Europe's deepest mine to become giant gravity battery | Hacker News Reader

Europe's deepest mine to become giant gravity battery

independent.co.uk

137 pointsdithered_djinn115 comments

Isn't there a better article?

- 2 MW of energy

MW is a unit of power not energy, maybe they mean 2 MWh, but if that's the case, it is a joke. That's like 30 Teslas cars, or half of a Tesla Megapack, which is a shipping container sized battery. 2 MW of power is not that big either, that's about what you get from a typical wind turbine.

- 70TWh of energy

At least, we have a proper unit, but I wish they tell us a bit more about how they got a number 7 orders of magnitude larger than the previous one.

- A study last year by the International Institute for Applied Systems Analysis (IIASA)

What study? Source please

>Future GraviStores will store more than 20MWh

https://www.marketscreener.com/quote/stock/ABB-LTD-9365000/n...

In which case, this one is a joke. It stores less than $3,000 worth of electricity (15¢ per kWh).

Part of me certainly hated myself for not stopping to read right there.

But it's an interesting approach despite the bad writing: if you fill a 1400m shaft with a dense chain of buckets (my term, they seem to call them vessels) you'll need a surprising low amount of mass throughput for a given amount of power flowing in/out. Because there is just so much in transit at any given point in time.

A naive implementation would quickly run into limits in rope strength and the like, but the schematic drawing suggests that the system they suggest consists of a chain of shorter loops, each just carrying whatever low number of vessels is easiest to engineer, and handing them over bucket-brigade style. This sounds complicated, but a similar thing is routinely done by gondola lifts with intermediate stations between separate wire loops (but here, handover could presumably be done simpler and in less maintenance-demanding ways because latency is no goal at all). So you'd design a system that works for three loops in a shaft not much deeper than a deep cellar and then scale it out to a very deep mine.

The power in/out is simply the throughput of a single stage times how many of those stages can be stacked in the shaft (or rather: hung to the sides of the shaft on top of each other, they'd certainly not be stacked in the statical sense). And if your battery is ever considered full but you still have extra energy to store, you could always decide to dig more horizontal tunnel, like when the mine was still serving it's original purpose. All you need is room (and transportation) for a larger spoil heap in the sun.

Digression: it's hot down there. Could you, with sufficiently insulated pipes, spin up a geothermally powered loop of air where the hot air carries moisture up skyside? If the sand is drier on the way up than it was on the way down while discharging you could theoretically end up with efficiency > 100. (in reality, more energy will certainly be lost to uninvited water finding it's way down, but perhaps this geothermal harvest could help battle the losses to water ingress)

PS: what was up with my mind when I wrote this? (second paragraph) Some serious confusion about throughput and power: power and mass throughput are obviously the same at a given shaft height, the advantage of a chain with less gaps/more vessels in transit at the same time is that you don't need much speed to achieve throughput.

Still, the approach of stacking many copies of the same loop design, with a well designed handover mechanism remains the way to go, instead of one big elevator trying to achieve throughput by faster travel. The key core idea is that the structure that carries the upper parts of the whole thing is already there (all the ground that hasn't been dug into)

> maybe they mean 2 MWh, but if that's the case, it is a joke. That's like 30 Teslas cars

Reminded me of the punchline to this water storage video:

https://m.youtube.com/watch?v=CMR9z9Xr8GM

That guy went mechanical with rocks:

https://m.youtube.com/watch?v=MVuVJC8lGck

> At least, we have a proper unit, but I wish they tell us a bit more about how they got a number 7 orders of magnitude larger than the previous one.

The 70TWh isn’t for this mine, but globally. FTA:

“A study last year by the International Institute for Applied Systems Analysis (IIASA) estimated that gravity batteries in abandoned underground mines could store up to 70TWh of energy – enough to meet global electricity demands.”

(See https://iiasa.ac.at/news/jan-2023/turning-abandoned-mines-in...)

Which again is nonsense as stated. The average world energy consumption is about 3 TW and gravity storages produce exactly zero and can meet no demand at all. 70 TWh would be enough to store about one day of global electricity consumption, for example to smooth out solar and wind.

That's why these projects are called batteries, not generators.

The nuke and fossil lobbies make a big deal out of how renewables are intermittent, and this is one of many practical ways to fix that.

