Popular models of plug-in hybrid cars are polluting up to eight times more than official tests indicate when run in engine mode, according to a new study that highlights what it says are unrealistic assumptions underlying the tests.
The results have prompted the commissioners of the study to claim plug-in hybrids are “fake electric” cars.
Even on a journey starting with a full battery, a study found the cars emitted significantly more than official results from EU standard tests, which assume drivers will use the car mostly in electric mode.
The Mitsubishi Outlander, the second most popular plug-in hybrid in the UK, emitted 85.8g of CO2 per km, 89 per cent higher than the 46g/km advertised, on a “mild” drive on slower roads, starting with a full battery, analysis commissioned by NGO Transport and Environment found.
The Volvo XC60 was found to emit 115.3g/km, 62 per cent more than advertised, and the BMW X5 42.3g/km, 28 per cent more than advertised.
Transport and Environment said that the EU standard tests relied on assumptions that the cars run for longer in battery-only mode than is realistic. Its tests took the cars on the same 92km journey as EU tests for road pollution.
The Government will ban the sale of new combustion engine cars from 2030, but has extended the deadline for plug-in hybrids to 2035 after lobbying from the motor manufacturing industry.
It has said this will apply only to hybrids that can drive a “significant” distance on zero-emissions capability, but has not yet specified what that figure will be.
Transport and Environment compared the results of the tests, the latest to suggest plug-in hybrid vehicles are underperforming on their claims, to the diesel emissions scandal.
Julia Poliscanova, senior director for clean vehicles at T&E, said: “Plug-in hybrids are fake electric cars, built for lab tests and tax breaks, not real driving.”
The tests found that while driving on an empty battery the models produced three to eight times more than official values of CO2. The NGO said this scenario was more likely than manufacturers assume because the batteries are affected by higher payloads, acceleration, and motorway driving. When driven in battery-charging mode, which the NGO said was likely to occur when heading into congestion charging zones, emissions were found to be three to 12 times more than official figures.
Plug-in hybrids tend to have small electric batteries, which mean they need to be charged much more frequently than regular EVs if they are to run as zero-carbon, Ms Poliscanova said. Neither the BMW X5 or the Volvo XC60 are able to fast charge.
“Carmakers blame drivers for plug-in hybrids’ high emissions. But the truth is that most PHEVs are just not well made,” said Ms Poliscanova. “They have weak electric motors, big, polluting engines, and usually can’t fast charge.”
The UK is expected to continue using the same standards to measure CO2 emissions from hybrids after leaving the EU.
The motoring industry argues that hybrids are an important transition technology for car users that are nervous about the move to electric because of fears of running out of battery.
Mike Hawes, SMMT Chief Executive, said: “There will always be a difference between lab tests and real-world use, but the internationally regulated WLTP and RDE tests prove that plug-in hybrids deliver substantial emission reductions compared to pure petrol or diesel equivalents.”
He added: “We can’t comment on unverified, unregulated tests by commercial entities, but even these have found that PHEVs emit at least 25 per cent-45 per cent less CO2 than their pure ICE counterparts, and of course, they emit 100 per cent less when driven in battery mode.”
A spokesperson for Mitsubishi said: "Independent tests can produce unreliable / variable figures depending on conditions and a variety of other factors and we naturally contest any findings where we have no oversight of the testing or methodology.
"Disregarding a PHEV’s electrical powertrain during testing, for example, is like testing a petrol or diesel car and only using three of its gears.“
Volvo said: “Plug-in hybrids have zero, or close to zero, tailpipe emissions when driven in pure electric mode and our customer field data shows that Volvo plug-in hybrids are driven in pure electric mode on an average of 40 per cent of the time.”
BMW said the EU’s standard test “show clearly that PHEV technology, when charged regularly as intended, can save significant fuel consumption and emissions over the equivalent petrol or diesel models.”