Estimation of Distant Cloud Cover by All-sky Image Data for Forecasting Amount of Solar Energy for Short Periods

Abstract

We estimated the distant cloud cover by the all-sky image data for forecasting amount of solar energy for short periods. It is confirmed that the time variation of estimated cloud cover is leading and having similar shape to the observed solar radiation. The main result in this study is as follows. (1) According to the image processing results of the cloud, the JPEG data almost similar to RAW data. Therefore, JPEG data file is small memory capacity, high resolution and it is superior as image data collection file format. (2)The ceilometer observes the cloud cover in π/3 rad around the zenith. To the observed solar radiation, the time variation of estimated cloud cover is similar, but also lagged. (3)We presented the estimating method of distant cloud cover by using saturation level of the all-sky cloud image. To the observed solar radiation, the time variation of estimated-distant cloud cover is similar and leading for several ten minutes from several minute. (4)The data to use for an estimate of distant cloud cover is obtained by all-sky image camera with the GPS timer. Therefore, the presented method will be feasible easily.