so i've built an energy monitoring system based on the EmonLib library.
with a little bit of changes here and there to suit my requirement.

tested the long term accuracy for 24/7 operation with a cheap ESP8266 off aliexpress and the ADC loses its precision here and there causing erroneous spikes in the measurement.
also tested the ESP8266 with an external ADC through ADS1015 and ADS1115 and but the measurement lags here and there because of the ESP SDK messes around with the response.

got a good result using an arduino that acts solely as the measurement node and an ESP that is used solely for the data transmission.



calibrated the sensor response to a water kettle with a PF of 1.0

and proceeded to install the prototype inside my DB.



measurement is taken off the neutral line to get a total sum of the entire 3 phases.




data transmitted using MQTT to a central server through wifi.

For energy monitoring can buy off the shelf like this

https://maevi.my

But for power , u mean pq rite? maybe need to survey more.

i got it off aliexpress.
the current clamp is also available in ebay, gearbest, banggood, amazon, etc. i've posted the model before.

installed inside db because it's a current clamp, a non-intrusive to the circuit.
the sonoff uses a shunt resistor paired with a hlw8012 monitoring ic. the ic measures the current drop across the resistor.
it's an intrusive design where the line is inserted with that shunt resistor causing a voltage drop to happen across the resistor and measured by the ic.
not perfect if you consider the thermal drift on the resistor and thermal limit of the resistor with high load. but it'll work, suitable for low power devices.

the sonoff can be flashed to some other firmware that supports tweaking to the output messages, don't need to send it to sonoff server.
not well versed with sonoff since i don't use them. don't intend to use them since there's no exposed GPIO on sonoff pcb, which severely limit external sensors that be attached to the sonoff.