Battery Electric Leads in CO2 Reduction, Study Finds
As the global automotive industry accelerates toward decarbonization, a new comprehensive study from Germany’s Research Institute for Automotive Engineering and Powertrain Systems (FKFS) offers critical insights into the long-term environmental performance of next-generation vehicle technologies. The research, led by Dr. Tobias Stoll in collaboration with Hans-Jürgen Berner and André Casal Kulzer from both FKFS and the Institute of Automotive Engineering (IFS) at the University of Stuttgart, evaluates the full lifecycle carbon footprint of three leading powertrain systems: battery electric vehicles (BEVs), fuel cell electric vehicles (FCEVs), and internal combustion engine hybrid vehicles (ICE-Hybrids) running on synthetic e-fuels.
Published in the October 2024 special issue of Tongji University Journal (Natural Science), the study presents a cradle-to-wheel analysis that integrates vehicle manufacturing emissions with energy production and usage across different electricity grid scenarios. This holistic approach moves beyond tailpipe emissions to assess the true environmental cost of transportation in a future shaped by renewable energy transitions.
The findings come at a pivotal moment. The European Union has mandated a 100% reduction in CO2 emissions from new passenger cars by 2035, effectively phasing out the sale of new vehicles powered solely by fossil fuels. While this regulatory push has accelerated the adoption of electrified powertrains, it has also intensified debate over which technologies offer the most sustainable path forward—especially as automakers explore alternatives to full battery electrification, including hydrogen fuel cells and carbon-neutral synthetic fuels.
Stoll and his team emphasize that zero tailpipe emissions do not equate to zero greenhouse gas impact. The environmental footprint of any vehicle depends heavily on how its energy is produced. For electric vehicles, the carbon intensity of the electricity grid is a decisive factor. Similarly, for hydrogen and e-fuels, the source of electricity used in production determines their overall climate benefit.
To ensure a fair comparison, the researchers selected three representative C-segment sedan configurations projected for the year 2040, drawing on data from the FVV “Powertrain 2040” project. Each vehicle was optimized for its respective energy carrier: lithium-ion batteries for BEVs, hydrogen fuel cells for FCEVs, and a downsized internal combustion engine hybrid for e-fuel operation. All vehicles were assumed to be manufactured in the European Union, with a service life of 200,000 kilometers.
One of the most significant findings relates to vehicle weight. The BEV configuration was the heaviest, primarily due to the large battery pack. The fuel cell vehicle followed, with its hydrogen storage tanks and fuel cell stack adding considerable mass. In contrast, the e-fuel hybrid was the lightest, benefiting from the high energy density of liquid fuels and a smaller battery compared to full electric models. Weight differences directly influence energy consumption, particularly in urban and mixed driving conditions.
The study evaluated energy efficiency across four standardized driving cycles: Real Driving Emissions (RDE), commuter, motorway, and city driving. These were weighted to reflect typical usage patterns—50% RDE, 20% commuter, 20% motorway, and 10% city driving. Using advanced simulation tools, including the opt. MO-ECMS algorithm, the team calculated overall well-to-wheel efficiencies for each powertrain.
Results showed that the BEV achieved the highest average efficiency at 51%, followed by the FCEV at 22%, and the e-fuel hybrid at just 11%. These numbers reflect the inherent energy losses in each system. Battery electric vehicles convert grid electricity directly into motion with minimal losses. Fuel cell vehicles, while zero-emission at the tailpipe, suffer from inefficiencies in hydrogen production (electrolysis), compression, storage, and conversion back to electricity. E-fuels, meanwhile, require even more steps: capturing CO2 from the atmosphere, producing green hydrogen via electrolysis, synthesizing liquid fuel (via methanol-to-gasoline or MtG processes), refining, transporting, and finally combusting in an engine. Each stage incurs energy penalties, resulting in a much lower overall efficiency.
However, efficiency is only one part of the equation. The study’s central contribution lies in its cradle-to-wheel emissions modeling, which combines vehicle production (cradle-to-gate) with operational energy use (well-to-wheel). The researchers examined four distinct electricity grid scenarios, reflecting varying degrees of decarbonization: 5 g CO2-eq/kWh (a theoretical minimum for fully renewable grids), 50 g CO2-eq/kWh (a deeply decarbonized system), 200 g CO2-eq/kWh (current EU average), and 400 g CO2-eq/kWh (current German grid intensity).
Under the highest-emission scenario (400 g CO2-eq/kWh), the BEV still outperformed the conventional gasoline hybrid by a significant margin. Even with a carbon-intensive grid, the superior efficiency of electric drivetrains translates into lower overall emissions. The FCEV also surpassed the fossil-fueled hybrid but only when grid emissions fell below 350 g CO2-eq/kWh. The e-fuel hybrid, when using fuel produced in the EU, only became competitive below 113 g CO2-eq/kWh.
The most striking result emerged in low-carbon grid scenarios. As electricity becomes cleaner, the emissions gap between BEVs and other technologies narrows, but the battery electric vehicle consistently maintains the lowest total footprint. At 5 g CO2-eq/kWh, the cradle-to-wheel emissions for the BEV were approximately 20 g CO2-eq/km, compared to 35 g for the FCEV and 50 g for the EU-produced e-fuel hybrid.
