Electric drives, hydrogen-powered fuel cells and the use of synthetic fuels in combustion engines: Various technologies are currently being discussed to significantly reduce the climate-damaging CO2 emissions from road traffic. From a scientific point of view, not only the direct emissions during operation must be taken into account, but also those greenhouse gases that are generated during the production of the vehicles, the manufacture of the energy sources, their distribution and last but not least recycling at the end of the vehicle's life. In order to draw up a meaningful overall balance sheet, the life cycle analysis method has become established, usually abbreviated as LCA (Life Cycle Analysis).
One challenge here is that the results of LCA studies depend heavily on the assumptions made. In a meta-study commissioned by the Research Association for Internal Combustion Engines (FVV), the consulting firm Frontier Economics has now evaluated more than 80 individual studies from the past 15 years, which consider a total of 110 different scenarios and 430 individual analyses. In order to establish comparability, the results of all studies were standardized to a passenger car with a total mileage of 150,000 kilometers.
The uncertainty in life cycle analyses is huge
Calculated in this way, there is a relatively narrow band of total emissions over the entire lifetime for all combinations of drives and energy sources. The average value over all studies ranges from 25 to 35 tonnes of CO2 per vehicle, provided that fossil fuels are still used proportionately for the production of electricity, hydrogen or synthetic fuels. If, on the other hand, only regeneratively produced energy sources are used in operation, the average value is 9 to 16 tonnes of CO2 for the entire life of the vehicle. The remaining emissions then result mainly from the production of the vehicles, the manufacturing facilities and the infrastructure for the distribution of the energy sources.
All in all, the average values of the results of this study show large differences between the individual studies, which often amount to many times the differences between the individual technologies. »There is no clear winning technology,« summarizes Dr. David Bothe of Frontier Economics. »Above all, the meta-study shows how great the uncertainty in life cycle analyses still is at present.«
Plug-in hybrid vehicles and fuel cell passenger cars underrepresented
While vehicles with purely electric drive and conventional combustion engines were considered in almost all studies, only a quarter of all studies make statements on the overall balance of plug-in hybrid vehicles, which are expected to achieve a significant market share in the 2020s. Fuel cell passenger cars are also only included in 22 studies. Valid results for the use of synthetic fuels are almost completely missing.
»In addition, no one has yet investigated where mobility today, despite emissions, also contributes to climate protection,« says Bothe. »For example, the rotor blades of a wind power plant are transported by heavy fossil-fuelled trucks to their location across the country. In the electricity sector, these plants then avoid emissions. We find such cross-sectoral effects in many places in the economy.«
Electric mobility possibly makes a small contribution to climate protection
Despite the considerable uncertainties, a general statement can be made: Only a valid life cycle analysis allows an objective assessment of technological alternatives. In particular, it is important to avoid reducing the emissions from operations assigned to the transport sector by assigning additional emissions to the energy or industrial sector. For example, the study uses a sample calculation to show that if electric mobility were to be introduced on a broad scale without accompanying measures, 90 percent of the cumulative CO2 savings from passenger car traffic could reappear in other sectors and regions by the year 2030, and would thus be of little benefit to climate protection.
The goal is clear: By 2050, road traffic should become climate-neutral. In clarifying the question of which paths lead to the goal, one should also bear in mind the time dimension of one-off events, such as a narrow focus on a sector-specific annual target: Large one-off emissions could lead to emissions rising in other years and/or sectors and the total CO2 budget of the Intergovernmental Panel on Climate Change (IPCC) being exceeded. FVV Managing Director Dietmar Goericke sums up: »From the scientific point of view, the results of the meta-study initially only mean: We need more data and more detailed research as a basis for valid political decisions. To achieve this, we must make research open to new technologies.«