"An application is a little more wide than just home automation. The controlled objects are located in area of 1-2 km^2."

Is this a job for the power company?
If not, you should seek the approval of the power company first.

I don't know the specficic regime in your particular area but, over here, once you're outside the house the network belongs to the power company, and they have rules about what "noise" you can inject onto it. They probably have their own signalling schemes over their own lines...