I point to nuclear power simply because it's already proven to work. Overbuilt wind/solar should work in theory, but primarily nuclear-powered grids exist right now.

Where did you read that? Methane which already powers 40% of the US electrical grid can be created and then turned back in electricity in a Electricity→Gas→Electricity process with a round trip efficiency of 30–38% [0]. There is no way you'd need 7x production when you can use surpluses to make methane or hydrogen.

[0]: https://en.wikipedia.org/wiki/Power-to-gas

There's a whole spectrum of energy storage tech where the tradeoff is efficiency vs cost. At the extreme end of high cost with high efficiency you have magnetic energy storage, then slightly less-efficient but lower cost you have batteries, then in the middle you have things like synthetic methane, cracking hydrogen, and pumping water up-hill, and at the bottom for lowest-cost and lowest-efficiency you have compressed air.

Finding the right balance of overbuilding supply and storage efficiency is going to be a long process.

The goal was to have a long term hydrogen, mid/peaker battery setup with the minimum cost while providing for the entire grid.

Unfortunately I didn't take notes as to what the source was and I read this about a year ago. Google has been entirely useless as I've tried to dig it back up.