  The attainment of carbon neutrality requires a research agenda that addresses
the technical and economic challenges that will be encountered as we progress
toward 100% renewable electricity generation. Increasing proportions of
variable renewable energy (VRE) sources (such as wind turbines and photovoltaic
systems) render the supply-and-demand balance of VRE-dominated power grids
difficult. The operational characteristics and effects of VRE inverters also
require attention. Here, we examine the implications of the paradigm shift to
carbon neutrality and summarize the associated research challenges in terms of
system planning, operation, and sta-bility, and the need for energy storage
integration, demand-side participation, distributed con-trol and estimation,
and energy sector coupling. We also highlight the existing literature gaps, and
our recent studies that can fill in the gaps, thereby facilitating the
improvement of grid op-eration and estimation. The numerical results of
comparative case studies are also provided on the operational stability and
economics of power grids with a high level of VRE sources, assist-ing
stakeholders in establishing specific roadmaps and making relevant decisions.
