Energy balances for biogas and solid biofuel production from industrial hemp

Abstract

Abstract If energy crops are to replace fossil fuels as source for heat, power or vehicle fuel, their whole production chain must have higher energy output than input. Industrial hemp has high biomass and energy yields. The study evaluated and compared net energy yields (NEY) and energy output-to-input ratios (RO/I) for production of heat, power and vehicle fuel from industrial hemp. Four scenarios for hemp biomass were compared; (I) combined heat and power (CHP) from spring-harvested baled hemp, (II) heat from spring-harvested briquetted hemp, and (III) CHP and (IV) vehicle fuel from autumn-harvested chopped and ensiled hemp processed to biogas in an anaerobic digestion process. The results were compared with those of other energy crops. Calculations were based on conditions in the agricultural area along the Swedish west and south coast. There was little difference in total energy input up to storage, but large differences in the individual steps involved. Further processing to final energy product differed greatly. Total energy ratio was best for combustion scenarios (I) and (II) (RO/I of 6.8 and 5.1, respectively). The biogas scenarios (III) and (IV) both had low RO/I (2.7 and 2.6, repectively). They suffer from higher energy inputs and lower conversion efficiencies but give high quality products, i.e. electricity and vehicle fuel. The main competitors for hemp are maize and sugar beets for biogas production and the perennial crops willow, reed canary grass and miscanthus for solid biofuel production. Hemp is an above-average energy crop with a large potential for yield improvements.