A guy over on the Ruger forum just installed this electrical backup system for his house.  It runs on propane, and given the size of his tank, the system will fully power his house, he reckons, for up to 10 days.  I have to say that is a nice and clean installation, and ten days ought to be enough time for the electric company to get the power back on.  If you lived in part of the country where there was a concern about a lengthy loss of power, this is the type of professional set up that you ought to consider.  Nice work indeed.