A comparison of one-minute probability density distributions of global horizontal solar irradiance conditioned to the optical air mass and hourly averages in different climate zones

• High-frequency solar irradiance distributions are analyzed in different climates.
• Distributions are conditioned to hourly average values and air mass.
• Local distribution and type of clouds influence one-minute irradiance distributions.
• Local clear sky conditions highly influence irradiance distributions.

In this study, one-minute global horizontal solar irradiance distributions conditioned to the optical air mass, m, and hourly average of global horizontal solar irradiance were studied at sites in five different climate regions. For this purpose, the clearness index, kt, which accounts for the atmospheric transmittance, has been used. These distributions are fitted by functions based on the Boltzmann statistic.The one-minute distributions of kt conditioned to m found are either unimodal or bimodal, depending on the location and the value of m. These distributions are different for each of the locations analyzed. The one-minute distributions of kt conditioned to their hourly value (kth) are unimodal, and are in turn different at each of the locations analyzed. The one-minute kt distributions conditioned to both m and kth analyzed are also unimodal. These distributions were found to be the same (Kolmogorov–Smirnov test, p > 0.05) at different sites in 5% of the cases compared, the majority of which show very cloudy sky conditions and decrease monotonically at clearer-sky conditions. These results point to the importance of local distribution and type of clouds in one-minute solar irradiance distributions, and highlight the role of local atmospheric clear sky transparency in differentiating these distributions.