Reliable renewable electricity generation system on small animal farms for rural electric vehicle charging

The adoption of electric vehicles (EVs) in rural areas is constrained by limited charging infrastructure, while small-scale dairy farms remain significant sources of greenhouse gas (GHG) emissions from manure management. This study addresses both challenges by demonstrating a dispatchable renewable electricity generation system that integrates anaerobic digestion (AD) with an external-combustion, Stirling-type combined heat and power (CHP) unit to support rural EV charging. A trailer-based system incorporating a 2.25 m³ AD reactor and a 5.6 kW CHP unit was constructed and operated using 28 kg/day of dairy manure. Results from a 50-day demonstration informed scaling and modeling for a representative 30-cow dairy farm. The AD process achieved a methane productivity of 232 L/kg volatile solids, with electrical and thermal conversion efficiencies of 15.05% and 37.11%, respectively. When scaled to a 30-cow farm, the system produced 46.46 kWh/day of net electricity and 10.43 kWh/day of recoverable heat, sufficient to meet realistic rural EV charging demands. Techno-economic analysis estimated a total capital investment of $99,000, annual operating costs of $2,000, and combined energy revenues of $7,797/year, corresponding to a 28-year payback period. Sensitivity analysis indicated that system economics are most strongly influenced by revenue generation. Life cycle assessment showed substantial environmental benefits relative to conventional manure management, including annual reductions of 324.44 tons CO₂-eq in global warming potential. Compared with stand-alone photovoltaic EV charging systems that require large battery storage to ensure winter reliability in northern climates, the biogas-based system leverages biogas storage as a low-cost energy buffer, enabling on-demand electricity generation with lower capital intensity. Overall, this work demonstrates a compact and scalable pathway for integrating manure-derived biogas with EV charging to advance rural electrification and circular bioeconomy goals.