The article focuses on selected aspects of the technical and economic analysis of the 0.8 MW agricultural biogas plant. The electrical power, generated in a cogeneration system, fed power to the neighbouring overhead power grid, Węgrów – Sokołów Podlaski, while the heat energy recovered from combustion gases and liquids cooling the engine was used to heat digesters, a residential building, drying room and farm buildings. The planned annual production equals c.a. 6400 MWh per year given the 8000 h of engine operation. The substrates used as input for the digestive chambers were as follows: fermented maize, pig slurry and liquid digestate pulp.