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ABC Science
Topic:Electric Vehicles
A plug-in hybrid's actual emissions mostly depend on user behaviour, rather than engine size or other features. (Getty: Malte Mueller)
A new study of hundreds of thousands of plug-in hybrid electric vehicles (PHEVs) shows most users do not regularly recharge and the vehicles emit almost as much as a petrol car.
Australian PHEV users not regularly recharging could add millions of tonnes of planet-heating pollution by 2050, exclusive modelling shows.
Employees driving company-car PHEVs may be the least likely to recharge, with many using EV-mode only 20 per cent of the time, according to the peak body for fleet managers.
In recent years a new kind of vehicle has swept the Australian market, surprising analysts and dividing the electric vehicle (EV) community.
Plug-in hybrid EVs (PHEVs) have a combustion engine that burns fuel, and an electric motor that runs on power from a rechargeable battery.
They can be a cleaner alternative to conventional cars, emitting less and saving on fuel costs, but they only have low emissions if users regularly plug them in to recharge.
Now, exclusive data given to the ABC shows how low charging rates for PHEVs, multiplied across the national fleet, can add millions of tonnes of unnecessary carbon emissions.
It follows new research from Europe indicating most PHEV users recharge irregularly, meaning their EVs are effectively combustion-engine cars carrying heavy batteries.
Most PHEVs have enough battery range to handle a standard day's driving in an Australian city.
If a PHEV user depletes their battery every day but plugs in to recharge most nights, their emissions might be one-fifth of an equivalent petrol or diesel vehicle. 
But if they only recharge a couple of nights a week, the emissions are a lot higher.
You get a sense of the difference in cumulative emissions through money spent on petrol.
The difference between charging regularly or irregularly is a bit more than $1,000 of petrol a year, or about $20,000 over 15 years.
Given these fuel savings, it would make basic financial sense for PHEV owners to regularly recharge.
In Facebook groups of PHEV owners, members are adamant they charge all the time and are dismissive of media reports to the contrary.
"Have only fuelled the [PHEV] two or three times in the five months I've owned it," one owner recently wrote.
But analyses of fuel-consumption data commonly tell a different story.
The most recent, published this month, used data collected from hundreds of thousands of PHEVs in Europe, where devices measuring fuel consumption are mandatory for new cars.
It found that, on average, PHEVs are being mostly driven with empty batteries.
Because of this, PHEVs emitted almost five times more CO2 than the European Union's official estimates and were almost as polluting as petrol cars.
The EV Council, which represents EV car makers including major PHEV brands, referred the ABC to a 2024 online survey of 625 private PHEV owners in Australia, which found most plugged in every night and, on average, drove in EV-mode for about 65 per cent of their trip.
"Australians predominantly drive PHEVs in EV mode and charge them regularly," EV Council CEO Julie Delvecchio said.
BYD, which sells the most PHEVs in Australia, told the ABC odometer data obtained through servicing showed PHEVs were driven in EV mode about half the time.
"We do yearly 20,000km service and we're seeing about 10,000 of those kilometres in hybrid mode and 10,000 in EV-mode," BYD Australia product engineering manager Harry Li said.
He said Australians charged more regularly because they had better access to home charging, due to lower-density housing, and a higher uptake of rooftop solar.
New-model plug-in hybrids tends to have longer range, but the heavier batteries can also make them less fuel efficient. (Getty: Malte Mueller)
But others disagreed with this claim.
Brussels-based non-profit advocacy group Transport and Environment conducted the recent analysis of fuel-consumption data from PHEVs in Europe that found most users don't recharge often.
Data analysis director Thomas Earl said PHEVs in Australia might emit even more than those in Europe, as they tended to be heavier (therefore less fuel efficient) and were driven for longer distances.
Australians generally had better access to off-street parking and home-charging options, but this did not necessarily mean they charged more often, he said.
"In Europe we have much higher public charging availability," he said.
Surveys of private PHEV owners and their recharging habits were not representative of all PHEV users, as they did not include employees driving company cars.
Studies from Europe and the US also showed PHEV users driving company cars were less likely to charge, as they did not have a financial incentive to save on fuel.
