The growing integration of variable renewable energy sources (VRES) is steadily diminishing the capacity of conventional power plants to uphold grid stability. Consequently, alternative assets such as storage and control systems are essential to bridge the gap and uphold system stability. This study explores the impact of increasing vRES on Pantelleria island's off-grid power system. Through simulation and the integration of up and down reserves into the model, the research aims to comprehend the effects of down reserve requirements, starting from the formalization of the model variables and constraints. The model of the power system and the optimization problem is addressed using PYPSA, or “Python for Power System Analysis”, an open-source software tool for the modeling and analysis of energy systems.