Comparative study on different models for estimation of direct normal irradiance (DNI) over Egypt atmosphere

The results obtained by using seven-parameterization broadband models to estimate Direct Normal Irradiance (DNI) along with two spectral models for four sites in Egypt atmosphere were compared with ground DNI measurements. Some statistical indicators (MBE, RMSE and R2) have been used to measure the performance of the used models. MBE for all dataset is <1% to both spectral models (SPCTRAL2, SMARTS2) and broadband models (MLWT1, MLWT2 and REST) while is equal to 1.2% to YANG model. However, RMSE are around 2% for spectral models and 3% to the broadband models. The error in prediction of DNI to such models is below experimental errors a part from the big number of observations. On the other hand, Louche, Dogniaux and Rodgers models provide relatively bad performance, RMSE are at most cases >4%. Determination coefficient (R2) results to all models are near 1.0. If we excluded spectral models, the broadband models MLWT1, MLWT2 and REST along with YANG models provide the best performance in all tests, therefore, those models can be used in Egypt atmosphere.