Measuring Export with only on AC/AC


I have two arduinos, one measuring the house power with an AC/AC transformer, and another arduino measuring the PV production. The problem is, that i only have one AC/AC.

Since my arduino sketch prints the outputs via browser, can I get some value from the arduino number one to make some calculations and get the direction of the real power on the PV part? Or do I need to have another AC/AC on the second arduino?

I've tried to use the power factor, and the var from the arduino on, but It wont work...

Thanks for the help.