THE BEST pumped hydros have the greatest fall- and hence the most kinetic energy per M3 and hence the dams can be smaller. The small drop Hydros like Wivenhoe in Brisbane are high volume low kinetic, and only are cost effective where there is a nett large out flow of water- ie less than half pumped back up. New Zealand has a lot of these, which operate mainly as hydropower and partially as pumped.
Still, they have regular scares of running out of water, and most factories have a 500KVA backup diesel.
