
| pfdietz wrote:
| Pumped hydro consumes much less water than evaporative
| cooling of a thermal power plant with the same energy
| throughput. Pumped hydro doesn't have to be on an existing
| watercourse, so it doesn't cause the environmental issues
| that come along with that.
| ajb wrote:
| I think your answer is the correct one, rather than the
| replies. By keeping all the machinery at the top, initial build
| and maintenance costs are cheaper, they can use a cavern of any
| shape and at any depth, and they only need to use drilling
| techniques not mining techniques, which will be far cheaper .
| taneq wrote:
| The water's not there to directly store gravitational potential
| energy, it's there to provide a variable sized containment
| vessel under nearly constant pressure conditions. This has two
| advantages:
|
| 1) You're not losing thermal energy from the main body of air
| (assuming their thermal recovery at the compressor works well
| enough) because the change in air pressure only occurs at the
| compressor.
|
| 2) You get constant pressure and constant power output for the
| entire volume of your compressed air storage, instead of both
| dropping rapidly as air is released. This gives you far better
| bang for buck per unit volume of pressurized air.
|
| I haven't done the calcs but I'd guess that if they're
| bothering doing all this extra stuff the energy stored in a
| cubic meter of compressed air at these pressures is
| significantly higher than the energy you'd get from just
| lowering a cubic meter of water down to the reservoir.
| usrusr wrote:
| Compressed air and water head are in a balance, my physics
| instincts strongly suggest that the hypothetical sum is 2x
| the amount of energy stored by raising the water alone. But
| just like you I do hope that my instincts are missing
| something!
|
| (see nephew comment
| https://news.ycombinator.com/item?id=40273030 )
| taneq wrote:
| Hmm.. the more I think about it the more I agree with your
| intuition. If the air's at constant pressure then the work
| it's doing as it exits the chamber is coming directly from
| the water entering the chamber. There's no difference (in
| terms of energy) between having a turbine at the bottom of
| the column of water vs. having the water push the air and
| then the air spin a turbine. The whole thing seems like
| they started with "let's do compressed air energy storage"
| and realised half way through that the best way to do
| compressed air energy storage is for it to actually be
| pumped hydro.
| usrusr wrote:
| It's more capacity than just pumped hydro of identical
| head x volume: even if we ignore the "compressed spring"
| of the air involved, charging would require at least the
| energy for lifting the water plus the energy for heating
| up their heat source. If you close a valve in the water
| connection, then pop open the air pressure vessel letting
| all energy still in the compressed gas you to waste,
| you'd still have the heat storage, and you could let the
| water rush into the lower reservoir through a turbine,
| harvesting the entire energy contained in the water
| (minus inefficiency). So it's definitely more, the heat
| and the gas discharge we just wasted.
|
| The question is how much more, whether the symmetry
| suggested by the balanced state implies 2x energy storage
| or not.
|
| Another mental model to further separate the two storage
| media (water lift and air compression) is this: you could
| charge separately, first raising the water with a pump,
| with the dry cavity at ambient pressure via an open
| connection to daylight, then seal the cavity an charge it
| as a compression vessel in the non-isobaric way. I still
| can't decide between trusting the "balance implies 2x"
| intuition or not, but it should be easy enough to
| calculate. At least the thought experiments show that it
| can't be 1x the energy stored by lifting water alone.
|
| I consider starting with "let's do compressed air energy
| storage" as a given, the "do it by pumped hydro" does not
| come into play because pressure vessels are hard, it
| comes into play because building compressors and turbines
| that have good efficiency over a wide range of pressure
| is hard.
| davedx wrote:
| Yeah, I have to wonder how it compares to pumped hydro
| operationally too. They talk about capital costs but didn't
| explore what opex would be like at all. I would think with
| heat, air and water (as opposed to water in pumped hydro),
| maintenance and operations will be more expensive.
| usrusr wrote:
| I know of some pumped hydro sites that have been given up due
| to opex, with no clear change of mind due to changing
| circumstances in the decarbonisation age yet in sight. What
| they do have in common, I think, is low head. There's just a
| lot of water to carry traces of sediment into the mechanism,
| and so much reservoir ground to keep from leaking for a given
| amount of capacity.
