Implications of short-term renewable energy resource intermittency in long-term power system planning

Power system operational uncertainties of load fluctuation, and unplanned outage of generating units, or lines are normally handled by reserve generation or transmission capacity. The output of conventional generators is quite controllable, and load variation is predictable within a certain confidence limit. On the other hand, output of variable renewable generators is random and uncontrollable. Large-scale integration of these resources introduces additional uncertainty to an existing system. This drastic change in generation paradigm underscores the need for additional flexible capacity to maintain reliable system operation. Conventional long-term planning studies tend to overestimate system's ability to integrate renewable energy and underestimate flexibility requirement due to inherent modeling limitations. Mathematical models that are used in these planning exercises adopt simplified spatial and temporal resolution and often neglect real system operation. Therefore, there is an urgent need to develop new planning strategies to reflect short-term renewable energy resource intermittency in long-term decision making. In this article, the implication of RE intermittency in system operation and also their impact on long-term planning is discussed. Recent planning approaches from literature which aim to address these issues, have been highlighted. A critical discussion regarding their usefulness is also presented.