Nanoplastic and bio-mulch passively cool greenhouses

Described in the journal Nexus, the dual system uses a combination of a nanoplastic greenhouse covering and biodegradable mulch to significantly reduce heat. According to the study, the KAUST team was able to lower temperatures of miniature greenhouses by 25°C and increase crop yields of Chinese cabbage by nearly 200 per cent.

To create the covering, polyethylene was infused with nanoparticles of caesium tungsten oxide. These molecules absorb heat-carrying infrared light while still allowing the visible light that drives photosynthesis to pass through. 

"Most greenhouse covers, whether they are made of glass, polycarbonate or polyethylene, transmit more than 90 per cent of light, including infrared light, which has no benefit to crop yield but generates heat,” said KAUST Professor Qiaoqiang Gan, an expert in passive cooling systems who developed the nanoplastic.

To complement the passive cooling of the nanoplastic, the KAUST team also created a biodegradable mulch made from cellulose paper. Mulch is commonly used to reflect sunlight and retain 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.

“Most commercial mulch is plastic and extremely wasteful,” said Gan's postdoctoral researcher, Yanpei Tian.

“It results in about 1.5 million tons of waste, and more than 40 per cent goes unrecycled. Plus, this leaves microplastics in our soil that can enter the food chain.”

Testing the two technologies in miniature greenhouses in Saudi Arabia to grow Chinese cabbage, the researchers found excellent water retention in the soil and a crop yield that was 200 per cent that of commercially grown crops. Using public weather data, the KAUST team estimated that adopting their new system could reduce energy consumption in hot cities around the world - like Riyadh and Houston - by more than 40 per cent.

"The cooling of greenhouses can be extremely expensive,” said Gan. “Our approach can make a number of crops available to arid regions, increasing their food security while at the same time helping meet carbon emission targets.”