|
| But you don't arrive at isobaric storage looking at mineshaft
| pumped hydro wondering if it could be improved upon. You
| start looking at constant volume (A-)CAES, either in high
| pressure tanks at/near the surface or in salt caverns, and go
| from there, what of we did not have to deal with a very wide
| range of operation pressure.
| mozman wrote:
| Have you heard of Snowy 2.0? Massive failure. Pumped storage in
| AU.
| stefs wrote:
| I have not - why is it a massive failure?
| pfdietz wrote:
| They've had problems with tunneling, I believe.
| BurningFrog wrote:
| Most places don't have a suitable mountain where you can
| destroy the natural beauty with a dam.
|
| In contrast, there is underground everywhere on Earth.
| walrus01 wrote:
| The australian outback is not exactly known for its hills and
| mountains...
|
| Pumped hydro done on a large scale needs a reservoir that is at
| a considerable elevation gain.
|
| example:
| https://en.wikipedia.org/wiki/Taum_Sauk_Hydroelectric_Power_...
| hackerlight wrote:
| > 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 wrote:
| My guesses:
|
| 1. no degradation
|
| 2. cheap to expand? - simply expand the cave
| lukan wrote:
| "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 wrote:
| These are the costs of installation, but what about maintenance
| and replacement costs?
| aplummer wrote:
| Surely 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 wrote:
| > 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 wrote:
| BloombergNEF reports a cost of $115 per kWh for turnkey
| energy storage systems (in China) so their comparison is
| likely to hold up for complete systems in Australia and the
| US.
|
| https://about.bnef.com/blog/global-energy-storage-market-
| rec...
| pier25 wrote:
| What about emissions from lithium batteries manufacturing?
|
| And how long do lithium batteries last?
| hinkley wrote:
| Installing power capacity is not O(1) complexity.
|
| A battery UPS under my desk doesn't really affect my rent or
| mortgage. Buildings not only need to get built they also need
| to be maintained.
| richardw wrote:
| "VanWalleghem said there is room to push costs down as the
| company gains experience from these first few plants. The
| storage systems have a projected lifespan of about 50 years,
| which is an important data point when comparing it to battery
| systems, which have much shorter lives"
|
| So both longevity and working towards reduced costs for future
| plants. I guess someone thinks the long-term costs will end up
| below Li-ion, and likely lower environmental impact, at least
| compared to the battery component.
| hackerlight wrote:
| Another benefit is it's all onshore, the US has energy
| security and independence of critical industries from China
| as a priority.
| Ekaros wrote:
| How do cycles and lifetime compare? More cycles over long time
| would lower final unit cost. That is price of kWh at time of
| release. Which I don't think will ever go down for load
| shifting.
|
| In the end 3 figures really matter total capacity, power output
| and cost per "generated" kWh on average over lifetime.
| usrusr wrote:
| The compressor/turbine part will have predictable wear rates,
| not substantially different from what you see in fossil
| plants.
|
| The reservoirs will at some point see noticeable sediment
| buildup, but not at all comparable with surface pumped hydro
| based on blocking valleys, due to the cyclic nature of the
| water flow in the hydrostor facility. And occasional cleanout
| (measured in decades or centuries?) will be trivially cheap
| compared to construction cost. Very much unlike cleanout cost
| behind valley dams, which are would-be cleanout costs because
| that never ever happens as it would utterly dwarf the cost of
| the original dam. There's been an article linked here a few
| months ago (can't find it, unfortunately) about how the total
| capacity of pumped hydro is getting increasingly smaller each
| year, despite new sites getting built. This is because
| sedimentation already outpaces the buildup, and it will only
| get worse the more we build. The volumes accumulating behind
| a dam are just too big, unless you have zero natural flow
| from rainwater (and then just getting the working volume of
| water to the site would be prohibitively expensive, per
| capacity, even before you factor in evaporation - the cycle
| capacity per unit of water is just so much lower than what a
| hydrostor site would achieve with its much larger head plus
| the energy stored in air compressionand heat)
| RedRider73 wrote:
| Me I work with a turbine (Rankin Cycle) we use about
| perhaps every day 22 or 3 reservoirs of 20 m3 just for the
| air instrumentation....