Interestingly, the study found that an e-fuel hybrid using fuel produced in South America—where solar and wind resources are abundant and can power e-fuel plants with near-zero emissions—could achieve emissions as low as 45 g CO2-eq/km even under the EU’s current 200 g CO2-eq/kWh grid average. In ultra-low carbon scenarios, this option approached the performance of the FCEV, suggesting that geographically optimized production could play a strategic role in decarbonizing transport, particularly for existing vehicle fleets.
A key insight from the research is the trade-off between manufacturing and operational emissions. Battery electric vehicles have the highest production footprint, primarily due to battery manufacturing. The FCEV follows, with emissions linked to fuel cell catalysts and high-pressure hydrogen tanks. The e-fuel hybrid has the lowest production impact, thanks to its smaller battery and conventional engine architecture.
However, this advantage diminishes rapidly over time. While production emissions are fixed, operational emissions accumulate with every kilometer driven. In high-efficiency BEVs powered by clean electricity, the initial carbon debt from manufacturing is repaid within a few years. In contrast, the lower production emissions of e-fuel vehicles are offset by their much higher energy consumption and associated upstream emissions.
The study also highlights the importance of energy storage and transportability. While BEVs are highly efficient, they depend on a robust charging infrastructure and face challenges in cold climates and long-haul applications. Hydrogen offers faster refueling and higher energy density but requires costly new infrastructure and faces efficiency hurdles. E-fuels, however, can leverage existing fuel distribution networks and internal combustion engine technology, making them a potentially attractive option for legacy vehicles, aviation, and marine transport.
Stoll and his colleagues caution that while e-fuels can enable a circular carbon economy—capturing CO2 from the air and recycling it into fuel—their scalability is limited by energy availability. Producing enough e-fuel to power the entire automotive sector would require vast amounts of renewable electricity, potentially competing with other decarbonization efforts. Therefore, the authors suggest that e-fuels may be best reserved for sectors where electrification is impractical.
The research underscores that there is no one-size-fits-all solution. The optimal powertrain choice depends on the carbon intensity of the local energy mix. In regions with coal-heavy grids, even BEVs offer a climate advantage over conventional vehicles, though the benefit grows exponentially as grids decarbonize. In countries with abundant renewable energy, such as Norway or Iceland, BEVs achieve near-zero emissions. For hydrogen and e-fuels to reach their full potential, they too must be produced using clean electricity.
Policy implications are clear. To maximize the climate benefit of new vehicle technologies, governments must accelerate the decarbonization of electricity generation. Investment in renewable energy, grid modernization, and energy storage is as critical as promoting electric vehicle adoption. Subsidies and incentives should be designed to support the entire energy ecosystem, not just the vehicle itself.
Moreover, the study calls for greater transparency in emissions accounting. As automakers increasingly promote hydrogen and e-fuels as “green” alternatives, consumers and regulators need accurate, lifecycle-based data to make informed decisions. Marketing claims of carbon neutrality must be scrutinized in the context of actual production methods.
The authors also stress the importance of recycling and end-of-life management. While disposal emissions were excluded from this study due to their relatively small impact, future research should incorporate high recycling rates for batteries, fuel cells, and vehicle components to further reduce lifecycle emissions.
In conclusion, the FKFS-led analysis provides a robust framework for evaluating the true environmental performance of next-generation vehicles. It confirms that battery electric vehicles, when paired with a clean energy supply, offer the lowest carbon footprint across the full lifecycle. Fuel cell vehicles and e-fuel hybrids can play complementary roles, particularly in specific applications or regions, but their climate benefits are more sensitive to the carbon intensity of energy production.
As the automotive industry navigates the transition to sustainability, this research serves as a vital reference point. It reminds stakeholders that the path to decarbonization is not just about replacing engines with batteries, but about transforming the entire energy system that powers mobility. The vehicle of the future is not just electric—it is powered by a cleaner, smarter, and more sustainable grid.
The study’s methodology, combining detailed vehicle simulation with comprehensive energy chain analysis, sets a new standard for lifecycle assessment in automotive research. It also highlights the value of interdisciplinary collaboration between engineering, energy systems, and environmental science.
For consumers, the message is clear: choosing an electric vehicle is a step toward sustainability, but the full climate benefit depends on where and how the electricity is generated. For policymakers, the takeaway is that vehicle regulations must be accompanied by energy policies that prioritize renewable deployment. And for the industry, the research affirms that while innovation in hydrogen and synthetic fuels is valuable, the most effective near-term strategy for reducing transport emissions remains the electrification of vehicles powered by clean energy.
As the world moves closer to 2040—the horizon of this study’s vehicle projections—the findings offer both guidance and urgency. The technologies exist to achieve deep decarbonization in transport. What is needed now is the political will, infrastructure investment, and public engagement to make it a reality.
Battery Electric Leads in CO2 Reduction, Study Finds
Tobias Stoll, Hans-Jürgen Berner, André Casal Kulzer, FKFS and IFS, University of Stuttgart
Tongji University Journal (Natural Science), DOI: 10.11908/j.issn.0253-374x.24726