6 ms·

As for storage, shouldn't there be plenty of hydroelectric dams that could run "backwards"? Or is there an interconnection issue you mention?

• cesarb 9y ago
  For a hydroelectric dam to be able to "run backwards", it needs a lower reservoir. Many dams have only an upper reservoir.
  • mrfusion 9y ago
    Simply turning them off would be running backwards since water would build up behind them.
    • nothrabannosir 9y ago
      It’s not about building up capacity alone: you want to take power off the grid at negative energy price times.
      • vidarh 9y ago
        You are taking power off the grid: The power otherwise produced by the hydro plant. Of course with a lower reservoir, you can go into negative territory instead of "just" taking the plant down to 0.
        • jimktrains2 9y ago
          No, you need to consume what other methods, e.g. wind, are producing when there isn't the demand to use it.
          • vidarh 9y ago
            There is always demand. The issue is that sometimes demand exceeds supply. Taking away supply has the same net effect as increasing demand. EDIT: with the one caveat of transmission capacity, which certainly can be an issue.
            • jimktrains2 9y ago
              I don't think you're quite getting this. There are times where there is excess demand, even when removing these stores. What's so hard to understand? Prices go negative in the US at times and in Germany more often. That is exactly when something like this would be used: to store that capacity.
              • vidarh 9y ago
                The point is that you have a given supply and demand. As long as they are in the right positions in the grid that transmission capacity is not the limiting factor, then you can fix that by reducing supply, or by increasing demand - apart from the issue of transmission those options are equivalent from the point of view of bringing the supply under control. They may not be equivalent in terms of cost, but that is a separate issue. The original point was that you do not need to have a reservoir to pump from to take advantage of the fast start/stop capability of a hydro plant: Closing the sluice gates and/or bypassing the turbines is sufficient to reduce supply by the generating capacity of the plant. Having a reservoir as the potential to significantly increase the reduction in excess supply you can handle, that is true, but the lack of that option does not change the benefit of shutting off generating capacity. Hydro plants have been used to adjust grid supply for as long as they have existed in this way. Not least because with grid prices adjusting dynamically, as long as the reservoir is not full, most hydro plants yield better economic result if they respond to falling prices by letting the reservoir water levels build back up.
                • jimktrains2 9y ago
                  > Having a reservoir as the potential to significantly increase the reduction in excess supply you can handle, that is true, but the lack of that option does not change the benefit of shutting off generating capacity. The point is to not turn off generation capacity that we don't control the start of, like wind. Why should we not generate if the wind is blowing at night?
                  • vidarh 9y ago
        • Piskvorrr 9y ago
          Nope. Adding power to the grid is +X MW. Removing power to the grid is -X MW. Not producing any power is 0 MW.
          • vidarh 9y ago
            That's true when looking at an individual plant, but is not directly relevant when you're looking at the grid as a whole (though it may be an issue when you have transmission limitations), where the problem is that at some point you have a supply of +2X MW, and demand is only X MW, and you need to deal with the X MW of oversupply. If one of the suppliers can then turn off X MW of supply rapidly, that has the same effect as if you add X MW of demand. At a hydro plant you have multiple options: You can bypass the turbines; you can close the dam, as long as it's not near capacity; if you have a lower reservoir you can close the dam and pump water up to the upper reservoir. All of these help reduce the excess supply, but pumping up does so by increasing demand and reducing supply, and the other two options reduce supply. You can of course do pumped storage without normally producing electricity too - in places where the only convenient location for a reservoir is not "in line" with a water source with sufficient fall height, you can still pump up to a convenient location, in which case the plant is basically "only" storage.
• Tobias42 9y ago
  Unfortunately the capacity of these dams in most areas is far from enough to compensate all fluctuation in renewable energy production.
• usrusr 9y ago
  You not only need variable volume reservoirs on both ends, but you also want to have very high drop, because liars from seepage and evaporation scale with volume but not with height. Low-drop pumped storage might be useful for very short term storage, but usually you'd want something that is efficient over a wider range of usages.