In this paper a procedure for the optimization of the bit loading in a PLC system implementing OFDM modulation is presented. The optimization strategy aims to find the best compromise between the conflicting objectives of minimal Signal Power, maximal Bit Rate, and minimal Bit Error Rate. The optimization is performed off line by means of a Multi-Objective approach. A set of Pareto solutions is determined, among which the designer has to take the final choice on the basis of the custom requirements. The approach is used to optimize the communication within a distributed energy storage system, which exploits an available electrical car fleet. The power lines supplying the charging points are used for the communication, while the information concerns, for each car, the identification code, the charge state, the schedule of charging/discharging. A unique OFDM modulation is used to dialogue with the whole cars fleet, so that it has to be optimized taking into account the frequency response of any involved power lines.