Nano-heating for eco-sheds

I spent three hours up there yesterday, marking schoolwork. It worked exactly as planned, a quiet sanctuary in which I could blitz the workload before rejoining the family. It was pretty seriously cold up there, so after a short while my thoughts turned to heating. And that's there they stayed, more or less, until I returned to the house, except for the occasional diversion to wondering whether my toes were still there. 

It's well insulated with eco wool, but that doesn't get it warm in the first place. If it's going to be a proper, year-round alternative workplace, I'll have to heat it. I reckon I've got three options.

• some sort of low energy electric heater like this one, which, apart from the environmental cost of manufacture, should be fairly green once purchased given my windmill energy production. Although I'd really need a solar panel to boost input
• a tiny wood burning stove like this one, I do a bit of woodwork up there and always have plenty of off-cuts, so with sawdust and everything I might have enough to keep warm, carbon-neutrally. But the flue would cost, as it would have to be double-skinned to avoid burning the roof down
• the final option is some kind of wacky tiny solar set-up. I could put a little radiator in the shed linked to another one, painted black (as Mick Jagger suggested) in a glass-fronted box. A tiny solar-powered pump could circulate water round the system. This would be great but I can imagine all sorts of engineering problems and I don't really want to spend the whole summer setting it up.

I'll dwell on it some more, but I can imagine going for the little stove solution preferentially. It seems like the cosiest option. Unless anyone else has got a better idea.