【报告】储能未来研究：定义长时储能的挑战（英）-NREL.pdf

Paul Denholm, Wesley Cole, A. Will Frazier, Kara Podkaminer, and Nate Blair Storage Futures Study The Challenge of Defining Long-Duration Energy StorageSuggested Citation: Denholm, Paul, Wesley Cole, A. Will Frazier, Kara Podkaminer, and Nate Blair. 2021. The Challenge of Defining Long- Duration Energy Storage. Golden, CO: National Renewable Energy Laboratory. NREL/TP-6A40-80583. https://www.nrel.gov/docs/fy22osti/80583.pdf. Storage Futures Study The Challenge of Defining Long-Duration Energy Storage Paul Denholm, Wesley Cole, A. Will Frazier, Kara Podkaminer, and Nate Blairiii This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications. Acknowledgments The authors would like to thank the following individuals for their contributions. Editing and other research support was provided by Claire Bolyard, Michael Deneen, Madeline Geocaris, and Mike Meshek. Helpful review and comments were provided by Sam Baldwin, Jaquelin Cochran, Chris Namovicz, Keith Parks, Gian Porro, and Paul Spitsen. This work was authored by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE- AC36-08GO28308. Funding provided by U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Solar Energy Technologies Office, U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Wind Energy Technologies Office, U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Water Power Technologies Office and U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Office of Strategic Analysis. The views expressed herein do not necessarily represent the views of the DOE or the U.S. Government. This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. U.S. Department of Energy (DOE) reports produced after 1991 and a growing number of pre-1991 documents are available free via www.OSTI.gov. iv This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications. Preface This report is one in a series of the National Renewable Energy Laboratory’s Storage Futures Study (SFS) publications. The SFS is a multiyear research project that explores the role and impact of energy storage in the evolution and operation of the U.S. power sector. The SFS is designed to examine the potential impact of energy storage technology advancement on the deployment of utility-scale storage and the adoption of distributed storage, and the implications for future power system infrastructure investment and operations. The research findings and supporting data will be published as a series of publications. The table on the next page lists the planned publications and specific research topics they will examine under the SFS. This document explores the definition of “long duration” as applied to energy storage. Given the growing use of this term, a uniform definition could aid in communication and consistency among various stakeholders. There is large and growing use of the Advanced Research Projects Agency–Energy (ARPA-E) definition of greater than 10 hours. However, the term “long- duration energy storage” is often used as shorthand for storage with sufficient duration to provide firm capacity and support grid resource adequacy. The actual duration needed for this application varies significantly from as little as a few hours to potentially multiple days. This dual use of the term means that there cannot be a simple, uniform, and static definition of long-duration storage that captures its ability to provide firm capacity and also aids consistent communication. To address this issue, the National Renewable Energy Laboratory recommends that qualitative descriptions of long-duration energy storage always be accompanied by quantitative descriptions, and that power sector stakeholders be deliberate in how they choose to define long- duration energy storage technologies. The SFS series provides data and analysis in support of the U.S. Department of Energy’s Energy Storage Grand Challenge, a comprehensive program to accelerate the development, commercialization, and utilization of next-generation energy storage technologies and sustain American global leadership in energy storage. The Energy Storage Grand Challenge employs a use case framework to ensure storage technologies can cost-effectively meet specific needs, and it incorporates a broad range of technologies in several categories: electrochemical, electromechanical, thermal, flexible generation, flexible buildings, and power electronics. More information, any supporting data associated with this report, links to other reports in the series, and other information about the broader study are available at https://www.nrel.gov/analysis/storage-futures.html. v This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications. Title Description Relation to this Report The Four Phases of Storage Deployment: A Framework for the Expanding Role of Storage in the U.S. Power System Explores the roles and opportunities for new, cost-competitive stationary energy storage with a conceptual framework based on four phases of current and potential future storage deployment, and presents a value proposition for energy storage that could result in cost-effective deployments reaching hundreds of gigawatts (GW) of installed capacity. Provides broader context on the implications of the cost and performance characteristics discussed in this report, including the specific grid services they may enable in various phases of storage deployment. This framework is supported by the results of scenarios in this project. Energy Storage Technology Modeling Input Data Report Reviews the current characteristics of a broad range of mechanical, thermal, and electrochemical storage technologies with application to the power