Hybrid cars could provide a lower-risk way of reducing carbon emissions compared to plug-in hybrids (PHEVs), potentially helping to cut CO2 faster, according to a new report by Emissions Analytics.

The Emissions Analytics report warns that the emissions-reduction benefits of PHEVs are reliant upon driver behaviour compliance

The report doesn’t set out that hybrids are lower-emission than plug-in hybrids – but warns that the emissions-reduction benefits of PHEVs are reliant upon driver behaviour compliance. This is a key concern among some EU member states and a very real risk based on anecdotal evidence of drivers switching to PHEVs due to subsidies and attractive incentives but then never plugging their vehicles in and just relying on the internal combustion engine, as with a conventionally powered car, but potentially bringing worse fuel consumption due to smaller-than-optimal ICEs.

Latest figures from Emissions Analytics underscore the poor real-world results of PHEVs when not plugged in. Of all PHEVs tested by Emissions Analytics, which includes petrol and diesel versions, the average performance in this condition is 37.2mpg (7.6 l/100km) and CO2 emissions of 193.3g/km, which is 62.5% worse than the official NEDC results.

Its research follows high-profile concern over driver misuse of PHEVs in the last few years. According to ACFO, there have been widespread reports of fleets returning their cars early to leasing firms due to significantly higher-than-expected fuel consumption; the organisation has for some time been calling for Advisory Fuel Rates (AFRs) for all PHEVs to clamp down on this.

More recently, TMC has warned that its real-world mpg data has revealed many PHEVs actually cost more in fuel pence-per-mile than typical diesel or petrol company cars due to drivers not charging them.

As a result of concerns over such behaviour, the Dutch government withdrew previously generous PHEV subsidies at the end of 2016, followed by the UK in late 2018.

But, according to Emissions Analytics, the issue of drivers switching to PHEVs but not reaping the eco benefits of them could become more widespread. The firm says a wide range of new PHEVs are now being launched two years after the shift to the Worldwide Harmonised Light Vehicle Test Procedure (WLTP) started in September 2017 as carmakers use them to meet impending CAFE fleet average emissions. Although some plug-ins performed poorly under WLTP, disallowing them from various subsidies and benefits and leading some models to be axed, new models are now arriving as carmakers turn to using larger batteries to help ensure their PHEVs score sub-50g CO2/km emissions, providing them with ‘super-credit’ status whereby they can initially be counted twice in the CAFE fleet average CO2 calculation.

Emissions Analytics is at pains to point out that PHEVs are not without a claim to virtue; their primary strength is offering electrification without range anxiety, since an internal combustion engine remains present, whether as a part of the drivetrain or as a ‘range-extending’ battery generator.

It adds that research studies have shown that some duty cycles – for example commuting to and from work every day but charging overnight and avoiding long distances – can result in virtually no use of the ICE. The consumer has in this case had an EV ‘on the cheap’, without the weight and cost of a large battery pack. This is a PHEV at its best.

But it also highlights that the real-world performance of PHEVs rests to an unusually large degree on user behaviour and journey length, rather than instantaneous combustion performance – and this can vary wildly. One study, based on 1,831 Chevrolet Volts in the US, the authors found generally excellent utility factors, the average being 78%. However, in Dutch research, which included smaller-battery PHEVs and owners who typically didn’t bother to plug in, the average utility factor was 24%.

And if drivers aren’t using PHEVs right, this clashes with EU policymakers’ purposes to reduce real greenhouse gases as quickly as possible.

However, in contrast, the firm says full hybrids offer much faster and more certain emissions reductions of up to 30% – as they are not reliant on drivers using them correctly. And its position is that on reasonable assumptions PHEVs will deliver less and less certain reductions in CO2 than non-plug-in hybrids.

It adds that the case for future PHEVs may lie principally in the light to medium commercial fleet, where the advent of zero-emission city centres may force dual-drivetrain approaches, prompting a growing focus on ‘geo-fencing’.

Mitsubishi has commented on Emissions Analytics’ work. The carmaker’s latest Outlander PHEV is listed in the research, which says the larger, new petrol engine (2.4-litres as opposed to 2.0-litres) and increased battery size crucially allowed the SUV to retain a sub-50g rating (46g/km) while EV range fell from 33 miles under the NEDC cycle to 28 miles under the much more stringent WLTP cycle.

However, Mitsubishi says much of the evidence relating to plug-in hybrids not being charged regularly can be attributed to those models that had a nominal EV range and which have since been removed from sale thanks to the switch from NEDC to WLTP. A spokesperson said the Outlander PHEV, in contrast, had a substantial electric range from its 2014 launch to ensure it could realistically be used an electric vehicle for most journeys, with a petrol engine for longer trips. And a study of the charging habits of UK Outlander PHEV customers showed that two-thirds of owners charged every day and 90% charged at least two or three times per week. Moreover, approximately half of the daily average mileage was conducted in EV mode.

A spokesperson for the company added: “We don’t disagree that PHEVs need a degree of behavioural adjustment but in most cases that adjustment comes naturally. In the case of the Outlander PHEV, customers have found it is considerably more cost-effective to run than an ICE vehicle day-to-day and brings added benefits of reducing urban noise and air pollution especially during peak times when petrol and diesel are at their least efficient. For private customers, there are now no VED savings, no charging incentives and no plug-in car grant to reduce the purchase price. They buy purely for the driving experience and because PHEVs are more considerably affordable and more convenient to own.

“For business users, there are many mechanisms to encourage the correct use of a PHEV including, for example, linking taxation to charging (with data obtained from electricity providers, smart charger or the vehicles themselves), adjusting fuel card benefits and proactively ensuring that charge points are available at work and at home for PHEV buyers. None of these are difficult to introduce and would ensure that PHEVs are used as intended, reducing emissions (even on longer journeys a fully-charged battery can drastically reduce fuel consumption by working in tandem with the ICE) and introducing a whole new wave of consumers to electric driving.

“We have stated all along that PHEVs are an important segue to pure EV motoring, giving consumers confidence to take the electric plunge by proving to them than in actuality an EV will be more than sufficient for the majority of their journeys. Our study revealed that 25% of Outlander PHEV drivers are actually considering a pure EV next.

“Finally, for clarity, the cylinder capacity increase of the petrol engine in the Mitsubishi Outlander PHEV was due primarily to the adoption of the Atkinson Cycle engine which adjusts valve timing to effectively reduce the capacity of the cylinder when under light load, making it even more efficient than the model it replaces.”