Optimal sizing of battery storage for stand-alone hybrid (photo-voltaic + diesel) power systems

An important element of hybrid photo‐ voltaic(PV) + diesel sytem is battery storage. Size of battery storage plays a role in optimum operation of the hybrid system. Emphasis needs to be placed on this issue. In this perspective, hourly solar radiation data, for the period 1986–93 recorded at Dhahran, Saudi Arabia, have been analyzed to investigate the optimum size of battery storage capacity for hybrid (PV + diesel) power systems. Various sizing configurations have been simulated. The monthly average daily values of solar global radiation range from 3.61 to 7.96 kWh/m2. As a case study, hybrid systems considered in the present analysis consist of 225 m2 PV array area (panels/modules) supplemented with battery storage unit and diesel backup generators (to meet the load requirements of a typical residential building with annual electrical energy demand of 35,200 kWh). The monthly average energy generated from the aforementioned hybrid system for different scenarios has been presented. More importantly, the study explores the influence of variation of battery storage capacity on hybrid power generation. The results exhibit a trade-off between size of the storage capacity and diesel power to be generated to cope with annual load distribution. Concurrently, the energy to be generated from the diesel generator and the number of operational hours of the diesel system to meet the load demand have been also addressed. The study shows that for optimum operation of diesel system, storage capacity equivalent to 12–18 h of maximum monthly average hourly demand need to be used. It has been found that in the absence of battery bank, ∼58% of the load needs to be provided by the diesel system. However, use of 12 h of battery storage (autonomy) reduces diesel energy generation by ∼49% and the number of hours of operation of the diesel system get reduced by about ∼82%. The findings of this study can be employed as a tool for sizing of battery storage for PV/diesel systems for other regions having climates similar to the location considered in the study.