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.

Thanks for that, I thought it would give around a couple of days of backup, however I had completely fudged the numbers somewhere along the line.

I don't have time to look for the cite now, but I've read a proposal to build electric traction railways up some steep slopes in SoCal, then load up cars of rocks, mine tailings, slag, etc. The trains would head up the mountain at night when electricity is in surplus, then back down in the daytime when demand is near peak.

Seems outlandish, but the calculations predicted very high efficiency and comparatively low cost per MWh of storage.