The agroecosystem without external energy supply can provide compensation for the needs of the agroecosystem in liquid fuel, heat and electricity at the expense of plant biomass as a renewable energy source. Based on the analysis of the energy balance of the agroecosystem, the area under rapeseed needed for biodiesel production and the area under crops needed for bioethanol production were calculated for the needs of the agroecosystem, as well as additional quantities of straw to compensate for the loss of humus in crop rotation, which sets the amount of plant biomass that can be used to produce heat and electricity using cogeneration gas plants. It was found that the average typical needs of the agroecosystem in diesel fuel from 60 to 80 kg/ha, and the ratio of the area under rapeseed needed for biodiesel production for the needs of agroecosystem to the total area of crop rotation with grain yield of canola from 1500 to 2500 kg/ha is from 8.3 to 18.5%. At the average typical demand of the agroecosystem for gasoline is from 15 to 16 kg/ha, the ratio of the area under wheat, barley and corn required to produce bioethanol for the needs of the agroecosystem to the total area of crop rotation with a crop yield of 3000 to 5000 kg/ha is from 0.7 to 0.9%. The increase in grain yield from 3000 to 5000 kg/ha causes an increase in the supply of organic matter to soil to a greater extent than its mineralization, and accordingly, the deficit of organic matter and humus decreases from 507 to 180 kg/ha, the volume of plant biomass (mainly straw) to compensate for the deficit of organic matter and humus decreases from 1867 to 217 kg/ha, which causes an increase in the possible volumes of plant biomass for energy production for sale from 27 to 2963 kg/ha.Respectively, electricity production increases from 48 to 2301 kWh/ha and heat power from 0 to 25,5 GJ/ha, while providing its own needs for heat and electricity by burning biogas in a cogeneration plant.

Assessment of production costs to get biomethane and electric power on its basis in agriculture is impossible without assessing the impact on this indicator of the price of digestate. In Ukraine, where chernozem soils are the basis of agricultural production, the issue of restoring their fertility is an urgent problem. The production of biomethane should take into account the costs of manure before fermentation and the sales revenue of digestate after fermentation using it as organic fertilizers. The article suggests a methodology for economic assessing of production costs to get biomethane and electric power on its basis provided that the costs for the production of biomethane include production costs with taking into account the difference in prices of the biomass of liquid manure before fermentation in the digester and digestate after fermentation in the digester. The technique is based on the calculation of such indicators as a requirement in biomass to receive one m 3 of biomethane and to get one kW hour of electricity. These values for liquid manure in accordance are 93.3 kg•m -3 and 23.9 kg•kWh -1 . The zero production costs of biomethane and biomethane-based electricity production will be when the price of digestate will be more than the price of liquid manure before fermentation in the range from 1.1 to 2.0 EUR•t -1 . The zero-profit of biomethane production will be when the price of digestate will be less than the price of liquid manure before fermentation in the range from 1.3 to 2.1 EUR•t -1 . The zero-profit of electricity production will be when the price of digestate will be less than the price of liquid manure before fermentation in the range from 4.1 to 6.6 EUR•t -1 . The suggested methodology may be useful for the assessment of production costs when carrying out measures for the utilization of digestate and in the training process of biotechnologists.