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by 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.