The following is a post I placed on another board:
A post about generator efficiency and fuel consumption. For understanding.
1) A portable generator is not an efficient device. Regardless of brand or type.
2) Generator produced power (for our purposes, portable and stationary household sized) is very expensive when compared to the utility company, regardless of fuel type and fuel costs. Even with free fuel, the costs exceed the utility company's charges per KWH.
3) Inverter generators are NOT more efficient in many situations. They are quieter and better suited to very low/no load conditions.
Here are some numbers: (note, look at KWH/gal, higher is better)
Honda EU2000i inverter generator
1,600W 4.75 kWh/gallon Run time 2.97 hours/gallon.
555W 4.47 kWh/gallon Run time 8.06 hours/gallon
The Honda is almost as efficient at low loads as it is at high loads. This is fantastic when you need very little power. But it's not as good as a conventional genset at high loads, as we will see below.
Generac GP3250
2300W, 5.53 KWH/gallon
1900W, 5.35 KWH/gallon
1150W, 4.45 KWH/gallon
744W, 3.84 KWH/gallon
Yamaha EF3000is
2300W, 4.50 KWH/gallon
1900W, 4.42 KWH/gallon
1150W, 4.38 KWH/gallon
744W, 3.89 KWH/gallon
Notice the inverter Yamaha is not better than the Generac until it's at 1/4 load or lower. At which point, you will save some fuel.
Listeroid 6/1 diesel with belt drive ST generator head (notice that it's twice as efficient as the Honda/Yamaha inverter generators when heavily loaded, and exceeds the inverter's efficiency all the way down to 500W) (at which point, it consumes about 1/10 gallon per hour, on par with the Honda)
3000W, 8.57 KWH/gallon
2000W, 7.69 KWH/gallon
1000W, 5.71 KWH/gallon
500W, 4.2 KWH/gallon Run time 8 hours per gallon (exactly the same as the Honda, this showcases the diesel's efficiency)
15000W Generac portable (gasoline) (note, the bigger the generator, the more efficient)
15KW, 8.3KWH/gal
7.5KW, 5.9KWH/gal
3750W, 3.8KWH/gal
30,000W John Deere turbodiesel generator (note, diesels are often very efficient at a wide range of loads, and sometimes worse at very high loads)
30KW, 11.4KWH/gal
15KW, 11.5KWH/gal
200,000W JD turbodiesel generator
200KW, 15.5KWH/gal
100KW, 15.5KWH/gal (or roughly 20c/KWH at $3/gal) (still double the local utilities price, and the unit's capital costs are enormous)