Assessment of battery energy storage systems for reliable power supply on Uganda’s electricity grid

Abstract

Uganda’s grid still faces significant reliability challenges, with frequent prolonged outages at times lasting up to 15 hours, far beyond the 4-hour target. While several remedies have been deployed to combat reliability like solar energy integration and infrastructure upgrades, these interventions also face their own challenges. The intermittency limits solar energy’s effectiveness and infrastructure upgrades suffer from vandalism plus a constrained government budget. As a solution, this study explored deploying a utility-scale battery energy storage system to improve network reliability by smoothing power supply during outages. Supply-demand curves of selected feeders were analyzed to identify the critical outage times for battery discharge, focusing on the distribution network. The study identified vital feeders such as Mutundwe-Masaka Central 33 kV, Masaka Central- Mitala Maria 1 33 kV, among others where the battery energy storage system deployment would yield the most significant impact towards network reliability improvement. Using data of 3 years for load flow analysis, this thorough process helped determine the optimal size and location of the battery energy storage system using a particle swarm optimization algorithm. The algorithm focused on reducing the cost of energy not served and improving key reliability indices like system average interruption duration index, system average interruption frequency index, loss of load probability and energy not served. The optimal placement was found at buses with the highest loss reduction along critical feeders, which resulted in reduced reliability interruption indices and a significant reduction in the cost of energy not served. The optimized reliability indices from MATLAB were validated against those from DIgSILENT Power Factory using the IEEE 14-bus system as a bench mark, showing acceptable error margins. < 10%. A cost benefit analysis comparing the deployment of a battery energy storage system and a feeder upgrade option showed that while both strategies were viable; the financial analysis portrayed the battery energy storage system having a slightly shorter payback period of 7.9 years, IRR-7%, ROI-2.73% compared to 8.06 years, IRR-5%, ROI-2.5% for the feeder upgrade option. Hence the battery energy storage system offered a more profitable investment which would be recovered in a shorter period, making it a more cost-effective solution in the long run. Consequently, the economic analysis which shows the overall socio-economic benefit of the society as a whole is expected due to increased production through improved power reliability.