Utilization of Low Cost, Sky-Imaging Technology for Irradiance Forecasting of Distributed Solar Generation

This paper presents an intra-hour cloud forecasting methodology for distributed solar generation by predicting irradiance changes in five minute intervals throughout the day. This approach is designed to assist in the creation of a low-cost, sky imaging system for experimental field-testing. The image processing techniques are presented in the following sections: Forecasting Inputs Required, Masking, Segmentation, Filtering & Binary Conversion, True North Orientation, Optical Flow & Cloud Motion, and Ray Tracing & Irradiance Predictions. Sky/Cloud images were acquired on site at the National Renewable Energy Laboratory (NREL) and were processed by the above procedure for five individual days under a variety of cloud conditions. Lastly, the irradiance change predictions were validated using NREL's direct solar irradiance measurements* for comparison.