Imagine a future 100% renewable electricity system, based on wind + solar + green hydrogen.

If wind and solar (with batteries, demand response, and interconnectors) can supply X% of electricity demand directly, then you need (100-X)% dispatchable electricity from hydrogen.
If your electrolyzers have an efficiency of 67% and your hydrogen power plant has an efficiency of 60%, that gives a roundtrip efficiency of 40%. This means you need 2.5 times more wind and solar electricity for that remaining X% of demand.
That 2.5 times X could of course be produced in hours that wind and solar can produce more than needed for the electricity demand at that time. "Excess electricity", which would otherwise have to be curtailed (since we already used batteries etc. to match supply and demand).
The question is: What is the value of X?
That's a matter of climate, the mix of wind and solar you use, and optimization with respect to batteries, demand response and interconnection.
But in Europe, X could e.g. be 15. Then you'd get 85% of your electricity directly from wind and solar, and 15% from green hydrogen.

Then you'd need wind and solar production to be (100 - X + 2.5X) % of electricity demand = (100 + 1.5X)% = 122.5%.
On the electricity production cost side, that's not too bad. But of course, you need quite some equipment: electrolyzers, hydrogen infrastructure, hydrogen storage, hydrogen power plants (which could be modified gas-fired power plants).
Quite a challenge, but seems doable to me. And probably a lot cheaper than e.g. building nuclear power plants to fill in the 15% dispatchable electricity.
Oh dear, now I see that I mixed up the definition of X between the first and the second tweet of this thread. Anyway, I think you got it. From the second tweet onwards, it's (100-X)% direct wind and solar and X% electricity from green hydrogen.
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