3 ms·

Yes, basically that, but using solar/wind to power the pumps, turning the lake into a giant battery to store the energy from the solar/wind power, which seems t

Yes, basically that, but using solar/wind to power the pumps, turning the lake into a giant battery to store the energy from the solar/wind power, which seems to be one of the major drawbacks of wind/solar.

frankus 14y ago
That's an interesting and seemingly obvious approach, so I'm curious why it's not really discussed. I'm guessing that at current wind/solar capacity, any fluctuations can be absorbed by just slowing down the flow out of the reservoir, rather than ever having it reverse. You also need a downhill source of water, which means any dam that's the last one downstream can't really use this approach. You could maybe even get away with an entirely closed-loop system, but if you look at the scale of the problem, you need either a huge pair of reservoirs (lake-sized) or a huge elevation difference (mountain-sized), or preferably both. It doesn't appear economical to build e.g. a tank on a tower.
- mlwarren 14y ago
  One of the major reasons pumped storage isn't used more is because the energy loss associated with pumping and storing the water. I can't find the exact amount right now but from a lecture I watched some time back[1], pumped storage is a few orders of magnitude more expensive than using conventional fossil fuel generated electricity per kWh. It's just not very cost effective right now. [1] http://www.youtube.com/watch?v=MoAFiL1UdSg http://www.youtube.com/watch?v=MoAFiL1UdSg
  - maxerickson 14y ago
    The orders of magnitude doesn't pass the sniff test. If it were true, utilities would not be building pumped storage capacity. I can certainly believe the capital requirements are much higher for pumped storage than for natural gas peakers.
- aidenn0 14y ago
  It takes a huge space. 1 kWh means moving a metric ton (a cubic meter) of water 400m of elevation. Round trip efficiency isn't great, but also not terrible. It beats the fuel-cell/electrolysis cycle, but loses to batteries. It can be profitable though because energy rates can reach near zero (and even occasionally slightly negative) at night. 99% of installed energy storage is pumped hydro.

frankus 14y ago

That's an interesting and seemingly obvious approach, so I'm curious why it's not really discussed. I'm guessing that at current wind/solar capacity, any fluctuations can be absorbed by just slowing down the flow out of the reservoir, rather than ever having it reverse. You also need a downhill source of water, which means any dam that's the last one downstream can't really use this approach. You could maybe even get away with an entirely closed-loop system, but if you look at the scale of the problem, you need either a huge pair of reservoirs (lake-sized) or a huge elevation difference (mountain-sized), or preferably both. It doesn't appear economical to build e.g. a tank on a tower.

mlwarren 14y ago
One of the major reasons pumped storage isn't used more is because the energy loss associated with pumping and storing the water. I can't find the exact amount right now but from a lecture I watched some time back[1], pumped storage is a few orders of magnitude more expensive than using conventional fossil fuel generated electricity per kWh. It's just not very cost effective right now. [1] http://www.youtube.com/watch?v=MoAFiL1UdSg http://www.youtube.com/watch?v=MoAFiL1UdSg
- maxerickson 14y ago
  The orders of magnitude doesn't pass the sniff test. If it were true, utilities would not be building pumped storage capacity. I can certainly believe the capital requirements are much higher for pumped storage than for natural gas peakers.
aidenn0 14y ago
It takes a huge space. 1 kWh means moving a metric ton (a cubic meter) of water 400m of elevation. Round trip efficiency isn't great, but also not terrible. It beats the fuel-cell/electrolysis cycle, but loses to batteries. It can be profitable though because energy rates can reach near zero (and even occasionally slightly negative) at night. 99% of installed energy storage is pumped hydro.