Plug-in hybrid vehicles are often promoted as a bridge to fully electric vehicles. They promise to cut emissions by operating on battery power for short trips while relying on gasoline for longer journeys. However, they only deliver on that promise if drivers regularly charge them. Real-world data drawn from the vehicles’ own computers shows that is often not the case.
A study by the Fraunhofer Institute used this data to determine how much energy came from charging. It found that less than a third of one million plug-in hybrids in Germany were plugged in either occasionally or not at all. This data should be a note to U.S. automakers who are promoting future plug-in hybrid models as appealing alternatives. By blending gasoline with electricity, these companies hope to boost their overall fleet efficiency without a wide rollout of electric vehicles.
Yet the study shows plug-in hybrids seldom deliver on their efficiency promises. At best, Toyota drivers used electricity for 44 percent of the energy needed for driving, suggesting they plugged in the most frequently. The worst performance was from Porsche drivers, at just 0.8 percent, averaging only 7 kilowatt-hours of charging over two years. This means the average Porsche plug-in hybrid driver charged the battery less than half of its capacity just one single time.
Previous studies have shown that plug-in hybrids produce about 3.5 times more emissions than their official ratings suggest. This new study explains why, as it directly assesses how much electricity the vehicles gained from being plugged in. The research used data from the vehicles to separate electricity use from gasoline use.
One shortcoming of plug-in hybrids is their limited battery capacity, which only powers the vehicle for short distances. Some can only go a handful of miles, while many sold recently can operate on battery power for about 20 to 30 miles. Regulators and automakers have proposed longer ranges for future models, hoping a more capable battery will encourage more frequent charging.
That outcome is not guaranteed. These vehicles often remain compromised even when driving on electricity. Most plug-in hybrids are based on traditional fossil fuel platforms, meaning their electric motors cannot deliver 100 percent of the vehicle’s power needs. When a driver accelerates hard, the gasoline engine must kick in. In other cases, the engine turns on in cold weather to heat the cabin. When this happens, many drivers apparently ask themselves why they should bother plugging in at all.
This raises another question: why bother with plug-in hybrids at all? They have been touted as a way to ease cautious consumers into electric vehicles. The argument suggests drivers will become accustomed to plugging in while public charging networks expand, so they can transition to a full electric vehicle later.
But if drivers are not plugging in their plug-in hybrids, they are not developing that habit. Without regular charging, the electric drivetrain provides no benefit. The public still suffers from worse air pollution, and drivers carry hundreds of pounds of extra weight, face more recalls, and endure costlier service visits due to the complex drivetrain.
Tweaking the formula to make these vehicles more reliant on batteries could help. One interim solution is the extended-range electric vehicle, designed to run solely on battery power until the charge is depleted, at which point a gasoline engine recharges it. So far, no such vehicle has required the owner to plug in; they could easily run on gasoline alone. BMW once made an extended-range electric vehicle, the i3, but ended production years ago. Ford and Stellantis have both announced extended-range electric pickup trucks, which have yet to go on sale.
Meanwhile, electric vehicle charging networks continue to expand. It is possible that by the time automakers are producing plug-in hybrids and extended-range vehicles in large quantities, drivers will no longer need the comfort of a gasoline engine.
Legacy automakers, which have repeatedly second-guessed their electrification strategies, could be forced to change direction once more. Plug-in hybrids might have been a clever solution on paper, but they have largely failed to deliver in the real world.