Abstract
Rapidly increasing levels of variable inverter-based renewable energy sources(are quickly changing electric power systems and prompting questions abouthow the systems will be operated when renewable generation becomes thedominant technologies. In this article, we review the status of this shiftingparadigm in power systems throughout the world. We then review the implica-tions of this shift, focusing on the rising challenges, and we provide an over-view and technology-readiness classifications of some proposed mitigationstrategies. Finally, we highlight outstanding questions that will require solu-tions to reach these ultrahigh shares of variable inverter-based renewable energy sources.