Comment Re:Talk about creating a demand (Score 1) 334
Trouble is you need very large tanks of water, or to seperate them a long way. For instance a house might use 2 kWh overnight, that's about 7 MJ.
It isn't intended to be your primary source. Just as with other pumped systems, it's a supplement which stores during periods of excess and supplements during periods of shortage (or higher expense... some systems are now charging more for peak-period usage).
Pumped storage wasn't available UNTIL a couple of decades ago. I worked for an engineering company designing one and it was groundbreaking for its day.