Why is PHEV fuel consumption so low?

Just read a media report which claims the Ranger PHEV would have a range of 2400km. They have taken the ADR fuel consumption of 2.7L/100km and divided it by the 70L fuel tank. That works for any car except a PHEV (plug-in hybrid electric vehicle).

Non-PHEV hybrids have small batteries that can only be charged by the car, or regen. The ADR fuel consumption cycle is representative for them as the driver has very little control over the battery, and the electrics are really only there to supplement the ICE. Electric-only range is short, a few km, and most can’t even do 100km/h in their EV modes.

PHEVs are different. In the case of the Ranger you’ve got a claimed range of 49km on electric, which gets you a decent way into the test cycle before you’ve used a drop of fuel, or minimises the fuel use all the way through. This is how 4×4 PHEVs like Shark and Ranger achieve under 3L/100km official figures.

But after the shortish test cycle is complete the battery is depleted and then the car behaves like a normal hybrid, and fuel consumption shoots right up as there’s no bank of electric power to draw on, it’s just regenerated when slowing or from the engine itself.

This is why the PHEV use case makes best sense for short trips; if you can charge the vehicle cheaply, and use electric power for short trips, then you can save a lot of money especially considering that ICE vehicles have high fuel consumption and wear when cold on short trips.

If however you do a lot of long-distance work and have no opportunity to plug your PHEV in, and when you do, it’s expensive…the cost/benefit of a PHEV starts to disappear.

Essentially, the further you drive a PHEV, the higher the fuel consumption until it stabilises.

Should also note that a PHEV will use less fuel than a non-PHEV as it can harvest energy when slowing through regen, and use spare engine cycles to charge the battery. This is where BYD have been smart with the Shark’s series hybrid design; the engine can rev high whilst the car is slowing and charge the battery, whereas Ranger PHEV cannot.

The ADR fuel consumption testing needs an overhaul. I think that for PHEVs the start point should be with a battery depleted to normal operating state of charge, with a note that for short trips it’d be 0L/km – the current 2.7, 2.9 or whatever is misleading.