Intra-hour forecasting with a total sky imager at the UC San Diego solar energy testbed |
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| Authors: | Chi Wai Chow Bryan Urquhart Matthew Lave Anthony Dominguez Jan Kleissl Janet Shields Byron Washom |
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| Affiliation: | aDepartment of Mechanical and Aerospace Engineering, University of California, San Diego, United States;bMarine Physical Laboratory, Scripps Institution of Oceanography, University of California, San Diego, United States;cStrategic Energy Initiatives, University of California, San Diego, United States |
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| Abstract: | A method for intra-hour, sub-kilometer cloud forecasting and irradiance nowcasting using a ground-based sky imager at the University of California, San Diego is presented. Sky images taken every 30 s were processed to determine sky cover using a clear sky library and sunshine parameter. From a two-dimensional cloud map generated from coordinate-transformed sky cover, cloud shadows at the surface were estimated. Limited validation on four partly cloudy days showed that (binary) cloud conditions were correctly nowcast 70% of the time for a network of six pyranometer ground stations spread out over an area of 2 km2. Cloud motion vectors were generated by cross-correlating two consecutive sky images. Cloud locations up to 5 min ahead were forecasted by advection of the two-dimensional cloud map. Cloud forecast error increased with increasing forecast horizon due to high cloud cover variability over the coastal site. |
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| Keywords: | Sky imager Red blue ratio Cloud forecast Intra-hour forecast Solar irradiance |
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