Optimization design and techno-economic assessment of integrated solar photovoltaic thermal systems for modern agricultural greenhouses

Amid intensifying global climate change and a deepening energy crisis, the high energy consumption of agricultural greenhouses has become increasingly problematic. To address this issue and enhance environmental control within modern agricultural greenhouses, this study proposes an optimized design for a solar photovoltaic thermal (PVT) integrated system tailored for northern solar greenhouses. This design aims to achieve greenhouse energy self-sufficiency and promote sustainable agricultural development. The study outlines a system optimization methodology and a PVT unit layout strategy. This strategy includes double-sided placement on both interior and exterior surfaces of the bilateral gable walls, the use of adjustable racks on the rear wall, and the configuration of an internal heat dissipation system within the greenhouse. These measures collectively enhance the system's year-round comprehensive energy utilization efficiency. Using a typical solar greenhouse case in Shouguang City, Shandong Province, a system performance evaluation model is established. Theoretical analysis indicates that the system generates 35,422 kWh of electricity and 208,945 MJ of heat annually. This achieves an electrical energy self-sufficiency rate of 130.9 % and a thermal energy self-sufficiency rate of 139.4 %, effectively resolving the seasonal mismatch between energy supply and demand in the greenhouse. Comprehensive techno-economic analysis shows a total system investment of approximately CNY 172,300. The static investment payback period is 6.25 years, while accounting for equipment performance degradation yields a dynamic payback period of 9.1 years and an internal rate of return (IRR) of 10.6 %, demonstrating sound economic feasibility. Sensitivity analysis identifies initial investment costs and electricity price fluctuations as key factors influencing system economics. Environmental benefit assessment reveals that the system can displace 17.4 tons of standard coal annually, reducing CO₂ emissions by approximately 45.5 tons. Over a projected 25-year operational lifespan, cumulative CO₂ emission reductions are estimated at approximately 1139 tons. This study provides a technically viable, economically feasible, and environmentally friendly solution to the high energy consumption challenge of agricultural greenhouses, demonstrating significant practical value for advancing sustainable agriculture and optimizing energy structures.