Plug-in hybrid cars can emit up to three times more carbon dioxide than advertised as real-world tests show some are more polluting than lighter petrol vehicles.
Hybrid cars make use of a battery-powered electric motor to support their internal combustion engine and are often touted as a green choice.
However, aseries of studies have revealed that the fuel consumption rates of the hybrid vehicles are far greater in the real world than in testing conditions.
The reason for this is that hybrids — which contain an extra electric motor and battery — tend to be heavier than their petrol counterparts.
In addition, many plug-in hybrid owners are neglecting to charge their vehicles, running them on petrol alone and losing the benefits of the dual system.
The findings come in the wake of the UK Government’s announcement on Thursday that sales of petrol, diesel and hybrid cars will be banned from 2035 onwards.
The move — intended to reduce air pollution and carbon dioxide emissions — advances the timeline for phasing out fossil fuel-driven cars by five years.
‘When charged appropriately, plug-in hybrid vehicles allow drivers to complete the majority of trips in all-electric mode,’ Ewa Kmietowicz, Transport Team Leader at the Committee on Climate Change told the Telegraph.
‘However, there is a concern that plug-in hybrids are not being used as intended, achieving less than one-third of miles in electric mode, and risking higher emissions.
‘By the end of the year, most new models of fully electric vehicle will be able to cover 150 miles on a single charge, and the need for plug-in hybrids will inevitably decline.’
A study by fuel management firm The Miles Consultancy audited the consumption of various popular plug-in electric hybrid vehicles among car fleet drivers.
The Crewe-based company found that the vehicles — produced by such manufacturers as BMW, Mercedes, Mitsubishi and Volkswagen — often returned fuel consumption figures between 2.5–3 times higher than had been advertised.
An audit of 187 regularly-charged plug-in hybrid BMWs, for example, found an average fuel economy of only 42 miles per gallon, compared to the claimed 137 miles per gallon.
Similarly, experts have found that cars with ostensible carbon dioxide (CO2) emissions of less than 50 grams per kilometre often emit three times as much under real driving conditions.
In fact, a 2018 study of plug-in hybrids by researchers in Norway concluded that ‘the average yearly estimated CO2-emission was about 2.5 times higher than the value stated in the type approval official CO2-emission test’, the Telegraph reported.
Nevertheless, plug-in hybrids have proven popular with the motoring public, with industry predictions suggesting that sales of the cars will increase in Europe this year from 220,000 to 590,000 units.
Some of this interest has been driven, perhaps, by the tax breaks offered to company car owners.
Unfortunately, experts fear that the drivers of these vehicles may be being incentivised to eschew recharging their cars at home at their expense in favour of topping up with petrol alone on the company credit card.
‘There is a real risk that drivers are adopting plug-in hybrid electric vehicles for completely the right reasons, but unknowingly actually increasing their fuel bills,’ The Miles Consultancy’s managing director Paul Hollick told the Telegraph.
‘On the evidence of our sample, one has to question whether some plug-in hybrid electric vehicles ever see a charging cable.’
‘In a lot of cases, we see plug-in hybrid electric vehicles never being charged, doing longer drives and this is not a good fit for a lot of car users.’
‘This is all very confusing for motorists,’ Emissions Analytics chief executive Nick Molden told the Telegraph.
‘The problem is the official figures are very sensitive to assumptions about how plug-in hybrid electric vehicles are being charged and driven.’
‘The Mitsubishi Outlander plug-in hybrid electric vehicle was originally tested for emissions and fuel economy in a fully charged state,’ a Mitsubishi UK spokesperson told the Telegraph.
The Outlander is one of the most popular plug-in hybrids on the market.
‘The additional performance that the energy stored in the battery provides naturally has a significant impact on its overall efficiency.’
‘We state in our promotional material that the official figures are only for comparison to similar vehicles and that they may not reflect real-life driving results,’ they added.
According to the firm, a survey of Mitsubishi plug-in hybrid electric vehicle owners found that 96 per cent claim to charge their car at least once a week and 68 per cent said that they recharged their vehicle on a daily basis.
Meanwhile, a spokesperson for Kia told the Telegraph that the proper method for operating plug-in hybrids is explained to customers when they purchase and take possession of such vehicles.
‘But Kia cannot ensure that owners will always follow that advice once the vehicle leaves the supplying dealership – that responsibility lies with the owner.’
‘Used correctly a plug-in hybrid electric vehicle will improve fuel economy and reduce tailpipe emissions.’