Optimal Lithium-Ion Battery—Supercapacitor Energy Storage System Capacity for Off-Grid Intermittent Renewable Energy Mini-Grids

Deployment of off-grid intermittent renewable energy mini-grids (IREMGs) instead of fossil fuels for electricity generation positively contributes to reduction of greenhouse gas emissions. However, in off-grid IREMGs power supplied by renewable energy sources as well as demanded by loads fluctuates. These fluctuations accelerate aging of lithium-ion battery (LB) energy storage systems (ESSs) installed in such systems. This study focused on designing optimal LB and supercapacitor (Sc) ESS capacity for deployment in off-grid IREMGs. In this regard, an aging-based controller was utilised to design optimal LB-Sc hybrid ESS (HESS) and optimal LB single ESS (SESS) capacities for an off-grid IREMG. Data were collected from an existing off-grid IREMG system. Simulation results show that optimal LB-Sc HESS improves the annualised cost of the system (ACS) of the ESSs by 33.15% in relation to optimal LB SESS. Furthermore, LB daily utilisation fractions improve by 1.02% in LB-Sc HESS as compared to LB SESS. Also, the loss of power supply probability is less than the defined 5% in all simulations for both systems. Finally, the study recommends experimental validation of the performance results. It also recommends designing an overall optimal size of an off-grid IREMG using a similar controller to further improve the ACS.