The parent comment said the price settlement period was a half-hour at a time, I was trying to maximise income to see if it was feasible to scale down to garden size and make a useful amount of money for a small-ish build cost. If it takes longer to pump and longer to drain, it earns less, but you could do it. It doesn't make much difference, it's impractical whatever period.
Going over it again today I'm a factor of a thousand out, in the unhelpful direction, by using mass in grams instead of the correct mass in Kg. So after that adjustment it would take
~180,000 Kg = 3.6e6 Joules in a KWh / 9.81 grav accel / 2 meters
approx 180,000 Kg of water, 180 tons raised 2m to store a single KWh. So approx 60,000,000 Kg of water, 60,000 tons raised 2 meters to store my 333KWh to get a salary style income from doing that best possible trade every day. Approx twenty Olympic swimming pools worth of water. So it's even less relevant whether it's half an hour or not.
As well, a UK home power feed tops out about (240Volts * 60Amps = ~15KW) so the max one could store in a half hour period is ~7KWh. Trading that peak-to-trough would get you ~£2.20/day for moving 1200 tons of water up 2m and back with perfect efficiency, or £1.65/day with Dinorwig's 75% efficiency. Much much smaller, simpler and more convenient to get a 10KWh Li-Ion battery pack for £4k[1] and trade that for £700/year (even then it can't charge or discharge quickly enough for one half-hour period).
(I came to the realisation when working out that I could eat a biscuit, use that energy to walk up two flights of stairs, and then have a KWh of potential energy; free energy means I went very wrong somewhere).
Going over it again today I'm a factor of a thousand out, in the unhelpful direction, by using mass in grams instead of the correct mass in Kg. So after that adjustment it would take
approx 180,000 Kg of water, 180 tons raised 2m to store a single KWh. So approx 60,000,000 Kg of water, 60,000 tons raised 2 meters to store my 333KWh to get a salary style income from doing that best possible trade every day. Approx twenty Olympic swimming pools worth of water. So it's even less relevant whether it's half an hour or not.As well, a UK home power feed tops out about (240Volts * 60Amps = ~15KW) so the max one could store in a half hour period is ~7KWh. Trading that peak-to-trough would get you ~£2.20/day for moving 1200 tons of water up 2m and back with perfect efficiency, or £1.65/day with Dinorwig's 75% efficiency. Much much smaller, simpler and more convenient to get a 10KWh Li-Ion battery pack for £4k[1] and trade that for £700/year (even then it can't charge or discharge quickly enough for one half-hour period).
(I came to the realisation when working out that I could eat a biscuit, use that energy to walk up two flights of stairs, and then have a KWh of potential energy; free energy means I went very wrong somewhere).
[1] https://www.renugen.co.uk/huawei-luna-10kwh-battery-pack/