I would love to have a place like that as well. I bet it would be extremely cozy.i would love to build i tiny place with huge water tanks under it that i can shove extra heat into throughout the summer and then use that for heat during the winter. it is pretty efficient to solar gather heat and then move it around with small water pumps if you don't have much resistance in the system. any solar needed to run the system electrically can be sized to the needs of the pumps and so you don't need batteries at all because they are just moving water when it is actually sunny anyways.
i also like a hot water system design that would be similar in that the pumps are only needed when it gets sunny enough and otherwise the whole system drains back to where nothing can freeze in the winter on the cold days.