Just a bit late to the discussion, but I'll just add my story.
We have always had electric outages - a few hours at a time, until the October 2011 (Halloween Storm) and October 2012 (Sandy) when we had multi-day outages.
After the October 2011 storm, I purchased a 5500 KW portable unit (along with a bunch of extension cords
) and figured that's all I needed.
When Sandy hit, I was still out of luck since I had no protected area to run the unit (can't run in the rain) and I did not want to risk putting it into the garage - with the doors open - as others have done in my area. In fact, one guy a few blocks away had it in a shed, but the shed caught fire since he had the exhaust directed too close to the frame
Anyway, we had a 20 KW unit installed this past March to handle the entire house. We're in our mid-60's, both retired, and spend +95% of our time in and around our home. It was different when we were both employed. At least if we lost power we probably had it at our respective places of employment, and we didn't go the entire 24-hour day without heat and/or AC.
Additionally, during the 2011 storm, we were thinking about going to a hotel/motel out of the area. However, with two dogs and not having a place to put them (along with worrying about melting frozen food and raising water levels in the sump pit) leaving the house was not a simple option to execute.
Our HVAC firm (used them for two decades, since we built our home) became a dealership for Honeywell (e.g. Generac) backup generators. They did a study of our home electric use (peak loads) along with getting the records from our electric utility (we've always had a digital meter) which shows the highest KWH used every hour, on every day for the last 24 months.
With the information at hand, they recommended the 20KVA unit, which is the largest air-cooled unit on the market (regardless of maker). To go above 20KVA, you need to go to a 4 or 6 cyl. automotive type engine; it's quieter, but it also doubles the price since you are now including water cooling (radiator, water pump, etc.)
Upon running the installation stress test, we had all our appliances turned on and the unit did not trip the main breaker. In other words, it could handle the load even without dropping any of the four "controlled" 220v circuits that drop off (one at a time) if a possible overload is sensed.
It comes on automatically every week and does its self-test, a ten minute run to keep the seals lubed and to ensure that all portions of the system run as normal. And power outages? We've had three since early July (a total of 5-6 hours), and 15 seconds after a failure, everything starts running without a hitch. In fact, we've been unaware of when the power comes back on-line since there is no interruption and the unit (as placed at the back of our home) is fairly quiet and hardly noticeable while we are in our home.
We leave for our China trip next week (for 3 weeks). For the first time, I won't be worrying about what may happen if the "lights go out"
BTW, we're number four in our area (I can see the other three from our back deck) that have a similar size unit installed. We may be the latest, but I don't think we'll be the last to have one installed.