Business fleet sales account for about half of all new cars sold in Australia.
Plug-in hybrids now account for a quarter of electric vehicle sales, as Australians reluctant to entirely drop the fuel tank opt for a compromise.
Mace Hartley, head of the industry peak body for fleet managers, the Australasian Fleet Management Association, said fleet managers in Australia had told him it was a struggle to get employees to recharge company PHEVs. 
"[Private PHEV owners] mostly charge them, but with fleets you have to drag people kicking and screaming to recharge."
Some managers of large business fleets recently switched from standard combustion-engine cars to PHEVs, only to find fuel use went up.
"Absolutely we're seeing in Australia the same kind of charging rates as coming out of reports overseas," he said.
"Maybe 20 per cent of [fleet users] plug them in."
He advised fleet managers tasked with meeting corporate emissions reductions targets to skip PHEVs and go straight to fully battery electric EVs.
"PHEVs sound awesome, but the reality is a different thing," he said.
And the popularity of PHEVs could have an impact on national efforts to decarbonise transport.
More than 60,000 PHEVs have been sold in Australia over the past two years, partly due to federal government tax incentives for "low-emission" cars.
The emerging vehicle type now accounts for about 5 per cent of new car sales, and the sales boom is rewriting emissions projections.
Robin Smit is the research director of Transport Energy/Emission Research (TER), an independent Australian consultancy that conducts detailed modelling of emissions for the transport sector, using a database of 10,000 vehicle classes.
In 2023, before the PHEV sales boom, TER published a study that assumed the percentage of PHEVs in total EV sales would continue to drop from their then-current level of 15 per cent, reaching 0 per cent in 2042.
The modelling found the total well-to-wheel (WTW) emissions of the Australian transport sector would peak during the period 2032–2035, and then steadily fall. WTW emissions include operational emissions (on-road driving) and upstream emissions due to the production and distribution of fuels and electricity.
New modelling by TER reflects the growing popularity of PHEVs.
It assumed PHEVs would account for half of EV sales for the period 2025–2035, and then decline to 0 per cent by 2050, which is broadly in line with statements from car makers.
The modelling showed the PHEV sales boom was having a measurable impact on emissions, although it was relatively small compared to the sector's total.
But this assumed most PHEV users regularly recharged. What if they did not?
The projection above assumed the average PHEV was driven in EV mode for 80 per cent of kilometres travelled.
But if the real figure is 20 per cent, which is in line with the research from Europe, emissions are much higher.
If PHEV users are not regularly recharging, it adds more than 100 million tonnes of CO2-equivalent for the period 2025–2050.
For comparison, that is about the amount emitted by all cars, vans, buses, motorcycles and trucks in Australia in one year.
"The fleet-wide impacts of increased PHEV sales strongly depend on the average [share of driving in EV mode]," TER's Robin Smit said.
"It comes down to the electric range of the PHEVs sold in Australia and how often and how long PHEV owners actually charge the battery."
Although irregular charging means PHEVs may not be as low-emission as advertised, they still generally emit less than standard combustion-engine cars.
The real issue for Australia's emissions reductions targets is the possibility PHEVs are displacing sales of fully electric cars, which have zero tailpipe emissions.
This is hard to prove and partly depends on the availability of equivalent and affordable fully electric cars (BEVs).
But the classification of PHEVs as low-emission cars in federal regulation (using a method that assumes PHEV users regularly recharge) could give suppliers less of an incentive to stock BEVs, Dr Smit said.
Under the updated New Vehicle Efficiency Standard (NVES), suppliers of low-emission vehicles earn a type of carbon credit that can be traded to sellers of high-emission cars and trucks.
This means PHEVs may not only be displacing sales of BEVs, but, through the credits their sale generates, underwriting the ongoing supply of high-emission vehicles.
"The problem is that the NVES counts PHEVs as low-emission vehicles 'on paper', but in reality these assumed emission reductions may very well not materialise," Dr Smit said.
"Because of the way [this regulation] is designed and implemented now, it is more likely that PHEV sales will replace the sale of BEVs.
"It effectively reduces the pressure on suppliers to sell more BEVs."
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