Plug-in hybrid electric vehicles (PHEVs) are those which can run on both electricity and fossil fuels. But how environmentally friendly are they? And how well can they help prepare for an eventual transition to a fully fossil-free vehicle sector? A unique study from Chalmers University of Technology, Sweden, now shows that PHEVs with, in this case, a range of about 56 km, have an important role to play and can result in the same amount of kilometres driven electrically as short range fully electric cars.
“In comparing a number of multi-car households, we can see that households which own a fossil-fuel vehicle and a PHEV can drive as many purely electric kilometres as a household owning a fossil fuel vehicle and a fully electric one,” says Ahmet Mandev, doctoral student at the Department of Space, Earth and Environmental Science at Chalmers, whose doctoral studies were supervised by Associate Professor Frances Sprei.
Despite the fact that over 20 years have passed since the first mass-produced PHEV car appeared on the market, many questions remain regarding optimal usage of such vehicles. These are questions that Ahmet Mandev aimed to answer. “There are different views on PHEVs’ role in electrifying personal transport. It is vital to learn as much as we can about their electrical potential, to determine which policy instruments – laws, regulations and subsidies – can be most effective for such vehicles,” he explains.
In the first of the studies included in his licentiate thesis The Role of Plug-in Hybrid Electric Vehicles in Electrifying Personal Transport – Analysis of Empirical Data from North America, he processed and analysed one year of driving data for 71 households in California using either the Nissan Leaf, a fully electric vehicle, or different PHEV models with various ranges.
“It is easy enough to see the breakdown of the kilometres between electric and fossil fuel operation. But the unique thing about this study is that we looked at the household level – mapping all the vehicles in different multi-car households. We saw how many kilometres a household travelled using electric power and compared that between households which own a fully electric car, or a PHEV, alongside a conventional vehicle,” he explains.
As usual with all types of electric vehicles, range is an important factor. The study showed that households with a fully electric car and a conventional car drove on average 45 percent of their total kilometres on electricity, while the households owning a long-range PHEV and a conventional car, reached 46 percent electric operation on average. This is despite the fact that the range for the vehicles at full electric operation was 130 km for the fully electric car and just under half that for the plug-in hybrid – 56 kilometres.
The reason that the PHEV performs better, despite the considerably shorter range, is that it is taken more often on longer journeys. “That means that at least some of the distance of those trips is driven using electricity. The figures also reveal that the PHEVs are more often used at the same time as the fossil vehicle, by another member of the household.
“All in all, this shows that plug-in hybrid vehicles have an important role to play when it comes to electrification of personal transport,” says Associate Professor Frances Sprei.
Important conclusions relating to charging
In addition to these findings, Ahmet Mandev can also say, after processing the data of four million driving days of the plug-in hybrid model Chevrolet Volt collected over a ten-year period, how charging should take place to maximise the share of electric driving, while minimising fuel consumption and emissions.
The most positive effects result from fully charging your car every night – perhaps not so surprising. But he made a further discovery which did stand out.
“If you decrease from fully charging your car every night, to 9 out of 10 nights, emissions triple – from 1.7 kg of carbon dioxide to 5.7 kg for 100 kilometres of driving. Fuel consumption increases in a similar way, from 0.7 liters for 100 kilometers to 2.5 liters. These are still low emissions and low levels of fuel consumption, but it is a big difference for such a small change in behaviour,” he explains.
The PHEVs in the study achieved a high of 76 percent electric power usage, provided that they were fully charged once every 24 hours. Ahmet Mandev and Frances Sprei point out that supplementary charging during the day also gives positive effects, but for maximum effect, full charging every night is the best option.
For more information:
Read more about the studies on Chalmers’ website:
Read Ahmet Mandev’s licentiate thesis, The Role of Plug-in Hybrid Electric Vehicles in Electrifying Personal Transport – Analysis of Empirical Data from North America, in Chalmers’ research database.