While gasoline and diesel fuel both have more energy per unit weight than either propane or natural gas, we're talking about emergency generators here. Reliability is more important than efficiency. Propane, BTW, has more energy than natural gas, since its molecule is bigger than the methane molecule that constitutes most of natural gas.

The other important question that each of us must answer for ourselves is, what fuel do I already have available? I installed my propane-fueled generator because I had propane on the property to run the house (I wouldn't put in propane just for a generator). That was years before I discovered diesel cars or I might have made a different decision. Having two diesel cars and a diesel tractor means always having fresh diesel fuel on the property.

Another question is the availability of inexpensive but reliable generators. My Onan was a commercial unit but I was able to get it on the surplus market (7.5KW for $700). A new commercial generator capable of maintaining an entire household for several days of continuous operation will not be cheap, regardless of the fuel it is designed to use. If you can save a significant chunk of change by picking up a generator on the used market, I suspect that you'll take what you can get and not be picky about the fuel.

As for natural gas, it is clean and convenient but I'd be concerned about reliability in any kind of major disaster. If the gas stops coming out of the pipe, your generator stops working. For disaster preparation, I'd prefer to be entirely self-contained, with the fuel actually on my property. If my propane tank runs dry, I can always switch back to gasoline, which my Onan was designed to do.

Jeremy

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970