We set up a fully automated propane generator for my aged parents after the last major ice storm, when we realized that firing up and re-fueling the old gas powered generator was out of the question.
The generator is in its own shed, battery operated (needs to be checked once every year), and requires no major switching for the residents. My mother does switch off the electric water heater, which may or may not be necessary. The propane tanks will keep the system going for about a week without refueling; we once had an outage of ten days but they do live a mile from the main road and there are a lot of potential trees that could (and do) come crashing down.
We did have the system installed by a master heating technician.
I believe the whole system ran $7000 to $8000, which we believe is well worth the investment. We live half an hour away and are greatly relieved that our parents are independent of the grid. They also have a Jitterbug mobile phone (which needs to be periodically charged) so they can communicate with the outside world if the phone lines go down as well.
The part of the house that is heated in the winter is about 1600 square feet. There's a refrigerator and a freezer, the electric water heater, gas kitchen stove, computer, and lighting.
I'll have to look up what the technical specs are, if anyone is interested, but it works great.