Comparison of solar spectral irradiance measurements with pyrheliometer total solar irradiance data.

Accurate solar irradiance measurements are critical for optimising solar energy systems, understanding atmospheric processes, and advancing climate research. Pyrheliometers, which provide Direct Normal Irradiance (DNI) measurements over a broad spectral range, are widely used due to their simplicity, cost-effectiveness, and ease of deployment. However, they cannot provide detailed spectral information, which limits their application in advanced studies requiring wavelength-specific insights. In contrast, the Bi-Tec Sensor (BTS) spectroradiometer system measures spectral solar irradiance from 300 nm to 2150 nm with high spectral resolution, covering almost ~96.5% of the solar spectrum, and is traceable to the International System of Units (SI). This detailed spectral data enables in-depth studies of solar energy distribution across different wavelengths but excludes approximately 3.5% of the total solar spectrum in the infrared region (2150–5000 nm).

To overcome this limitation and enable full-spectrum comparisons, this study utilized libradtran, an atmospheric radiative transfer model, to extend the BTS spectral range, whereas due to the requirement of computational resources and expertise, A comparatively simpler functional model was developed based on libradtran simulations, focusing on critical parameters such as solar zenith angle, water vapor, and aerosol properties. This function closely matched the results from libradtran and achieved high precision with a mean value of 96.52% and a standard deviation of  0.20% that can be used to accurately extend the BTS measurements to cover the full spectrum. The comparison between pyrheliometer and BTS spectroradiometer yields a mean ratio of 0.9897 with a standard deviation of 0.0149, achieving a good correlation with pyrheliometer data while maintaining precise spectral details.

The results confirm that BTS spectroradiometers, combined with the spectral extension model, provide an effective and detailed alternative for solar irradiance monitoring. Unlike pyrheliometers, BTS instruments deliver wavelength-specific data crucial for advanced solar energy studies and atmospheric research. Moreover, integrating the extension model into BTS systems simplifies data processing, making high-quality measurements accessible for non-expert users and resource-limited regions.

This approach bridges the gap between the spectral detail of BTS systems and the broad range of pyrheliometers, offering a reliable solution for comprehensive solar irradiance measurements. These findings mark a step forward in solar energy research and environmental monitoring, with the potential to address global data gaps in cost-effective and scalable ways.