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by brashrat 3699 days ago
Is pumped hydro dependent on geography? I'm no expert and I'm skipping over the research and calculation part, but I'd be somewhat surprised if solar panels on my house could generate enough electricity to pump more water up to a tank on my roof than I could run through for power generation.
4 comments
epistasis 3699 days ago
It's highly dependent on geography, you need two separate, very large, reservoirs at very different elevations. It takes a lot of water across a big height differential to store electricity.

It kind of reminds me of people that think that we should use the exercise bikes in gyms to power the lighting; yes, brilliant, but actually run the numbers and you realize that humans output very very little energy even at peak exercise. The amount of waste on generators would be phenomenal.

There are some cases where pumped hydro makes sense, but there's limited scalability.

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maxerickson 3699 days ago
Wikipedia has a nice illustration of the amount of power stored

For example, 1000 kilograms of water (1 cubic meter) at the top of a 100 meter tower has a potential energy of about 0.272 kW·h (capable of raising the temperature of the same amount of water by only 0.23 Celsius = 0.42 Fahrenheit).

https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricit...

Given the much smaller height of a rooftop tank, every 1000 kg of water pumped would support a number of minutes of normal household usage (a decent refrigerator would need several thousand kg per hour).

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astrodust 3699 days ago
You can water pump uphill, or, as they're experimenting with here, you can pump air underwater: https://www.torontohydro.com/sites/electricsystem/GridInvest...

I'm sure compressed air in other forms would be a good store. You could also raise and lower weights into a mine, it doesn't matter so long as you can convert between electric energy and kinetic potential of some kind.

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MrsPeaches 3699 days ago
Quick calculation:

1000L tank on a roof which is ~4m high.

E = m * g * h = 1000 * 9.8 * 4 = ~40,000J

Which is about 12Wh not taking into account any losses.

You could maybe improve this by having the water fall into a well but still nowhere near what a battery can provide for a fraction of the cost/complexity.

A standard 100Ah battery will provide 1200Wh.

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