Classifying ground-measured 1 minute temporal variability within hourly intervals for direct normal irradiances

Abstract

Variability of solar surface irradiances in the 1 minute range is of interest especially for solar energy applications. Eight variability classes are defined for the 1 minute resolved direct normal irradiance (DNI) variability inside an hour. They combine high, medium, and low irradiance conditions with small, medium, and large scale variations from one minute to the next minute.A reference data base of 333 individual hours with ground-based 1 minute DNI observations was created by expert review from one year of observations at the BSRN station in Carpentras, France. Each variability class is represented by 16 to 63 members.Variability indices as previously published or newly suggested are used as classifiers to detect the class members automatically. Up to 77 % of all class members are identified correctly by this automatic scheme. The variability classification method allows the comparison of different project sites in a statistical and automatic manner to quantify short-term variability impacts on solar power production.

Keywords

• variability
• global horizontal irradiance
• direct irradiance
• automatic classification
• ground-based observations