Each 35MWh system requires about 1.62 acres of land. That seems perfectly reasonable to me, especially since there are still optimizations to explore.

Here's some totally useless back-of-the-envelope calculations on land requirements for this sytem.

The United States, in total, used 1,819,393,805 MWh of energy in 2016. If one plant provides 35MWh of storage, that means 51,982,680 plants are required.

That comes to 84,211,942 acres of land. There are 2.3 billion acres of land in the United States, so it would require 3.66% of the US. That's obviously a huge overestimate.

The beauty of this is the simplicity. This is something we could have built 40 years ago. And unlike LIBs, there's much less worry about degradation and we can put these out in the desert near a solar power source without worry.

Imagine it combined with solar thermal, which has dropped immensely in price per KWh.

Also, concrete reabsorbs around 43% of the co2 used to create it over a period of time.

https://www.nature.com/articles/ngeo2840.epdf

Reservoirs are restricted in where they can be built, because water. And that real estate is in high demand for many other uses. I think it's a safe assumption that, in general, coastal properties (including those on lakes and rivers) are more than twice as valuable as inland property on average.

Reservoirs have a tendency to emit biogenic methane though so they're not great at scale for climate change mitigation.

< The selling point of this is low relatively low capital cost and well tested technology.

I'm sceptical of that. As the sibling comment noted, the technology is well-tested, yes but for a completely different usage pattern. You don't know how reliably construction cranes are in lifting heavy loads in back-to-back cycles, 24/7.

Additionally, I'd guess you will have to modify the cranes to realize the "recover energy" parts. I'm no expert, but I could imagine, traditional parts spend energy for both raising and lowering a weight because the design goal is reliable control of the load, not making energy. So you'd probably have to modify the motor assembly.