Assessment of a combined cooling, heating and power system by synthetic use of biogas and solar energy

Anaerobic digesters should always be kept warm for a stable biogas yield. The conventional method for digester temperature maintenance results in a considerable waste of energy and pollution of the environment by directly firing biogas. Biogas-driven trigeneration systems can improve biogas utilization efficiency; however, the waste heat from the power engines is limited by the digester's thermal insulation, and additional fossil fuels are consumed to supplement the thermal power. To ease fossil fuel energy consumption and enhance the efficiency of biogas utilization, this paper presents a combined cooling heating and power (CCHP) system with synthetic use of biogas and solar energy. Solar energy is first transformed into syngas chemical energy through a chemical reaction called biogas steam reforming, and then the chemical energy is used for trigeneration in a conventional CCHP subsystem. Experimental research was conducted on the key process of biogas steam reforming to validate its feasibility. Hourly dynamic simulations of the proposed system were conducted by the mathematical models established using Lhasa, Tibet weather data. A biogas-fired CCHP system and a solar Dish/Stirling power system were adopted as reference systems, and a comparative analysis showed that the synthetic use of biogas and solar energy in the proposed system improves the annual electricity production by 8.70%, improves the refrigeration by 2.57%, and reduces the natural gas consumption by 8.66%. In addition, the direct CO2 footprint in the proposed system is 8.20% lower than that in the reference systems. Finally, an economic study was conducted to validate the technical feasibility of the new system. The study offers a new method of using biogas and solar energy for an improved integrated performance.