Estimation of Confidence Intervals of Global Horizontal Irradiance Obtained from a Weather Prediction Model

In this study, we investigated forecast errors of the global horizontal irradiance (GHI) of the numerical weather prediction model developed by the Japan meteorological Agency (JMA) based on the surface-observed data at the JMA stations. We found seasonal variations of forecast errors of the GHI values. From the information of forecast errors, we tried to estimate the confidence intervals of the hourly GHI values. We also compared with results in both for a pinpoint forecast and relatively wide-area forecast. About 68% of the reduction of confidence intervals for the wide-area forecasts compared with the results for the pinpoint forecast is confirmed.