[ephbit]

I'd guess we'll see mid to large scale electrolyzer plants pop up in many locations throughout a country as soon as the build out of PV on roofs of private houses (also everywhere else) leads to daily overload on the electric grid.

These electrolyzers will then take up the excess electricity and convert it to hydrogen as seasonal storage and thus stabilize the grid.

Additionally, you'd combine these sites with either fuel-cell or hydrogen powered gas turbine plants, to then generate enough electricity when PV generation cannot meet demand.