Modeling and experimental validation of light-splitting semi-transparent solar water heater using NIR cut-off film as the rooftop of a greenhouse for arid regions

This study introduces a novel solution to the pressing challenges of water scarcity, high temperatures, and excessive radiation in arid agricultural regions: a semi-transparent solar water heater. Used as a greenhouse roof, this approach provides shade, fresh water, and a reduction in cooling load. The system’s design splits incoming light into photosynthetically active radiation (PAR) for crop growth and near-infrared (NIR) for water heating. Through rigorous modeling and experimental testing, the study validates the system’s optical and thermal performance. Key findings include a PAR transmittance of 0.5 for incidence angles less than 65∘, an aggregate transmittance as low as 0.3 for the spectrum ranging from 300 to 2500 nm, and an overall thermal efficiency of approximately 22.5%. A case study in Phoenix, AZ, demonstrates the system’s potential to meet crop light requirements, fulfill water demands, and reduce cooling load by around 17.4%. These results affirm the feasibility and benefits of the semi-transparent solar water heater as a roofing solution for energy-efficient greenhouses.