Testing and Diagnosing the Ability of the Bureau of Meteorology’s Numerical Weather Prediction Systems to Support Prediction of Solar Energy Production

The ability of the Australian Bureau of Meteorology's numerical weather prediction (NWP) systems to predict solar exposure (or insolation) was tested, with the aim of predicting large-scale solar energy several days in advance. The bureau's Limited Area Prediction System (LAPS) and Mesoscale Assimilation model (MALAPS) were examined for the 2008 calendar year. Comparisons were made with estimates of solar exposure obtained from satellites for the whole Australian continent, as well as site-based exposure observations taken at eight locations across Australia. Monthly-averaged forecast solar exposure over Australia showed good agreement with satellite estimates; the day-to-day exposure values showed some consistent biases, however. Differences in forecast solar exposure were attributed to incorrect representation of convective cloud in the tropics during summer as well as clouds formed by orographic lifting over mountainous areas in southeastern Australia. Comparison with site-based exposure observations was conducted on a daily and hourly basis. The site-based exposure measurements were consistent with the findings from the analysis against satellite data. Hourly analysis at selected sites confirmed that models predicted the solar exposure accurately through low-level clouds (e. g., cumulus), provided that the forecast cloud coverage was accurate. The NWP models struggle to predict solar exposure through middle and high clouds formed by ice crystals (e. g., altocumulus). Sites located in central Australia showed that the monthly-averaged errors in daily solar exposure forecast by the NWP systems were within 5%-10%, up to two days in advance. These errors increased to 20%-30% in the tropics and coastal areas.