If I had the underfloor heating you had (rather than the electric I'm stuck with) I'd be using my existing 50 square metres of solar on my 60,000 litre swimming pool and put a heat exchanger for a heat pump into it to raise the temperature from the low grade mid winter 5-10 degrees or so to the 30 required for the UFH.
I guess your winters are too cold for that but if you have an equivalent size of insulated tank (maybe doubling as a pool in summer?) then I worked out that I could pull 75kw/hr from it for every 1C drop in water temperature. Mid winter sun would put about 20kw per hour for 4-5 hours a day into it which may balance the heat losses.
The upshot is that it would provide 4-5 days of heating with no sun input before I'd have to worry about ice (worst case conditions here!!).
Since I can't change the heating, I planted 300 trees for the log burner - I start cutting in 2 years :-)
Robin - Down Under (or are you Up Over)
