One, also inefficient, way to get to storage is by using surplus renewables (wind, solar) to generate bio gas (CNG or even LPG) for later use. Not the most efficient solution, but does that really matter when marginal costs for wind and solar are basically zero?

Depends on the cost relative to other options.

I would guess that if costs keep dropping you'd get a certain amount of overbuilding for the low energy demand season so you'd have capacity there for some kind of clean gas technology.

I wish the boffins would start crunching the numbers though. If my gas boiler breaks today, should I replace it or fit a heat pump? If I replace my kitchen should I keep a gas hob or move to electric?? These are less than once a decade purchasing decisions and theres absolutely no visibility on whether gas to the home is going to be a thing in the medium term.

It's as much seasonal as it is spread over time. Solar is strong around noon when demand is, as of now, rather low.

Intraday, batteries would make more sense. Higher efficiency, quicker to react, 365 cycles a year to recoup costs.

You are probably never going to get to a point where you're charging a battery now for use sometime in January. That's where some kind of bio gas would come in, because it is feasible to store it long term.

Exactly that!