Comparison of numerical weather prediction solar irradiance forecasts in the US, Canada and Europe

• NWP irradiance models are evaluated at 34 sites in Canada, Europe, and the US.
• Global NWP models tend to outperform mesoscale models in all locations tested.
• The skill of the best forecast models is ∼50% when compared to persistence.

This article combines and discusses three independent validations of global horizontal irradiance (GHI) multi-day forecast models that were conducted in the US, Canada and Europe. All forecast models are based directly or indirectly on numerical weather prediction (NWP). Two models are common to the three validation efforts – the ECMWF global model and the GFS-driven WRF mesoscale model – and allow general observations: (1) the GFS-based WRF- model forecasts do not perform as well as global forecast-based approaches such as ECMWF and (2) the simple averaging of models’ output tends to perform better than individual models.