Comparative analyses of carbon emissions from electric and hybrid vehicles: who’s right after all?
The evaluation of greenhouse gas (GHG) emissions over the lifecycle of electric and hybrid vehicles, using fossil fuels and biofuels under various conditions, results in the publication of studies with discrepant and even contradictory results, requiring careful analysis.
Luiz Augusto Horta Nogueira
Use of biofuels in mobility will be a theme at the BBEST – IEA Bioenergy Conference 2024
São Paulo, October 2024 – What is the best technology for the rapid decarbonization of automobiles to effectively meet the need to reduce greenhouse gas (GHG) emissions? Battery electric vehicles, pure ethanol or gasoline hybrid vehicles, or plug-in hybrids?
“Every moment, a new study is published suggesting that, in terms of greenhouse gas emissions, one technology is better than another for decarbonizing automobiles,” says Luiz Augusto Horta Nogueira, an expert in energy studies from the Interdisciplinary Center for Energy Planning (NIPE) at Unicamp. “In reality, the results depend on the criteria used for the analyses, which, unfortunately, often serve more economic and geopolitical interests than technical and scientific ones,” he adds.
This is indeed the case with recently published studies comparing vehicle propulsion technologies in terms of decarbonization, which present distinct and sometimes contradictory data, primarily because they use different methodological criteria (see infographic at the end of the article).
Carbon Accounting
The definition of objective criteria for evaluating the decarbonization level of biofuels was the subject of a formal request from the Brazilian government to the International Energy Agency (IEA). The rationale was the need for a formal document that could guide discussions on the topic at the G20 meeting, scheduled for November in Brazil.
This request resulted in the report “Carbon Accounting for Sustainable Biofuels,” presented by the IEA in October during the preparatory meeting of the G20 in Foz do Iguaçu (PR). The document does not define the specific technical criteria for assessing carbon emissions associated with the production and use of biofuels but points out several factors that should be considered in the analyses.
According to Nogueira, there is good agreement in the carbon emission estimates in most biofuel studies and policies. He notes that results may vary between different biofuels and production contexts, but life cycle analysis methodologies are robust and well-understood. “The difficulties arise mainly in evaluating emissions related to indirect land use change, known as ILUC (Indirect Land Use Change), used in some studies, which rely on hypothetical scenarios that are difficult to prove,” says Nogueira.
He explains that, for example, if sugarcane is planted on land previously used for corn cultivation, there is no way to guarantee that the corn production moved to another non-deforested area, meaning that using one area for ethanol production may indirectly cause deforestation elsewhere. Nogueira highlights that, in reality, it is impossible to know the destination of the original crop. It could have moved to pastureland or been introduced as a second crop in areas where soy was recently harvested. “Additionally, there are other factors. What is the influence of agricultural productivity or the prices of agricultural products on this indirect land-use change effect? There are many possibilities and uncertainties,” Nogueira notes.
According to the NIPE expert, the IEA clearly reaffirmed life cycle analysis as the basis for evaluating biofuel carbon emissions while excluding the controversial ILUC from the assessment, as it cannot be consistently measured and should not be used as an evaluation criterion for biofuels, though it should be monitored in public policies. Moreover, dedicated (non-energy related) policies are needed to bring down deforestation or negative land use changes, for whatever purpose. “This report has significant political relevance, as it clarifies the ILUC issue, which is often mistakenly used as a criterion to reduce the decarbonization potential of biofuels in favor of other technologies,” says Nogueira.
Comparative Studies
In addition to the use of ILUC, there are other significant variations between comparative evaluations of automotive technologies. For instance, the striking difference in results presented by two studies published in 2023 on the evaluation of GHG emissions from electric, combustion, and hybrid vehicles that consider Brazil’s reality. One, a scientific article, was produced by a team of researchers from Unicamp, while the other, a white paper by the international think tank ICCT, presents discrepant results.
The ICCT study includes ILUC emission factors, while the Unicamp study does not. There are also significant differences in the vehicle’s life cycle time considered in the reports. The Unicamp study considered a life cycle of 160,000 kilometers, or approximately 10 years, corresponding to the approximate warranty period for batteries as indicated by manufacturers. The ICCT study considered an average vehicle lifespan of 288,000 kilometers, or about 22 years, without battery replacement.
As a result, GHG emissions from battery manufacturing are spread over a much longer period and mileage. “Without common rules, each study uses data from different sources and specific analysis criteria. Despite the contradictory results, in essence, both studies are theoretically correct according to the chosen assumptions, but which is truly the best option for Brazil?” Nogueira asks.
