A passive solar application using thermal energy storage in phase change materials for frost damage protection of citrus trees

Increasing frequency of extreme weather conditions due to global climate change is threatening citrus orchards. Young seedlings and some citrus varieties like lemons are especially susceptible to frost damage. Many orchards have installed expensive wind machines that use electricity to ward off cold air. When the temperature falls below −4 °C, even for several hours in a year, frost damage can kill citrus trees, thus causing serious economic loses. In this experimental study, we developed new phase change material (PCM) packages for passive solar protection of citrus trees from frost damage. Aqueous solutions of ethanol, ethylene glycol, and propylene glycol were evaluated as three PCMs due to their suitable chemical properties and abundance. Flexible packaging for the PCMs that can be easily applied to citrus trees were developed, and thermal protection performance of developed packages were tested on citrus seedlings. Supercooling of PCMs was seen as a problem during the tests, which was solved by adding a nucleating agent based on silver iodide developed in our laboratory. Results show that the ethanol containing PCM provided the longest thermal protection and succeeded in keeping seedling temperatures within the target interval for 10.5 h, while ethylene glycol and propylene glycol containing PCM packages provided 6.9 and 6.0 h of protection, respectively.