This paper discusses the issue of energy-efficiency in power line communication (PLC) systems and introduces decode-and-forward (DF) energy-harvesting based relaying. The performance of the proposed system is analyzed in terms of the energy efficiency for which accurate analytical expressions are derived. To highlight the achievable gains, we also evaluate the performance of both the conventional DF relaying and the direct-link systems. The presented simulated results clearly demonstrate the correctness of our analysis as well as the advantage of the proposed system over the conventional relaying and direct-link approaches. Additionally, it is shown that the proposed scheme will become more energy efficient as the harvested noise energy becomes larger.