I understand that but the statement 70 TWh is enough storage capacity to satisfy the world electricity demand makes no sense. Electricity demand is a power not an energy.

>Isn't there a better article? >maybe they mean 2 MWh, but if that's the case, it is a joke.

There are tons of equally bad articles about this story, which is sad to see. Quality journalism might not be dead but it sure is outnumbered!

However, reading about the proposed mechanism I might charitably interpret it as being able to deliver 2MW peak power, for however long it has available sand.

So an interesting aspect of this is how much area is available for sand, not just how tall the shaft is. If it has sand for 10 hours of operation it can store 20 MWh, if it has sand for 100 hours it stores 200MWh.

Many questions remain, but if it is more efficient than generating hydrogen, and takes less space than pumped hydro (or can be made in areas unsuitable for pumped hydro) there might be a point to it.

It's not just that the journalists are technically illiterate. It's also that the people making these claims are trying to deceive. You needs lakes of water to have enough mass to make gravity batteries practical. Those are called pumped-hydro. Anything talking about dropping heavy things is probably about 6 orders or magnitude too small and a scam to get government funding.

They probably mean 2MW peak output/input with the chain at maximum weight and velocity.

This would be a great plot element in a post-apocalypse film. Mad Max meets The Coal Miner's Daughter.

Another completely misleading article on gravity batteries. All the solid weight stuff is bunk, probably designed to suck out money from naive investors / corrupt state officials. Moving solid weights gives only a very small electric power, so building the proposed solid weight batteries gives units of MW at most, which is uneconomical. Unless it transports a large lake of water up and down a hill like in pumped-storage hydroelectric plants, and can provide tens or hundreds of MW. Such installations are very expensive to build today, because all the low-hanging fruit options seem to have been already built.

> Unless it transports a large lake of water up and down a hill

https://gravity-storage.com/ are trying to make compact hydroelectric plants by putting weight on the fluid. Wish someone would give them loads of money :/

These kinds of gravity batteries worry me a little, because when I've seen the economics, they actually look pretty decent… and yet, that economic calculation ignores the other impacts, like them being terrible energy density and thus needing absurd volumes dedicated to them.

Most proposals are even worse, as they suggest concrete rather than sand. The monetary cost works out even then, but concrete production currently emits CO2, and the combination of that with the low energy density means they'd have to run for around a century to only be as bad as fossil fuels.

My thoughts exactly. It makes the engineer in me go mad if I see projects like Energy Vault [1] getting massive funding that could be used to try and develop technologies that make sense. Thankfully there are some people who see through the charade [2].

If you are into this thing and looking for an even more stupid idea to store energy, I present to you the StEnSEA [3]. Rolls right off the tongue, right? It is a hollow concrete sphere that is lowered to the bottom of the lake. Pumps then remove water from it, creating a vacuum. Letting the water back in and using the pumps as generators, the energy is reclaimed. Curiously absent from all documentation of this project is the amount of energy stored. I did some back of the envelope calculations a while back and it is 3.8kWh, for a multi-million-euro prototype!

[1] https://www.energyvault.com/ev1

[2] https://www.youtube.com/watch?v=iGGOjD_OtAM

[3] https://www.iee.fraunhofer.de/de/projekte/suche/2013/stensea...

> 3.8kWh

That seems very low. Their website mentions 20 Mwh+.

Though my back of the envelope agrees with yours.

If I understand it correctly, ~20MWh is for the full size model at 700m depth and with a radius of 15m (prototype radius is 1.5m and it is located at a depth of 100m).

And building concrete spheres that can withstand the pressure of a 700m water column is probably an interesting design challenge on its own.

Gravity batteries are so appealing, until you calculate the cost per kWh. Any weight that you have to manufacture is already too expensive and you want manufactured weights since you want your weights to be as dense as possible and not just made out of compressed dirt.

The best option i know of for a mine is compressed air, and there some storages like this already built and operational. Just seal mine/cavity/empty oil well/etc and pump air in. There are some loses on friction, heating-from-compression but overall good economically speaking

>The decommissioning of mine shafts is a costly and time-consuming process for mining companies.

I wonder if that is part of the impetus - make cleanup/decommissioning happen in distant future dollars helps the balance sheet today.

https://www.marketscreener.com/quote/stock/ABB-LTD-9365000/n...