| davedx wrote:
| Yeah, also it takes 3 years to build. I predict that there will
| be so much more lithium-ion batteries deployed by the time this
| is finished that it will change the economics of operating it.
| usrusr wrote:
| One thing that hasn't been mentioned in siblings yet: the bulk
| of the money, more if you lean further towards capacity in the
| capacity vs throughput decision, is in the excavation. This is
| not only a "forever" investment, it's also money spent on the
| local economy. This isn't the case at all for battery cost,
| unless you happen to be the world center of the battery
| business, all the way from mine to recycling.
|
| Another aspect, completely unrelated and I'm not sure hydrostor
| already makes that part of the design (but it could totally be
| introduced later, without invalidating any of the excavation
| investment): some of the energy stored in an A-CAES system is
| stored as heat. When you do need heat, for a district heating
| system, for a swimming pool site or whatever, you can decouple
| some of the heat from the pressure storage. Worst case some of
| the joules repurposed end up missing in discharge, but it's
| also possible that they are simply joules not lost to cycle
| inefficiency. And if you happen to need cooling (datacenter on
| site?), at the time of discharge you can just keep some of the
| stored heat untapped, substituting with energy from the warm
| end of the coolant cycle that you want to freeload on the
| A-CAES. Compared to other waste heat/cold coupling schemes, at
| hydrostor pressure levels you would get considerably higher
| heat/cold deltas to work with. Huge potential, and with the
| reservoir shaft having very few site requirements, coupling
| opportunities should be plentiful (as compared to e.g.
| opportunities that only ever arise in remote valleys)
| jillesvangurp wrote:
| The economics of batteries are a function of cycle limits (none
| in this case, probably) and how much energy you can store and
| discharge over time and the price difference between charging
| and discharging. All that minus the upfront installation cost.
|
| The article says this thing should last at least fifty years.
| There's no good reason it couldn't last longer as it shouldn't
| really degrade over time. If you assume daily charge/discharge
| cycles, that would be about 18250K cycles over 50 years. Times
| 4GWh is about 73TWh of energy sold to the grid at, hopefully,
| some profit. Of course that all depends on demand, utilization,
| and whether there are any cheaper ways to store energy. It's
| probably going to end up some percentage of that. But best case
| that's energy you buy cheap and sell at a higher price. Even a
| few cents difference starts adding up to billions pretty
| quickly. And that's before you consider the alternatives
| (buying energy on the open market from another provider,
| investing in more energy generation, etc.).
|
| The prices you cite are just the purchase price. And of course
| lithium batteries don't last forever. So you'd be writing them
| off at some point. But in fairness, there are some battery
| chemistries that are getting quite good cycle times. So, the
| comparison might become a bit more fair over time.
| humansareok1 wrote:
| >I wonder what the case is for it.
|
| That there is a finite supply of Lithium available on Earth?
| aoeusnth1 wrote:
| Probably these costs have a lot faster learning curves as they
| are not as widely deployed yet.
| jeffbee wrote:
| Also curious since the CPUC storage credit maxes out at 4h, so
| 8h seems particularly pointless.
| foreigner wrote:
| How 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 wrote:
| I'll assume the inlet is below water level / at the bottom of
| the tank...
| ulrikrasmussen wrote:
| I 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 wrote:
| Why three? Their diagram shows two (plus the cavern, which
| must already exist)
| ulrikrasmussen wrote:
| To 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)
|
| 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 wrote:
| It 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
| Slartie wrote:
| Put the air inlet/outlet at the top of the cavern, and the
| water inlet/outlet at the bottom. Then just stop pumping air
| while the water level in the cavern is still above the water
| outlet. A little water has to remain in the cavern at all
| times.
| Cthulhu_ wrote:
| As long as the water pipe inlet is below the water level that
| isn't going to happen. Think of a plant spray or super soaker,
| same principle.
|
| Nothing personal to the commenter I'm replying to, but I love
| watching HN re-engineer long existing basic systems.
| tromp wrote:
| > 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 wrote:
| Yes, the diagram shows that the same water is used
| usrusr wrote:
| They 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 wrote:
| I 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 wrote:
| Suppose 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 wrote:
| Because 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 wrote:
| Several 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.
