Analysis of the life cycle of fuels found in 45 scientific articles shows the pros and cons of each technology

Biogas is an efficient and promising alternative, in environmental terms, to substitute diesel as fuel in cargo trucks, according to a systematic review study published by Brazilian researchers in the magazine WIREs Energy and Environment, at the beginning of the year. The study analyzed 45 scientific articles focused on the so-called “life-cycle assessment” of the fuels of the highway cargo transportation sector. This type of analysis follows the entire process of the use of materials – from their extraction from petroleum and natural gas wells, the agricultural production of raw materials, or the generation of electricity through their eventual discarding or recycling.

The economic and environmental aspects of the different types of fuels were analyzed, such as the emission of greenhouse gases (GHG) and pollutants, including particulate materials and carbon monoxide (CO). Besides biogas, which is produced by the bacterial decomposition of organic materials, the fuel cells supplied with hydrogen are also indicated as a good possible alternative, as regards the reduction of greenhouse GHGs. The article’s authors stress that the life-cycle assessments show which technologies have the best chance of reducing emissions, by that varies according to locale, technological development, highway conditions, weight, materials used, and the energy matrix from which they are taken.

“Brazil has great potential for adopting biogas, because it could take advantage of the residues from the production of ethanol, for example,” says electrical engineer Pedro Gerber Machado, a researcher in the Chemical Engineering Department of Imperial College London, in the United Kingdom, who is the principal author of the article, which is also signed by Ana Teixeira, Flávia Collaço, and Dominique Mouette from the University of São Paulo (USP). “However, this would require heavy investments, which investors generally do not like, and there is no central production site. Another study that we did shows that the State of São Paulo could substitute all of the natural gas it currently consumes with only biogas, but that would come from over 355 mills or plants, and not from a single source.” The study was carried out within the scope of the research of the FAPESP Shell Research Centre for Gas Innovation (RCGI).

The authors emphasize that there is a lack of investigations and information regarding the environmental impact of the various fuel options, especially related to biogas. Few studies compare all the alternatives with all environmental concerns. While throughout the world there are many countries whose trucks are powered in part by liquid natural gas or electricity, diesel fuel still predominates in Brazil, Machado says. Government leaders of several countries are seeking solutions in a variety of economic sectors for achieving zero GHG emissions, which are indicated as being responsible for climate change. The transportation sector faces major issues, because it is responsible for approximately 30% of the world’s energy consumption and for 16% of the greenhouse gas emissions.

Although the electrification of the highway transportation system is a global trend, this option is the one that presents the most uncertainties since the environmental gains depend upon the country’s energy matrix. With a clean energy matrix, with high percentages coming from renewable sources, the authors of the article state that electric trucks (especially those with hydrogen fuel cells) are the best alternative. “But are we capable of maintaining a renewable energy matrix, if we have a huge demand from the transportation sector? That is the big question,” Machado puts forth. “It is no use to electrify if, to meet the demand of cars by producing electricity via natural gas.”

Since natural gas is a fossil fuel, it practically makes no reduction of GHG emissions, even though it produces lower emissions of particulate materials. Within compressed natural gas (CNG) technology, greenhouse gas emissions vary, according to efficiency and possible methane leaks during the transportation of natural gas. Opting for biodiesel, on the other hand, indicated few environmental advantages, because the scientific articles analyzed revealed elevated energy consumption and emissions during the production phase.

From an economic perspective, the best options were CNG or liquified natural gas (LNG) and hybrid trucks. “Natural gas is a cheaper option than diesel and, with the added benefit of emitting fewer particulate materials, it could be chosen as an alternative. The price linked to environmental quality will likely be used in a large marketing package deal. However, it must not be ignored that this is a fossil fuel and, therefore, emits greenhouse gases,” Machado states.

A summary of the article “Review of life cycle greenhouse gases, air pollutant emissions and costs of road medium and heavy‐duty trucks” can be reads at https://onlinelibrary.wiley.com/doi/abs/10.1002/wene.395. A text by researcher Pedro Machado, commenting on the data from the study, can be read in the blog of the Sustainable Gas Institute, of the Imperial College London at http://wwwf.imperial.ac.uk/blog/sustainable-gas-institute/2021/04/07/what-are-the-best-options-for-road-freight-transport/.