I think that the cost(or even profits) of filling a mine back in after excavation should be considered from the beginning. Hell we could even sell the futures now to recoup the cost of building a mine tomorrow.

I believe that's how the US superfund was supposed to work (tax miners now so we can use that money to fix the damage they did if they won't) but this is no longer the case.

Wouldn't that require knowing how far down/across you're going to dig? Most mines have a known seam to begin with, but a lot of exploration and geology work comes later when there's a big hole to work from. There's only so much you can tell at the surface before you start.

You can (and a less corrupt industrialized country's government sometimes will) require that they give you the money [or lock it into a fund they don't control] before they get permission to make the hole bigger. You need government inspections (so they can't make it bigger without permission) to make this possible, but those are needed for safety anyway.

If you let them, they'll eventually walk away leaving you with a toxic mess and a hole in your budget. The same thing applies for a government securing clean-up funding or a musician securing royalties from a label/ publisher, make sure you get paid first, if you're supposedly getting paid last it will always turn out that whoops, there is no money left, thanks for making us rich, bye.

Why do we want to fill them back in anyway? A new valley/hole doesn't seem like the biggest priority.

Dry sand has a mass of 1600kg/m^3

Potential energy, U = mgh. So the energy required to raise 1m^3 of sand 1400m is 1600 x 1400 x 9.8 = 22MJ = 6.1kWh

I've no idea how large their mine galleries are, but lets say they're 3m wide x 2m high - in 500m of gallery, we can store 3000m^3 of sand, so that's 18MWh.

I'm sure they've got a lot more space than that, but it just gives some idea of how much sand you're talking about.

> Potential energy, U = mgh. So the energy required to raise 1m^3 of sand 1400m is 1600 x 1400 x 9.8 = 22MJ = 6.1kWh

If you lowered 10 m^3 of sand (61kWh of potential energy), to generate the minimum 100kW power to participate in grid stabilization markets, you'd have to drop that 16000kg of sand for 61kWh/100kW = 0.61hr = 2196 sec. 1400 meters in 2196 seconds is 0.64 m/sec. That seems reasonable, but you'd need a lot of these (so a wide mineshaft) to generate a more meaningful amount of power (like at least 1 MW). Current grid scale batteries are capable of outputting hundreds of MW of power.

https://en.wikipedia.org/wiki/Battery_storage_power_station

> we can store 3000m^3 of sand, so that's 18MWh.

> I'm sure they've got a lot more space than that, but it just gives some idea of how much sand you're talking about.

They're going to need 3 orders of magnitude more space then because current generation grid scale batteries store GWh of energy, and generally speaking lower cost energy storage competes by offering much higher storage capacity.

Yeah, my surface level evaluation of these projects is that they're just not going to be viable - you have the height but you don't have the volume - mineshafts are by definition narrow - and some sort of automated load/unload system is going to run into issues of complexity and reliability and ease of access for maintenance to whatever's at the bottom end.

It's always going to be easier to move water around in an automated fashion, though, so I'm immediately skeptical of any system that isn't some variant of two tanks and a pump/turbine.

If you really do want to use gravity as a power source and don't want to go the hydro route you're better off building narrow-gauge train lines up the sides of hills. The lower-impact and lower-output version of that would be aerial ropeways.

I've participated in grid stabilization in Switzerland (ancillary services), and 100kW is absolutely nothing. As far as I recall, 10 years ago, the minimum needed to become a participant was 10MW

Even in the US, I'd bet that few entities bid into the ancillary services markets at only 100kW because the economics don't add up when you are using batteries (due to high fixed costs).

However, having the lower minimum has the advantage of allowing smaller firms to participate (i.e. companies controlling 100s of electric water heaters), instead of just massive utilities.

Thinking out loud here, but why sand and not water? Yes, water is only 1000kg/m^3, but probably much easier to transfer around using pumps and pipes. Water can make good use of the horizontal space within the mine, unlike sand. (The graphic in the article shows them using conveyor belts or trucks to move the sand horizontally which seems silly.) Thus the mine could basically be a mini pumped hydro power station, build a new reservoir at the top and use the mine as the bottom reservoir, then pump water water between the two.

When I thought about that silently, my answer was that storing water underground is a challenge when unprotected walls can turn into sludge. Water would require expensive preparation of the existing mine volume, whereas dry material could just be filled in, even stabilising the mine a little in the process. Water and sand sit at different points in the cost per W vs cost per Wh spectrum.

