Design and sizing of short term energy storage for a PV system

Power generation in a PV system is defined by its V-I, and V-P characteristics. These curves are function of instantaneous solar irradiation and cell temperature; and outline the maximum power that the system can supply at any given moment. As a consequence of this PV systems lack overload capacity, which is common in traditional rotating generators; and therefore, PV systems cannot supply short term or transient load demands. To solve this issue two approaches can be taken; one is to constantly operate the PV system below its maximum power level, which has the drawback of non-optimal energy harvesting. The other is integration of energy storage elements to the power conditioning system, which allows optimizing power generation, while adding overload capacity. In addition, this approach also allows smoothing out short term irradiation variations allowing the system to improve energy harvesting. Focusing on the second approach analysis of short term energy storage requirements in PV systems is performed in this paper. As a result, sizing guidelines and a design procedure for a supercapacitor based energy storage system are developed. In addition, effectiveness of the proposed method on improving PV generator performance is tested and verified through computer simulations.