Evaluation of 24-Hours forecasts of global solar irradiation from IFS, GFS and McClear models

The knowledge of the global solar irradiation available at ground level is a key element in many fields, environment, agriculture, architecture, health, and photovoltaic power generation where the knowledge of the amount of radiation available on the earth’s surface a few hours in advance allows investment decision-making, electricity grid management, and better management of the energy produced. Different methods are used to forecast global solar radiation. The objective of this study is to validate three different models for forecasting solar radiation. This paper reports the validation results of the hourly forecasts of the global horizontal irradiation (GHI) of two numerical prediction models: GFS (Global Forecasting System) and IFS (Integrated forecasting System) which are global numerical weather prediction models. As clear sky situations are very frequent in Morocco, the performance of the clear sky model McClear was also evaluated. This model uses forecasts of aerosols, ozone and water vapor as inputs. The validation was done by comparing the 24-hours forecasts of these models with high-performances ground data from four meteorological stations installed in Morocco. The analysis is declined in two parts: an assessment for all skies types as well as for clear skies. In this case, the comparisons were made for automatically selected cloudless moments of all-skies pyranometric measurements. For all-sky conditions, the performances of the two IFS-based models are better than those obtained with the GFS model. In most cases, IFS surpasses GFS with a Mean Bias Error (MBE) ranging from 1.78 W/m2 and 26.19 W/m2 versus -1.96 W/m2 and 49.54 W/m2 for GFS, and a correlation coefficient (CC) between 0.93 and 0.98 for IFS versus 0.83 and 0.95 for GFS. For clear sky conditions, McClear+IFS exhibits the best performances outperforming GFS with an MBE ranging between 7.40 W/m2 and -18.25 W/m2 versus 32.16 W/m2 and -45.16 W/m2 for GFS. Generally, the validation results are satisfactory. The IFS and GFS models proved their ability to capture the temporal variability of GHI. The combination of the McClear and IFS models improved the clear sky forecasts for the whole stations, while a slight improvement was noticed for the all- sky forecasts. 0n the whole, the three models are reliable sources for solar radiation forecasting for Morocco.