Electric vehicles, hydrogen vehicles and those that consume biofuels or synthetic fuels with a low or zero carbon footprint have been postulated as the main technological and energy bets to decarbonise mobility in passenger vehicles. However, what is the true impact of these new alternatives on the carbon footprint of road transport?
There are numerous studies focused on answering this question and, however, the data available to carry out a rigorous analysis are limited.
The carbon footprint linked to manufacturing and use
When studying the carbon footprint of road transport, a large part of the analyzes carried out to date apply the approach well-to-wheels (WtW) or from the well to the wheel. In other words, they only consider the life cycle of the fuel –which includes the production and transportation of the raw material, as well as the production, distribution and use of the energy source–, but they omit the life cycle of the vehicle, which includes the manufacture, distribution, maintenance and management of the vehicle at the end of its useful life.
However, is this last part of the total carbon footprint relevant? Is it correct to ignore the emissions of the vehicle’s life cycle in the calculation of the total carbon footprint?
battery electric vehicles they do not present emissions in the phase of use of the energy source. However, its true capacity to contribute to the reduction of greenhouse gas emissions can only be adequately assessed through a complete life cycle analysis, that is, from cradle to grave, and not only including the energy source. The manufacture, distribution, maintenance and management of the vehicle at the end of its useful life must also be included.
Emissions during the life cycle of the vehicle
From a bibliographic review compiling information from scientific publications (highlighting as main references: ANL, 2020; ICCT, 2021; lewis et al.2014; Ma et al.2012; RE&E, 2020; Qiao et al.2019; Wu et al.2018), I have compared in terms of mass of CO₂ equivalent emitted per kilometer traveled for the life cycle of the vehicle and I have established the comparison in relative terms shown in Figure 1.
It is necessary to emphasize the variability in the results obtained from the different bibliographical references, as a result of the considerations that are taken into account in each of the studies. Some of the factors that influence the results include the type of vehicle considered, the size of the batteries or the useful life of the vehicle.
I have assigned the value of 100 to internal combustion vehicles (ICEV) that use fossil fuels and the comparison is shown against other technologies: hybrid (HEV), electric (BEV) and plug-in hybrid (PHEV). For each technology, the values are represented in the form of a bar, collecting the entire range of values of the results obtained from the different bibliographic sources.
Javier Pérez based on data from various sources, such as ANL, 2020; ICCT, 2021; Lewis et al., 2014; Ma et al., 2012; RE&E, 2020; Qiao et al., 2019; Wu et al., 2018., Author provided
Comparing the results, it can be seen that hybrid technologies increase the carbon footprint of the vehicle’s life cycle by 3-9% compared to conventional combustion technologies. In the case of plug-in hybrid vehicles, the increase amounts to 11-33%.
Finally, in the case of electric vehicles, the increase in emissions during the life cycle of the vehicle amounts to values of 18-58%, depending on the source consulted, assuming a significant difference with respect to conventional combustion vehicles.
Vehicle life cycle and energy source
The previous results concern only the life cycle of the vehicle, that is, all the processes that comprise the manufacture, distribution, maintenance and management of the vehicle at the end of its useful life.
However, and to answer one of the initial questions, it is necessary to give an overview of the contribution of this cycle, the total life cycle, considering both the vehicle and the energy source.
Figure 2 shows these contributions for the four compared technologies and in the case of a medium-sized passenger car (in the case of internal combustion vehicles, fossil gasoline, biofuels and diesel have been considered fuels). synthetic; for hybrids and plug-in hybrids, only gasoline of fossil origin).
Javier Pérez based on data obtained from RE&E, 2020 and Prussi et al., 2020., Author provided
In general, the electric vehicle has lower emissions throughout the life cycle (fuel and vehicle) than the internal combustion that uses fossil fuel, although they depend on the electricity generation matrix of each geographical environment and each time period.
However, the life cycle of the vehicle plays an important role in electric vehicles. Its contribution is around 46% of total emissions, considering the average of all EU Member States in 2020 as the electricity generation mix (figure 2).
For internal combustion, hybrid and plug-in hybrid vehicles using fossil fuel, the relative importance of the vehicle life cycle is around 14%, 19% and 34%, respectively; lower than in the case of electric vehicles, but by no means negligible.
In the case of internal combustion vehicles that use alternative fuels, such as bioethanol, biodiesel or synthetic diesel, emissions throughout the life cycle are comparable and even, in certain cases, lower than those of electric vehicles (figure two). Greenhouse gas emissions from these fuels will depend on the route chosen for their production.
The importance of the vehicle life cycle
As the carbon footprint associated with the life cycle of the energy source is reduced, the relative importance of the emissions produced during the life cycle of the vehicle increases. Relative to electric vehicles, battery manufacturing tends to be intensive in energy and greenhouse gas emissions.
Additionally, the weight of electric vehicles is, as a general rule and equal to the range, higher than that of internal combustion vehicles, as bulky batteries are used and the rest of the vehicle becomes heavier to provide the necessary structural support. These factors cause the life cycle of the electric vehicle to have a greater contribution to GHG emissions than that of conventional technologies.
On the other hand, while in other technological sectors the development of more compact and smaller models is sought, the automotive sector is betting on ever larger and more powerful vehicles. These increasingly heavy models require more materials and energy to build and power them, increasing the environmental impact associated with this part of the life cycle.
Consequently, the emissions generated during the life cycle of the vehicle must be taken into account when making comparisons in terms of carbon footprint in the road transport sector. The stages of production, maintenance and management of the vehicle at the end of its useful life represent important contributions that must be analyzed in detail. It is necessary to work to minimize its impact.
Increasing the weight of electric vehicles, as well as the size of the batteries, increases the environmental impact associated with the life cycle of the vehicle, which is not in favor of the decarbonisation of the sector.
Javier Perez Rodriguez, Professor of the Department of Industrial and Environmental Chemical Engineering. Member of the Environmental Technologies and Industrial Resources Group, Polytechnic University of Madrid (UPM)
This article was originally published on The Conversation. read the original.