Abstract
The South African Weather Service (SAWS) manages an in situ solar irradiance radiometric network of 13 stations and a very dense sunshine recording network, located in all six macroclimate zones of South Africa. A sparsely distributed radiometric network over a landscape with dynamic climate and weather shifts is inadequate for solar energy studies and applications. Therefore, there is a need to develop mathematical models to estimate solar irradiation for a multitude of diverse climates. In this study, the annual regression coefficients, a and b, of the Ångström–Prescott (AP) model, which can be used to estimate global horizontal irradiance (GHI) from observed sunshine hours, were calibrated and validated with observed station data. The AP regression coefficients were calibrated and validated for each of the six macroclimate zones of South Africa using the observation data that span 2013 to 2019. The predictive effectiveness of the calibrated AP model coefficients was evaluated by comparing estimated and observed daily GHI. The maximum annual relative Mean Bias Error (rMBE) was 0.371%, relative Mean Absolute Error (rMAE) was 0.745%, relative Root Mean Square Error (rRMSE) was 0.910%, and the worst-case correlation coefficient (R2) was 0.910. The statistical validation metrics results show that there is a strong correlation and linear relation between observed and estimated GHI values. The AP model coefficients calculated in this study can be used with quantitative confidence in estimating daily GHI data at locations in South Africa where daily observation sunshine duration data are available.
Highlights
Solar radiation data are important because they are required in many research fields such as meteorology, agriculture, hydrology, ecology, and environment [1,2,3,4]
South African Weather Services (SAWS) re-established a global horizontal irradiance (GHI) radiometric network with 13 solar radiometric stations located in all 6 macroclimatic zones of
The observed 1-min GHI data used in this study were collected from 8 SAWS solar radiometric stations during the periods shown in Table 1, which shows the geographical locations and the climatic zones in which the stations are located
Summary
Solar radiation data are important because they are required in many research fields such as meteorology, agriculture, hydrology, ecology, and environment [1,2,3,4]. South African Weather Services (SAWS) re-established a global horizontal irradiance (GHI) radiometric network with 13 solar radiometric stations located in all 6 macroclimatic zones of. SAWS manage a very dense sunshine duration recording network over South Africa to the extent that sunshine duration data have been continuously measured for several years [8]. To compensate for this, reliable measurements taken from a sparse network are needed to develop and validate empirical models that can be used to estimate and forecast the availability of solar energy at other locations [10]. The main objective of this study is to calibrate the Ångström–Prescott (AP) model regression coefficients a and b that could be used to estimate GHI in different climatic zones of South Africa, increasing the density of available solar radiation data in the country
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