Crop damage and water waste targeted by new greenhouse ‘sunglasses’

Greenhouses allow producers to grow more fruit and vegetables while using less land, water and fertilisers. But in warm climates known for their fresh produce, such as the Mediterranean or California’s Central Valley, they can become extremely hot, damaging crops.

Cooling greenhouses usually involves using fans or evaporative cooling, but this can consume large amounts of energy and water. Researchers from the University of California Davis set out to tackle those challenges with a new multilayer film that reflects heat while letting through the light needed for photosynthesis.

Described by a university announcement as “sunglasses for plants”, the new film could provide an alternative to shade screening, a common practice that blocks photosynthetically active radiation (PAR), which is critical for plant growth. 

Known as Cool-Cover, the new film is made up of stacked layers of materials, including zinc oxide, calcium fluoride and silver. 

The team of engineers, led by postdoctoral researcher Amrit Kumar Thakur, used simulation software to design the multilayer film for optimal performance. The results predicted that glass coated with the film would reduce near-infrared light passing through by almost 90%, while allowing about 51% of the PAR optimal for photosynthesis. 

The researchers also used an established model of a standard greenhouse to predict how the film would perform in environments with hot, dry summers and milder winters. The models showed that the coating could dramatically reduce water use and energy consumption in greenhouses, with only a small reduction in crop yield. 

The trade-off between potential savings and crop yield is “critical to consider”, the authors wrote, especially in regions with high solar radiation and water scarcity. 

The team is working with Lawrence Berkeley National Laboratory to produce a version of the multilayer coating. A provisional patent has been filed. 

The film was described in a recent paper in Advanced Energy & Sustainability Research. 

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