[mlyle]

A few prototype / demonstration units at 10MW scale and lower is not proven, off the shelf technology. Fullstop.

[philipkglass]

Electrolytic hydrogen plants of up to 250 MW were constructed in the 20th century by the use of smaller electrolysis units in parallel. All of them were for producing ammonia from hydrogen. See table 3-2 on page 99 of this NASA report from 1975:

"Survey of Hydrogen Production and Utilization Methods"

https://ntrs.nasa.gov/api/citations/19760008503/downloads/19...

250 MW, Rjakon, Norway, built 1965

170 MW, Kima, Egypt, built 1960

125 MW, Nangal, India, built 1958

90 MW, Trail, Canada, built 1939

25 MW, Curco, Peru, built 1958

[mlyle]

??? Those are input powers of terrifically inefficient and expensive electrolyzers. That 250MW plant put out 17MW of hydrogen -- (120 (megajoules / kilogram)) * ((0.000236 kilograms) / (cubic foot)) * (2 200 000 ((cubic feet) / hour)) = 17,306,667 Watts.

[philipkglass]

I think that you slipped a decimal point. The mass of a cubic foot of hydrogen is about 0.00236 kg, not 0.000236 [1]. That means that the output power is an order of magnitude greater than you calculated -- 173 megawatts.

[1] https://microsites.airproducts.com/gasfacts/hydrogen.html