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.
Chosen because it features an ESP32-WROOM32 module with ethernet PHY and 2 relays for switching external loads.
BMP280 Temperature + pressure sensor
Used to monitor the temperature within the fridge
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.