Truths and Lies
Ricardo Simões de Abreu
For Ricardo Simões de Abreu, Unicamp doctoral candidate, and sustainable mobility consultant, even with the use of widely accepted protocols by the scientific community regarding the full life cycle of batteries and vehicles and the actual decarbonization level of biofuels, using different data and criteria creates gaps for decarbonization studies to show very disparate results. “As the saying goes, it’s possible to tell a big lie by only speaking truths,” he warns.
Abreu notes that, in general, studies that include life cycle inventory follow ISO 14040 and subsequent standards, but it is a generic norm defining minimum procedures to be observed. “The definition of the data framework to be used in the study is up to the researcher. These data are usually outlined in studies, but the reasons for their selection and the implications for the outcome are not always clearly expressed,” he explains.
Abreu also believes that the discussion of the best technologies for fleet decarbonization, with a focus on sustainability and immediate impacts on global warming reduction, is often sidelined by economic and geopolitical interests. According to the mobility consultant, sustainability analysis involves three dimensions: environmental, social, and economic. “Unfortunately, in the case of automobiles, many developed countries have opted to downplay the social and environmental factors of sustainability. The focus is clearly on the economy and the pursuit of energy security,” he notes.
He points out that these countries have the technology to make their electricity grids cleaner through renewable energy sources and significantly reduce their dependence on other countries. “From that standpoint, electric vehicles are an excellent opportunity for them, but that doesn’t justify pushing this technology onto the rest of the world,” he adds. Abreu laments that investments in biofuel production could help develop parts of the world that are currently impoverished, distribute wealth, and reduce poverty. “The energy transition presents this opportunity, and we risk losing it,” he cautions.
Alternatives
Amid the discussion about the criteria adopted by studies, is it possible to point out the best option for automobile decarbonization? Abreu believes so. He notes that various studies conducted by researchers or independent organizations worldwide, including in Europe, indicate that hybrid vehicles, especially those using low-carbon fuels, are currently the best and most sustainable option for fleet decarbonization in the medium term, and for many places, possibly even in the long term. “There are already European entities strongly questioning the exclusive option for electric vehicles,” he points out.
Abreu explains that hybrid vehicles have combustion engines assisted by electric motors powered by small batteries compared to the large batteries used in pure electric vehicles. He argues that both hybrid models that do not use the electric grid (HEV) and plug-in hybrids (PHEV), which have combustion engines but can also be charged from the grid, when fueled with ethanol or biomethane, may be more appropriate decarbonization options for many countries than purely electric vehicles (BEV). “Especially in countries where heavy infrastructure investments will be necessary, like Brazil, which already has a well-established ethanol distribution network,” he adds.
Abreu further states that for ethanol and biomethane-producing countries, or those with the capacity to produce these fuels, non-plug-in hybrids (HEV) are the first choice. “When talking about fleet electrification, we must also consider the investments in facilities to charge electric vehicle batteries. This can easily reach billions of dollars, depending on the country’s size, road network, and fleet. Brazil needs to pay attention to this,” he emphasizes.
In the future, Abreu suggests that if battery-producing countries manage to significantly reduce fossil fuel dependency in their energy grids, purely electric vehicles may take the lead in the decarbonization process.
Clarity in Choices
Marcelo Gauto, a doctoral candidate, researcher, and bioenergy expert who coordinated a vehicle decarbonization study under the Interinstitutional Graduate Program in Bioenergy at USP/UNICAMP/UNESP, believes that sustainability should be a key factor in mobility technology choices.
He stresses that all available technologies are important and valid in the energy transition process, but it is crucial to understand the level of benefits each one brings and for each country to seek solutions that are most suitable to its reality. “What’s important is having clarity about choices and their reasons. Solid scientific foundations help in making good decisions,” he reflects.
The researcher also notes that the lack of specific and widely accepted criteria for evaluating the full life cycle of vehicles, batteries, and biofuels contributes to studies presenting divergent carbon emission results. However, Gauto explains that life cycle analysis is always complex and depends on a variety of parameters, such as the materials used in vehicle, battery, and fuel production, average annual mileage, consumption in standardized tests, and the carbon intensity of the energy sources used, among others.
He emphasizes that a common rule cannot define all the parameters used in studies, as it would be impossible to have a universal carbon assessment framework. “The benefit of this debate is the opportunity to clarify many aspects that are often misrepresented in the public eye. What is important is that decision-makers have this clarity and choose technologies that are best for their realities. Each country has different characteristics, and choices should take these realities into account,” Gauto concludes.
Views expressed in the article do not necessarily represent the views of IEA or of its individual Member Countries.