A machine for lifting/lowering loose material is more complicated than a pump, no doubt about that. But a deep shaft would mean that you don't build one machine per shaft, you build a few dozen smaller ones with a good handover mechanism and start getting small serial production benefits right from the first installation. Capacity would be virtually infinite, because with excess energy you could just mine more of whatever stuff is down there.

I guess if it's expensive to switch the dry mass mechanism between directions or speed states, it might be worthwhile to prepare some basin volume up and down and run a small capacity pumped storage in parallel at the same site for higher frequency load changes and short peaks. You might even find yourself discharging the wet battery while charging the dry one or the reverse if there is a sufficient delta in dispatchability.

You'd think that in an article specifically about energy storage, in the introductory paragraph, they'd get the units right.

> The Pyhäsalmi Mine, roughly 450 kilometres north of Helsinki, is Europe’s deepest zinc and copper mine and holds the potential to store up to 2 MW of energy within its 1,400-metre-deep shafts.

It's frustrating, every article just repeats "2MW capacity." Gravitricity hasn't announced this project themselves yet, hopefully when they do they give the actual storage capacity.

But I think 2MWh might be correct - in press elsewhere Gravitricity says 500t over 800m produces 1MWh. This is a deeper depth but not that much, and this is very much an experimental project so I think they might be sticking to 500-750t mass. They anticipate larger systems using multiple masses rather than a single larger one. Still, they've also announced a 4MWh project in the UK, so it's not like they see 2MWh as a limit.

It’s a sad reality now, 1Mwh is sloppily called “1MW” when it’s about energy, but “1MW” when it’s about power. It’s just like the ship sailed on 1 kilocalorie.m being called “one calorie” I think we can give up on this one as well.

No. Never.

kcal and cal atleast is the same unit.

It all gets confusing when integrating power over a strange quantity of time. I wish we had some kind of rational unit to quantify energy

Joules? Maybe you're facetious but it's hard to tell over the internet.

I’m sceptical about this technology, but it seems it is a lot lower cost than batteries (they claim a plant can last 50+ years with 50k+ cycles), can provide bursts of power, and can offset the decommissioning cost of mines.

A slightly better article: https://eepower.com/news/gravity-energy-storage-systems-tran...

The company: https://gravitricity.com/

I'm curious about the running costs. I expect that heavy moving parts will cause more wear & tear than a LFP grid-scale stationary battery, but I could be wrong.

Huh...this is literally the "heavy weight" sort of gravity battery rather then pumping water. I'm...not really convinced this is going to be viable. 2MWh (which is what I assume the article means) is not a lot of power at all (about 40 days of my roof top solar production) - and that's with "the deepest mine in Europe".

The basic problem is that your heaviest, cheapest weight is concrete or stone which is only about 2.5 times as dense as water. But the cost you pay for that is you can no longer pump or flow it so by definition you're limited.

I'm not sure that the density of the material itself really matters much; having the weight take up less space doesn't really reduce the overall power of the system very much (the weight is probably not occupying a very large portion of the shaft's height). That said, lead is also dirt-cheap and is more than 11x denser than water.

Gravity batteries are cool. They don't make a lot of economic sense by themselves, but they do if the vertical height already exists and doesn't need to be constructed.

The heavier you make your counterweight, the more strength you need in your cables.

The problem is that you could solve this by say, lowering a small pallet of whatever to the bottom of the shaft and moving it sideways out of the way - trading "power" for "energy storage".

But if you extend that idea you wind up at "pump a liquid" as the obvious way to do it, since that has essentially no limit on flow-ability.

The other problem of course it lead in the first place: 1000kg of lead at 1500m high is about 4kWh of potential energy. 1000kg of Lead-Acid batteries is about 25 kWh of potential energy. I suppose you could put the batteries on a cable for the extra 4kWh but I suspect the complexity isn't worth it.

> 1000kg of lead at 1500m high is about 4kWh of potential energy. 1000kg of Lead-Acid batteries is about 25 kWh of potential energy. I suppose you could put the batteries on a cable for the extra 4kWh but I suspect the complexity isn't worth it.

That's just so well said. Should be the top comment every single time this dumb idea is surfaced.

I'm convinced now people are pulling stunts like this just to make renewables look bad.

