I plan to buy a dual-fuel Gasoline/propane generator for those rare occasions when the battery has run out. Here's my plan:

1. add a large battery and inverter to power the heater system when its cold. Battery will be 48V and expandable to add run-time. (I have inverter, plan to buy Nissan Leaf modules)
2. Add dual-fuel generator ($1200?)
3. Add solar panel array, basic 48V and ensure its expandable.

Edit: the reason for paying extra for dual-fuel is that gasoline is problematic in the winter, and propane is more likely to start during a severe cold spell. Also, relying on only gasoline or propane is limiting. In a power outage (which can happen at any time of year), I want to have options such as solar, gasoline, propane...