Plug-in hybrid cars emit up to 10 times the CO2 stated in official figures, according to a new study.
The results of the study suggest that in real-world driving conditions the hybrids - which are marketed as having incredibly low CO2 emissions - are far more polluting than suggested by the industry-standard WLTP test.
As a result, the group which commissioned the study has branded PHEVs “fake electric cars” and urged the Government to end tax breaks for the vehicles.
The tests, carried out by Emissions Analytics on behalf of the zero-emissions campaign group Transport and Environment examined the real-world performance of three popular models - the Volvo X60 T8 PHEV, BMW X5 XDrive 45e and Mitsubishi Outlander PHEV.
The plug-in variant of the BMW X5 was among the models tested (Photo: BMW)
They found that even when started with a fully charged battery, all three cars emitted more CO2 than claimed in the WLTP test and showed massive differences depending on which mode the cars were in.
On a 92km drive, started with a full battery, the BMW emitted 42.3g/km against an official figure of 32g/km but when run with the petrol engine recharging the battery, this shot up to 384.6g/km.
The Volvo, with official emissions of 71g/km managed 115.5g/km in the best-case scenario with a full battery, and 241.8g/km when the engine was charging the battery. The Mitsubishi showed similar differences, recording 85.8g/km and 216g/km against an official figure of 46g/km.
Julia Poliscanova, Transport and Environment’s senior director for clean vehicles, said: “Plug-in hybrids are fake electric cars, built for lab tests and tax breaks, not real driving. Our tests show that even in optimal conditions, with a full battery, the cars pollute more than advertised. Unless you drive them softly, carbon emissions can go off the charts.”
She added: “Carmakers blame drivers for plug-in hybrids’ high emissions. But the truth is that most PHEVs are just not well made. They have weak electric motors, big, polluting engines, and usually can’t fast charge.”
However, car makers have hit back and questioned the accuracy and validity of the testing.
Mike Hawes, chief executive of the Society of Motor Manufacturers and Traders, 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.
“PHEVs provide flexibility, with the ability to drive in zero emission mode for typically 25 to 40 miles - more than ample given that 94 per cent of UK car journeys are less than 25 miles.
“We can’t comment on unverified, unregulated tests by commercial entities, but even these have found that PHEVs emit at least 25 to 45 per cent less CO2 than their pure ICE counterparts, and of course, they emit 100 per cent less when driven in battery mode.”
Volvo XC60 T8 hybrid (Photo: Volvo)
A BMW spokesperson said: “The WLTP test is designed by the international regulators as a standardised method of comparing vehicle efficiency. 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.
“The tests are conducted in a laboratory environment to ensure that all vehicles are tested in exactly the same way and under the same conditions and can be compared. While we cannot comment on the test method used in this report, it is no surprise that different emissions figures are reached as on-the-road driving conditions are infinitely variable.”
Volvo said: "The existing emissions testing regime provides a useful industry standard that allows customers to make comparisons between cars, but real-world variations will apply.
“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, making them a crucial step in our path to full electrification.”
The Mitsubishi Outlander is the UK's best-selling plug-in hybrid (Photo: Mitsubishi)
Responding to the report, a Mitsubishi spokesperson said: "Our published MPG and CO2 figures are the numbers that are produced as a result of a standardised WLTP test that was specifically designed for PHEVs.
"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.
“There is mention of the fact that our PHEV can be driven distances up to 28 miles in pure EV mode between charges, well within the average daily commute in England and Wales for example, meaning drivers will effectively use no fuel and produce no tailpipe emissions.”