Google says density of concrete is 2400 kg / m^3. Multiply that by 5x5x5 m^3 and you have 300,000 kg of concrete (300 metric tons). m = 300000 kg g = 9.

Google says density of concrete is 2400 kg / m^3. Multiply that by 5x5x5 m^3 and you have 300,000 kg of concrete (300 metric tons). m = 300000 kg g = 9.8 m/s^2 h = 10 m The total amount of potential energy you can store is: m * g * h = 29400000 J = 29.4 MJ The more customary unit of energy in electric circles is the kW hr. Converting a kW hr to joules gives: 1 kW hr = 1 kJ hr / s = 1000 J hr / s * (60 s / min) * (60 min / hr) = 3600000 J = 3.6 MJ So the potential energy stored in the parent's system is: 29.4 MJ * (kW hr / 3.6 MJ) ~ 8.17 kW hr. Probably needs to be bigger to supply a decent sized household. Not to mention issues with inefficient conversion of potential energy to electricity, maintenance, and a backup plan for cloudy days.