Are plug-in hybrids as green as they seem?
The ecological benefits of PHEVs are only viable if drivers charge them, say car manufacturers
The mismatch between the quoted and actual fuel economy of plug-in hybrids (PHEVs) is coming under greater scrutiny as EU authorities look to tighten the testing process in reaction to data harvested from the vehicles.
The EU and the UK (which copied over the legislation) have since January 2020 required all new cars to monitor and store fuel consumption data for inspection by authorities, including electricity usage for PHEVs, to be able to calculate more precise CO2 emissions figures.
PHEVs combine a battery with a petrol or diesel combustion engine to theoretically cut CO2 levels to under 50g/km in most cases – well below that of even the most economical hybrid without a socket. That in turn unlocks a range of tax incentives, the most generous of which in the UK is a discount on benefit-in-kind tax.
However, a number of recent studies have openly challenged whether the official testing procedure for PHEVs is so far removed from real-world reality that we’re actually incentivising the wrong technology.
The most recent, published by the International Council on Clean Transportation (ICCT) in December, following tests on a “representative” 2020 BMW X1 xDrive25e to work out where the modern WLPT test procedure was going wrong.
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The testing discovered that an ambient 23deg C temperature was just too generous. At -5deg C, for example, CO2 emissions shot up to 94g/km, or 40 times higher, while the car was still in ‘charge depletion’ mode (ie. draining its battery of mains-supplied electricity). Add in driving in ‘charge sustaining’ mode and the figure should be closer to 122g/km, it reckoned, not 43g/km.
The ICCT also blasted the ‘charge increasing’ modes that use the combustion engine to replenish the battery, which it reckoned bumped the CO2 to 246g/km, even in ambient temperatures.
The pressure is having an effect. The EU is “discussing” plans to change the PHEV test from 2025, according to reports from Reuters in February.
The EU’s plans, copied by the UK, already called for an assessment of the data collected from all cars, including PHEVs, by 1 June 2023. Should they find that the emissions data is excessively out (which it almost certainly will be), the EU will in 2027 put in place “a mechanism to adjust the manufacturer's average specific emissions of CO2 as of 2030”.
That means PHEVs will stop becoming a useful tool to reduce overall emissions.
PHEVs have become an incredibly important technology for car makers to reduce their average CO2 emissions, especially for premium brands.
Last year, eight out of the top 10 best-selling PHEVs in the UK were made by premium brands, topped by the BMW 330e, according to SMMT figures. In fact, the 330e M Sport was BMW's top-selling model overall in the first three quarters of the year, according to Department of Transport figures, while the Mercedes-Benz A250e AMG Line was Stuttgart's best-seller.
Ford is also heavily reliant on plug-in hybrids to cut emissions, specifically the Ford Kuga PHEV. “It’s a no-risk way to electrify,” the head of Ford in the UK, Lisa Brankin, told the SMMT Electrified conference on 23 March. Car makers are insistent they are used as intended. “Most people, for most days, are running on battery because of the way their journeys are structured,” Brankin said.
PHEVs are incredibly vulnerable to sudden changes in legislation. For example, in Norway, sales plummeted 78% in the first two months of this year compared with the same period in 2021 after tax breaks were removed from 1 January, increasing the share of electric cars to 80%, up from 50%.
Already PHEVs are unlocking fewer tax benefits in the UK. For example, they stopped qualifying for free entry into London’s Ultra Low Emission Zone (ULEZ) from 25 October 2021, and their purchase grant was axed in 2018.
Car makers are starting to take action to prove to the authorities that PHEVs can be a useful tool for emissions reduction if people actually charge them as intended – not a given when they’re already saving a fortune in tax.
“We know, based on 200 million kilometres of results, the fuel economy and what we need to influence the number of people charging," Citroën boss Vincent Cobée told us at the recent launch of the Citroën C5 X plug-in hybrid.
One tool? A digital nudge to get out your charging cable. “The less often you charge it, the more often you get a reminder,” Cobée said.
BMW meanwhile has expanded the number of city centre ‘e-Drive zones’ to 13 in the UK, having launched the scheme in 2020. This encourages PHEV drivers to save their battery charge for use in city centres to improve air quality by rewarding them with points to be redeemed at BMW-linked charging stations.
However, given what the ICCT has said about the CO2 penalties for ‘charge increasing’ modes to give you adequate battery-only driving when you get there, the CO2 penalty of this could be high.
Car companies are increasing the size of the batteries in PHEVs to extend their electric-only ranges.
For example, the PHEV versions of the new Range Rover are claimed to be capable of 70 miles on electricity alone, pushing them into an even more generous BIK tax band 5 April this year.
The penalties for PHEVs remain the same. Weight goes up to an average of 1921kg for PHEVs sold in 2020, compared with 1686kg for electric cars and 1457kg across all fuel types, according to ICCT figures (although the fact that big SUVs are over-represented in the PHEV category partly accounts for this).
They also usually end up losing boot space, due to battery packaging. But for many people, they're the only practical solution for reducing company car tax and keeping a practical range.
Whether they remain in favour with authorities depends partly on how frugally owners drive them. If even just a small percentage fail to take the charger out of the wrapping, the resultant hike in fuel use will be logged to bring down the reported average to the point that the penalties could prematurely kill the category for good.
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At the recent launch of the Vauxhall Astra Hybrid-e PHEV, we questioned the gap between the quoted 37-mile electric range and the 43-mile measurement for working out its BIK tax band.
The difference is a money-saver, dropping the car out of the 12% band and into the 8% band from 5 April this year.
Why the two figures? Amazingly, this is due to a decision from HMRC from 6 April 2020 to allow companies to quote what’s called the ‘equivalent all-electric range’ (EAER), rather than the ‘all-electric range’. The latter is what you would expect: the range covered on battery power alone in ‘charge depleting’ mode before the combustion engine kicks in. But the EAER range includes an element of ICE running too, meaning it’s not emissions-free.
Why? Many PHEVs don’t completely decouple the engine in electric mode, so EAER is as good an approximation as you will get, despite it not being completely emissions-free.
BMW, for example, warns in the small print that pure-EV mode isn’t available in sub-zero temperatures “until after the vehicle has travelled a few miles”. In the world of PHEVs, zero emissions isn’t quite as billed.