There are two major generators in my life:

1) At home. I have a portable gasoline generator & a transfer switch that keeps the "essentials" (water pump, septic pump, refrigerator, freezer and some lights and outlets) running. I have a rotating store of 20 gallons of stabilized gasoline that gets renewed regularly (every month, the oldest 5 gallon fills a vehicle, and is refilled and sent to the back of the line of 4 five gallon-cans.) This method works well - we were able to run the house for 2 weeks this way in 2012, and have run the house for 24 to 72 hours quite a few times since then. Run the generator every month and look after oil changes and so on and this works find.

2) At the Firehouse. There we have a much larger whole-building system and that runs on Propane. Propane is much less efficient than gasoline, but we have a massive tank there, and we have yet to determine the run-time possible - it's likely at least 7 days, maybe more. Propane has some big advantages though. Does not gel like diesel and does not "go stale" like gasoline. As long as the generator is well maintained, with propane, it WILL PRETTY MUCH ALWAYS START IN COLD WEATHER unlike with gasoline and propane, which may run into challenges.

The main issue with propane in a long-term situation is resupply. While there are portable generators that can use propane and gasolone, when you have a huge in-ground tank and you need a refill, the truck has to come to you, you can't go get enough propane to refill your big tank. This can be a problem when supply lines are down. You can drain a variety of other gas-powered devices if needed to get a few hours of run time.

I love solar, am a HUGE advocate and want everyone to have solar everything. But. But. If you have to generate HEAT directly from electric, solar is going to require an epic amount of battery storage. I mean kilo-dollars of battery. It's possible, but over the last few years, I've gotten into RV Solar power retrtofits and learned that solar electric is not ideal for heat. I've set up an RV with a pair of 100 amp-hour batteries that are charged by an array of solar panels on the roof and watched a toaster oven just obliterate the stored energy in the batteries in a weekend. For solar heat, a better solution is a closed loop hot water system. We installed one of these on a freind's house using two panels and it consistently generated far more heat than expected.