Reduction of solar photovoltaic system output variability with geographical aggregation

Abstract

Variable power outputs are one of the largest challenges facing the widespread adoption of renewable energy systems. The inherent variability of solar resources makes it challenging to integrate large amounts of solar energy into the electric grid. However, the weather factors that influence solar production are often local in nature. In this study, eleven solar photovoltaic systems with publicly available historical data were identified for analysis. The systems are located within a circle with a diameter of approximately 130 km. The historical power output data for each system were acquired, and quality control measures were applied. A comparison is made between the variability of the time-varying power output from individual systems compared to the variability of the aggregated output of the eleven systems combined. Next, the effect of increasing the geographical spread of the aggregated systems is investigated. This is done by comparing the variability of the aggregated time-varying power output from closely-spaced systems against the variability of the aggregated time-varying power output from systems spread out over a large geographical area. Next, the correlations between the outputs from each of the individual systems are explored. The data show that the correlation decreases by approximately 0.1 for each 80 km of separation distance. Finally, the historical solar output data is used to define the “expected output”, and the deviation from this expected output is compared for individual systems and various sets of aggregated systems. The four aggregated systems located far apart are 31% more likely to have a combined output that is close to their expected output, defined as having a normalized power output deviation less than or equal to 0.2 kW/kW. Furthermore, the four aggregated systems located far apart are 54% less likely to have a combined output that is significantly different from their expected output, defined as having a normalized power output deviation greater than or equal to 0.4 kW/kW.