In system sizing, the designer goal is to maximise reliability and minimise installation cost. The Loss Of Load Hours (LOLH) is a suitable parameter to assess the reliability: LOLH represents the number of hours per year whenever the inverter is switched off by the charge regulator, in order to allow the charge of batteries by the PV modules. High reliability and low installation cost represent two opposed requirements, hence a trade off is needed, in particular about PV power and battery capacity.

Energy management is a logical algorithm which determines the energy flow in the system from Pv generator to load in order to use energy as efficiently as possible. The State of Charge (SOC) of batteries plays a key role for the energy management [3], [4]. To find a true optimal solution, it is necessary to take into account both system design (component sizing) and control strategy (proper set points) [5]. In the system under study, the charge regulator implements an operation with two set points at p = 30% and 100% for the SOC. Really the charge regulator measures the battery voltage as an indicator of SOC. A hysteresis band between 30% (corresponding to 22.2 V) and 50% (25 V) is allowed at the aim of charging partly the batteries, while around 100% (28.2 V) an equalisation charge by Pulse Width Modulation (PWM) current is included. In such a way, the periodic boost charge stirs the electrolyte, levels the cell voltages and completes the chemical reactions.