Carmakers pass the buck onto consumers for plug-in hybrid emissions

Tests on plug-in hybrid vehicles (PHEVs) show they pollute significantly more than carmakers claim. But despite a big part of the problem being inherent in the vehicles’ design, manufacturers are trying to blame consumers instead. In reality, weak electric motors, range and slow charging speeds are to blame, not only users.

Research by T&E shows that current PHEV models lack the necessary EV power, range and charging speeds required to maximise electric use. Two of the three cars tested, for example, the BMW X5 and Volvo XC60, cannot fast charge. What’s more, the Outlander’s manual even states that the engine may start if the PHEV system is too hot or too cold, if quick acceleration is applied, or if the air conditioning is operating.  

Anna Krajinska, emissions engineer at T&E, said: “PHEVs sold today are much closer to conventional combustion engine cars than battery electrics. It is simply not enough for manufacturer’s to fit a battery and electric motor to a combustion engined car for tax and regulatory advantages, then pat themselves on the back for a job well done. PHEVs actually have to deliver the official CO2 savings on the road or they cannot be called low-emission.”   

Once the battery is flat, the three plug-in hybrids tested can only drive an estimated 11-23km in engine mode before they overshoot their official CO2 emissions per km. This contradicts the narrative peddled by carmakers that the PHEVs on sale today are suited for long journeys. In fact, they have to be charged much more frequently than battery electric cars, which do around 300km on a single charge.


T&E’s results also show that even when tested under optimal conditions, the three PHEVs emitted 28-89% more CO2 than advertised on Real Driving Emissions (RDE) tests. When running using the engine, emissions were comparable or worse than equivalent combustion engined cars. The worst results were observed when driven in battery-charging mode, which could become more common as motorists charge up ahead of using electric mode in low-emission and geo-fenced zones, where the PHEVs tested up to 12 times more than official values.

BMW doubled down on the notion that the problem lies in the vehicles’ usage rather than their design. “The WLTP test is designed by the international regulators as a standardised method of comparing vehicle efficiency,” a spokesperson said. “These tests show clearly that PHEV technology, when charged regularly as intended, can save significant fuel consumption and emissions over the equivalent petrol or diesel models.”

Anna Krajinska responded: “The WLTP test fails to account for real-world driving conditions where the engine may come on even if the driver has requested for the car to drive electrically. It also uses unrealistic assumptions on the share of electric kilometers driven by PHEVs which have been shown time and time again to not reflect their real world use. This allows manufacturers to claim unrealistically low CO2 emissions for these cars.” 

Most manufacturers fail to educate or encourage drivers to charge more effectively and, as T&E’s report shows, the design flaws in PHEVs would undermine even the most diligent driver’s attempts. Therefore, only truly zero emission vehicles should be eligible for purchase subsidies.

When it comes to tax benefits, T&E said that only PHEVs with an electric range of more than 80km, sufficient power to use zero emission mode, and the ability to fast charge, should be eligible for support. PHEVs brought as company cars should demonstrate access to workplace or home charging.