The energy balance of biogas production from perennial grass silage has been investigated in this paper. The anaerobic digestion process parameters and grass species have influence on biogas yield such as organic load. The model of technological process of biomass preparation and its digestion to biogas has been performed. The variation of digester organic load (1.0; 1.5 and 2.0 kg VS.m -3.d -1) shows the difference in total (direct and indirect) energy input from 490 MJ.t -1 biomass at 2.0 kg VS.m -3.d -1 up to 570 MJ.t -1 biomass at 1.0 kg VS.m -3.d -1. The laboratory experiments of biogas production from grass silage show the highest biogas yield (115 l.kg -1 biomass) at 1.0 kg VS.m -3.d -1. By increasing the organic load up to 2.0 kg VS.m -3.d -1 the biogas yield decreases down to 93 l.kg -1 from biomass. The methane (CH 4) concentration in the obtained biogas had a little dependence on digester organic load and was in the range of 58-60%. Such biogas has a sufficient methane concentration and is suitable for cogeneration.
