[heattemp99]

I've got an idea.. we build a wall at the edge of a huge mountain area. Water collects behind the wall during the winter, and then in the spring and summer we let the water out through a hole in the wall, which spins generators while the water flows out the hole.

[lordfrito]

Interestingly, there's a lot of current work around grid energy storage. Storing excess wind/solar power for use overnight, etc.

Everybody assumes batteries (lithium etc.) as the way to go. However the greenest / most efficient way to store the energy is actually just pumping water uphill to a reservoir, and extracting the energy by letting it flow back down.

Of course this storage system only works wherever there is someplace "higher" to pump the water. My understanding is that it's not worth the trouble to build a hill/mountain to pump the water up.

[0x53]

An excellent blog post on this idea: https://dothemath.ucsd.edu/2011/11/pump-up-the-storage/

[kwhitefoot]

> greenest

What does green mean here? Most of the developed world's easily used hydro sites are already in use. Expanding them in most countries means relocating lots of people, building huge dams, drowning towns, villages, and historical artefacts, losing agricultural land, disturbing river flows and irrigation systems.

Not always very 'green'.

[ElectricalUnion]

And when you have the space and the ability to build such pumped-storage hydroelectricity facilities, they require much cheaper and much more environment friendly materials.

And most already build hydroelectricity facilities can be retrofitted (although at high cost) to become pumped-storage hydroelectricity facilities.

[kwhitefoot]

> And most already build hydroelectricity facilities can be retrofitted (although at high cost) to become pumped-storage hydroelectricity facilities.

Really? You need a huge downstream reservoir to hold the water that you are going to pump to the upstream reservoir.

[ElectricalUnion]

What prevents you from digging a very deep downstream hole to store such water besides cost?

[kwhitefoot]

I think you need a bigger word than digging, it wouldn't be a gang of navvies with shovels. The cost would be enormous, there are better ways to spend the money: solar, wind, better electricity networks, DC interconnects.

[NikkiA]

500m is plenty 'high'...

https://en.wikipedia.org/wiki/Dinorwig_Power_Station

[perilunar]

I don't think "everybody assumes batteries". Pumped hydro has been around for a long time, and anyone with any interest in the subject knows it's cheap and effective.

[fbdab103]

What about all of those open pit mines? Surely some of them have access to a lower elevation location where the water could be piped. Or, two adjacent pit mines.