Plug-in hybrid vehicles: an asset or an obstacle to decarbonizing road transportation?

This article was originally published in our newsletter "Mobility Analysis," December 17, 2020. To receive future articles by email as soon as they are published, Subscribe now.

As the year comes to a close, at a time when the automotive industry is shifting toward electric vehicles, hybrid cars seem like a wonderful Christmas gift1, don’t they? According to automakers and government agencies, they significantly reduce CO2 emissions without requiring us to compromise on how we use them: long range, fast refueling (with gasoline or diesel) when needed. However, as with many things, the reality isn’t quite that simple.

Let's start with a brief review of terminology: there are non-rechargeable hybrid vehicles² and rechargeable hybrid vehicles (RHVs)³. Non-plug-in hybrid vehicles are an incremental improvement over conventional internal-combustion vehicles with greater electrification, which would allow for energy recovery, among other things, but they are currently powered exclusively by petroleum-based fuels. Whereas Plug-in hybrid vehicles have both an internal combustion engine and an electric motor., which allows them to drive in either mode, depending on the battery charge—which generally provides a range of about 40–70 km in electric mode. It is therefore this second category of vehicles that we are focusing on here. Why don't plug-in hybrid vehicles deliver the expected CO2 reductions? First of all, because the certified emissions (based on the NEDC or WLTP cycles) do not accurately reflect actual emissions. According to a recent study by the ICCT and the Fraunhofer Institute, the actual emissions from a plug-in hybrid vehicle are 2 to 4 times higher than the certified emissions. [1] ! In addition, Hybrid vehicles are inherently heavier (and more expensive) than their internal-combustion counterparts, because they have two powertrains (internal combustion and electric). However, any additional weight on board results in additional energy consumption and, therefore, a loss of energy efficiency for the same level of use. It follows that Driving a plug-in hybrid vehicle primarily in internal combustion mode results in higher emissions than the equivalent internal combustion model, as demonstrated by the NGO Transport & Environment (see graph below) [2]. We must therefore prioritize vehicles that are as light as possible, as we explained in a previous article.

Comparison of Emissions from Unloaded Hybrid Vehicles (PHEVs) and Their Internal Combustion Engine (ICE) Equivalents - gCO2/km

Transportation & Environment

Finally, and most importantly, The actual electric mileage rate of plug-in hybrid vehicles is actually much lower than its theoretical rate : According to the ICCT, only 37% of kilometers are driven in electric mode, compared with 69% under the NEDC cycle for passenger cars, and 20% compared with 63% for company cars. This also contributes to emissions being significantly higher than certified emissions.

So should we just throw plug-in hybrid vehicles in the trash? No, of course not (the trash can is too small). They allow us to decarbonize certain specific segments for which electric vehicles are not suitable, for example, for taxi drivers or people who frequently take long business trips and short personal trips4. But In the vast majority of cases, electric vehicles can meet 90–95% of people’s needs. So we have to accept that rethink one's relationship with cars and mobility in general, with a short-range electric vehicle for everyday use, and alternative options for occasional trips such as vacation getaways: range extender, train, car rental… hybrid?

--------------- 1. Primarily for automakers, who see this as a convenient way to meet their European regulatory obligations (the well-known average target of 95gCO2/km). 2. MHEV stands for Mild Hybrid Electric Vehicle, and FHEV stands for Full Hybrid Electric Vehicle. 3. PHEV stands for Plug-in Hybrid Electric Vehicle. 4. It should be noted that a vehicle running on biomethane or carbon-free hydrogen could be an alternative solution.

Article written by Nicolas Meunier (Consultant) nicolas.meunier@carbone4.com

Sources: [1] ICCT & Fraunhofer Institute [2] Transportation & Environment