Plug-in hybrids not as good as they first appear

New research suggest that CO2 emissions from plug-in hybrid cars are as much as two-and-a-half times higher than official tests suggest.

Plug-in hybrid vehicles are powered by an electric motor using a battery that is recharged by being plugged in or via an on-board petrol or diesel engine.

They account for approximately 3% of new car sales.

But recent analysis from pressure groups Transport and Environment and Greenpeace suggest their emissions are different from official testing:

PHEV CO2 EMISSIONS
OFFICIAL CO2 - 44g/km
REAL WORLD ESTIMATION - 120g/km

They suggest they emit an average of 120g of CO2 per km.That compares with the 44g per km in official “lab” tests

Plug-in hybrid electric vehicles (PHEVs) are sold as a low-carbon alternative to traditional vehicles and conventional hybrids – which cannot be recharged from an external source – and are proving increasingly popular.

The new research is published at a time when EU legislation considers whether to bring forward a proposed sales bans of new petrol, diesel and conventional hybrid cars from 2035 to 2030.

Official versus real world

One suggestion is that plug-in hybrids should be given a stay of execution, with new sales allowed to continue until 2035. That’s because they can offer a 20- to 40-mile range as a purely electric vehicle and are therefore potentially significantly less polluting than other vehicles.

But the new analysis from Greenpeace suggests they don’t offer anything like the carbon dioxide savings claimed for them by manufacturers. The pressure groups have analysed what they say is “real-world” data on fuel efficiency collected from some 20,000 plug-in hybrid drivers around Europe.

These are drivers who have chosen to record their mileage and fuel consumption for surveys or who drive company or leased vehicles whose fuel efficiency is recorded.

According to this data-set the lifetime emissions of a plug-in hybrid average around 28 tonnes of CO2.

By comparison, the average petrol or diesel car is estimated to emit between 39 and 41 tonnes of CO2 from fuel during its lifetime, a conventional hybrid would typically emit more like 33 tonnes.

According to these figures a plug-in hybrid would only deliver an emissions reduction of about a third on a typical petrol or diesel car – far less than the official estimates.

The motor industry acknowledges that lab tests don’t always reflect real-world use but criticised the report, saying it uses emissions data from a test that is two years old.

PHEVs provide a flexibility few other technologies can yet match with extended range for longer, out-of-town journeys and battery power in urban areas, reducing emissions and improving city air quality. Range and performance will continue to improve, making them an "essential stepping stone to a fully electric vehicle.

What about driver behaviour?

Common analysis suggests a key problem with plug-in hybrids is that many owners rarely actually charge their cars, meaning they rely on the petrol or diesel engine. Charging cables are often returned unopened after a lease. 

Another is that many plug-in hybrid models include design features that automatically turn on the petrol/diesel engine at start-up on a cold day, or will kick in that engine if driver accelerates hard.

The latter mode means that the car’s emissions will depend a lot on the driver’s behaviour. 

Equally, more aggressive drivers will impact fleet cost  through increased tyre and brake wear for example.

The key to any change of vehicle policy is understanding driver needs. Recent studies have shown that over 80% of drivers can switch to a PURE EV vehicle, some urbanists with challenges for home charging not taken into account. Plug-in hybrid vehicles certainly have their merits as a stepping stone towards EV’s; as more models are available and range anxiety is covered. However, plug-in hybrids are only a viable alternative for specific mobility profiles. In principle drivers that mostly drive trips below 50 km are a good fit. Fleet360 can help you map mobility profiles to ensure drivers are stepping into company vehicles with the right powertrain. Car policies should reflect this and should include monitoring of charging the PHEV and limits to fuelling.

Bart Vanham
Want to know more?

Take a look at the related articles below. A great starting point is aiming to understand how to electrify your fleet and how to understand driver patterns and expectations.

A quick guide to the pros & cons of different vehicle powertrains
ProsCons
Great around town centresNot so economical on motorway
No need to plug in to chargeNo longer exempt from road tax 
Better economy than regular carsMild hybrids aren’t full hybrids
ProsCons
No ‘range anxiety’

Owners need charging facilities

Suits an urban lifestyleExtra weight affects drive
Zero-emission commuting

Engine’s economy not great

ProsCons
Very low running costs

Need to be plugged in to charge

Zero tailpipe emissions

Charging can take a long time. But improving all the time

Relaxing to drivePossible range anxiety

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