Estimation of total solar irradiance on vertical surfaces for all-sky conditions adaptive to coastland surfaces

This paper presents an algorithm for estimating three components of total solar irradiance on vertical surfaces in coastlands, including direct, sky diffuse and ground reflection irradiance. The algorithm aims to cover changeable weather and ground surfaces in coastlands. For this purpose, Sanya located on Hainan Island of China has been selected as a representative city. Initially, a dataset of horizontal irradiance measured from 2005 to 2014 has been used to statistically analyze the frequency distribution of sky conditions, resulting in a classification of coastal weather into 4 categories. Afterward, using the vertical irradiance data collected by a novel measurement system, the performance of 15 sky diffuse irradiance models has been compared under coastal weather types. As a result, an algorithm for vertical sky diffuse irradiance adapted to all-sky conditions (Alg-s) is developed. Concurrently, regression models of reflection irradiance from sea and beach on vertical surfaces (Mr) are established using correlation analysis and the least squares method. Combining the above two sub-models, an all-sky conditions total solar irradiance model on vertical surfaces in coastlands is developed. Compared to previous studies, the new model improves the prediction accuracy of total vertical irradiance, with RRMSE and MAPE reduced by 14.2 % and 10.6 % respectively.