When I moved into my new appartment wanted to record my power usage. I managed to install a rather cheap three-phase power meter into the distribution box:
This is an EASTRON SDM630-Modbus (German distributor). It is a three-phase power meter that allows you to query voltages, currents, power, power factor, thd etc. over a Modbus RTU connection. You can buy these in Germany for about 90 Euro - make sure to get the Modbus version, there are other versions around!
I wrote a simple Modbus-to-JSON-Adapter in Go. Now I have the most relevant values exported into my OpenHAB installation:
The “Strombezug” graph shows the power on three different phases. My software, along with hardware and software documentation, is available on github:
Let me know what you think.