methane

So when the sun is shining, and the wind blowing, and the methane not burning, you store that excess for later.

What about gravity+water->electricity->hydrogen->methane->electricity (assuming storage/transportation of methane, so there's a point)?

Messing with the gut is really dangerous, your probably far better off just harvesting some sugars from the blood stream than trying to use methane.

That's why I said methane: The best thing to do is grab some carbon and make methane with your hydrogen, methane you can store.

Is it just the cycle of methane decay through UV light, or is it cryovolcanism also at work?

But - how about methane fluxes into the atmosphere due to permafrost melting, or due to ocean heating?

If they'd thrown in a guesstimate on possible massive arctic permafrost/clathrate methane leaks, it'd make this estimate look conservative.

This is not really a solution for anything though, round trip efficiency of solar cell->electricity->hydrogen->methane->electricity would be quite low.

Those two planets are made up mostly of a water/ammonia/methane mixture with a solid core and a H/He outer atmosphere.

There are many more ways to produce methane geologically/biologically than there are to produce liquid hydrocarbons.

Isn't it dangerous due to some (methane?) gas leakage, and it collapsing, without proper calculation?

Water is useful as fuel (LOX and liquid hydrogen or methane), as reaction mass, and as radiation shielding when you're flying around.

There's a tiny little bit of difference between methane and methanol and "all that shit in crude oil and coal".

There are three basic ingredients which go into making planets: rock (including pure metals), "ice" (a catch-all term which includes all phases of water along with methane and ammonia) and hydrogen/helium mixture.

Methane is _much_ more abundant than liquid hydrocarbons.