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Comment by yongjik | Hacker News Reader

Sorry for repeating myself, but gravity is weak. If you hang a 500t weight in a 150m vertical tunnel, it only holds 500 * 1000 * 9.8 * 150 = 735000000 J, or 735 MJ, that is, 204 kWh.

A Tesla model 3, basic model (MSRP ~$38k) has battery capacity of 50 kWh, so we're talking about four Tesla 3's.

I don't think digging a 150m hole is cheaper than four Teslas - and Teslas come with the rest of the car you can use for driving.

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Gravity is weak, but it's cheap. It is indeed surprising, but plenty of research shows that the levelized cost of gravity storage is cheaper than Li-ion batteries - even if you assume that Li-ion will get 4x cheaper in the next 20 years. There are other problems with Li-ion as well that will prevent it from scaling up to the amount of storage that our grid will need. I discuss all this with lots of citations in a white paper here https://github.com/syllable-hq/uphs-feasibility-study

> Gravity is weak, but it's cheap.

I'm sorry, I'm not trying to be pedantic, but what does "gravity is cheap" even mean?

No worries. Here is a good resource that talks about the levelized costs of gravity storage. It's estimated to be much cheaper than Li-ion battery storage on large scales.

https://www.storage-lab.com/gravity-based-storage

The primary benefit is reliability and lifetime. Your lifted rock isn't going to "malfunction" and suddenly weigh less.

I agree that gravity based energy technologies are mostly junk though. There are two important factors: cheap weights and unlimited scalability. Doing something "cute" such as using a mountain side or old mineshaft is reducing the scalability.

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