A photovoltaic energy system includes a photovoltaic field configured to convert solar energy into electrical energy, cloud detectors configured to detect a cloud approaching the photovoltaic field, and a controller. The controller uses the cloud detectors to predict a disturbance in the electric power output of the photovoltaic energy system. The controller determines a time at which the disturbance is expected to occur and determines an amount by which the electric power output is expected to decrease. The controller can preemptively adjust the electric power output of the photovoltaic energy system in accordance with a predetermined ramp rate.