Hi,
Woodburner with a backboiler? Its sounds like you're going to have a few radiators linked to it. If so, and you don't need to go upstairs with it, tgen then definitely look into gravity fed heating system. It's dead easy, needs no electricity, creates no noise and distributes the heat very efficiently.
After installing one in my home (took 3 days for 1 plumer and 1 helper) I even rid of an Ecofan (that was also spreading dust s along with circulating hot air).
So really it's not only thinking about how to preserve heat but also how to avoid need for electricity. That will essentially reduced number of solar panels, size of battery bank.
Besides, don't forget in winter here in uk the solar gain drops drastically.
Days are lot shorter, and sun sparse.