| pjc50 wrote:
| I would have thought this is like the Carnot cycle: the greater
| the difference across which you're generating energy, the
| better. So you want the low side at as low a pressure as
| possible.
| masteruvpuppetz wrote:
| I 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 wrote:
| Exists, 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_syste...
| jimnotgym wrote:
| What stops the air from just bubbling up the water pipe?
| caf wrote:
| The water tunnel/bore would be connected to an opening at the
| bottom of the chamber, not the top.
| nashashmi wrote:
| . pipe | | | |
| |---|-|---water level --| | |_| pipe end below |
| |_______________________|
|
| When the pipe is below the water level, air can't travel up the
| pipe.
| ourmandave wrote:
| Well this changes the whole look and feel of future Bartertown
| entirely.
|
| They probably won't even _have_ a Thunderdome. =(
| littlestymaar wrote:
| How 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 wrote:
| If 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 wrote:
| The 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 wrote:
| The air still is there whes you need it. The thermal energy
| is lost but the pressure isn't.
| littlestymaar wrote:
| Yes, but without the thermal energy you cannot
| depressurize it in a turbine, because it gets so cold the
| air will start condensing, and then you'll have droplets
| of nitrogen destroying your turbines!
| gcanyon wrote:
| No 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 wrote:
| Compressed 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 wrote:
| Compressed 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 wrote:
| This 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 wrote:
| From 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 wrote:
| Insightful, thanks!
| pfdietz wrote:
| I 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 wrote:
| I'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.
| lazide wrote:
| If you empty that compressed gas, it cools everything it
| comes in contact with. Room temperature gas still has a lot
| of thermal energy.
|
| The effect the prior poster was discussing is most apparent
| at large scales when someone is doing actual efficiency
| analysis - compressed air is not a very efficient way of
| storing or transporting energy in most contexts. No one would
| use compressed air for a power grid, because it would quickly
| be apparent how terrible it is.
|
| It _is_ however a great way to transfer and use energy in
| many industrial contexts, as turbines and pistons using high
| pressure compressed air can be very compact while also being
| very powerful, and have built in cooling.
|
| At the level of typical household use, the efficiency effects
| aren't notable. No one is going to care or even notice if it
| cost 1/2 cent of electricity (at the compressor) to use that
| air impact wrench vs 1/10th of a cent to use an electric one.
| Especially when the electric one is heavier and has less
| torque.
| gparke wrote:
| I think you are right about the closed system. When the
| compressed air spins the dynamo, it will cool, and then
| absorb heat from the environment. In an ideal, lossless
| scenario, that heat is equal to the heat given off when it
| cooled. So maybe you can view it as a battery that stores the
| energy in the environment?
| pfdietz wrote:
| The room temperature compressed air still has some internal
| energy, and some of _that_ energy can be converted to work by
| expanding the air through a turbine. The air at the outlet of
| the turbine will be really cold. Expanding compressed air
| through expanders like this is part of how air liquefaction
| plants operate.
| kobalsky wrote:
| the article doesn't mention how heat is stored, it just says
| "the system extracts heat from the air and stores it above
| ground for reuse".
|
| do you know how they do it?
| pfdietz wrote:
| I don't know in detail, but they could do something like
| this: compress the air, making it hot, then run the hot air
| through a packed bed of small objects (pebbles, bits of
| iron). As the air goes through the bed the heat is
| transferred to the material. This ends with a temperature
| gradient across the bed (hot at one end, cooler at the
| other). To discharge, the flow of air is reversed: in at the
| cool end, out at the hot end.
|
| This sort of design (a counterflow heat exchanger, basically)
| keeps the delta-T at each point low, so the system has low
| entropy production.
|
| A similar heat exchanger could be designed with a liquid
| thermal storage medium, where the air and the liquid are
| flowed past each other in opposite directions (separated by
| solid walls, most likely). The hot storage tank would be
| insulated. An advantage of this design is the pressure of the
| liquid storage tanks needn't be high, unlike the vessel
| containing the pebbles in the earlier described system.
