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by XorNot 864 days ago
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.
2 comments
shellfishgene 864 days ago
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.
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kibwen 864 days ago
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.

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XorNot 864 days ago
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.

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15457345234 864 days ago
> 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.

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mnw21cam 864 days ago
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.
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XorNot 864 days ago
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).

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