I want to measure the used Watts of at least 10 channels (probably 15+).
I am situated in Europe.
The rest of the automation will run on knx and 1wire.
I would prefer a wired solution over any wireless solution.
If possible I would also prefer true power over apparent power measurement.
I could use a knx actuator with power measurement, unfortunately that would set me back about 56€/channel, so that is out of the question.
Alternative would be a cheapo energy meter with an S0 interface and a knx-binary input. That would cost around 42€/channel.
Openenergymeter (I know, wireless) would cost around 20€/channel
The Brutlech GEM would be slightly cheaper, have ethernet, unfortunately I did not find any source in Europe so far.
I have a DIY power consumption reader. I use an SDR RTL dongle to listen to the PG&E Smart Meter transmission of power consumption. So your meter has to be SMART also. You have to know which transmission is for your meter. A SDR radio is powerful enough (my antenna is in the backyard, and can pickup transmissions even from aircrafts and military). During my development, I could pickup 300+ Smart Meters from my area THe hardest part was figuring out which transmission was mine.