Same reason I have issues with the Uk Green party, makes them look foolish when they push to stop fossils but the only current practical solution is nuclear(which they're against)
How about gas produced by electricity, e.g. through electrolysis.
You might benefit from looking at systems like Compressed Air Energy Storage. Highly responsive, compatible with CHP, virtually no scarce materials involved, and pairs dramatically well with renewables.
As an additional bonus, it also doesn't leave vast tracts of land uninhabitable if it goes wrong.