Combinatorial optimization of a fuzzy logic-controlled grid connected photovoltaic with hybrid energy storage systems using time of use tariff

South Africa is facing challenges with limited electricity supply and frequent blackouts. To address this, the use of renewable energy sources like wind and solar has gained attention to meet the load demand. However, the intermittent nature of renewable sources requires the integration of various energy storage technologies to balance the demand-supply mismatch. A hybrid energy storage system (HESS) that combines different storage technologies, such as supercapacitors, pumped hydro storage, and battery energy storage is proposed to leverage the unique characteristics of each technology for improved grid stability management. Furthermore, the study aims to develop a mathematical model to optimize the daily operation of the HESS in a microgrid-connected renewable energy system. The proposed strategy employs a two-stage combinatorial system: an optimal system and a control system. Therefore, the focus of this paper is on the development of a universal rule-based fuzzy logic controller (FLC) as the control system, which responds to load demand fluctuations based on time-of-use and consumption rate. The FLC is designed to prioritise the use of renewable energy and efficiently manage the HESS to ensure adequate energy supply, while also prolonging the lifespan of the battery energy storage and supercapacitor by leveraging the unlimited charge/discharge rate of the pumped hydro storage and taking advantage of Eskom's Time-Of-Use tariff. The performance of the proposed FLC is analysed using a 3D surface viewer, which demonstrates the optimal utilization of renewable energy and the complementary operation of the different storage technologies. The developed control system can be applied to future microgrid-connected renewable energy systems with HESS, regardless of their component sizes or load demands. • A model for the optimal control of a grid connected photovoltaic with hybrid energy storage systems is developed. • The hybrid storage is composed of battery, pumped hydro and supercapacitor. • An optimal energy management controller is developed using fuzzy toolbox. • The controller maximizes the use of renewable energy to recharge the respective storages.