An energy storage system includes a photovoltaic energy field, a stationary energy storage device, an energy converter, and a controller. The photovoltaic energy field converts solar energy into electrical energy and charges the stationary energy storage device with the electrical energy. The energy converter converts the electrical energy stored in the stationary energy storage device into AC power at a discharge rate and supplies a campus with the AC power at the discharge rate. The controller predicts a required load of the campus and an electrical generation of the photovoltaic energy field across a time horizon and optimizes a cost function subject to a set of constraints to determine a discharge rate of the AC power to achieve a desired power factor. At least one of the set of constraints applied to the cost function ensures that the energy converter can convert the electrical energy stored in the stationary energy storage device into AC power having the determined power factor and discharge rate.