The difference is that 1000kg of lead costs ~US$2000, and lasts forever, but 1000kg of lead-acid batteries costs ~US$9000, but only lasts for 10 years.

The mechanical equipment and supporting plant equipment to turn that 1000kg of lead into a power storage system is not free, does not last forever, and experiences mechanical wear and tear - in fact it likely needs constant maintenance on a cycle of weeks to months.

Whereas those Lead-Acid batteries will do their thing for 10 years, then can be recycled into new Lead-Acid batteries and do it again. The support equipment is all solid-state electronics (though still about a 20 year reasonable lifespan).

I agree. Keeping a 1.4 km long chain of elevators with buckets of sand running, with as little friction as possible, in a hard to access mineshaft, probably with high humidity, and sand everywhere, sounds like a very expensive operation.

I admit in the past I've been skeptical about the use of gravity batteries when they involved things like towers and stacking large weights as their energy density is relatively quite low, but this seems like it makes a ton of sense. That is:

1. The shaft is already dug, so no need to build a tower.

2. As the article points out, many/most of these sites are already well-connected to the grid.

3. Also as pointed out in the article, this could be a boon to depressed areas and help broaden economic value generation.

Am I missing something?

A gravity battery doesn't need a well or a tower. The slope of a hill will do. More or less put railroad tracks up the slope, and have the "car" winched up and down. Just like the ratcheting trolleys that go up and down hills.

| Just like the ratcheting trolleys that go up and down hills.

https://en.wikipedia.org/wiki/Funicular

There was recently an article here about an electric truck that never needs charging. It drives up a hill, collects a load of rock from the mine there, and by the time it has driven back down with the heavy load, regenerative breaking has recharged the battery.

Soon we will be hearing of the global flattening.

While that makes perfect sense, I have read journalists claiming that Teslas were 110% efficient because of regenerative braking.

A pile of rocks on a hill is a renewable energy source if you are prepared to wait a few billion years for plate tectonics to recharge it.

Would you happen to have a link?

"This massive 45-ton electric dump truck never uses more energy than it generates on its own — here's how that works"

https://www.businessinsider.com/edumper-121-ton-electric-dum...

(You can find more articles if you search for "eDumper")

This must be orders of magnitude more expensive than pumped hydro and I would expect more expensive than lithium batteries. And unless the mine is close to an existing high voltage substation then there will be significant costs hooking it up to the grid. The pilot will be a 2MW generator but you can fit a 2MW inverter and a 2MWh battery into a single shipping container so the scale is really minimal.

> The IIASA analysts noted that mines already have the basic infrastructure for such an endeavour, while also being connected to the power grid. “This significantly reduces the cost and facilities for the implementation of Underground Gravity Energy Storage (UGES) plants,” the study noted.

Not that your wholly unsupported naysaying isn't compelling.

Connected to the grid yes but usually the interconnect is simply enough for running the mine not enough to cover many megawatts of storage capability. The battery storage companies have found that there is an abundance of fields and brownfield sites close to existing substations to place their batteries where the cost of connecting to the grid is minimal.

The hoist at this mine is 2.5MW, there's typically some ore processing on site, mines end up requiring a lot of ventilation and cooling, dewatering, most of the work vehicles used in deep mines today are electric (and these aren't light battery vehicles but heavy equipment trailing high voltage cables), I think it's very conservative to say that the mine consumed over 5MW when it was fully operational.

> Connected to the grid yes but usually the interconnect is simply enough for running the mine not enough to cover many megawatts of storage capability

Mines can use a LOT of electricity. I found a presentation from EPRI[1] talks about varoius electric vehicles and machines used in underground mining. One slide references a "mining system" that alone draws 5-10Mw. Even if you take that as "the whole mine uses 5-10MW", it means that it's grid connected well enough to handle Mw of storage.

[1] EPRI is a respected R&D non-profit in the electricty sector. The slides: http://mydocs.epri.com/docs/publicmeetingmaterials/1203/jkn2... the slide I reference is #14.

There are plenty of engineering projects which don't sound like a great idea, then turn out not to be a great idea [1].

(admittedly on that one I'm not really onboard with "oh lol why are we using wood for a bridge when we have steel" as an explanation, but conversely there were serious problems with engineering design of how wood was used on this bridge and it did collapse in the end - complexity of design versus known elements is an important consideration. A casual observation of "does this really make sense?" might've concluded that stepping so far out of bounds of normal design should have been more carefully treated or had exceptional requirements in the first place).

