Role of Bioenergy in Sustainable Energy and Food Systems

Abstract

To combat climate change, the Paris Agreement established a global warming limit of 2℃ by the century's end. Numerous countries aspire to attain carbon neutrality by 2050, as evidenced by initiatives such as the European Union Green Deal. As the sole renewable energy that can provide negative emissions, bioenergy emerges as an appealing option yet with an unclear role in both long-term policy and current models. The challenge of understanding sustainable roles of bioenergy stem from both supply and demand sides. Supply-wise, there are inconsistent definitions of “sustainable bioenergy” among models as well as between policy and models, among which land-use change is the major concern. Demand-wise, there are competing uses of bioenergy without a coherent strategy. Moreover, bioenergy uniquely serves as a bridge between the energy transition and food system sustainability where energy-land-food nexus may impose complicated trade-offs and synergies. Accordingly, this thesis aims to model the potential roles of sustainable bioenergy, taking into account both energy and food systems, to contribute to a more cohesive bioenergy policy framework aimed at achieving climate neutrality. The thesis answers this overarching research question by three contributions that investigate (1) the challenges and opportunities of bioenergy deployment, (2) strategic uses of land-free ancillary bioenergy in a carbon-neutral Europe, (3) the option space and trade-offs between sustainable bioenergy provision and food system designs. The first contribution examines the historical deployment, current policy support, and potential future roles of bioenergy in the European case. I identify three major challenges and proposes the corresponding opportunities. The first challenge pertains to the supply side, highlighting difficulties in securing bioenergy supply, particularly for liquid biofuels and countries with high per-capita bioenergy consumption. The second challenge addresses inconsistencies in the definition of "sustainable bioenergy" between modelling studies and EU policies. The third challenge is the conflicting uses for bioenergy from the demand side, which is lacking a clear long-term strategy in Europe. To address these challenges, future research could explore untapped bioenergy potential with low environmental impacts to enhance supply security. Establishing a clear and harmonized definition of "sustainable bioenergy" would facilitate conveying modelling results to policymakers. Additionally, this contribution proposes the land-free alternative “ancillary bioenergy” that rules out all land/food/feed conflicts with untapped potential from by-/co-products and residues from agricultural, forestry, and municipal sources. The second contribution further explores the potential role of ancillary bioenergy based on energy system optimization modelling (sector-coupled energy system model Euro-Calliope). Findings reveal a limited future potential for ancillary bioenergy in Europe (2394-10,342 PJ, that is 3-6 times lower than other estimates including dedicated biomass). By modelling various use cases of ancillary bioenergy, this contribution finds that fully utilizing ancillary biomass could help phase out controversial nuclear or land-intensive dedicated biomass, potentially enhancing societal acceptability. Employing ancillary biomass as a negative-emissions source at stationary BECCS plants in a nuclear-free system provides added climate benefits. Leaving ancillary bioenergy unused slightly increases total system cost but preserves agricultural nutrients. This study concludes that strategic uses of ancillary bioenergy entail synergies and trade-offs, offering guidance for a more cohesive European bioenergy strategy. The third contribution assess the trade-offs and option space between ancillary bioenergy and circular agroecology. The global mass-flow food-system model SOLm models the availability and environmental impacts of ancillary bioenergy by modelling 190 different future circular agroecological strategies combinations. Findings reveal a diverse option space for the future food and energy system, allowing for a similar range of ancillary bioenergy (60-70 EJ) across varied food systems, encompassing organic agriculture levels and waste and concentrate feeding reductions. Three trade-offs between food system sustainability and ancillary bioenergy provision emerge. First, a trade-off exists between nutrient recycling and negative emissions – providing negative emissions by using bioenergy with carbon capture and storage can make the food system incompatible with medium to high organic farming due to increased risks for nutrient deficits. Second, reducing feed from croplands impacts ancillary bioenergy production inversely based on organic agriculture share. Third, food waste reduction diminishes ancillary bioenergy provision. Overall, these embedded trade-offs could better assist in bridging the energy and food systems and in understanding the systematic role of sustainable bioenergy. This thesis makes three contributions to the literature. Empirically, this thesis contributes to resolving the inconsistent definition of “sustainable bioenergy” by proposing a land-free alternative of “ancillary bioenergy”, along with identifying its strategic roles towards climate neutrality and its bridge between energy transition and food sustainability. In terms of data, this thesis provides the open dataset of further ancillary biomass potential covering over 120 biomass feedstocks at the national resolution for 2050 Europe. Regarding modelling, the thesis enhances the Euro-Calliope sector-coupled European energy system optimization model by providing a detailed representation of national-level bioenergy feedstocks paired with compatible conversion technologies. They contribute to the bioenergy modelling community by offering free, open, and reproducible data and model. Correspondingly, this thesis provides policy implications both on the European and global scales. For the European energy system, this thesis provides sector-coupling insights to help bioenergy policymakers answer systematic questions, like when, where, and how to best utilize what bioenergy. The identified synergies and trade-offs of different bioenergy use cases can help enhance the coherence of bioenergy policy framework. For the global energy and food systems, this thesis identifies a diverse option space allowing policymakers to explore the potential economic/environmental/emission impacts of different policy mixes. This option space also implies the trade-offs between enhancing the sustainability of the food system and maximizing ancillary bioenergy potential for energy provision or negative emissions. However, higher ancillary bioenergy provision or additional negative emissions may conflict with food system sustainability through nutrient deficits. Thus, policymakers should align planning for sustainability in the energy system with planning for sustainability in the food system.