The Performance Assessment of Six Global Horizontal Irradiance Clear Sky Models in Six Climatological Regions in South Africa

Brighton Mabasa,Sabata J Moloi,Henerica Tazvinga,Nosipho Zwane,Meena D Lysko

doi:10.3390/en14092583

Brighton Mabasa, Sabata J Moloi + Show 3 more

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https://doi.org/10.3390/en14092583

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Abstract

This study assesses the performance of six global horizontal irradiance (GHI) clear sky models, namely: Bird, Simple Solis, McClear, Ineichen–Perez, Haurwitz and Berger–Duffie. The assessment is performed by comparing 1-min model outputs to corresponding clear sky reference 1-min Baseline Surface Radiation Network quality controlled GHI data from 13 South African Weather Services radiometric stations. The data used in the study range from 2013 to 2019. The 13 reference stations are across the six macro climatological regions of South Africa. The aim of the study is to identify the overall best performing clear sky model for estimating minute GHI in South Africa. Clear sky days are detected using ERA5 reanalysis hourly data and the application of an additional 1-min automated detection algorithm. Metadata for the models’ inputs were sourced from station measurements, satellite platform observations, reanalysis and some were modelled. Statistical metrics relative Mean Bias Error (rMBE), relative Root Mean Square Error (rRMSE) and the coefficient of determination (R2) are used to categorize model performance. The results show that each of the models performed differently across the 13 stations and in different climatic regions. The Bird model was overall the best in all regions, with an rMBE of 1.87%, rRMSE of 4.11% and R2 of 0.998. The Bird model can therefore be used with quantitative confidence as a basis for solar energy applications when all the required model inputs are available.

Highlights

Clear sky models are used to estimate the amount of solar irradiance that reaches the Earth’s surface under cloudless atmospheres
Clear sky irradiance data are important for various applications such as solar radiation forecasting and the calculation of maximum possible output yield of solar photovoltaic systems [1,2,3,4,5,6,7,8,9], cloudiness index calculation [2,3,5,7] and data quality control [3,4,5,6,7,10]
Clear sky solar irradiance is used as the basis for deriving solar radiation estimates from satellite images [1,5,8,10], the calibration of sensors [3,4], the evaluation of cooling loads of commercial structures [1,4,5,8], the building of databases for testing radiation separation models [2,5], determining geographical areas where irradiance estimates are uncertain [4] and for the filling of missing historical data records [10]

Summary

Introduction

Clear sky models are used to estimate the amount of solar irradiance that reaches the Earth’s surface under cloudless atmospheres. Clear sky radiation model is an algorithm that is solved by providing inputs that describe the state of the cloudiness atmosphere at a specific location and time to output theoretical. There are no sensors to measure clear sky irradiance nor a universal model; the only way to generate clear sky irradiance data is by filtering in situ readings taken from pyranometers for periods when there are no clouds or by trying different models at different locations. Even though there are advanced methods to derive GHI data, ground monitoring using a pyranometer remains the most accurate way to collect data [11,12]

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