[1] https://en.wikipedia.org/wiki/Tretten_Bridge

Allow me to support the completely unsupported naysaying: https://cleantechnica.com/2024/01/16/gravity-storage-101-or-...

Cliff's Notes: any currently-considered form of gravity storage that isn't pumped hydro is orders of magnitude more expensive and more stupid than a Tesla Megapack.

Michael Barnard's abrasive tone aside, is he wrong?

They aren't building it from scratch.

He addresses using existing mineshafts in the article.

From your link:

> The alternative idea is to put a lot of sand on a single elevator with huge winches that just goes up and down in a big, deep mine shaft. This one at least has the potential to be viable.

Did you read the part immediately after that?

Yeah I did. He immediately dismisses the prospect, cuts the size of everything in half with a glorious hand wave, and then explains how that's not enough.

I don't think it's viable either FYI. Just pointing out your rebuke acknowledges the feasibility.

had to look up some price comparisons.

Fengning Pumped Storage Power Station stores 40 GWh and cost 2 billion or 20 Wh/USD

Tesla megapack 2 stores 3.8 Mwh = Costs 1.5 million, or approximately 2.6 Wh/USD

It seems like pumped hydro is about an order of magnitude cheaper.

https://en.wikipedia.org/wiki/Fengning_Pumped_Storage_Power_...

https://en.wikipedia.org/wiki/Tesla_Megapack

That wasn’t the comparison. The comparison was every form of pumped storage EXCEPT pumped hydro vs a megapack. I’m sure you’re correct about pumped hydro though, it does seem like something we should do more of.

That was the comparison I felt compelled to make. I have been a big fan of pumped hydro for many years.

Contrary to what skeptics say, there are countless locations all over. [2]

There is a suitable location 3 times larger than the Chinese one I linked That could use California's sites reservoir [1] under construction as a lower basin. It would have a similar 400m head, and an upper reservoir with 3 times the capacity or 120 GWh.

https://en.wikipedia.org/wiki/Sites_Reservoir

https://re100.anu.edu.au/#share=g-e5955e35f1c7f3677ac265bcdd...

another: https://maps.nrel.gov/psh

Here in the PNW,

"The Columbia River Gorge is a canyon ... up to 4,000 feet (1,200 m) deep [and which] stretches for over eighty miles (130 km) as the river winds westward [toward Portland]." - WPedia

Hmmm. Now I'm wondering how many reservoirs already (or could) exist above and along 80 miles of river. (No need to dig tunnels to the generators.)

Exactly one reservoir (or a number of tiny ones not worth mentioning), because even all the way from Richland to Portland there is hardly any elevation drop.

PS: oh, you meant reservoirs in contributory valleys left and right of the main river. Sorry about the misread, "above and along" should have been clear enough.

this works for water storage, and some for hydro generation, but for hydro stroage, you really want two large basins with as big of a elevation change as possible.

This is because dams are very expensive, have height limitations, and some inherent risk. Hover dam is only ~200 meters high. The big hydro storage projects have height changes ~400 meters.

Nice hit piece that looks like written by someone deeply invested in chemical batteries (or going mercenary for patrons who are). But his dismissal of mine shafts omits some important parts: when you have a mine, you don't just dangle a mass from an elevator winch, you fill the entire volume at the low end with ballast while discharging and get all that mass up again when charging. That's a many orders of magnitude difference in capacity versus the naive block-on-a-winch approach. And you don't just operate one winch with a Very Large Rope, you form a bucket-brigade of identical, cheap, short loops with a good handover mechanism. Or you equip the shaft with a pair of linear induction motors all the way up/down if you'd rather go solid state.

Then why not pour water down the mine shaft and pump it back out? That seems a lot less complicated than transporting any kind of solid material up and down. I can think of three possible reasons - material density, loses in pumps and pipes, and potentially measure to make the mine suitable for storing water.

That's what GP suggested. But unless the mine happens to be in particularly water-friendly rock or is carefully prepared for safe repeated flooding/dewatering, that would only speed up the conversion from mine to uncontrolled sinkhole. Many given up mines are expected to have active dewatering running forever, because the cost of letting them collapse or for safe filling would be so much greater than the cost of continued dewatering for the next couple of generations.

