Progress 04/15/22 to 12/14/22

Outputs
Target Audience:Individuals who will be served by this project include first- and last- mile users of cold storage for fresh food supply chains. We are developing technology that will allow remote applications of cold storage, which serves small farms and farmer cooperatives, persons in direct to consumer sales such as community supported agriculture operations, and non-profit food security groups such as food banks, all of which may desire improved access to cold food storage options. Radiant has partnered with Frontline Farming, a farmers advocacy and food justice group for training black indigenous and persons of color as apprentice farmers, and with East Denver Food Hub, a social equity group providing farm-fresh food to the local community and promoting equity and inclusion in the local food system. These two groups were recruited to be first users of our product and represent our target audience. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Extensive one-on-one mentoring and training of a young engineer by a senior research and development engineer extended over the entire grant period. How have the results been disseminated to communities of interest?Outreach activities included user training events provided to users of both prototype units. These users included BIPOC farmers who were the primary users of the first unit which was used for collection of produce and for distribution to community supported agriculture subscription members, and warehouse workers who used the second unit for regular pick-up and distribution of repackaged perishable products. Training events included discussions of maintenance, of optimal use for off-grid reliability, and of user safety. Additional activities include extensive outreach to an array of stakeholders along the supply chain. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Localizing (i.e., shortening) of food supply chains as a potential pathway for equitable food distribution requires new technologies that make short supply chains more efficient, cost-effective, and sustainable. Rapidly deployable, cold storage that eliminates the need for utility-supplied grid electricity can be one such technology that enables efficient and sustainable local supply chains for fresh produce and perishable foods. Cold storage that relies on locally generated solar electricity can provide new economic opportunities and fresh food diversity in rural communities and in urban regions with fresh food scarcity. In this project, Radiant Innovation is developing the architecture and controls for solar-powered refrigerators that enable reliable off-grid operation and thus rapidly deployable, distributed cold-storage for applications where grid connections are costly in money and/or time. Radiant's solar-powered refrigerators equipped with adequate battery energy storage are being integrated with cloud-based model predictive controls that rely on dynamic weather forecasting to expand off-grid reliability over a broad range of climatic conditions to support local fresh food supply chains. Successful deployment of two prototype units with cloud connections for remote data storage and controls provides a framework to test the viability of off-grid solar-powered cold storage for many applications. Manual and automated controls to date have been used to adjust refrigerator storage temperatures based on product needs and ambient weather to facilitate maintenance of off-grid usage. To achieve reliable off-grid performance, thermal/energy models of the prototype solar-powered refrigerated containers (modified 20 ft. shipping containers) were implemented to accurately simulate energy flows between solar panels, Li-ion batteries for energy storage, and the refrigeration equipment. These models are being calibrated by comparison with performance data from the deployed prototype units and stored in the cloud for continued model training. These same models have been integrated with dynamic weather forecasting to provide a basis for adjusting thermal and ventilation setpoints to maintain adequate battery state-of-charge during periods of less than optimal solar irradiation. To understand how the dynamics of off-grid operation impacts fruits and vegetables, experiments were performed to test produce quality, shelf life and food safety for high ethylene producers (apple and tomatoes) and for vegetables highly sensitive to ethylene and carbon dioxide (broccoli and lettuce) in the deployed prototype units. Controlled experiments were performed throughout the summer and fall growing season. The first experiment, in July, tested romaine and iceberg lettuce, the September experiment tested tomatoes and apples, while the October experiment tested broccoli. These first three experiments were performed in the first unit at a farm site. A fourth and final experiment was performed in the second unit at a warehouse site and was a 60% load test, using several varieties of lettuces, broccoli, brussel sprouts and cabbage. Environmental parameters such as temperature, humidity, carbon dioxide and ethylene concentration were factored into the analysis. Humidity levels fluctuated between 38% and 80%, averaging 72%. Evidence of humidity variability was visually detected in wilting and yellowing of specimens. Carbon dioxide levels fluctuated between 500 and 10,000 ppm, indicating a need for improved ventilation to maintain carbon dioxide levels close to ambient concentrations. Ethylene did not show significant accumulation when the unit was entered and exited on a daily basis. Each of the first three tests collected samples at 7 day intervals and were analyzed for nutritional and microbial quality of the crop. Microbial analysis showed some moderate growth over the testing period but was a lesser factor to produce quality and shelf life than carbon dioxide and humidity. These experiments provided an assessment for how unique conditions with fully off-grid cold food storage can impact produce and provided a preliminary basis for adding food quality, food safety and produce life into the predictive models.

Publications