Integrating high levels of variable renewable energy into electric power systems

As more variable renewable energy (VRE) such as wind and solar are integrated into electric power systems, technical challenges arise from the need to maintain the balance between load and generation at all timescales. This paper examines the challenges with integrating ultrahigh levels of VRE into electric power system, reviews a range of solutions to these challenges, and provides a description of several examples of ultra-high VRE systems that are in operation today.