Grid Integration and the Carrying Capacity of the U.S. Grid to Incorporate Variable Renewable Energy

In the United States and elsewhere, renewable energy (RE) generation supplies an increasingly large percentage of annual demand, including nine U.S. states where wind comprised over 10% of in-state generation in 2013. This white paper summarizes the challenges to integrating increasing amounts of variable RE, identifies emerging practices in power system planning and operation that can facilitate ability to respond to change in demand and supply, as they must accommodate variable and uncertain load. Power system operators have thus been able to accommodate increased variable RE largely without substantial new investment in system flexibility, such as new storage, demand response, or generation dedicated to addressing RE variability and uncertainty. To achieve higher penetration levels, multiple grid integration studies in the United States have evaluated scenarios where an economic carrying capacity of at least 30% is achieved via transmission expansion and largely understood changes to system operations. Studies have also demonstrated that carrying capacity is not fixed and can be improved through technical and institutional changes. This creates the possibility to achieve even higher penetration levels through strategic investments in both demand- and supply-side sources of flexibility.