The role of state-of-charge management in optimal techno-economic battery energy storage sizing for off-grid residential photovoltaic systems

With increased photovoltaic (PV) penetration in residential areas, an off-grid PV system is a sustainable solution to meet the zero net emissions goal by 2050. However, an off-grid PV system has a significant technical issue: low power supply reliability. Typically, battery energy storage (BES) is necessary to overcome the technical issues associated with PV systems. Conventionally, BES is operated to maintain a power balance between generation and load. However, techno-economic feasibility is a crucial aspect of BES adoption. Although BES can effectively support off-grid PV systems, it may not be available when its state-of-charge (SoC) reaches the minimum allowable limit, creating power supply failures (outages). Therefore, this study proposes, for the first time, a BES power control strategy that collaborates with SoC management to improve the reliability of an off-grid residential PV-BES system. A simulation study is performed using a residential load profile from the urban area of Bangkok, Thailand, obtained from the Metropolitan Electricity Authority (MEA). A comparative study is conducted to compare the proposed strategy's performance with that of the conventional control strategy. Following the comparative study, the role of SoC management in BES sizing is quantitatively illustrated. Moreover, the impacts of SoC management parameter setting (i.e., SoC restoration threshold and maximum SoC restoration power) are evaluated using techno-economic performance indicators. The simulation results reveal that BES power management with SoC management could reduce BES capacity and levelized cost of energy (LCOE) by 28% and 26.28% compared with the conventional strategy.