The most pressing concerns prioritize sustainability by addressing local pollution issues (including noise and air quality) and encouraging affordability through strategies that promote independence from fluctuations in fossil fuel costs, increasing production from renewables-based energy systems. For remote and off-grid areas, characterized by a mix of renewable energy sources, energy storage, and conventional generators that meet local energy demands, the absence of a backbone network poses additional technical challenges to this change in paradigm. Optimized Energy Management Systems (EMS) play a pivotal role in enhancing such isolated systems' efficiency, reliability, and sustainability. This paper presents a mathematical model for an optimized energy management system and the compelling techno-economic advantages of using it on a real photovoltaic, battery, and diesel generator hybrid power system located on Bora Bora, an island in the Pacific Ocean. Based on real historical data from the island power system operation, the analysis elaborates on fuel consumption reduction and generation spinning reserve margin based on the N-1 criteria. The paper further describes the impact of battery energy storage systems on spinning reserve management.