Power Line Communications (PLCs) enable new and highly convenient networking functions in the framework of Smart-Grids and use an already built-in network. A Multiple Input Multiple Output (MIMO) architecture can strongly improve the PLC performances and links' reliability. In this contribution the effect of self-interference generated by relay nodes has been considered and the MIMO potentials for spatial multiplexing and interference suppression have been taken into account. The importance of channel knowledge has been also considered from a numerical result point of view in order to give some instruments for network planning.