I hope it will work well! I agree with you Calvin; the cost of heating is a bit scary since it's still at the beginning of the winter.
Around here (zone-2), we have a hot spring resort which is into renewable energy. They operate a high-tech greenhouse, but they have access to geothermal heat I think.
http://www.uaf.edu/files/snre/MP_09_10.pdf
It can sustain 85F when outside temp is -45F (130F differential), which is amazing.
Additionally, in north, we have a challenge of not much light in the winter. Chena hot springs' greenhouses use lots of LED (they are off-grid, so they have to save electricity generated from geothermal plant).
It would be cool to have a passively solar/geothermal greenhouse (with large water tank buried below ground to store the heat). Mostly passively solar residential house is possible (with enough money), but insulating greenhouse is more of a challenge. I think that even triple or quad wall polycarb has single-digit R-values.
---------- Post added at 09:32 PM ---------- Previous post was at 09:17 PM ----------
Keris, actually the famous quote in your signature is by Theodosius Dobzhansky, not by Darwin. Dobzhansky is one of the most significant contributors to the modern synthesis of evolutionary theory in 1930-40's. Not trying to be nit-picky or snobby, I just thought that you might want to know this.