Sustainable energy solutions for dairy farms under the bio-circular economy approach: dynamic modelling and energy and economic analysis

This study presents a dynamic thermo-economic analysis of an integrated renewable energy system for a dairy farm in Campania, Southern Italy, promoting bio-circular economy. Two configurations are proposed: (PS1) a hybrid photovoltaic-biogas-cogeneration systems based on cheese whey digestion, and (PS2) an enhanced layout integrating a Power-to-Gas system with solid oxide electrolysis and methanation, utilizing surplus renewable power and captured CO2. The main innovation lies in a coupled MatLab-TRNSYS simulation model, combining detailed anaerobic digestion dynamics with real-world energy loads measured over one-year period. The system models hourly variations in ambient conditions, user demand, and renewable availability, providing a realistic evaluation of energy efficiency, emissions, and cost. Results show that the first configuration achieves 80 % electricity self-consumption, 88.6 % primary energy savings, and a 7-years payback period. The second configuration, while requiring higher investments, achieves 83.7 % primary energy savings, roughly 5473 tons of CO2 emissions avoided through carbon capture and synthetic methane production, and a 13-year payback period. The sensitivity analysis shows that while PS1 is only modestly affected by electricity prices and carbon taxes, PS2 feasibility improves significantly with higher carbon tax rates – reducing the payback period from over 13 to under 4 years – highlighting the crucial role of carbon pricing in supporting such systems.