The electric power sector around the world is undergoing long-term technical, economic, and market transformations. Part of these transformations is the challenge of integrating high shares of renewable energy, particularly variable wind and solar. The concept of flexibility of a power system is key in terms of balancing these variable sources while keeping the lights on. On the supply side, flexibility arises from innovations in flexible coal and gas power plants, energy storage, and renewables. On the demand side, many distributed resources—generation, flexible demand, storage, and electric vehicles—can also contribute, and likewise transmission and distribution networks, grid operations, and market designs. Experience with measures and innovations for grid integration in all these categories is given, from several jurisdictions like Germany, Denmark, and California, where renewables already provide 20–40% shares of electricity and plans to reach 50% exist. Questions point to areas of technology, economics, planning, operations, business, and policy that need further understanding and learning from experience.


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  • Article Type: Review Article
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