For small capacities, using water as the ballast medium would certainly be cheaper. But there's a break-even point in capacity beyond which the cost for readying the volume for water would be higher than the premium you'd have to pay for handling dry mass instead of liquid.

Mines are heavy industrial electrical consumers already, so generally have strong grid ties.

Yeah, I'd be surprised if mines weren't in the multi MW range... but nothing like a modern hyperscale data center. Those damn things are 100MW and larger!

The current hoist at this mine is 2.5MW, so that gives an idea of the existing connectivity.

I actually wondered if it might be possible to reapply the main hoist at a mine for this kind of application, many already have some energy recovery. But I don't think it would be practical in that many situations because these deep mines often have other "tenants" (this one has a cosmic ray observatory for example) that will want to continue use of the main hoist---and of course it is appealing to install this type of system in operational mines when there's a disused shaft.

You might be surprised how few sites are suitable for pumped hydro and how costly it is to build. I can easily see this being both cheaper and more efficient. Most pumped hydro installations outside of northern Europe end up requiring large dams to create a big enough impoundment uphill. A direct weight solution should have better conversion efficiency as well, Gravitricity quotes 80% which is on the high end of pumped hydro. The charge/discharge rate and response time also look better than a similar pumped hydro setup, unsurprisingly considering the lower inertia.

It so happens that pumped hydro was considered for the same site but abandoned last year due to the high cost estimate.

You might be surprised at the enormous numbers of sites that are potentially suitable for pumped hydro, if you go looking for them in areas with vertical relief.

https://re100.eng.anu.edu.au/global/

"ANU has identified 616,000 potential sites around the world." (note that not all countries are included in this because of lack of geographical elevation data)

A place like Nevada has an enormous surfeit of opportunities for pumped hydro, due to the Basin and Range geography. Here's a project going forward right now. Look how tiny the basins are for the energy stored:

https://www.whitepinepumpedstorage.com/

More holes than we have fresh water to fill them with. Maybe someone will solve corrosion and we can use salt water.

Fresh water consumption is small compared to that evaporated cooling a nuclear plant of the same average power throughput.

Your second link describes itself as "a 1,000 megawatt energy storage project".

I'm interested in how much energy the site can store, about which there is no indication on that page. Do you think maybe they mean 1,000 megawatt hour?

It's to be a 8000 MWh storage facility that can charge/discharge at 1000 MW. So, eight hours of storage.

I doubt any pumped storage project can beat solar and battery hybrid projects these days, especially in sunny places like Nevada.

People get very laser focused on the storage part, but energy you generate is entirely fungible with energy that you've stored so pumped hydro needs to compete with generation too.

edit: looking further into this to try to put some rough numbers on it, the 5 years it'll take to dig the holes means in this particular case I wouldn't be too surprised if batteries alone could beat it by the time it connects to the grid in 2031.

I'm pretty pessimistic on storage these days, but I will admit that after running some back of the envelope numbers I'm actually a lot more optimistic about chemical batteries then any of the physical storage schemes.

Pumped hydro has a recharge problem - if your reservoir is much larger then your pump, you can't recharge the system in the time of cheapest energy (daytime when solar is active) before you'll be discharging again. The "roughly 4 hours" output of batteries lines up a lot better with this.

It's still too expensive, but when you plug that into the fact batteries can go in anywhere there's space, and they look a lot more attractive and definitely way faster to build. If Sodium-Ion batteries can be made to work and hit the right price point, things could change pretty dramatically though that's pinning hope on an unproven future technology.

Pumped hydro may work better with wind than with solar.

Consider the mismatch between supply and demand as a function of time; it has a Fourier transform with components at different frequencies (this is completely separate from the frequency of AC current in the system, please note). Some storage technologies are more suitable for different frequencies and different average charging times. Form's iron-air batteries, for example, would be suitable for frequencies an order of magnitude lower than Li-ion batteries. Operating a combined system with multiple storage technologies may at times involve discharging one to charge another.

I've been thinking about a similar system to drop weights into the ocean for a while, like with attached pressurized air tanks to inflate balloons for resurfacing. Not an engineer, so I haven't been able to calculate if any of this would work, at all.

