How Often Do Owners Actually Charge Their PHEVs?

• European Commission report examines real-world fuel economy and CO2 emissions data from 600,000 vehicles from 2021, discovering a significant gap between the type-approval figures for PHEVs and real-world data.

• The report also examined the fuel economy and CO2 data for gas and diesel models, finding a smaller gap between the official WLTP type-approval numbers and real-world data collected from cars.

• The European Commission plans to change the WLTP test procedures for PHEVs starting in 2025 as a result of this report to account for the observed gap.

For a long time plug-in hybrids have been viewed as a logical stepping stone to a battery-electric future, offering a battery that can be charged along with an all-electric mileage that would be suitable for most local driving tasks and commutes. At least in theory.

And as EV demand softened in 2023—along with the overall EV adoption rate crawling at a snail's pace year over year—automakers are once again looking at plug-in hybrids to offer energy-conscious buyers an EV-like option.

But a recent study by the European Commission confirms what many in the industry have suspected about plug-in hybrids: People don't actually charge them very often to take full advantage of the EV driving mode.

The report used data collected from some 600,000 vehicles in Europe over the course of 2021, including gasoline, diesel, and plug-in hybrids of both fuel types, using fuel consumption monitors installed in the vehicles to measure actual fuel consumption versus the advertised consumption.

The on-board fuel consumption monitoring (OBFCM) devices have been a requirement since January 2021 in all new cars and small vans sold in Europe, with manufacturers collecting the data remotely and during service visits.

As expected, the actual emissions of gas and diesel vehicles saw a gap between the official type-approval average CO2 emissions and the vehicles' actual consumption as measured by OBFCM devices. Gasoline cars that were part of the study saw a gap of 23.7% on average, while diesel vehicles saw a gap of 18.1%.

But this gap was not particularly surprising for study managers or manufacturers.

"Such a gap was anticipated as there are different factors affecting real-world emissions which cannot all be fully replicated in a laboratory test, such as the traffic conditions, landscape, road conditions, ambient temperature, use of air-conditioning and on-board electronics, and driver behavior," the commission noted.

The real surprise was the gap shown by plug-in hybrids that were part of the study, with real-world CO2 emissions being 3.5 times higher, on average, than the WLTP (Worldwide harmonized Light vehicles Test Procedure) type-approval values, which are the European equivalent of EPA numbers. Likewise, real-world fuel consumption numbers of PHEV models were significantly higher than the WLTP values.

"The large discrepancy found for these vehicles between the real-world and the WLTP values shows that they are charged and driven in electric mode much less than how they were expected to be used and that assumptions used for calculating the WLTP test result do not hold in real-world conditions," the report states.

The WLTP calculation for fuel consumption and CO2 emissions uses a so-called utility factor, which is the expected share of distances driven in EV-only mode in PHEVs.

As a result, starting in 2025 the European Commission already plans to overhaul the official WLTP test procedure for PHEVs to account for this gap.

It's prudent to remember that this report applies to vehicles sold in the EU in 2021, so it doesn't account for absolutely all PHEVs on the road in the EU, and it also doesn't reflect PHEV usage in other regions where their emissions data is calculated based on other assumptions, including in the US.

The report also noted quite a bit of variability among automakers in collecting the data, as well as other peculiarities in the sample population of cars. So additional studies on PHEV usage will likely be needed to nail down other key pieces of data.

The electric ranges offered by PHEVs in the EU and elsewhere are also a factor in their usage, as we can think of plenty of commutes that even with daily charging would deplete the EV range of PHEV models pretty quickly.

These are all factors that are difficult to account for in such a study, which is primarily about WLTP expectations of vehicle usage.

But the report, at first blush, also tends to confirm what some EV industry observers have long suspected: If owners wanted to charge a vehicle frequently and use it primarily for local driving, they would buy an EV from the start instead of a PHEV and would invest in a Level 2 charger for their garage.

Since car owners don't have to charge a PHEV to get it out of the garage or driveway in the morning, then charging habits can vary widely from owner to owner. Not all PHEV owners might even have regular access to an EV charger based on where they live, which is another interesting variable that is difficult to pin down in such a study, unless owners themselves report such things.

The circumstances of how owners end up with plug-in hybrids shouldn't be overlooked as well, we'd add. A PHEV model might well have been the sole example at a dealership with the options the buyer wanted, or may have been discounted at the end of a model year and purchased by someone who did not specifically seek out a plug-in hybrid from the start because they wanted to take advantage of its electric range.

Owners' motivations in buying or leasing a plug-in hybrid perhaps should not be taken at face value when it comes to their everyday usage, we suspect.

But the implications of the report, at least in the EU, could end up being quite unfavorable for PHEV manufacturers, as automakers are required to achieve a certain type-approval emissions rating across their lineups. An overhaul of the WLTP calculations for PHEVs in 2025 could change these fleet-wide averages drastically, and a closer look into EPA numbers for PHEVs might also yield some surprises about their usage and real-world emissions.

Do you view plug-in hybrids as a useful stepping stone to EVs, or are they a veneer of more energy-conscious driving habits? Let us know what you think.