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Comment by abdullahkhalids | Hacker News Reader

The video has some numbers in it about performance. They say dig a shaft of 150-1500m and hang a weight of 500-5000 tonnes. This translates to energy storage of between 204-20400 KWh storage.

Obviously, this seems very technically challenging. 500 tonnes is 64 m^3 of iron. We will see if their engineering is good enough to pull off their claimed 171 US$/MWh.

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26 m^3 of tungsten is what, less than a 3x3x3m cube? If they stack 10 cubes at the bottom they get mostly the full storage (-3m at least) for each weight. Seems feasible.

There is 280x difference in price between iron and tungsten.

https://www.metalary.com/tungsten-price/

2000 tonnes of tungsten is 60 million USD, of iron is 200k USD.

Tungsten costs around $30k/ton, so you'd be looking at a cool $15M for that 500T cube.

Lead goes for around $2k/ton, so this might be a more feasible compromise.

Depleted uranium prices are very hard to find, but should come as cheaper than tungsten.

Civilian sales look at least possible, I heard of at least one sailboat with a DU keel.

This is a technology where energy density doesn't matter at all because the amount of energy stored per ton is the same. So you want as many tons as cheap as possible. Therefore we either use water or concrete.

I assume the weight would be at least partially some of the dirt they dug out of the hole. Cost is the name of the game.

Quite a few similar companies are looking at compacted earth mixed with concrete to reuse some dirt and rock that is excavated. See also https://energyvault.com/

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