Assessment of Global Horizontal Irradiance Data Quality and Calibration Uncertainty in a Tropical Monsoon Region: A Case Study in Kamphaeng Phet, Thailand 10.32526/ennrj/25/20260133
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Abstract
Ground-based solar radiation data are useful for environmental studies and solar-energy assessment, especially in tropical monsoon regions where sky conditions change throughout the year. This study investigated the quality and variability of hourly global horizontal irradiance (GHI) measured at Kamphaeng Phet Rajabhat University, Thailand, from January to December 2025. GHI was measured using an SMP10-V thermopile pyranometer. The instrument recorded data every 5 s, and the data were later averaged into hourly values. The dataset was checked by separating daylight hours, assessing data availability, and applying preliminary physical range screening. Nighttime periods were not treated as missing data, and no gap filling was performed. During the study period, 4,420 daylight hourly records were expected. Of these, 4,355 records were available and passed the physical range screening, giving an overall daylight-data availability of 98.53%. The record-weighted annual mean hourly GHI was 404.63 W/m2. Monthly mean GHI ranged from 322.50 W/m2 in July to 474.36 W/m2 in March. The seasonal results showed that mean GHI was highest in summer and lowest in the rainy season. The rainy season also showed the highest relative variability because atmospheric conditions were more variable during this period. The pyranometer calibration certificate reported an expanded calibration uncertainty of 1.39% at k=2. These results provide a local reference for measured GHI characteristics and data-quality evaluation in a tropical monsoon environment.
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