Interesting article advocating the use of “off-river pumped hydro energy storage” (yay gravitational potential energy) to solve the renewables storage problem.

That’s so elegant and elemental and clean, it’s kind of beautiful.

gravity storage… I love it

I understand that economies of scale makes a difference, but I’d love some numbers on smaller (household or apartment sized) solutions. Given that infrastructure costs are so massive now¹ I’d like to see how reasonable it would be to go completely off the grid.

[1] Yeah, over-investment led to this issue, but debating the reason for the price rise doesn’t stop the actual price rise.

It’s been quite a while since I did physics, so someone else, please check my maths here:

E = mgh

where:

E: Gravitational potential energy in joules

m: Mass, in kilograms of the elevated object

g: gravitational constant (9.8)

h = height difference between the high (e.g. 100% capacity used) point and low point (e.g. storage completely drained), in metres

According to this, a two-person household in Queenscliff (where I happen to reside) averages 14.5kWh per day.

14.5kWh = 52,200,000 joules

Assuming a two-story home, with a 3000L water (recall, 1L of water weighs approximately 1kg) tank on the roof (at an elevation of 8.5m), draining to a lower reservoir at ground level (You could bury the lower reservoir to further increase the height differential), the maximum amount of energy storable (ignoring pump / turbine inefficiencies) would be:

3000 * 9.8 * 8.5 = 249900J

or ~69Wh, unfortunately, well short of even a day’s worth of energy.

Unless I’ve done the math wrong (which could be likely, as I said, it’s been quite a few years since I last did any physics study), it would seem that this method of energy storage is really only useful at much larger scales, typical of centralised installations.

Yeah I did some checking, and your numbers appear to be fine. Oh well, I’ll keep dreaming

Yeah, as far as I can tell, to get even close (13.6kWh) to a day’s worth of energy stored, you need a truly massive tank (100,000L) and a pretty substantial height differential (50m), which would be far, far too costly for any kind of decentralised scenario.