Evaluating trade-offs of net private and net social benefit – an integrated assessment framework for biomass utilization pathways

Technical Summary: Evaluating Trade-offs of Net Private and Net Social Benefit

Problem Statement
Biomass is a finite yet increasingly demanded renewable resource, creating competition among sectors for its use in energy, materials, and carbon removal. Existing assessment methods for biomass utilization pathways often suffer from fragmentation. They typically evaluate economic performance (Techno-Economic Assessment, TEA) and environmental performance (Life Cycle Assessment, LCA) in isolation, or fail to consistently account for environmental externalities. Furthermore, current literature often lacks a unified functional unit for comparing heterogeneous pathways (e.g., heat vs. biochar vs. carbon credits), conflates avoided emissions with permanently removed emissions, and frequently omits revenues from carbon removal credits (CRC). These gaps hinder the ability to guide pathway-level trade-off assessments and policy design that align private investor incentives with societal welfare.

Methodology
The authors propose an integrated assessment framework that synthesizes TEA, LCA, and the monetization of environmental externalities to derive two central metrics: Net Private Benefit (NPB) and Net Social Benefit (NSB).

1. Functional Unit: To ensure consistent comparison across pathways with diverse outputs, the framework utilizes an input-related functional unit: 1 metric ton of dry biomass at market (Mg biomass).
2. Techno-Economic Assessment (TEA): Calculates levelized capital (CAPEX) and operational expenditures (OPEX) and revenues from marketable products (e.g., heat, biochar). Crucially, it includes revenues from Carbon Removal Credits (CRC) for pathways that achieve permanent storage. Results are discounted to present values and adjusted for taxes to determine NPB.
3. Life Cycle Assessment (LCA): Quantifies emissions and resource use across multiple impact categories (e.g., Global Warming Potential [GWP], acidification, eutrophication, water use). The framework rigorously distinguishes between:
   • Positive pathway emissions: Burdens generated during the process.
   • Permanently stored emissions: Carbon sequestered for long-term periods (e.g., in biochar or geological storage), constituting Carbon Dioxide Removal (CDR).
   • Avoided emissions: Substitution effects where the biomass product replaces a conventional alternative.
4. Monetization and Benefit Calculation:
   • NPB: Calculated as the sum of revenues (including CRC) minus costs (CAPEX, OPEX), adjusted for taxes.
   • NSB: Derived by adding the monetized value of externalities to the after-tax NPB. Externalities include avoided emissions and net other emissions/resource uses, monetized using damage cost factors (e.g., from ReCiPe or similar methods) to reflect societal harm or benefit.

Case Study Application
The framework was applied to two miscanthus utilization pathways in Germany:

• Bioenergy (BE): Combustion for district heating.
• Biochar Carbon Removal (BCR): Pyrolysis to produce biochar for soil application and heat.

Key Results

• Private vs. Social Incentives: The BE pathway yielded a positive NPB, driven by heat revenues, but offered no permanent carbon removal. Conversely, the BCR pathway resulted in a negative NPB under current market conditions due to high operational costs, despite generating CRC revenues.
• Societal Value: Both pathways demonstrated a positive NSB. For BE, this was driven by avoided emissions from substituting fossil fuels. For BCR, the positive NSB was driven by the long-term removal of CO₂eq and avoided emissions, highlighting that BCR provides significant societal value despite its lack of private profitability.
• Emission Accounting: The study confirmed that GWP is the dominant impact category. When avoided emissions were excluded (simulating a decarbonized grid), BE resulted in net positive emissions, whereas BCR maintained net negative emissions due to permanent storage.
• Price Discrepancy: The analysis noted that current CRC market prices (€155/MgCO₂eq) were lower than the calculated societal damage costs of GWP (€166/MgCO₂eq), suggesting that current market mechanisms do not fully capture the societal value of CDR.

Key Contributions

1. Integrated Metrics: The framework successfully links private and societal perspectives through NPB and NSB, expressed per unit of biomass input, enabling direct comparison of heterogeneous pathways.
2. Rigorous Emission Accounting: It explicitly distinguishes between avoided emissions (substitution) and permanently removed emissions (CDR), preventing double-counting and ensuring accurate crediting for CRC.
3. Monetization of Externalities: By monetizing multiple environmental impact categories (not just GWP), the framework normalizes diverse environmental burdens, allowing for a holistic trade-off analysis.
4. Identification of Trade-offs: The approach reveals specific conflicts where pathways with high societal value (like BCR) may lack private viability, and pathways with high private returns (like BE) may lack permanent carbon removal capabilities.

Significance and Claims
The authors claim that this framework provides a structured, transparent basis for evaluating biomass utilization pathways, addressing critical gaps in existing literature regarding functional units, revenue inclusion, and emission accounting. By integrating economic and environmental dimensions, the framework supports decision-makers in:

• Identifying where policy interventions or market mechanisms (e.g., higher CRC prices) are needed to align private incentives with societal goals.
• Prioritizing public funding for technologies with high NSB but low NPB (such as emerging BiCRS technologies).
• Distinguishing between pathways that merely substitute fossil emissions and those that deliver genuine, permanent carbon removal.

The paper concludes that while the framework is robust, its application relies on the quality of input data and the chosen monetization factors. It serves as a versatile tool for researchers, investors, and policymakers to navigate the complex trade-offs inherent in the sustainable use of finite biomass resources.