I've seen some posts about heated greenhouses. I wonder if the problems could be solved by a solar greenhouse. The greenhouse would have an insulated roof and walls with vertical glazing on the south side only. Thermal mass in the floor could store and release heat at night, roof overhang(s) would prevent overheating in summer. We had one like this at school, and the temp never dropped below 55, no matter what. I know that's not optimum tomato weather, but they won't freeze. Heat mats can be used to germinate seed, and other measures could be taken to increase soil temps. Here is a little sketch, please give feedback. If anyone ever needs a landscape or anything else drafted, please let me know.