Utility factor

The utility factor is the assumption, fixed in the WLTP methodology, about what share of the kilometres a plug-in hybrid covers electrically. Because a PHEV sometimes runs on the battery and sometimes on the combustion engine, the test procedure weighs both modes with this factor to arrive at one stated consumption and CO2 figure. The larger the electric range, the higher the assumed electric fraction.

The result is that the stated WLTP consumption of a PHEV contains an assumption about charging behaviour, not a measurement of your use. A driver who charges rarely will in practice consume considerably more than the statement; someone who charges almost always and drives short distances can sit below it. The methodology has been revised to come closer to observed charging behaviour, but the deviation per individual remains large.

That is why on plug-in hybrids we explicitly set the WLTP statement next to the real-world picture from the reviews and name the utility-factor assumption as the source of the difference. The stated figure is a weighted laboratory value, not a forecast of your consumption.