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Table 2 Overview of drivers of GHG in biomass production and biofuel conversion systems and associated uncertainties in accounting for these drivers within the LCA method

From: Benchmarking biofuels—a comparison of technical, economic and environmental indicators

Pathway step Drivers of GHG emissions Relevant aspects Uncertainties related to drivers
Biomass production    
Oil, sugar, starch, lignocellulosica dLUC/iLUCb Change in carbon stocks [54],[55] Carbon inventory
Lack of primary data
Biomass management practices for increased yields [52],[56] Nitrogen (N) fertiliser use and N losese[57]-[62] Amount of N2O releasesh associated with parameters mentioned [58]
Cultivation and transport [18] Fuel consumptionf Parameters influencing fuel consumption
Soil compaction [63] Lack of primary data/site specificity for soil compaction and GHG emissions
Biofuel conversion    
Biodiesel, HVO/HEFA, bioethanol, BTL/FT Biomethane Energy consumption Upstream emissions from fossil and renewable energy chainsg Uncertainties related to the emission factors for energy productioni
Auxiliary materialsc Upstream emissions due to the production of required chemicals/catalystsg Use of generic values taken from available databases e.g., Ecoinvent [64], NRELj
Overall conversion efficiencyd The overall efficiency of the biomass used has an impact on the upstream emissions from biomass production per MJ of biofuel Uncertainties related to data availability for the assessment of advanced biofuel technologies [56]
  1. aLignocellulosic raw materials, cf. Table 1.
  2. bLand use change occurs when areas not used for agricultural purposes (e.g., forest areas and grasslands) are converted to produce biomass, indirect LUC (iLUC) can occur when existing agricultural areas and non-agricultural areas are converted to other crops/land uses to meet demands for increasing demands for bioenergy and agricultural products [65].
  3. cAuxiliary materials (e.g., process chemicals and catalysts).
  4. dCf. Section 3.
  5. eN fertiliser use refers to type of fertiliser used e.g., calcium ammonium nitrate or urea.
  6. fVariability in fuel consumption due to soil conditions at harvesting, machinery used, field structure, distance to intermediate storage or bioenergy plant, etc.
  7. gThe term upstream emissions refer to the emissions associated with the production and provision of the energy carriers or materials used (e.g., emissions from the production of electricity provided via the public grid and used in the biomass conversion process).
  8. hThe amount of N2O emitted from biomass production depends on a number of parameters such as, type of fertiliser, application technique and time, crop rotation systems, climate, soil types, etc..
  9. iUncertainties associated with the upstream emissions from the production of the energy used for conversion processes (e.g., electricity from public grid) refer to the many different processing scales and technologies involved.
  10. jUncertainties in relation to data/data sources available on the various drivers and relevant aspects. NREL, National Renewable Energy Laboratory.