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Comment by elihu | Hacker News Reader

Batteries will probably be cheaper, but pumped hydro storage will probably cost about the same since it's a mature technology.

I could see Norway or Switzerland being major players in pumped hydro storage, given their geography.

Awhile back I did a bunch of math to try to figure out how much stored gravitational energy is in Lake Mead, and if I didn't make any major mistakes it came out to be about as much energy as the U.S. uses (as electrical energy) in 24 hours. The idea of moving that amount of water around on short time scales is hard to fathom.

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The cost of batteries is actually rising, now that manufacturing costs only make up ~25% of a battery's cost [1]. The remaining 75% is raw materials, dominated by the cathode and anode, which are having trouble keeping up with demand [2].

1. https://www.visualcapitalist.com/breaking-down-the-cost-of-a...

2. https://www.cnbc.com/2022/05/18/ev-battery-costs-set-to-spik...

The cost of batteries is immaterial to anything being discussed here.

As you already knew.

From the previous comment:

> Batteries will probably be cheaper,

The above commenter clearly thinks that batteries are going to provide cheap storage.

If you have some alternative plan for storage at the scale of tens of terawatt hours, please do tell.

I'd imagine we'll probably continue to store power the same way the vast majority of power is stored now, using pumped hydroelectric storage.

Pumped storage is geographically limited: as more convenient sites are developed, viable locations become more and more remote. Hydroelectric storage is great, but not the pumped kind. The energy storage supplies by the Hoover dam, the Coolie dam, dwarf pumped hydro.

It's great for countries that have it, but you're not going to be storing much hydroelectricity outside of mountainous regions.

The overwhelming majority of storage will not be batteries, unless a massively cheaper battery chemistry takes over.

Lake Mead stores (well, stored) radically less energy than mountaintop reservoirs with thousands of feet of "head" can hold behind cheap earthen dikes. Look up "penstock".

I suppose I should have clarified that I meant "lake Mead if at capacity" which it isn't.

Stored energy (in a fixed gravitational field) is the product of height and mass. Hoover dam has a "hydraulic height" of 576 feet according to a government website, though the average height of any given drop of water is less than that because the lake is deep (or it was, anyways).

The thing about lake Mead is that the volume of water is absolutely huge. I don't think there are any mountaintop reservoirs anywhere close to it because though the altitude difference could be a lot more, it's hard to store large amounts of water on a mountaintop.

If we estimate that the average height of water in Lake Mead is 400 feet and it holds 26 million acre feet, then a pumped hydro storage system with 4,000 feet of altitude difference would need to hold 2.6 million acre feet to be equivalent. I'm pretty sure there's nothing like that in the U.S. The Bath County Pumped Storage Station in Virginia has an upper reservoir of about 35.6 thousand acre feet and a vertical distance of 380 meters (1,246 feet).

There are dozens of such reservoirs in the Sierra Nevada range in California. None of them will take as much water as Lake Mead, but they don't need to.

Sweden has lots of high mountains that may have shallow reservoirs built cheaply on top of. Reservoirs with earthen dikes are radically cheaper than the sort of dams needed for traditional hydro power, and may be placed almost anywhere, because they do not need or destroy a watershed. Lots of small ones, placed close to users, are better than one big one like Lake Mead.

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