Low Cost Heating for a Garden Office

[Triassic]

I have a 20 foot container I'm thinking of converting to a garden office and gym. The container would be insulated internally and clad on the exterior with Larch, with a mono pitch wriggly tin roof.

 

With the price of energy I was looking at heating options, I was wondering if anyone has experience of solar hot water systems, or solar panels for heating. Links to working DIY schemes would help ( I like pictures rather than dense text).

 

Or has anyone spotted any other novel ideas for providing heat into a small space?

[Nickfromwales]

I doubt you'll have enough solar during the winter to provide space heating tbh. A2A A/C ( which will heat in winter and provide cooling in summer ) would be my choice. Very cheap to run, and only about £2k to buy for a reputable make, but you can get much cheaper.