Modeling and performance analysis of solar energy and biogas complementary heating system in rural areas

Abstract

The current solar heating systems encounter significant losses of excess heat during peak daytime hours, while biogas heating systems suffer from a substantial reduction in biogas production under low-temperature conditions. To address the issue of limitations in the practical application of these two energy sources for heating, in this study, a novel solar and biogas complementary heating system is proposed. Through theoretical analysis, the energy and mass coupling balance equation of the system is established, and the mathematical models for key equipment are developed. Then, a flexible feeding anaerobic digestion experiment is conducted, and the existing biogas production kinetics model is updated. The thermal performance of the heating system is analyzed in the case area. Finally, a comparison is made between the complementary heating system and a traditional solar energy and biogas combined heating system in terms of thermal performance. The results indicate that intermittent flexible feeding has a negative impact on biogas generation, and the shorter the feeding time, the higher the biogas production attenuation rate, with a maximum attenuation rate of 6.3 %. With the scale of the solar collector area increasing from 5,000 m² to 10,000 m² while maintaining the biogas subsystem size constant, the solar contribution rate rises from 42 % to 50 %. Similarly, when the daily feeding rate input increases from 40 t/d to 80 t/d with the solar system size held constant, the biogas contribution rate increases from 25 % to 46 %. Under the same operating conditions, the renewable energy contribution rate of the complementary heating system is 4.44 % higher than that of the combined heating system.