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The Integration Topic pages on Greening the Grid provide in-depth discussion and resources related to particular mechanisms for supporting increased penetration of variable renewable energy (RE) on the grid. However, many pioneering power systems around the world are implementing actions that span several of these topics. The following resources include several recent reports that more generally frame current and anticipated challenges and potential solutions related to variable RE integration. These cross-cutting works cover a wide range of key topics, providing both an introduction and a “big-picture” perspective on grid integration. The resources below also include relevant case studies from around the world that discuss grid integration policies, regulations, and practices in power systems with high levels of variable RE penetration.


Reading List and Case Studies

Getting Wind and Solar onto the Grid

International Energy Agency, 2017

This report provides a comprehensive review and clarification of the challenges and solutions for integrating grid-connected wind and solar energy. Intended for policymakers and staff at energy ministries, the report reviews measures to maintain the cost-effectiveness and reliability of power systems over four stages of increasing VRE deployment. Policy and regulatory measures covered in this report include grid codes, power system planning, renewable energy forecasting, and transmission and distribution network improvements, among others. 

Maintaining Reliability in the Modern Power System

U.S. Department of Energy, 2016

This report summarizes traditional and new approaches to maintaining a reliable electric system in the U.S., with a focus on approaches that can facilitate higher levels of distributed and variable generation. Four essential “rules” for maintaining electric system reliability are described: power generation and transmission capacity must be sufficient to meet peak demand for electricity; power systems must have adequate flexibility to address variability and uncertainty in demand and generation; power systems must be able to maintain stable frequency; and power systems must be able to maintain voltage within an acceptable range. New approaches for adhering to these “rules” with higher shares of variable RE generation include demand response and smart grid technologies, energy storage, flexible generation and transmission, power electronics, and others.


Grid Integration of Renewable Energy: Flexibility, Innovation, Experience

Eric Martinot, 2016

This report provides a concise global overview of grid integration challenges and emerging solutions, covering topics such as supply-side flexibility innovations, flexibility from distributed generation, curtailment, transmission and distribution system planning, and electricity market design. The report draws on experience from several jurisdictions where renewables provide 20%–40% of electricity generation, with particular emphasis on experiences in Germany, Denmark, and California. The report also references actions by developing countries (China, India, and South Africa).


RE-Powering Markets: Market design and regulation during the transition to low-carbon power systems

International Energy Agency, 2016

This report provides a detailed assessment of market designs, reforms, and regulations that can enable a least-cost transition to low-carbon power systems while maintaining security of electricity supply. Covering a broad range of topics including low-carbon investment strategies, short-term market design, reliability regulations, capacity markets, demand response, distributed resources, and retail price design, the report seeks to provide power system stakeholders with guidance to achieve the worldwide carbon reduction targets set forth in the Paris Agreement at the UNFCCC COP21 conference in December 2015.


Integration of Variable Renewables

International Energy Agency Renewable Energy Technology Deployment, 2015

This two-part report aims to inform policymakers and other non-technical power system stakeholders about specific policy tools that can create favorable conditions for higher variable RE penetration in a power system. Volume I outlines the analytic approach and presents findings to address three key questions:

1)      What are the typical country-specific factors that determine the choice of integration measure?

2)      Which options are applicable and effective in which context?

3)      What general lessons may be drawn by countries with similar underlying characteristics?

Volume II presents detailed case studies of variable RE integration measures in ten jurisdictions across eight countries in North America, Europe, and Asia. These case studies were developed through surveys, interviews, and face-to-face meetings with stakeholders to understand the policy pathways that countries can take to improve the policy landscape for variable RE integration.


Power System Flexibility Strategic Roadmap: Preparing power systems to supply reliable power from variable energy resources

Ecofys, 2015

This report and its associated webinar outline the general steps that can guide a power system's transition to RE as the primary source of electricity generation. The report synthesizes many technical reports, including some of those listed below, to summarize the large body of work on RE integration for a non-technical audience. The result is a strategic roadmap that outlines key challenges, immediate actions, and long-term planning strategies to enhance system flexibility. Topics covered include demand-side management, power markets, variable RE controls, resource diversity, energy storage, and smart grids.


The Age of Renewable Power: Designing National Roadmaps for a Successful Transformation

International Renewable Energy Agency, 2015

This report informs national policymakers about relevant actions they can take to develop a national roadmap for variable RE integration. The authors present a roadmap development framework that consists of five key steps:

1)      Stakeholder engagement

2)      Data collection for energy planning

3)      Flexibility assessment

4)      Evaluation and identification of relevant technologies

5)      Selection of appropriate variable RE integration measures.

The chapters in this report explain these steps in detail and also include brief case studies of policy actions in Germany, Japan, the United States, Denmark, and others to illustrate key concepts. The report concludes with several recommendations for designing a national roadmap for variable RE integration.


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

National Renewable Energy Laboratory, 2015

This white paper summarizes the challenges to integrating variable RE, identifies emerging practices in power system planning and operation that can facilitate grid integration, and proposes a unifying concept—economic carrying capacity—for evaluating actions to accommodate higher penetrations of RE. Economic carrying capacity refers to the limit of variable RE in a power system as determined by economic, rather than technical, factors such as transmission capacity and operational flexibility. This concept provides a framework that enables power system planners to answer the question: “how much wind and solar can our electricity grid handle?”


Status Report on Power System Transformation

21st Century Power Partnership, 2015

This report provides a collection of examples of power system innovations from both developed and developing countries around the world. This collection of examples serves as a source of real-world evidence to enable decision makers to undertake innovative steps toward power system transformation. The report organizes examples into eleven domains of innovation:

1)      Environmental stewardship

2)      Transmission systems

3)      Distribution systems

4)      Transmission-distribution system interface

5)      Finance, markets, pricing and cost allocation

6)      Static and dynamic load

7)      Flexible generation

8)      Integration with heating and cooling

9)      Integration with transport

10)    Energy storage

11)    Microgrids.


Flexibility in 21st Century Power Systems

21st Century Power Partnership, 2014

This report provides a brief overview and clarification of the key concepts, concerns, and misperceptions related to power system flexibility, and presents a series of analytic frameworks that help to address the question “How much flexibility does my system have and how much renewable energy can I add while maintaining system reliability?” The analytic frameworks presented here are designed to enable power system stakeholders to evaluate system-specific flexibility, and can help inform policymakers about least-cost measures to integrate higher levels of variable RE while maintaining power system reliability.



Regulatory and Policy Examples

Beyond 33% Renewables: Grid Integration Policy for a Low-Carbon Future

California Public Utilities Commission, 2015

This white paper is a public utilities commission thought piece intended to inform and educate power system stakeholders and to facilitate a shared understanding of grid integration challenges and solutions, specifically with reference to California’s electric power system. California is a historic leader in variable RE integration, with a target of 50% RE capacity by 2050. The paper takes a deep dive into the potential reliability concerns of grid integration and outlines short- and long-term practices and policies that the California Public Utilities Commission can initiate to achieve RE penetrations beyond 33%.

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