Cutting peaks and costs: Techno-economic design guidelines for solar PVT and GSHP in land-constrained multi-family buildings

• PVT + GSHP 20-year TRNSYS simulations for land-constrained undersized boreholes. • Five PVT absorber types assessed across different layouts and control strategies. • Optimal case: 1.15 m 2 of PVT per kW th of heat pump capacity at 80 l/h-m 2 flow rate. • PVT integration lowers peak electricity demand by up to 10% • High electricity prices shift economic optimum toward larger PVT array sizes. This study conducts a detailed techno-economic analysis of photovoltaic-thermal (PVT) collectors integrated with ground-source heat pumps (GSHPs) for land-constrained multi-family buildings in cold climates. Using dynamic TRNSYS simulations, the system is designed around an undersized borehole field and incorporates realistic electricity pricing models, including dynamic spot prices and capacity-based tariffs, and peak demand considerations. A stepwise analysis evaluates five PVT absorber types, array sizes, layouts, and control strategies. The most cost-effective design combines 60 m 2 of unglazed finned collectors, pre-borehole layout, and 80 l/h-m 2 fixed flow, achieving a seasonal performance factor above 2.7 and a minimum total life-cycle cost (TLCC) of €451 k€. Among all design variables, array size has the greatest impact on system performance and cost, with flow rate being the next most critical factor. Relative to a stand-alone GSHP, the hybrid system lowers peak electric load by 10 % and reduces total life-cycle cost by 4–23 % when benchmarked against alternative heating configurations including district heating, air-source heat pump, and PV-assisted GSHP. Scenario analyses show that electricity pricing structure and volatility significantly influence optimal collector sizing, with higher electricity prices favoring larger PVT array sizes. The results provide actionable design guidelines for researchers and practitioners seeking to improve performance and cost-effectiveness of heat pump systems, and to support their broader deployment in space- and grid-constrained urban environments.