As a waste neutralization facility, the landfill is a kind of bioreactor producing landfill gas or (LFG) - biogas, which should be captured and neutralized for environmental reasons. One of the ways of its utilization is the combined production of heat and electrical energy in combined heat and power (CHP) cogeneration systems. For that purpose, the assessment of the energy efficiency of a cogeneration unit has been undertaken in this work on the basis of the unit’s performance over the last 5 years. The analysis of the CHP system energy performance has demonstrated that the ratios range at the lower limits for units up to 0.5 MW. The lower efficiency of fuel chemical conversion in the CHP plant (0,70) stems from failure to use the rated thermal and electrical power fully (74,2%), which is caused by the insufficient stream of biogas collected from the landfill (161,46 m3∙h-1). The analysis of the use of the generated energy, particularly in terms of heat, has shown a surplus which is not used and therefore is a loss. The proposed solutions in this area should optimize the use of heat generated from the renewable source, that being landfill biogas.