In this paper a simulations-based evaluation of the energy efficiency performance of relay Power Line Communication (PLC) networks is reported. Our system model is based on two PLC modems as source/destination and one relay modem with time division Decode-and-Forward (DF) scheme. In addition to the transmission power, we consider the static power of PLC modems in our energy consumption model and find the best energy efficiency performance for DF strategy by optimizing the transmission time of each link. Through extensive numerical results and two representative scenarios, we show that the use of PLC relaying with optimal time allocation allows for better performance than direct transmission, yet achieving the same rate of the direct transmission.