Optimal Coordination of Solar-assisted Geothermal-based Integrated Energy Systems Considering Soil Thermal Dynamics*

To address escalating carbon emissions from heating in cold regions and seasonal mismatches in renewable energy utilization, this paper proposes a solar-assisted geothermal-based integrated energy system that ensures sustainable geothermal utilization and resolves solar energy intermittency by replenishing soil thermal reserves with surplus solar energy during non-heating seasons. A mixed-integer linear programming framework is developed to model the spatiotemporal thermal dynamics of the soil thermal energy storage system, incorporating operational constraints of energy supply and storage devices. The framework incorporates thermal interference between boreholes and employs piecewise linearization techniques to address nonlinear energy conversion constraints inherent to ground source heat pump (GSHP) operations. Numerical results demonstrate that the proposed method reduces the soil thermal imbalance ratio from 42% to 3%, effectively mitigating thermal depletion of GSHP under cold climates. Simultaneously, the system achieves 100% solar energy utilization efficiency and reduces operation costs by 5% through seasonal thermal storage. This work provides a cost-effective and sustainable paradigm for optimizing clean heating systems in cold regions, balancing economic viability with long-term environmental benefits.