Modeling and integration of photovoltaic thermal hybrid solar collectors in a fifth-generation district heating and cooling network

District heating and cooling (DHC) networks with electric heat pumps are one of key enabling technologies in the decarbonization of the building energy sector, particularly when integrating renewable energy sources such as solar energy. Photovoltaic Thermal (PVT) hybrid solar collectors combine PV modules with heat-recovery configurations, providing simultaneous electrical and thermal outputs from the same array. This dual functionality makes PVT systems highly suitable for DHC networks, as they can efficiently meet both electrical and thermal needs.

Fifth-generation DHC networks offer enhanced energy efficiency, characterized by its close-to ground level operating temperature and its capability to provide simultaneous heating and cooling through decentralized heat pumps. Additionally, their lower operational temperatures facilitate the integration of low-grade thermal energy sources and reduce thermal losses through underground pipes. Therefore, the integration of PVT collectors in a fifth-generation DHC network paves a promising way to enhance the overall energy efficiency and sustainability of the district energy system.

This paper explores the modeling and integration of PVT solar collectors into a fifth-generation bidirectional heating and cooling network. PVT is modeled in Modelica and based on experimental data. The proposed DHC network incorporates PVT hybrid solar collectors and water-to-water heat pumps, designed to meet the energy requirements of a diverse building community (including a hospital, commercial buildings, and residential units) in Denver, Colorado, USA. EnergyPlus is utilized to generate annual building thermal loads using the U.S. Department of Energy (DOE) prototype building models.

Modelica serves as the modeling language for the fifth-generation DHC network integrating with PVT. Compared with a baseline model using PVT hybrid control strategy (i.e., simultaneously generating heating and electricity), this study developed a rule-based control strategy of switching among three PVT operating modes (i.e., heating-only, electricity-only, or hybrid generation modes) to enhance the overall energy efficiency of the PVT-DHC system. The full paper will evaluate the impact of different PVT sizes and PVT control strategies on the system energy performance, followed by a detailed analysis of annual energy usage and utility costs.

The results will highlight the substantial benefits of combining DHC with PVT technology for sustainable and efficient district energy systems.