Originally Posted by **********

I was a little skeptical at first. I was thinking that it was a dumb idea because the energy it would take to generate the electricity is lost downpipe, or, they have to use more energy to pump the water through the pipe to offset the energy converted back to electricity. Dumb..!

...but actually, this makes sense if like they say in the video, the water is flowing down. The energy that the water gains from gravity is converted into electricity. For a while it is slower coming out the other side (energy lost) but it can pickup more energy again thanks to gravity as it travels further down the pipe.

Smart!