Energy Balance of Hemp (Cannabis sativa L.) Grown for Energy Purposes

This article discusses the energy balance of the hemp biomass from the autumn and spring harvest which was used for the production of briquettes. The hemp plant (Cannabis sativa L.) used in this work is the variety Bialobrzeskie that was harvested on a trial plot in Prague-Suchdol in 2009 - 2010. Moisture content (MC), gross calorific value (GCV) and other technical parameters were evaluated for samples from the harvest of both periods. The autumn harvest results led to the assumption that the gross energy yield of the culture per superficies was 186.3 GJ ha-1. As compared to the previous results the spring harvest gave a gross energetic output of 161.4 GJ ha-1. The autumn harvest required more energy inputs compared to the spring harvest with values of 22.2 GJ ha-1 and 16.9 GJ ha-1 respectively. The most energy-consuming aspects of the biomass production were fuels (autumn) and the energy linked to the chemicals used (spring). Regardless of the higher net energy yield in autumn it was found that a spring harvest should be preferred because of its Energy Return on Energy Invested (EROEI) is 8.6. This is higher than for the autumn harvest (7.4).