4 ms·

Is it possible to scale that trade down to something one could do at home, without much equipment and therefore not require much in the way of planning permissi

Is it possible to scale that trade down to something one could do at home, without much equipment and therefore not require much in the way of planning permission? Scale that transaction down 1/3000th to get £100 for the trade. If you could do that every day it would set you up for a yearly pre-tax income of £36k; instead of trading 1GWh the trade would be 333KWh, equivalent to 1.2 Gigajoules. Solve the Pumped Hydro storage equation E = mgh (Energy = mass * gravitational acceleration * height) for 1.2e9 = mass * 9.81 * 2 meter lift => 60 Megagrams of water => 60 tons of water lifted 2 meters will do it. Water is ~1 ton per cubic meter, that's 60 cubic meters, about a 4x4x4 meter cube. Twice the volume of a small outdoor pool. And it would need enough pumping power to move it two meters in half an hour for one settlement period. One millimeter per second. That seems infeasibly huge. (Even scaling it down another 1/10th is 6 tons of water which is large. maybe if it could be lifting a cubic meter of Iron, 8 tons, by one meter, it could be £5/day or £1500/year. A tenth the size again it would never pay for itself, and now I'm almost at the systems of dragging lumps of rock on rails up a slope to store energy and letting them roll down to release it).

adgjlsfhk1 5y ago
you're also not accounting for the fact that the smaller pumps won't be nearly as efficient as big ones.
- jodrellblank 5y ago
  Deliberately so, because if it the numbers are still wildly far from plausible with an easy model of perfect efficiency, there's no point making a more complex model of heat loss and equipment purchase and install and maintenance costs.
jodrellblank 5y ago
A quicker way to get to the same conclusion is that storing 333KWh in a half hour settlement period needs a 666KW electricity feed, way more than a home supply. Does make me wonder if elevators in tall office buildings lifting ~10 people per ton, dozens of people overall, up dozens of meters, could be arranged so their work starts at cheap time and finishes at peak time to regenerate money as they ride the elevator down.
- tialaramex 5y ago
  The elevator is counter-weighted, there is electricity used whether you're going up or coming down, the point of the elevator is to change where people are, not generate electricity, so you're imagining an entirely new (and perhaps more dangerous) machine.
anamax 5y ago
> And it would need enough pumping power to move it two meters in half an hour for one settlement period Why do you need to move all of the water in half an hour? (Suppose that you just want to do time-arbitrage for residential use.)
- jodrellblank 5y ago
  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). [1] https://www.renugen.co.uk/huawei-luna-10kwh-battery-pack/ https://www.renugen.co.uk/huawei-luna-10kwh-battery-pack/

adgjlsfhk1 5y ago

you're also not accounting for the fact that the smaller pumps won't be nearly as efficient as big ones.

jodrellblank 5y ago
Deliberately so, because if it the numbers are still wildly far from plausible with an easy model of perfect efficiency, there's no point making a more complex model of heat loss and equipment purchase and install and maintenance costs.

jodrellblank 5y ago

A quicker way to get to the same conclusion is that storing 333KWh in a half hour settlement period needs a 666KW electricity feed, way more than a home supply. Does make me wonder if elevators in tall office buildings lifting ~10 people per ton, dozens of people overall, up dozens of meters, could be arranged so their work starts at cheap time and finishes at peak time to regenerate money as they ride the elevator down.

tialaramex 5y ago
The elevator is counter-weighted, there is electricity used whether you're going up or coming down, the point of the elevator is to change where people are, not generate electricity, so you're imagining an entirely new (and perhaps more dangerous) machine.

anamax 5y ago

> And it would need enough pumping power to move it two meters in half an hour for one settlement period Why do you need to move all of the water in half an hour? (Suppose that you just want to do time-arbitrage for residential use.)

jodrellblank 5y ago
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). [1] https://www.renugen.co.uk/huawei-luna-10kwh-battery-pack/ https://www.renugen.co.uk/huawei-luna-10kwh-battery-pack/