Technology to passively cool greenhouses in hot environments is being advanced by researchers from King Abdullah University of Science and Technology (Saudi Arabia), Chongqing University (China) and Huazhong Agricultural University (China). Internal heat is reduced by use of a nanoplastic greenhouse covering and biodegradable mulch.

As most greenhouse covers in use, primarily composed of glass, polycarbonate or polyethylene, transmit more than 90% of heat-generating light, an alternative was sought to lower facility temperatures. To control heat transmission and generation, polyethylene was infused with nanoparticles of cesium tungsten oxide. These molecules absorb heat-carrying infrared light while still allowing the visible light that drives photosynthesis to pass through. Bubble wrap underneath the cover acts as a thermal barrier between the outdoor air and the internal greenhouse environment. The nanoplastic was tested as a greenhouse cover material.

The nanoplastic cover absorbs infrared radiation to mitigate input thermal load while transmitting visible light for crop growth. Source: King Abdullah University of Science and Technology

In addition, a biodegradable mulch made from cellulose paper was applied to the soil. The material reflects sunlight and retains moisture, keeping soil cooler and enhancing photosynthesis. As plants mature and grow leaves that provide shade, the biodegradable mulch vanishes from the soil, providing a secondary solution to passive greenhouse cooling.

When tested in miniature greenhouses in Saudi Arabia, the technologies described in the journal Nexus demonstrated excellent water retention in the soil and a crop yield that was 200% that of commercially grown crops. Greenhouse temperatures were effectively lowered by 25° C.