[vilda]

Don't mix MWh and MW (it's commonly used to mislead, but not here). The article is declaring 20MHh of storage while using 5MW power turbine. 5MW output from 20MWh storage gives you 4h output.

Edit to add: If you want to make proper calculations, don't forget that these types of storages are very inefficient. You can't compare them with pumped hydro.

[tinco]

Ah thanks, I misread that. I get that these types of storages are inefficient, that's the point I was trying to emphasize, a solution like this looks interesting, but it's not a serious competitor to nuclear power, or even pumped hydro (it's basically pumped hydro, but with a human made reservoir).

[lutorm]

it's not a serious competitor to nuclear power

How can you say that off-hand without knowing what the costs are? It's not at all obvious to me that building 3000 concrete spheres with turbines and a bunch of PV panels is any harder or more expensive than building giant nuclear power plants.