Solar powered, "thermal battery" refrigerator intelligently controlled with μPython on an ESP32-EVB

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This project was inspired by and follows most of the same hardware choices, however, instead of controlling it with a Haskell program on a full Linux OS, I decided to build the controls in MicroPython running on an ESP32-EVB from Olimex (
  • 1 × 16 cubic ft chest freezer
  • 2 × 7 gallon containers filled with water. Water stores a lot of energy. When 14 gallons of it is chilled to near freezing temperature, it is able to keep the fridge cold for a long time when there is no external power (solar) available.
  • 1 × Olimex ESP32-EVB Chosen because it features an ESP32-WROOM32 module with ethernet PHY and 2 relays for switching external loads.
  • 1 × BMP280 Temperature + pressure sensor Used to monitor the temperature within the fridge
  • 1 × DHT22 Temperature + humidity sensor A second sensor monitors the temperature at another location within the fridge. This also provides humidity reading which should be useful information to record.

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