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Comment by retzkek | Hacker News Reader

Both TFA and the Bloomberg article it references [1] mention the 100MW power throughput of the battery, which is pretty meaningless without also knowing the energy capacity. For reference, the similar 100MW battery installation in Australia has 129MWh capacity [2].

This project is less remarkable when you read "About 2,100 megawatts of battery storage ... are in advanced stages of connecting to Ercot’s grid." [1].

1. https://www.bloomberg.com/news/features/2021-03-08/tesla-is-... 2. https://arstechnica.com/cars/2017/12/tesla-beats-deadline-sw...

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Also for comparison: a single pumped-storage plant will often have storage capacity in the GWh; e.g. the Linth-Limmern pumped storage part in Switzerland can store 33 GWh and provides 1000 MW peak power.

When I overlay the population density map, on top of the elevation map. I think there aren’t many opportunities in Texas for grid scale pumped hydro storage. Although pumped hydro has huge potential it is not homogeneously distributed all over the world according to this map. https://www.hydroreview.com/world-regions/22-million-gwh-of-...

Bill Gates mentioned pressurized pumped-hydro storage in his book, (which was the first I had heard of it), and it sounds quite promising and something Texas is well-suited for:

> GLIDES costs as low as $13/kWh and $346/kWh and roundtrip efficiencies as high as 80% can be achieved using depleted oil/gas reservoirs and high-pressure pipe segments as pressure reservoirs, respectively.

https://www.energy.gov/sites/prod/files/2019/12/f69/02_ORNL_...

> pumped-storage plant

Seeing the title, I jokingly thought of generating hydroelectric power off a dam, and storing excess power by pumping the water back up, Sisyphus like. I'm very surprised this is actually a thing.

Taken to extremes of solar+pumped-storage, we could end up with a situation where the earth spins more quickly in the early morning when the moment of inertia of the planet is lower because the solar panels haven't started moving all that water mass to its higher elevation yet.

There is always a morning somewhere!

This is an excellent point and I can't believe I overlooked it. Obviously there could still be significant lopsidedness since places where you'd be moving mass around might not be evenly distributed, though. No idea why someone downvoted you for this observation. :D

Yes!

It's also only slightly less efficient than batteries.

https://www.npr.org/2021/01/27/961242867/the-worlds-biggest-...

Elevation translates in to 'head' and that's the single reason that this works well in Switzerland which has something that many other places do not have: very high mountains. With sufficient head the potential energy of a reservoir of modest size can be very impressive, and without you can have a huge reservoir that barely moves the needle.

I wonder if you could do something similar with underground storage in a mine?

Not really enough volume you could only use the lowest levels, and even the largest mines are dwarfed by small lakes. You'd have to put the generators and pumps at the bottom where they'd be easily submerged.

Typically pumped storage uses two lakes, one high and one low. But points for creative thinking :)

> which is pretty meaningless without also knowing the energy capacity

I disagree. You can reasonably assume a battery bank will have a capacity between an hour and a few hours.

Safe assumption, at least for Tesla Megapack based projects. The Megapack has a default inverter that supplies 1/4W of power per Wh of energy. But there are options to buy bigger inverters.

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