Active Management of Photovoltaic System Variability with Power Electronics

Grid-connected photovoltaic (PV) energy systems present a variable power source. They are often treated as 'negative load,' especially for small systems, and require grid reserve margins and management resources to address their stochastic operation. However, inverters linked to PV energy systems probably represent the fastest resource on the grid, able to adjust operation on a cycle-by-cycle basis. This work reviews and quantifies PV variability, with emphasis on fast time scales. Operating needs if batteries are used to manage variability are presented. A reference case establishes the rates of change and storage needs in megawatt-scale installations. Alternative power electronics operating strategies are explored to mitigate variability directly at the source. Variability measures based on a time-window standard deviation lead to fast adaptive strategies. Controls that trade off energy production against variability are presented. Measured data are used to determine and compare performance expectations among several different control methods. Results, validated with scaled experiments, show that fast variability can decrease by about an order of magnitude given the right control strategy, implying battery capacity reduction of about 5× compared to systems in which batteries manage variation. System-level economics strongly favor large variability reduction linked to modest energy reduction.