I would imagine energy density to be a bigger shortcoming (gravitational acceleration times height difference) -- especially for typically accessible height differences. Eg for 500m this is something like an order of magnitude lower than chemical batteries (which are themselves presumably at least an order of magnitude lower than gasoline). This would mean that we need reservoirs to be much larger than equivalent chemical batteries.

> simply damming up a mid-sized valley can store such a ginormous amount of water that is it hard to compete.

I would love to see an analysis of whether it is feasible to build enough such large scale reservoirs (and how many we would need) to store an order one fraction of the daily energy needs. (at city/country/world levels)

> This would mean that we need reservoirs to be much larger than equivalent chemical batteries.

Yes we know. It is still cheaper on a cost-per-kwh basis than batteries, by a significant margin.

> I would love to see an analysis of whether it is feasible to build enough such large scale reservoirs (and how many we would need) to store an order one fraction of the daily energy needs. (at city/country/world levels)

No it is not, there are not enough suitable sites in most places in the world to make this work for world levels. That said, it is entirely up in the air if there would be enough mineable lithium to make batteries for similar amounts of storage.

Efficient electrical energy storage at scale is currently unsolved.

I quite like what this startup is thinking. https://www.energybank.nz/. For offshore wind energy storage.

This Energy Bank system could possibly be practical.

Unlike "Energy Vault" (NRGV), a purely fraudulent investment scam. Energy technologies seem to be favorites of frauds (fusion especially so). It seems like nothing is so obviously nonsensical as to attract the attention of regulators.

There are, in fact, far more than enough suitable sites to store as much energy as we could ever care to store. Hydro power generation needs a watershed, but storage really needs only a hill.

But there are lots of different storage technologies, and costs are falling fast, so pumped hydro may be undercut in places.

Lake volume is just that: it's volume, plus the dam, times two for the lower reservoir. Battery storage facilities however mostly consist of maintenance access, scaffolding, temperature control and fire suppression, we don't just dump cells on a big heap and call it an energy storage solution. Pumped hydro is doing fine in density, particularly since we rarely think in volume for large facilities, we think in acres, and nobody would build a battery facility vertically stacked.