Industrial hemp (Cannabis sativa L.) – a high-yielding energy crop

摘要

Bioenergy is currently the fastest growing source of renewable energy. Tighter sustainability criteria for the production of vehicle biofuels and an increasing interest in combined heat and power (CHP) production from biomass have led to a demand for high-yielding energy crops with good conversion efficiencies.Industrial hemp was studied as an energy crop for production of biogas and solid biofuel. Based on field trials, the development of biomass and energy yield, the specific methane yield and elemental composition of the biomass were studied over the growing and senescence period of the crop, i.e. from autumn to the following spring.The energy yield of hemp for both solid biofuel and biogas production proved similar or superior to that of most energy crops common in northern Europe. The high energy yield of biogas from hemp is based on a high biomass yield per hectare and good specific methane yield with large potential for increases by pretreatment of the biomass. The methane energy yield per hectare is highest in autumn when hemp biomass yield is highest.The energy yield per hectare of hemp for use as a solid biofuel is highest in autumn when the biomass yield is highest. However, important combustion-related fuel properties, such as moisture, alkali, chlorine and ash content and ash melting temperature, are significantly improved when industrial hemp is harvested in spring instead of in autumn. Major fuel properties of hemp are not significantly influenced by annual cultivation conditions, latitude or choice of cultivar.Net energy yields per hectare and energy output-to-input ratios of hemp are above-average in most applications, and are highest for use of hemp as solid biofuel. Use of hemp as a biogas substrate suffers from higher energy inputs and lower conversion efficiencies, but produces a high-quality vehicle fuel.Advantages over other energy crops are also found outside the energy balance, e.g. low pesticide requirements, good weed competition and suitability as break crop in cereal-oriented crop rotations. Improvements in hemp biomass and energy yields may strengthen its competitive position against maize and sugar beet for biogas production and against perennial energy crops for solid biofuel production.