The Latest Update of JMA Numerical Weather Prediction Models and its Solar Power Forecasting Errors

High penetration of photovoltaic power systems has been accelerated in the Japanese islands. Needs of both intraday and several days-ahead forecasts that are calculated from a numerical weather prediction model (NWP) have been required to make safe control of electric power systems. Since 5 December 2017, the Japan Meteorological Agency (JMA) started to provide the solar irradiance forecasts from operational NWPs for research and/or commercial areas. This paper describes the specification on JMA operational NWPs (global spectral model (GSM), meso-scale model (MSM) and local forecast model (LFM), respectively). MSM and LFM have been updated from a conventional non-hydrostatic model (NHM), “JMA-NHM”, to a new NHM “asuca” after 28 February 2017 for the MSM and 29 January 2015 for the LFM, respectively. Physical processes (including cloud-radiation process) in GSM were also updated after March 2016. This study showed the latest validation results of intraday ahead and several-days ahead solar forecasts from the GSM, MSM and LFM during the four years period from 2014 to 2017. Daily-based validation results for the GSM suggested that positive biases had been found compared with surface solar irradiance observation as well as the conventional GSM. Seasonal variations in biases have been remained in the MSM and LFM. LFM forecasts are improved for a coastal area under cloudy conditions after the update to the new model, asuca.