Biomass enables the transition to a carbon-negative power system across western North America

Sustainable biomass can play a transformative role in the transition to a decarbonized economy, with potential applications in electricity, heat, chemicals and transportation fuels1–3. Deploying bioenergy with carbon capture and sequestration (BECCS) results in a net reduction in atmospheric carbon. BECCS may be one of the few cost-e ective carbon-negative opportunities available should anthropogenic climate change be worse than anticipated or emissions reductions in other sectors prove particularly di cult4,5. Previous work, primarily using integrated assessmentmodels, has identified the critical role of BECCS in long-term (preor post-2100 time frames) climate change mitigation, but has not investigated the role of BECCS in power systems in detail, or in aggressive time frames6,7, even though commercial-scale facilities are starting to be deployed in the transportation sector8. Here, we explore the economic and deployment implications for BECCS in the electricity system of western North America under aggressive (pre-2050) time frames and carbon emissions limitations, with rich technology representation and physical constraints. We show that BECCS, combined with aggressive renewable deployment and fossil-fuel emission reductions, can enable a carbon-negative power system in western North America by 2050 with up to 145% emissions reduction from 1990 levels. In most scenarios, the o sets produced by BECCS are found to be more valuable to the power system than the electricity it provides. Advanced biomass power generation employs similar system design to advanced coal technology, enabling a transition strategy to low-carbon energy. An assessment of BECCS deployment as part of a suite of lowcarbon technologies is a critical research need9. Such an analysis requires detailed spatial and temporal assessment of distributed biomass supply, electricity demand, deployment of intermittent renewables, and electricity dispatch capabilities. We employ the SWITCH optimization model for long-term strategic planning of the electric system10,11. SWITCH leverages a unique combination of spatial and temporal detail to design realistic power systems that meet policy goals and carbon emission reduction targets at minimal cost12. The version of the SWITCH model used here encompasses the region of the Western Electricity Coordinating Council (WECC), which includes the western United States, two Canadian provinces and a small portion of Mexico. WECC contains high-qualitywind and solar resources, but relatively limited bioenergy resources: the eastern United States, for example, has a larger absolute bioenergy resource13. Existing studies of low-carbon transitions in western North America have generally reserved biomass for biofuels production, rather than for electricity10,14. Western North America contains biomass resources from forestry, wastes, agricultural residues and dedicated energy crops, although supply is limited by land and sustainability practices (Fig. 1)13. In total, we identify 1.9 × 109 MMBtu (2,000 PJ) of economically recoverable bioenergy available annually from solid biomass by the year 2030, sufficient for ∼7–9% of modelled demand for electricity in 2050. Our estimates for availability in California are smaller than other studies, which tend to focus on ‘technical potential’ rather than ‘economically recoverable’ resources14,15. Although barriers to biomass recovery exist even for economically recoverable resources, we choose these resources as a reasonable approximation of biomass potential. We model solid biomass fuel costs as a piecewise linear supply curve disaggregated by 50 regions across western North America. Biomass supply from dedicated energy crops represents only 7% of the total supply, so direct land use impacts from the biomass feedstocks used in this study would be minimal. Dedicated feedstocks, such as switchgrass and pulpwood, tend to have higher prices than wastes and residues. The implications of BECCS for the economics and carbon emissions of regional power systems to 2050 have not been previously investigated in detail. To address this gap, we explore scenarios for the electricity sector that are consistent with economywide decarbonization, but vary the allocation of biomass across sectors of the economy (Supplementary Table 5). We explore scenarios withWECC-wide power sector CO2 emissions reductions from 1990 levels by 2050 ranging from 105% to 145%, which previous work has found would be consistent with economywide goals should biomass be used for electricity16. To understand biomass deployment in carbon-neutral and carbon-negative power systems, we mandate a 105% reduction (−105%), 120% reduction (−120%) and 145% reduction (−145%) in CO2 emissions by 2050. These scenarios require aggressive research and development on CCS and BECCS over the coming decades. Our case without biopower mandates an 86% reduction in CO2 emissions from 1990 levels by 2050 (−86% No Biomass). We vary this scenario by disallowing CCS technologies (−86% No CCS No Biomass) and allowing biomass (−86%). We continue operation of some existing nuclear plants, but do not allow new nuclear power. We do not conduct a complete economy-wide assessment of CO2 emissions across WECC or optimal biomass allocation among sectors. Without biomass technologies (−86%No Biomass), the resource mix is reliant on other renewable energy technologies including