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Comment by jimktrains2 | Hacker News Reader

Very naïve question:

What are the issues with moving a liquid (water?) from a low storage tank (in say your basement) to a high storage tank (say in your attic) and then at night let it flow in the opposite direction to produce electricity? I haven't done the calculations, but would it require too much liquid or maintenance?

I'm also not sure what this would be called? Gravity Battery?

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I'm also too lazy to actually do the calculation, but to a Fermi approximation XKCD has already more or less proven[1] that it's not terribly practical for a homeowner as an energy storage solution.

[1] https://what-if.xkcd.com/91/

converting to and from mechanical energy is inefficient. But it has been done in some places.

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

I mean, I figured it was worse than a battery, but if you can store it much more cheaply it might have been worth it? EDIT: The link also goes through some of the pros and cons. Thanks!

And cool, my guess at a name wasn't too far off:)

Well, back of a fag packet calculation...

Let's lift 1KG of water up 5 meters.

That will require 50 joules of energy (5 * 9.81).

Suppose I want to store 5kWh of energy (half my usage).

1kWh = 3600000J

5kWh = 18000000J

1KG of water is 1 litre.

I need to store 360,000 litres of water - that's a bit too much did domestic use :-)

Is large here - but I think that's about right.

It's called pumped storage. It exists, but only at larger scales than a household system. It's ~80 efficient.

http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity

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