4 ms·

My guess is to get an economically height difference to the dam.

• phire 8y ago
  No, any extra height to pump water up compared to the height of the dam is just wasted power. They wouldn't do that without a good reason. My understanding is you can't just stick an inlet on the river, otherwise you could only pump water up when the dam was running (defeating the point). You need to build some kind of reservoir. Additionally, with hydropower it's not enough to build a dam above your generators. You also need to get rid of the water exiting your generators fast enough. If there is any restiction on the outflow, the back pressure will decrease the generation capacity. My guess is the distance is needed to meet these requirements. Enough space to let the water slow down, then enough space to build a reservoir.
  • progfix 8y ago
    Why would it be wasted power? Height difference = stored potential power. I was talking about that maybe 20 miles downstream the pump-size/-energy consumption to stored power is more efficent.
    • phire 8y ago
      Because the height difference that matters is the difference between the water level in the lake and the turbines. If your pumping station inlet is 20m below the turbines, then any energy used pumping water upto the height of the turbines is wasted, because it can't be recovered when the water comes back down.