Accuracy analysis of sun position calculation algorithms : ineichen and SPA

Abstract

Sun position calculation algorithms are widely used in solar tracker photovoltaic plants and softwares to design photovoltaic projects. The scientific community has several algorithms that compute the sun position, and they vary in accuracy, complexity and validity time. The accuracy analysis of the algorithms is important because the different applications require different levels of accuracy. In applications such as measuring instrument callibration, e.g., it is required high precision algorithms. This work presents a statistical analysis of the accuracy of two sun position algorithms: the algorithm proposed by Ineichen, which is used for PVSyst ® software, and the Solar Position Algorithm, taking into consideration both the standard deviation and the maximum errors, as well as quartiles and quantiles. The algorithm that has the highest accuracy is the SPA, where 99% of the samples have solar vector errors below 0.1187695°