Experimentation of an autonomous solar cold room with thermal emulation of virtual food storage

The development of autonomous solar cold rooms faces challenges in regions with abundant solar resources but limited electrical grid infrastructure. Key issues include reliable energy storage, efficient refrigeration, and system portability for agricultural goods storage. Previous studies often neglected the dynamic temperature evolution of stored goods, crucial for food preservation. CEA and AIRWELL collaborated to design and test a Cold Room Solar Autonomous (CFSA) system prototype. The CFSA system includes a lead-acid battery, a 4 kWth refrigeration unit, a configurable PV field with 20x 500 Wpeak PV modules, an 8000 VA DC/AC inverter, DC MPPT chargers, and a cold room connected to a backup electrical network. CEA developed an emulation method of the actual internal thermal load for such system test, under dynamic conditions to maintain food temperatures, using heating resistors controlled by a dynamic thermal simulation. Testing on the CEA platform from August to November 2024 included various sensors and controllers while the Scilab models and simulation of the thermal mass provided performance insights. The battery maintained continuous refrigeration with 32 hours of autonomy without solar input during virtual matter’s temperature drop phase. The PV field ensured operational autonomy with 3kWh/kWc/day under reduced sunshine, requiring a backup source approximately every 3 days under low sunshine and temperature difference conditions. The experimental methodology developed in this work opens further development perspective of the CFSA hybrid micro plant to support the local grid balance by adjusting its energy storage and consumption in response to grid operators' signals. The estimated flexibility is about 1%/t.K referring to the CFSA system nominal power consumption, food mass stored and ind/out temperature difference.