Systems and methods for controlling a renewable energy system based on actual reactive power capability of the renewable energy system are provided. The reactive power output of the renewable energy system can be controlled based at least in part on an initial reactive power limit. The initial reactive power limit can be determined based on rated reactive power for the power generation units in the renewable energy system. When a difference between a reactive power demand and the actual reactive power production of the renewable energy system fall outside a threshold, the initial reactive power limit can be adjusted to a corrected reactive power limit that is closer to the actual reactive power capability of the renewable energy system.