Electricity grids across the nation are undergoing a rapid transition. The principal contributor to this transition is the increased deployment of renewable energy resources by utilities, driven in part by declining costs of these resources relative to conventional, fossil-fired resources. A second factor contributing to the current grid transition is increased adoption of distributed energy resources (DER) by customers. This trend is driven by customers who see value in DER, which provide them with choice in their energy source and the ability to proactively manage their energy use. Effective integration of renewable resources into electricity supplies and grids is the central challenge of our industry, both from a technical and from an economic point of view.