Originally Posted by Whatfur
This IS cool and the use of the caverns inside the mountain to hide the workings is amazing...but it proved to validate my first feeling when I read Jeff's proposal...that it would take more energy to raise the water than it would produce by its lowering. Sure costs of such can be offset by time management but seems to still be a bit counter-productive to overall goals.
I guess the same can be said about batteries right??...if it takes 10 mw to store/charge 8 mw which it turn becomes 6mw of usable energy we only gain something if the energy was going to be lost or shed in the first place. Unless we are talking $$$ where 6mw during the day may be >= 10mw at off-peak. (My numbers are guesses...osmium might have some actual)
yeah, that's the general idea. You're always going to get less energy out than you put in, but the considerations are efficiencies and costs (both $$ and environmental, which in a perfectly operating market would be equivalent). Batteries can be 90% efficient, fuel cells can be 60% (reversible cycle with hydrogen), and turbines with fossil will be something less than 40%. But fossil fuel stuff is cheapest due to 100 years of optimization and the relative ease that you just take it out of the ground.
For pumped hydro storage (I am not an expert, but this is my impression), it won't scale down very far in size. I think you need a lot of gravity behind water to get that kind of power back out of it, so you essentially need a mountain. (But if you happen to own a mountain already, I bet it's pretty cheap.) Batteries, fuel cells, and turbines can all probably work on a scale small enough to distribute them fairly evenly through a city, and if one breaks, then the others can bring up the slack, much like the internet.
I don't know the numbers either, Whatfur, but those ones you give in your last sentence capture the idea.