Energy return on investment (EROI) of biomass conversion systems in China: Meta-analysis focused on system boundary unification

Abstract As China continues to focus on renewable energy in its future development, the energy performance of biofuels has become a hot research topic. However, existing bioenergy assessments have used diverse indexes and inconsistent system boundaries, hindering the comparative analysis of different technologies. Generally, improvements in energy quality (e.g., from solid to gaseous fuel) are accompanied by increases in nonrenewable energy investment. To quantify this trade-off, this study examined the energy return on investment (EROI) of typical biomass conversion systems in China—namely, biomass compression, biodiesel, bioethanol, biogas, biomass gasification, and biomass power generation. Various feedstocks were considered, including first-generation (e.g., corn), second-generation (e.g., corn straw), and third-generation (e.g., algae) feedstock options. The system boundaries of previous biomass footprint calculations are unified to make the results comparable. The results showed that converting raw biomass feedstock to solid fuel had the highest EROI (8.06-24.13), followed by biomass power (2.07-16.48), biogas (1.24-11.05), biodiesel (1.28-2.23), second-generation bioethanol (1.18-9.90), first-generation bioethanol (0.68-3.12), and biomass gasification (1.12-1.57). Compared with fossil fuels (e.g., gasoline, diesel), biofuels had a higher average EROI, indicating obvious energy-saving benefits. Among all biomass conversion pathways, pyrolysis gasification had the highest EROI opportunity cost for both straw and wood residues. This study's findings highlight the need for consistent system boundaries in bioenergy technology deployment to quantify the EROI opportunity cost of each biomass conversion pathway, and recognize the importance of energy efficiency promotion to enhance the economic feasibility of biomass energy industries.