Performance optimization of a solar assisted CCHP based on biogas reforming

Using renewable energy in the distributed energy systems has large potential to ease the excessive use of fossil fuels and the environmental problems. Selecting a new and efficient system scheme of utilizing the renewable energy to meet various user load is decisive to improve the technical, economical and environmental performances. This work presents a detailed research on a new CCHP based on synthetic utilization of biogas and solar energy. Unlike the conventional biogas-fired CCHP in which biogas is directly burned for utilization, biogas in the hybrid system is first transformed to the syngas via biogas reforming reaction which is assisted by the solar energy, and then used in an efficient tri-generation system. A system optimization model based on the comprehensive evaluation criteria is established under Lhasa Tibet weather data to optimize the key parameters of the CCHP following the electric load (FEL) by genetic algorithm (GA). The optimal engine capacity and hydraulic retention time are 1052 kW and 260.2 h, respectively. A biogas-fired CCHP and a solar Dish/Stirling power system are adopted as the reference systems, and the comparative analysis is presented to show the advanced annual efficiency of the hybrid CCHP. The saving ratios of natural gas and electricity from outside the system reach 3.3% and 77.8%, respectively. Moreover, a sensitivity analysis is carried out to indicate the effects of the prices of electricity, natural gas and refrigeration on the system dynamic operation performances. The electricity price has the biggest impact on the dynamic payback period of the proposed system. The research may provide a mutual beneficial way to use biogas and solar energy efficiently and economically.