Clear sky solar irradiance models derived through interdependent parameterization

This study introduces two parametric models for estimating solar irradiance under clear sky conditions. Unlike most existing parametric models, these new models are based on an interdependent integration of source spectral atmospheric transmittances. The integration is applied without approximating and without assuming a prescribed atmosphere. The approach ensures a high level of generality. It is grounded in spectral modelling, which encapsulates the physics of radiative transfer in the atmosphere. To investigate how the source spectral models influence the resulting broadband parametric models, each proposed model is derived from a distinct spectral model. This comparative analysis introduces an additional layer of novelty. The performance of the new models is benchmarked against two leading models for estimating solar irradiance components under clear sky conditions. Furthermore, the performance is evaluated in relation to a widely used and readily available estimation model. Results show that the proposed models achieve high accuracy, comparable to the reference models. However, the new models stand out due to their simplicity. Their equations are significantly less complex while still delivering precise results. This combination of high accuracy and ease of use makes the proposed models particularly suited as practical engineering tools.