It buys storage flexibility rather than performance: bottled gas keeps indefinitely where petrol degrades, which suits a machine that sits unused between outages. Output is commonly lower on gas, and makers publish a separate rating for each fuel.
Dual fuel changes what a generator is like to own more than what it is like to use.
The storage argument
A generator for power cuts spends nearly all its life waiting. Petrol left in a tank and in a carburettor for a year is the commonest reason such a machine will not start when it is finally needed. Bottled gas has no equivalent problem, and a cylinder can sit for years.
The output trade
Running on gas typically yields less than running on petrol, and makers publish a rating for each. Sizing has to use the fuel that will actually be used, not the larger of the two numbers.
The handling trade
Gas cylinders bring their own storage and connection requirements, set by local regulations and by the cylinder supplier, and they are not lighter or simpler — merely different. Petrol brings storage limits of its own.
What dual fuel does not relax
Exhaust, and therefore where the machine may be run. Noise, and therefore where it may be run without complaint. Maintenance intervals, earthing and refuelling procedure, all of which are in the manual and none of which the fuel choice relaxes.
What people ask before they order
Why is output lower on gas?
The energy density delivered to the engine differs, so the same engine produces less. Makers state both figures, and the gas figure is the one to size against if gas is the fuel it will normally run on.
Does petrol really go off?
It degrades in storage, which is why manuals cover stabilisers, storage periods and draining before a long idle. The instructions are per engine and they are specific.
Last reviewed 16 September 2026