Hybrid photovoltaic–thermal and solar thermal collectors with integrated phase change materials: toward sustainable greenhouse energy systems

Greenhouses require substantial energy for heating, cooling, and electricity, yet current renewable solutions rarely provide all three simultaneously. Most existing systems supply either thermal or electrical output and lack integrated storage, creating mismatches between solar availability and greenhouse demand and reinforcing dependence on fossil fuels. This study addresses this problem by developing and analyzing a hybrid photovoltaic–thermal (PVT) and solar thermal (ST) collector system integrated with phase change materials (PCMs) for combined power generation and heat storage in greenhouse applications. A three-dimensional numerical model examines the effects of PCM type (RT21, RT31, RT35) and heat transfer fluid flow rate under typical summer conditions in Sherbrooke, Québec, Canada. Results indicate that low-melting PCMs (RT21) achieve rapid phase change before solar noon, offering early-day cooling but limited afternoon buffering. Conversely, higher-melting PCMs (RT31, RT35) extend heat absorption throughout peak irradiance, optimizing PV thermal regulation. Parametric analysis reveals that reduced HTF flow rates maximize PCM utilization and outlet temperatures, whereas higher flow rates prioritize electrical stability. Exergy results indicate a fundamental trade-off: RT21 maximizes daily-average thermal exergy through superior temperature gradients, while RT35 optimizes electrical exergy by maintaining lower cell temperatures. Increasing HTF flow rate enhances electrical exergy but reduces thermal exergy by lowering the temperature level of the delivered heat. A 100 m 2 installation yields approximately 455 kWh/day of thermal energy and 35.5 kWh/day of electricity (July/August), satisfying nearly all thermal loads and 30–34% of electrical demand. This configuration achieves a significant mitigation of 77–78 kg CO 2 e/day, primarily through the displacement of carbon-intensive natural gas heating.