I dont see the point in making an emergency option convienient. Forget solar thermal, this is to much hussle for anything. PV plus battery more likly the solution you want.
Work out the amount of solar + batteries you need in the winter when the power goes out and your COP is less than 2 because it’s very cold and you need more BTU’s than normal because it’s very cold. Solar thermal is just significantly cheaper on a large home in a cold climate.