You need to pump a lot of water to store the equivalent energy of a 50 Amp hr car battery. In fact, you'd need to pump all the water from a typical size swimming pool up 8 feet. And for a 10 KWhr system you'd need at least 16 batteries or 16 swimming pools. That suggests a new unit of energy - the swimming pool = at a height of 8 feet, the energy storage capacity of one car battery. Here are my calculations:
A typical car battery is rated at 50 Amp hr.
To get energy, multiply by battery voltage of 12.5 V.
Max energy stored in battery = 50 Amp hr * 12.5 V = 625 Watt hr.
Battery could supply 625 Watts for one hour or 62.5 Watts for 10 hours.
1 Watt hr = 3600 Joules
1 Joule = 0.7376 ft lb
625 Watt hr * 3600 Joules / Watt hr = 2,250,000 Joules
2,250,000 Joules * 0.7376 ft lb / Joule = 1,659,600 ft lb
1,659,600 ft lb * 1 ton / 2000 lb = 830 ft tons
Must lift 1 ton 830 feet or 10 tons 83 feet to store the same energy as a car battery.
1 gallon of water weighs 8.34 lb.
24,000 gal of water weighs 100 tons.
An average swimming pool holds 20,000 gal of water or about 100 tons of water.
Must pump all the water in a swimming pool up 8 ft to store the same energy as a car battery.