Looks cool but I just don't see this ever getting to grid scale unless it could be integrated into natural geography like a shear cliff face to give it much greater capacity and throw. Especially with days or weeks of storage like we'd need to cover 2-3 standard deviations of renewable output.
1. The energy overhead seems quite significant - as the concrete barrels don't really drop.
2. What guarantees non-collapse in case of winds (and ignoring floods)?
3. Does this really scale? I mean, concrete is more dense than water, but I think it's only... what, twice the density?
Not the person you responded to, but you correctly identified some of the serious flaws in this idea. They claim to be using commercially available crane technology, but existing cranes are generally not designed to operate in high winds, so they seem like a poor match for wind energy. According to [0] tower cranes are typically limited to operating in wind speeds of 20m/s or less, where as wind turbines[1] top out at ~35m/s. That would mean when the turbines are at peak production (i.e, when you want to be 'charging' your storage) wind speeds would be too high for co-located concrete block storage to work.
The design also seems to have quite poor power density; their website[2] shows a single tower in front of fields of turbines, but they only quote a power output of 4-8MW - the equivalent of 1-2 large turbines - so in reality you'd need dozens of them for a single installation.
The diagram seems a bit silly. They say the concrete weights are the most expensive part of the system. So many of those blocks go through a small elevation change (or none, in the case of those on the bottom layer).
Most "gravity" batteries don't consider the cost of the weight. So far the only two types of viable gravity based energy storage systems are pumped hydro storage and hydraulic hydro storage since both take their weights from the surrounding environment.
I will admit that the crane idea is at least fixing the flaw of most gravity batteries requiring a separate generator per weight. Doubling the length of the crane arm increases the capacity 4-fold.