Powering farm autonomy with green energy : achieving agricultural self-sufficiency: a Swedish case study on integrating biomass, photovoltaics, and dual-mode energy storage with autonomous electric tractors on an off-grid farm

Sammanfattning

As the global agricultural sector faces increasing pressure to decarbonize and mitigate energy market volatility, transitioning from fossil-fuel-dependent machinery to electrified alternatives requires robust, autonomous on-site energy infrastructure. This thesis investigates the technical feasibility of achieving energy self-sufficiency on a Swedish wheat farm by integrating renewable generation with advanced energy storage systems. Specifically, the study evaluates a hybridized system comprising photovoltaic (PV) and biomass-driven Combined Heat and Power (CHP) generation with an Organic Rankine Cycle (ORC) combined with a dual-mode storage configuration: a 1 MWh Battery Energy Storage (BES) for short-term electrical balancing and a 20 MWh Molten Salt Thermal Energy Storage (TES) for long-term exergetic buffering. Additionally, the system utilizes pyrolysis for carbon sequestration and as a thermal energy sink. A dynamic simulation model was developed in MATLAB/Simulink to analyze the system's performance over an annual cycle, with a specific focus on meeting the high-power charging demands of a fleet of autonomous electric tractors. The system’s efficacy was evaluated using Key Performance Indicators (KPIs), including the Self-Sufficiency Ratio (SSR), State of Charge (SoC) dynamics, and Carbon Sequestering Ratio (CSR). The results demonstrate that the integrated configuration can achieve energy autonomy under baseline conditions and identify the 20 MWh TES as the critical component for system stability. In a comparative scenario in which the TES was removed, the SSR collapsed to 56.5% because the CHP's thermal output was treated as “wasted,” and the inactive ORC engine was unable to mitigate fluctuations in electrical loads. Parametric sensitivity analyses revealed that biomass fuel quality and the CHP's operational efficiency are the primary technical bottlenecks governing the farm's energy balance. The findings suggest that while the transition to electric tractors is technically feasible through renewable integration, implementing high-capacity thermal storage is essential to provide the necessary flexibility for off-grid or weak-grid agricultural operations, but poses several technical challenges that require further inquiry. This research provides a framework for evaluating trade-offs between biomass storage, technical configurations, and system autonomy, offering a pathway to reduce the fossil-fuel dependency of modern food production.