That’s an interesting idea, but pressurizing air needs a lot of energy, and it needs to be pressurized more the deeper you’re going (because of well.. pressure). Not to mention the air volume at depth is much smaller, so you need a lot of air to start lifting, and once it’s buoyant and starts rising, you have a bunch of extra air volume that’s “wasted”.

How would you recover energy from that?

There was a plan, to use giant cylinders of landscape as hydraulic batteries.

The problem was the cost of excavation or building the cylinder. Then this came along, not even promoted as the future..

https://www.newcivilengineer.com/the-future-of/future-of-tun...

And it's ideal.as in they could turn testsites into batteries.

You could have such a battery in an any abandoned quary today. Chip the walls smoth, freeze an ice plug, pump water beneath and use the stored pressure.

Were going to read how this is an unsuccessful endeavor in about 5 years. I haven't seen a lot of great reports on gravity batteries. I wish something like this was highly viable and succesful. Seems like a great simple solution.

5 ? I'll give 2. See ya in 2026

I got a tidbit of amusing that a person named "boring" commented on a gravity mine article.

It will be interesting to see how much net energy is able to be stored after the energy cost of de-watering the mine is taken into account.

(An interesting tidbit of trivia I learned from miners is that deep underground mines only became feasible after reliable pumping was put in place.[1] Prior to that, they flooded out from groundwater intrusion.)

[1] https://en.wikipedia.org/wiki/Flooded_mine

Edited to add the wikipedia link.

Depends on base depth and water table - It's 1.4 km "deep" from the head .. which might be 2.5 km above sea level in Finland (what with all the steep bits and everything).

If the bottom is well above sea level and not in line of any underground rivers | streams | lakes it'll stay relatively dry.

For interest:

https://en.wikipedia.org/wiki/Pyh%C3%A4salmi_Mine

    The "main level" of the mine is at 1400 meters depth and can be accessed with either the mine hoist or via the access tunnel. The main level houses a cafeteria, washrooms, showers, workshops, storage facilities, as well as a safety area.

    It is also home to the world's deepest sauna, at 1,410 metres (4,626 ft) underground.

    Pyhäsalmi Mine has hosted numerous events due to its attraction as a unique location.

    It has hosted the deepest concert in the world (by Agonizer at 1271 m ) as well as dance performances.

    The 11 km long spiral-shaped main tunnel has also seen several uphill running and cycling competitions. 

    Pyhäsalmi Mine can be recognized as a filming location for the new sci-fi television series White Wall, premiered in 2020.

Ahhhh, Finland, Finland, Finland.

>which might be 2.5 km above sea level in Finland (what with all the steep bits and everything).

Steep bits? Are you thinking of Norway :-) there’s no steep bits in Finland, highest point above sea level is 1324M!

There was even a Norwegian campaign to gift a mountain for its birthday https://www.bbc.co.uk/news/world-europe-37662811

The bloody cheek of those Norwegians!!

It's all relative - I live in a state 3x bigger than Texas and the highest point is only 1248m .. when I visited (man years ago) lot's of places in Finland looked steeper than here.

One solution, you schedule pumping during times when the battery is charging, because presumably there is far more power available than can be used to charge the gravity battery anyways.

Mine flooding was the driving force behind the development of the original steam engines.

The phrase "2 MW of energy" makes no sense based on units. Shouldn't writers (and editors) be required to at least take high school physics or chemistry?

I took those things m, and I’m a successful software engineer and founder with an exit. I can never remember anything but joules for energy. Which I think doesn’t matter? And my RV has amp-hours? No fucking idea.

But are you writing articles about the topic?

Journalists are just failed CEOs.

As far as I can tell, they mean they can bring up to 2 MW of power online, with nothing said about the energy storage capacity of the site.

to be fair they might be somewhat confused by marketing copy. I've worked on installations like this, and its not uncommon for capacities to be specified as something like 50MW battery (4 hours). sometimes the number of hours is written in a different place to the base output capacity. I think it started because originally the idea is that the battery is some number of hours multiple of the production of a generating asset, like on-site wind. In fact capacity payments and stuff in some countries (read: subsidies) can be different based on the number of hours of the battery

Excellent to hear

Great, another Energy Vault grift... Hope this doesn't actually get built.

"giant battery" - 2MW ?

A typo ?

They probably meant 2TWh if it is to "to power the planet"

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