Statistical Characterization of Solar Irradiance Variability and Its Effect on Step Voltage Regulators

This paper examines the acceptability of two variability metrics, i.e., universal variability index (UVI) and natural variability index (NVI) for quantifying the variation of solar irradiance and PV power output under multiple timescales. Statistical characterization of irradiance ramp rate is investigated using high resolution irradiance measurement data of a PV plant over a considerably long period. The impact of solar irradiance and PV power variability on the tap change operations of step voltage regulators (SVR) is also analyzed. It demonstrates both UVI and NVI can be used as quantitative metrics for irradiance variation. A strong linear relationship is observed between UVI and NVI of irradiance ramp rate. Compared with UVI, NVI is more easily to be implemented due to its direct derivation from the statistical nature of the measured irradiance and PV power output. The results indicate that NVI has the potential to estimate the number of tap change operations of SVR by considering the operational strategies of SVR and proper selection of timescales.