running this sort of system - high efficiency 8 kw stove/boiler feeding an 800 ltr accumulator which also has solar thermal feeding in. We do have mains gas but havnt connected it to the system as not needed. Runs hot water and underfloor heating.
First 3 years solar ran everything from mid march to mid october - this year we are still having to light a fire occasionally - damn
Slight problem we have is that due to high insulation levels, the 8 kw stove overheats the open plan living area (approx 100m2) even though it is designed to put 70% of energy into the boiler and 30% to the room. Need to run the stove in winter for the heating and hot water, so burn approx 2 to 3 smallish tubs of wood a day if no solar assistance in the winter. Could be solved with a gas boiler, but looking at other options rather than capital expenditure, maintenance and running costs of a gas boiler.
Regarding cost of solar, it seems there have been a few cowboys around the market and you need to shop around for value for money.
These systems do cost a bit more up front, but careful shopping around and a willingness to do some of the installation work can pay dividends.
One important question is how complicated you want to go - ie keep it simple and DIY at the cost of efficiency or go technical with super efficiency but at an increased capital cost and reliance on lecky to drive expensive controllers and lots of pumps ???
Before all that though, if new building, put more thought into designing out as much energy demand as possible. It is quite feasible to have zero heating system these days with maybe a small stove for the few really cold nights, leaving just hot water demand.
Dean - would recommend the Navitron and Green Building forums for good information covering the questions you are asking, including the log cabin questions.