If the fan blades turns brown you can not rely on NG! Even this last cold spell showed that. I would have propane or gasoline/diesel for a back up gen rather than NG if I were you. Nuff said.I thought propane when I first started down the whole house genny but now that we have NG and not having to mess with trying to find a decent tank to buy or renting from some propane company that is what I have decided to go with is NG for now. Solar living in TN has me of two minds but that is just me.
Also look on homesteading forums there is usually a pinned or live thread that is all about solar and offgrid living.