First of all I am super fun of OpenEnergyMonitor project I was developing how to get the power factor and I found this answer and more.
Second, I dont understand why the suggestion for a installation is a CT 100A (In the shop you just can find this version and 200A version). In a standard installation (4.5kW) we are going to see currents peaks of ±4500W/220V = 21A before to the electrical company meter actuation, so if we choose a 30A/5V CT the resolutions is higher because you have 5V to represent 30A which is 5/30= 0.16Volts per Amperes resolution and not 5/100= 0.005Volt per Amperes which is 32 times smaller.
So I think that I am missing something.
With this thought I chose 50A/5V CT (SCT-013-050) and I dont finger out if it is fully compatible with emonTX V3 board.