GTEM started life a couple of years ago using an ESP8266, CT Clamp and Domoticz. For those of you that have also made these, will have found that they work OK to give Power Consumption but lack the Import (Active) /Export (Re-Active), and Power Factor information. This project also extended into the GTIE SDK (Grid Tie Inverter Extender for SUN-1000GTIL2 and SUN-2000GTIL2 series).

The project expanded over time to include the ESP8266 and ATM90E26, this proving the technology (based and inspired by Tisham Dharon [whatnick] excellent work and enthusiasm), but the ESP8266 lacked additional GPIO and features.

Increasing to processing power and GPIO flexibility offered by the bigger brother, ESP32, is an advantage. For this reason, the culmination of GTEM SDK brought the ESP32 and ATM90E26 together, complete with EEPROM and D1 USB compatibility using the CH340.

Safety, Safety and more Safety! An important criteria of the Energy Monitor was the ability to safely connect to mains.