My background was designing, selling, and servicing diesel and natural gas generator sets, from 1988 through 1995. I am still at the same company, but not in our Power Systems division any longer. We sold the Generac units at the time (branded with another name), as well as our prime brand (the yellow ones made in Peoria) We also built, or packaged, gensets with various diesel engines. We used Honda gasoline gensets for portable power.

Natural gas: easier; cleaner; no fuel maintenance such as stabilizers, etc; less power density so there is a higher capital cost (you need more displacement for the same output). It will be an installed unit, so you will need some kind of transfer switch, either auto, semi auto, or manual. Biggest negative is the potential interruption of your natural gas supply. In some localities, the gas is pressurized by compressors driven electrically. In those cases, if the power goes out the natural gas does as well. Some building codes require separate diesel gensets if you have a code requirement for standby power, over and above the natural gas unit.

The cost of fuel is not a factor for any of these choices. You will use it so infrequently that it is simply irrelevant.

You need to decide if you want whole-house standby, in which case you need 12-15 kw depending on HVAC loads, or partial standby because you want to run lights, TV, microwave, fridge, etc. For occasional outages, it makes the most sense to buy a Honda unit that is parked in your garage. We have had 4 or 5 in the family over the years, and I could get serious gensets at real discounts, but still bought Hondas regularly. At home we always installed a welder outlet (like a dryer outlet, but more amps) in the garage. We used a manual system of shutting off the main breaker, plugging in the genset, starting it up, and ensuring we didn't run all the electric heat at the same time. 5 kW is plenty for a partial standby. 3 kw is enough for some lights and a microwave. The capital cost of this approach is a fraction of the other options. When we saw the lights come on down the street, we waited 10 minutes and then manually switched back to utility grid power. You can make the system safer by using a manual transfer switch so that you don't blow the fuse on the genset by forgetting to isolate the utility power.

Whatever you buy, you need to exercise it every couple of months, and maintain it. Testing it is the key to knowing it will work when you need it.

How much you should invest depends on the frequency of outages, and the consequences of those outages. To avoid occasional nuisance outages, I would simply buy a Honda and rig up a welder outlet to use to energize the house circuits.

Jeff

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue

Thank goodness for the power.
Just do proper research when going for the used gen set.
We got power back on Sunday afternoon, and we were lucky to have been spared though with some minor damages.