Variability analysis of wind and solar energy for optimal power system integration

The development of renewable energy has made a significant contribution to the mitigation of global climate change and environmental pollution. In particular, the installed capacity of intermittent wind and solar power in the world has increased significantly in the past decade, and this growth is expected to be maintained in the future. Due to the intermittence and uncontrollability of wind and solar energy, the integration of wind and solar energy into power systems brings significant impacts on the operation and profit of power systems. This thesis focuses on exploring the wind and solar power variability and its impacts on power system integration. Chapter 2 proposes a new measure to assess the variability of wind power, solar power and mixed wind-solar at one site, and the variability of interconnected wind and solar power from different sites in both the time domain and frequency domain. In the time domain, the measure mainly includes inter-annual variation, smoothness coefficient and correlation coefficient; while in the frequency domain, it mainly includes frequency spectrum analysis, fluctuation rate, and cumulative energy distribution index. The implications of the proposed measure are explored to facilitate power system integration. Without loss of generality, enormous wind and solar data collected at various locations and spanning a long period are employed to assess the variability of wind and solar power, which are taken from National Renewable Energy Laboratory (NREL) databases. The measurement results indicate that the variability of solar power highly depends on the latitude of its geographic location; the interconnection of wind power can effectively reduce the variability of wind power in the high-frequency range; the intermittent wind/solar power in the time domain can be treated as a Quasi-Time-Invariant (QTI) source of power harmonics in the frequency domain. Based on the proposed variability measure, Chapter 3 investigates the impacts of the w