The energy involved in raising or lowering weights is easy to calculate...
...which comes out to ... er... 41kWh This is the theoretical maximum amount of energy this enormous and cumbersome lunacy will store. (Its what you get from your solar roof in 4 hours!)
Altho I haven't checked your figures, this sadly does appear to be the same conclusion I came to on my own for a gravity energy storage system. I did a "napkin math" analysis for building storage tanks for pumped hydro storage to power a one-family home.
The figure I came up with was that with a 30' drop from upper tank to lower, you'd need two tanks each about 10x the size of a typical backyard swimming pool to store as much energy as you'd need for a typical night for the single-family dwelling. This is, obviously, not economically practical.
To be fair to Robert Llewellyn -- which you definitely are not, Martin... no surprise there since Mr. Llewellyn is an enthusiastic EV promoter and you're obviously a dedicated EV basher -- to be fair to him, he did say that the amount of energy stored in just one of these installations wasn't that much, and that you'd need hundreds of them dotted across the landscape, to provide storage for solar and wind farms. If your figures are correct, though, Martin, then "hundreds" is off by more than one order of magnitude, and the overall cost would be prohibitive... which, again, is the conclusion I came to some time back.
Of course, using massive weights of stone or whatever would give significantly better energy density than using water, but OTOH maintenance would be considerably lower for pumped hydro energy storage. Pumped hydro needs only a single turbine to pump the water; the "heavy weight suspended by winches and cables in a mine shaft" needs a lot more investment in equipment and maintenance.
The most extreme proposal I've seen for a low-tech "gravicity" energy storage is cutting a massive round rock piston out of the middle of a mountain, and using pumped water to raise and lower that piston. That certainly would store a great deal of energy as compared to the much smaller system Mr. Llewellyn describes, and using hydraulics (water) it would be far cheaper and more efficient per kWh. I question that such a thing could ever be done on a practical level. But maybe I'm just guilty of thinking small!
For some details on the latter idea, see "
'Gravity Power' Energy Storage Plans in Germany"
And from a German language website, an illustration which needs no translation: