A new study from The International Council on Clean Transportation (ICCT) alleges fuel consumption and CO2 emissions of plug-in hybrid vehicles (PHEVs) in Europe are much higher than manufacturers’ claims.

The ICCT reports real-world fuel consumption of PHEVs is three to five times higher than the official numbers created using the mandated World Harmonised Light Vehicle Testing Procedure, known as WLTP.

Plug-in hybrids, which typically offer a fully-electric driving range of between 50 and 80 kilometres before the petrol engine takes over, claim average fuel consumption of between 1.6 to 1.7 litres per 100 kilometres on the WLTP cycle – but the paper claims the real figure is closer to 4.0 to 4.4L/100km.

As well as higher consumption, it alleges exhaust emissions are on average between 90 to 105g per kilometre – much higher than the 37-39g/km achieved using the WLTP standard.

The study, which was developed in collaboration with German research organisation The Fraunhofer Society, analysed data from 9000 vehicles across the European Union, Norway, Switzerland, and the United Kingdom.

While the report stresses the anomalies were found on models sold in Europe and neighbouring countries, it says the deviation between claimed fuel consumption figures and so-called “real-world” data has been growing by as much as 0.2L/100km each year since 2012.

The ICCT reports PHEVs used as company cars are at the higher end of the estimated range, with as much as 89 per cent of driving being conducted using the petrol engine on average.

The blame appears to lay at the feet of regulators and drivers rather than carmakers, who are merely reporting government-mandated results.

While a number of reasons are listed for the discrepancies, the paper says many cars in the real world are not fully charged before being driven, meaning owners are not taking advantage of the maximum all-electric driving range available from their vehicles.

When the batteries are depleted and the petrol engine is powering the car, the ICCT claims fuel consumption is much higher than the official figures, thanks to the electric component of the test artificially suppressing the real consumption figures.

The ICCT has presented a number of recommendations as part of the report, including “rescaling the existing formula for the assumed [battery] charge-depleting mode” to more accurately reflect real-world results.

Source: Fraunhofer/ICCT

The organisation also recommends PHEVs be excluded from financial incentives – a position backed by the Environmental Action Germany.

“Although plug-in hybrids consume an average of more than 8.0-litres of fuel per 100 kilometres, the [German] government still carries them under the [electric car] label, showers them with purchase premiums and promotes them with generous benefits in the company car regulation,” said Dorothee Saar, the head of traffic and air pollution control at Environmental Action Germany.

“At the same time, the car manufacturers … have been able to push these climate killers onto the market for years in order to polish up their fleet balance sheets. Climate protection, on the other hand, falls by the wayside,” she added.

Environmental Action Germany is currently suing Mercedes-Benz for allegations the car giant isn’t moving quickly enough towards an all-electric model range.