We live in what is considered to be a desiduous rain forest and our water shows up when it rains (fall, winter, and spring). Our stream is much smaller during the summer when there isn't as much rain but it never goes dry (we believe that it is possible that it is fed underground from a large lake on the other side of out mountain).

In the summer when we only have the smallest nozzle open it still exerts the same pressure in the penstock as the pressure when there is enough water that we can open all the nozzles, so the small nozzle is still a good force pushing against the wheel, just not as much as if one (or more) of the larger nozzles was on. In effect, the generator works (but not as well) when the amount of water we have is less. At that point we are getting good solar power.