Annual energy characteristics and thermodynamic evaluation of combined heating, power and biogas system in cold rural area of Northwest China

Abstract: In China’s rural areas, there is a sharp contradiction between the increased energy demand, serious environmental pollution and backward energy supply. The system of combined heating, power and biogas (CHPB) of multi-energy complementarity is examined in order to meet the multi-level energy demands of heating, electricity and biogas of 17 households in rural areas. Mathematical dynamic models for all operating modes of the system are established. The energy transfer rule, energy complementarity mechanism and annual dynamic characteristics of the system are analyzed and explored based on the climate condition and the variability of building loads. A comprehensive study is conducted by the method of thermodynamic performance analysis. Biogas from anaerobic digestion of cow manure is the main driving force of the system. The input energy of cow manure accounts for 77.81% of the total. Compared with the conventional system with separate electric and thermal generation, the primary energy saving rate of the CHPB system is negative for most of the year and the maximum renewable energy increasable rate is 600.46%.