Which is stupid and insanely expensive, since methane itself is an insanely potent greenhouse gas and methane has plenty of fugitive emissions.but, back up a second: isn't the main reason for banking so much methane in the winter... heating? Because we can easily 10x the efficiency and 100x the cost - efficiency, by skipping the hydrogen - methane crap and storing heat directly.

See, you can store heat trivially in insulated thermal mass. "Thermal mass" is basically just mass, I.e. dirt-cheap materials such as rocks or dirt. You can skip a whole raft of fluid-handling stuff (methane and hydrogen being fluids, and fluids requiring pipes, pumps, leakage handling, inspections etc) by just using electricity from summer solar to resistively heat a 20m-diameter cylinder full of rocks wrapped in 1m of insulation, and when you need heat in winter you can just run air through the vents to extract that heat. It's based on 1950s technology (probably older tbh) and most of the materials are literally dirt-cheap. Hook it up to district heating and you have an effectively infinite battery to handle your winter heating needs, based on informed summer renewables costs. Sand, insulation, a big cylinder (probably the most expensive part), resistive heating, an air vent. None of it is expensive (except the land, but those 300sqm can be located underground if it helps) and it'll last for a century because there's nothing that can even break.

It's basically just a bunch of sand wrapped in an electric blanket (and an actual blanket). It's dead simple.

Compare all that to a hydrogen electrolyser on a river, with a chemical plant to transform the hydrogen into methane (with carbon from where, exactly?) then a pipe or tanker or truck to transfer the methane to a big methane storage cavern, which is then piped to an individual furnace to burn. That's a Rube Goldberg machine.