Sizing and Selection of Battery Energy Storage System for Time of Use Arbitrage in a Commercial Building in South Africa

This paper presents the optimization, sizing and selection of battery energy storage systems (BESS) for grid-connected solar PV systems in South Africa. BESS optimization was realized by minimizing the annual cost of BESS and then evaluating the savings in electricity cost when BESS is used for Time of Use (TOU) arbitrage. The study used power demand, energy consumption and energy cost data from a commercial building in South Africa with an already existing solar PV system but without BESS. An Objective Function to minimize the cost of BESS with its associated constraints was then formulated and solved in order to get the minimized annual cost of the BESS. The annual cost of BESS was used to determine the savings in electricity cost realized if BESS is used for TOU arbitrage value stream. It was found that the use of BESS does yield savings in electricity costs when BESS is used for TOU arbitrage with the degree of autonomy set at either three hours, two hours or five hours per day that is for morning peak, evening peak and both peaks combined, respectively. There was no saving realized when the degree of autonomy is set to 24 hours in the calculation of battery capacity. Lead-acid batteries presented the lowest BESS cost compared to Li-ion batteries. The results indicated that that BESS can be installed on grid-connected solar PV systems to take advantage of TOU arbitrage.