Perhaps the most basic of electricity sector rules, one that has operated for over a century, is that electricity must be generated at precisely the same time it’s consumed. For years, grid operators have determined load on a system and adjusted supply by adding available generators to meet it, first with the lowest-cost units, then adding more expensive ones until all of the electricity demand was satisfied.

Today, this fundamental rule has changed. New technologies on the supply side include fast-ramping and fast-cycling generation, new demand-side technologies like controlled water heating and storage, as well as improved transmission capabilities and system operations. This has created significant opportunity.

This paper, adapted from a RAP roundtable webinar from earlier in 2019, looks at various sources of flexibility available today and their potential for contributing to a more affordable, reliable and resilient power system capable of accommodating large amounts of variable renewable resources.​