THE LOAD-MATCHING APPROACH TO SIZING PHOTOVOLTAIC SYSTEMS WITH SHORT-TERM ENERGY-STORAGE

This paper presents results obtained for sizing the photovoltaic array and the battery in PV systems with short-term energy storage. The method is based on maximizing the utilization of the array output energy, and minimizing losses associated with charging and discharging the battery. Results show that the two-dimensional problem of sizing the PV array and the battery can be replaced by a one-dimensional problem of sizing the array. Under the standard insolation model, the maximum electrical energy output from a 1 kW peak array over a 1 day period is approximately 6 kWh. However, due to the various losses in the system the useful daily dc energy is about 5 kWh. The array voltage at the maximum power point must be at least 1.35 times the battery open circuit voltage at full charge in the case of direct-coupled, or 1.6 if a power conditioning unit is used. The maximum depth of discharge of the battery is 65%. For maximum performance, the battery should be sized such that its state of charge varies between 0.35 and 0.85 per unit.