Passive cooling of greenhouses in extreme climates through spectral control film

A warming climate poses a major threat to agriculture globally, necessitating technological solutions to mitigate frequently occurring extreme heat stress. Greenhouses in hot regions can provide suitable growth environments throughout the year by active cooling systems such as pad-and-fan systems or heat pumps; however, this practice comes with significant water and/or energy costs. In this study, we demonstrate a solution for passive thermal regulation in greenhouse environments utilizing the combination of a spectrally selective cover and a radiative cooling ground film. The cover consists of a polyethylene film infused with cesium tungsten oxide nanoparticles (PCsW), which block near-infrared sunlight to reduce solar heating while maintaining a high mid-infrared transmittance of 0.74, effectively dissipating radiative heat flux. The ground layer is a biodegradable cellulose mulch with a solar reflectance of 0.93 and a high mid-infrared emittance of 0.95, facilitating sunlight redistribution and efficient radiative cooling. Field trials conducted in a hot desert climate demonstrated that the combination of the cover and ground film led to a remarkable 25.1°C reduction in soil temperature within the greenhouse compared with the control, resulting in an increased germination rate, an optimized thermal environment for crops during their most vulnerable early growth stages, and enhanced yield of the experimental Chinese cabbage. This innovative passive cooling approach with zero water or energy input can extend growing seasons while significantly reducing the environmental footprint of greenhouse agriculture, especially in hot regions. Furthermore, the biodegradable nature of the cellulose mulch offers a sustainable alternative to conventional plastic films. Broader context: The pressing challenges of food security demand sustainable solutions for agriculture, particularly in extremely hot climates. Our work on passive dry cooling for greenhouses addresses these challenges by employing spectrally selective cover films and biodegradable, radiative cooling ground mulch. This approach not only mitigates excessive heat to support plant growth but also eliminates the need for energy-intensive cooling systems and excessive water consumption. By enhancing the internal greenhouse environment without active cooling, our technology promotes sustainable agricultural practices that could be transformative for regions facing severe water scarcity and high temperatures. The scalable fabrication of these materials, combined with the significant temperature reductions observed, positions this solution as a viable method for extending growing seasons and increasing crop yield, directly contributing to resilience in global food production systems. This passive cooling method thus represents a critical advancement in the intersection of energy and environmental science, supporting a low-carbon agricultural future.