Probability prediction of solar irradiance in the tropic using ensemble forecasting

As photovoltaic (PV) power generation systems become more widespread, the instability of electric power grids with PV connection is becoming an issue. For appropriate management of the grids, probability prediction of solar irradiance is proposed. The lagged average forecasting method is used for ensemble forecasting. The 72 h ahead forecasting of solar irradiance is operated in Thailand once a day, and it contains intraday, next-day, and 2-day ahead forecasts. Ensemble forecasting has three ensemble members. The accuracy of intraday forecasting is higher than that of the other members, and it is employed as the most probable value of the forecast. The relation between spreads and forecasting errors is analyzed. From the result, the confidence intervals of the predictions are derived for an arbitrary confidence level. The probability prediction is performed with the most probable value and the confidence intervals. The interval changes its width due to spread changes and captures the observation in it.