Variability Assessment of Solar Irradiance for the Safe Grid Integration of Solar Photovoltaic Power Plants

The output power of a Solar Photovoltaic (SPV) plant depends mainly on the solar irradiance on the photovoltaic (PV) modules. Therefore, short-term variations in solar irradiance cause variations in the output power of solar power plants, making solar photovoltaic grid integration unstable. Solar irradiance variations mainly occur due to the weather conditions of a given location, especially the movement of clouds and seasonal effects. Consequently, assessing the variability of solar irradiance over the course of a year is essential to identify the extent of these variations. Geographical dispersion and cloud enhancement are two important factors affecting output power variations in a PV plant. Geographical dispersion reduces such variations, while cloud enhancement increases them. This study utilizes two ground station-based solar Global Horizontal Irradiance (GHI) datasets to assess the viability of solar irradiance in the Chittagong division of Bangladesh. The analysis reveals a significant number of days with high short-term solar irradiance variation. In addition to solar irradiance, the frequency and voltage at the interconnection point are important for safe grid integration. It was observed that the grid frequency exceeded the range specified by the International Electrotechnical Commission (IEC), but remained within the grid code range of Bangladesh. Grid voltage variation at the interconnection substation was found to be within the standard range during the daytime, but low voltage was observed at the grid level during the rest period. Therefore, it is crucial to implement necessary preventive measures to reduce short-term variations for the safe grid integration of large-scale variable SPV plants.