S23 - Session O7 - Off-grid cooling and refrigeration: Technical innovations for the storage of perishables for smallholder farmers

Authors: Randolph M. Beaudry, Sangeeta Chopra *, Rohit Sharma, Norbert Mueller, Sameer Dhingra

Stand-alone cooling systems for storage of perishables are needed in regions of the world lacking reliable electricity and the financial wherewithal to make sufficient investments in on-grid cold stores. A fully functional off-grid cold store would be beneficial for these areas. We designed and built cooling and refrigeration technologies that were low cost, reliable, and capable of being self-constructed by base-of-the-pyramid farmers. We have evaluated features of evaporative cooling (EC) and solar-powered refrigeration to achieve these goals. As part of a project supported by the USAID Global Center for Food Security Innovation at Michigan State University and, subsequently, the USAID PEER program, we have redesigned EC structures using novel inexpensive wall materials and have engineered the structure so that it is capable of being retrofitted with solar-powered refrigeration, using EC to reduce power needs. We compared the performance of EC wall designs and determined that fabric walls outperformed other EC design options. Further, we evaluated the potential for EC to improve storability of perishables for the globe on a 6 arc-minutes basis. Few locales are predicted to reduce ambient temperatures more than 10 °C for more than a few hours of the day and/or improve the storage life of perishables by more than 80% for three months of the year or less. To improve functionality of EC, we have fitted our EC room with a solar-powered refrigeration system to achieve temperatures as much as 35 °C below ambient. This system needs no grid-tie nor electrical battery to function effectively. Several innovative features have been incorporated including a water thermal reservoir to act as a "battery" and provide night time cooling, a split refrigeration coil to cool the thermal reservoir and air simultaneously, and a means to regulate power demand by the refrigeration compressor based on available solar energy. The hybrid EC-solar powered refrigeration system, termed Farm SunFridge, can achieve temperatures of 5 to 10 °C when ambient temperatures are over 40 °C. In February 2020, we installed our first on-farm solar-refrigerated, evaporatively-cooled (SREC) room and now have two years' worth of performance data. Lessons from the construction and testing of our prototypes and on-farm installations will be discussed. Future designs and construction plans will be presented.