Transitioning to net-zero emission energy systems is currently on the agenda in various countries to tackle climate change, a global challenge that threatens the lives of future generations. To fully decarbonize energy systems, a radical paradigm shift through deep integration of renewable resources supported by storage technologies is envisaged in multisector energy systems, especially in the electric power sector. As a result, inverter-based resources (IBRs), mainly wind, photovoltaics (PVs), and batteries, will dominate the electric power grids. This transition involves phasing out conventional fossil fuel-based plants and decommissioning associated synchronous machines, the grid’s primary reactive power sources. The ongoing removal of these primary reactive power sources introduces critical operational challenges that could compromise the reliability and stability of the grid. The inverters used for integrating IBRs can deliver diverse crucial ancillary services, particularly reactive power support. However, the potential of IBRs to address reactive power requirements in future decarbonized grids still needs to be fully addressed. The existing literature lacks a comprehensive approach to coordinating and harmonizing the efforts of various stakeholders and drivers to leverage the reactive power capability of IBRs. To bridge this gap, this article thoroughly reviews the reactive power implications for future grids with a considerable share of primary IBRs, comprising distributed and large-scale wind, PV and battery storage plants. This article starts with a summary of the concept, measurement methods, and importance of reactive power for voltage control and how it is managed today utilizing conventional sources. The reactive power transition from current to future grids within the context of the greater energy transition is then discussed by shedding light on its diverse aspects. Afterward, the reactive capability curve of each IBR is derived from the equivalent circuits and equations. Various grid codes and integration requirements of IBRs are then analyzed from a reactive power support viewpoint. Also, the concepts related to reactive power and voltage control comprising control extents, modes, and techniques are elaborated. Finally, recommendations are provided to set the stage for leveraging the capabilities of IBRs to address the reactive power requirements of future grids. The presented material sheds light on the pivotal role of reactive power in future grids and provides a roadmap for policymakers, utilities, and grid operators to manage a seamless transition to a decarbonized grid.
