Well, back of a fag packet calculation... Let's lift 1KG of water up 5 meters. That will require 50 joules of energy (5 * 9.81). Suppose I want to store 5kWh

Well, back of a fag packet calculation... Let's lift 1KG of water up 5 meters. That will require 50 joules of energy (5 * 9.81). Suppose I want to store 5kWh of energy (half my usage). 1kWh = 3600000J 5kWh = 18000000J 1KG of water is 1 litre. I need to store 360,000 litres of water - that's a bit too much did domestic use :-) Is large here - but I think that's about right.