|
| All these may need to dump some waste heat to the environment
| as a consequence of inefficiencies in the system.
| crazygringo wrote:
| I understand what you're saying, but your claim seems
| misleading to me.
|
| Compressing air absolutely does store energy. It takes work to
| compress it, and work will be done when it is allowed to
| expand.
|
| Yes, one way of measuring the stored energy is by the resulting
| increased temperature. Compressing air necessarily raises its
| temperature. And then if you want to you can transfer that heat
| elsewhere, go ahead. That's how air conditioners and
| refrigerators work, after all.
|
| But in the basic case, it seems entirely accurate to say that
| compressing air does actually store energy. Just like raising a
| heavy object against gravity stores energy.
| pfdietz wrote:
| It doesn't store energy in the sense that all that work you
| did compressing it doesn't increase its internal energy. It
| just has the energy it started with, floating around in the
| atmosphere. Now, some of _that_ energy can be converted to
| work, if the air is adiabatically expanded, but particularly
| at high compression it 's not large compared to the energy
| that went into compressing the air (and that was dissipated
| as heat when the hot compressed air was cooled.)
| crazygringo wrote:
| But it _does_ increase its internal energy. Its temperature
| goes up.
|
| Obviously if you let the compressed air cool, then you're
| letting the energy dissipate. So if you want to preserve
| all the energy, don't do that.
| pfdietz wrote:
| The air that is stored underground has been cooled, so
| yes, the energy that was added isn't there.
| KorematsuFredt wrote:
| Is compressed air in itself source of energy ? Or does it
| depend on the external air pressure as well ? For example I
| compress air in a canister and move it to outer space or deep
| underwater, does the energy we can exploit out of it goes up
| or down ?
| opwieurposiu wrote:
| You can store about 10kWh of heat energy in your water heater
| at home.
|
| https://www.pvh2o.com/faq
| foota wrote:
| Would it make sense to compress air, discard the heat
| generated, and then use the compressed air later to increase
| the efficiency of a turbine on a combined cycle plant?
| pfdietz wrote:
| Yes, that's how old style CAES systems worked (although those
| were not combined cycle). There are two of them.
|
| http://www.eseslab.com/ESsensePages/CAES-page
| zamadatix wrote:
| If I'm remembering this correctly from physics class then in
| math terms this is described as U=C*n*R*T where U is the
| energy, the constant C varies depending on the degrees of
| freedom the molecules of the gas have, n is the molar amount of
| the gas, R is the ideal gas constant, and T is the temperature.
| From that perspective it seems impossible to raise the pressure
| without also raising n resulting in a higher U even if you
| maintained a constant T while you did so?
| pfdietz wrote:
| I'm talking about internal energy per mass of air, not per
| volume. Sorry that wasn't clear.
| schiffern wrote:
| Funny, when I saw the headline I thought, "I _hope_ they 're
| using a trompe / Canot compressor or similar for efficient
| isothermal compression and expansion."
|
| https://www.youtube.com/watch?v=50fJ8Av_g7Q
|
| https://www.youtube.com/watch?v=uvf0lD5xzH0
|
| https://news.ycombinator.com/item?id=27066295
|
| Sad to see people are misinterpreting the cleverness of
| isothermal compression, and thinking it's "just" thermal
| storage.
| pfdietz wrote:
| How does that have anything to do with what I was saying? The
| internal energy (per unit mass) of the compressed air at
| given conditions is not a function of how those conditions
| were reached.
| Pxtl wrote:
| I 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.
| ck2 wrote:
| Why not lift super heavy but cheap objects like rocks or dirt and
| then let gravity be your battery?
| samcheng wrote:
| They definitely do that with water. It's called "pumped
| storage" and there are megawatt-scale installations all over
| the world.
| ninju wrote:
| https://en.m.wikipedia.org/wiki/Pumped-
| storage_hydroelectric...
| time0ut wrote:
| A 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/ [1]
| https://en.m.wikipedia.org/wiki/Helms_Pumped_Storage_Plant
| psadri wrote:
| While at it... they could try to extract some atmospheric CO2
| from the more concentrated air.
| coryfklein wrote:
| What 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 wrote:
| Totho, has graduated from snap bows.
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