Ancillary services for renewable integration

Renewable portfolio targets have been established in many regions around the world. Regional targets such as 20% renewable energy by year 2020 and 30% by year 2030 are not uncommon. With increasing penetration and reliance on renewable resources have come heightened operational concerns over maintaining system balance. Ancillary services, such as operating reserves, imbalance energy, and frequency regulation, are necessary to support renewable energy integration, particularly the integration of intermittent resources. Without supporting ancillary services as identified in the paper, increased risk to system imbalance is introduced by the uncertainty of renewable generation availability, especially in systems with significant penetration of resources powered by intermittent supply, such as wind and solar. Intermittent resources can suddenly cease supply to the grid with limited predictability, when the sun stops shining or wind suddenly stops blowing at point locations. Practical examples of such phenomena and their potential impact are identified. The described situation poses risk of disruption to grid-supplied electric service. The paper establishes procurement of ancillary services as a key component of renewable resource integration and a component of overall costs to deliver "green" power. Without ancillary services to support reliable delivery of electric service, end-use customers incur increased outage costs. Ancillary services are distinct components of electric service required to support the reliable delivery of electricity and operation of transmission systems. The paper summarizes regional definitions of ancillary services and identifies types of ancillary services competitively procured in electricity market environments. Regional estimates of ancillary service costs are researched and summarized to clarify cost adders associated with renewable integration beyond capital expansion cost. The cost adders comprise the reliability cost component of integra- ting renewable resources that are intermittent in nature. The paper provides data to establish that the costs for ancillary services are an important component of overall costs of renewable energy-supplied power. When such cost components are not explicitly recognized in overall electric service cost considerations, the full costs of integrating intermittent resources may likewise be under-recognized. The authors conclude by emphasizing the importance of accounting for reliability costs associated with renewable energy integration.