Plug-in hybrids emitting three times more pollutants than claimed, report finds

New research from Transport & Environment shows higher much higher emissions for half-electric cars

Plug-in hybrid cars have been promoted as a useful halfway house to full vehicle electrification, especially at a time when the public charging network for EVs is still in its infancy.

The combination of a small battery, which gives you a potential 50km (or more, in many cases) range for short commutes and regular journeys, plus a petrol (rarely a diesel) engine for longer journeys should in theory be an ideal compromise between combustion and electric power for many drivers.

However, new research from environmental pressure group Transport & Environment (T&E) claims to show that plug-in hybrid electric vehicles (PHEVs for short) can emit as much as 70 per cent higher emissions than claimed, even when driven with a full battery charge.

Anna Krajinska, vehicle emissions manager at T&E, told The Irish Times: “Plug-in hybrids are sold as the perfect combination of a battery for all your local needs and an engine for long distances. But real-world testing shows this is a myth. In city tests, just one of the PHEVs has the electric range advertised, while all three emit more than claimed in commuter driving. Lawmakers should treat PHEVs based on their actual emissions.”


T&E tested three PHEV models – a BMW 330e, a Peugeot 308 and a Renault Megane E-Tech. When driven on a typical commuter route, they did not perform as promised. Tests conducted by Graz University of Technology and commissioned by T&E found: “The BMW polluted three times its official rating, The Peugeot 308 and Renault Megane plug-in hybrids performed better but still polluted 20 per cent and 70 per cent more than claimed, respectively, despite the relatively short round-trip distance covered (55km)” according to T&E.

T&E’s tests showed that the BMW was only able to offer 74 per cent of its claimed official electric-only range on the test, while the Peugeot – on 53 per cent – did even worse. Only the Renault was able to offer its officially claimed electric mileage.

The figures become even worse once you start driving exclusively on the petrol engine on a flat battery. In the tests, when tested with an empty battery, the BMW, Peugeot and Renault emitted between five and seven times their claimed CO2 on the road.

The BMW comes with “geofencing” technology which automatically saves electric power for driving on zero-emissions power when in an urban area. This tech has been put forward as a potential mandatory fit for PHEV models in the future, to make sure that they live up to their emissions promises. However, according to T&E, geofencing technology does not guarantee zero-emissions driving in cities and, potentially, risks increasing CO2 emissions outside such zones.

One big issue is that PHEV models are currently taxed, both for private and company use, on their official CO2 figures, which tend to be exaggeratedly low owing to the ways in which the laboratory testing of cars tends to favour the electric half of their powertrain.

Effectively, then, their use is being subsidised by higher motor tax payers. Last year, the Government ended purchase incentives for PHEV models, but they are still taxed according to their CO2 emissions, meaning most owners will only pay €140 per year.

Even so, T&E suggests that switching from a PHEV to a fully electric model would still save car buyers considerable amounts of money: On average, an EU driver switching from the Peugeot 308 plug-in hybrid to a Citröen eC4 would save €4,800 over four years while the electric Renault Megane would save €1,300 compared to the PHEV version, and owning a Tesla Model 3 instead of the BMW 3 Series PHEV would save €2,600.

It is worth pointing out, though, that of the three cars T&E chose to test, only the Peugeot is really a new model. The 330e has been on sale for some time now, and its position in the market is under attack from newer rivals, such as the Mercedes C300e PHEV, which boasts a much bigger battery and a far longer electric range of 104km.

Meanwhile, the Megane E-Tech plug-in hybrid is no longer on sale at all in most markets, having been replaced by the all-electric new Megane E-Tech. In testing, we have noticed that many PHEV models perform poorly on longer journeys, with high fuel consumption and poor touring range thanks to small fuel tanks, but there are exceptions to this – notably the Toyota RAV4 PHEV and the Kia Niro PHEV. If T&E had tested these vehicles, the outcome may well have been different.

Others take a more nuanced approach. “People want independent, transparent information about the environmental impact of cars,” said GreenNCAP’s Niels Jacobsen. These PHEV results show why that is so important. Consumers could be forgiven for thinking that, by buying a car labelled ‘PHEV’ and keeping it charged all the time, they will be doing their bit for the environment, but these results show that this is not necessarily the case.

“The Mitsubishi Outlander shows that a big, heavy vehicle with a limited driving range is unlikely to offer any benefit over a conventional car. On the other hand, Toyota, with its long experience of hybrid technology, has done a terrific job and the Prius, properly used, can offer clean, efficient transport. It depends on the implementation and hybridisation strategy but what is true of all and driven as much as possible on battery power if they are to fulfil their potential.”

BMW points out that some of its PHEV models have one-charge electric ranges of as much as 88km, and that: “plug-in hybrid models are perfectly suited to urban and city driving by completing most commutes with pure-electric power The significant contribution plug-in hybrid vehicles can make to reducing tailpipe emissions in cities was demonstrated in an early trial of this technology, carried out in the Netherlands in 2018.

“Results of this research project showed 90 per cent of all routes within the trial zone in Rotterdam were driven in electric-only mode. As BMW anchors sustainability in the heart of its corporate strategy, there is a goal to avoid the emissions of over 200-million tonnes of CO2 by 2030. This is equivalent to more than 20 times the annual CO2 emissions of a city with over a million inhabitants, like Munich. To achieve this, the BMW Group is reducing its vehicles’ carbon footprint throughout their life cycle – from raw material extraction, through production and the use phase, to end-of-life recycling.”

However, a report by the Miles Consultancy and the BBC found that in 2020 a majority of plug in-hybrid cars bought were not being plugged in and charged up regularly, or in some cases at all. Driving a plug in-hybrid without charging it from the mains causes the fuel consumption to plummet, in some cases to well below the 9.0-litres per 100km mark, in cars which often claim overall fuel economy as high as 2.0-litre per 100km. Many buyers, including corporate fleets, were accused of buying plug in-hybrids simply for the tax advantages and the government grant which reduced the purchase price, but never intended to use the zero-emissions electric range of the vehicles.

Neil Briscoe

Neil Briscoe

Neil Briscoe, a contributor to The Irish Times, specialises in motoring