sector. Provides current and future projections of cost, performance characteristics, and locational availability of specific commercial technologies already deployed, including lithium-ion battery systems and pumped storage hydropower. Provides detailed background around the battery and pumped storage hydropower cost and performance values used as inputs to the modeling performed in this project. Economic Potential of Diurnal Storage in the U.S. Power Sector Assesses the economic potential for utility- scale diurnal storage and the effects that storage capacity additions could have on power system evolution and operations. Features a series of cost- driven grid-scale capacity expansion scenarios for the U.S. grid through 2050 and examines the drivers for storage deployment. Distributed Storage Customer Adoption Scenarios Assesses the customer adoption of distributed diurnal storage for several future scenarios and the implications for the deployment of distributed generation and power system evolution. Analyzes distributed storage adoption scenarios to test the various cost trajectories and assumptions in parallel to the grid storage deployments. The Challenge of Defining Long-Duration Energy Storage Describes the challenge of a single uniform definition for long-duration energy storage to reflect both duration and application of the stored energy. This report. Grid Operational Implications of Widespread Storage Deployment Assesses the operation and associated value streams of energy storage for several power system evolution scenarios and explores the implications of seasonal storage on grid operations. Considers the operational implications of storage deployment and grid evolution scenarios to examine and expand on the grid-scale scenario results found with the Regional Energy Deployment System (ReEDS). Storage Futures Study: Executive Summary and Synthesis of Findings Synthesizes and summarizes findings from the entire series and related analyses and reports, and identifies topics for further research. Includes a discussion of all other aspects of the study and provides context for discussion in this report. vi This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications. Table of Contents Preface iv 1 Introduction . 1 2 First Things First: Defining “Duration” of Energy Storage 2 3 Defining Long Duration To Communicate Consistently . 3 4 Defining Long Duration To Establish Its Ability To Provide Resource Adequacy 4 5 A Further Complication: The Impact of Economic and Technology Capabilities . 9 6 Conclusions 10 References . 12 1 This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications. 1 Introduction As the share of U.S. power generation from variable renewable energy (VRE) grows, a new vision is taking shape for long-duration energy storage (LDES) to ensure affordable and reliable electricity. In this vision, LDES is deployed at large scale to provide resource adequacy 1 to the grid and support decarbonization of the electricity system. However, the lack of a uniform definition of LDES inhibits clear communication about the needs of the current and future grid, including scenarios approaching 100% decarbonization relying primarily on renewable energy. Energy storage duration is typically expressed in terms of the number of hours a storage device can provide continuous output at its rated capacity. Definitions of LDES in the literature range from as little as 2 hours to as much as multiple days or even months. There are two main reasons to establish a consistent definition: 1. Create a common language to aid communication to ensure stakeholders are working under consistent assumptions and understanding. 2. Establish characteristics needed to provide firm capacity and support resource adequacy, particularly for establishing regulatory or market rules or other standards. It is relatively straightforward to define LDES for the first reason (a common communication framework) and a review of the literature suggests durations of at least 10 hours could approach a consensus-based definition, given its current use by a number of industry and government organizations and growing use in the academic and general literature. We suggest caution in general use of this definition, however, as it inherently conflicts with the second motivation for a definition of LDES (based on its ability to provide firm capacity). This application-based definition has important implications for maintaining a reliable grid, establishing market rules, and optimal planning for decarbonization of the power system. It is difficult—if not impossible—to reconcile the two different approaches to defining LDES and arrive at a single numerical value for duration (or even range of values) that defines LDES for both ease of communication and using this term as a shorthand description for storage that provides firm capacity. The ability of storage to provide firm capacity (measured in terms of capacity credit) ranges significantly based on regional demand patterns and grid mix, including the amount of renewable energy and storage already in place. Therefore, the duration of storage needed to provide high capacity credit can span an enormous range, from as few as about 2–4 hours for some locations in today’s grid to multiple days in future grids with very large renewable energy and storage deployment. As a result, LDES cannot simultaneously have a simple uniform numerical value and be used as a threshold value for measuring capacity credit. 1 Resource adequacy (or simply “adequacy”) is defined by the North American Electric Reliability Corporation (NERC) as “The ability of the electric system to supply the aggregate electrical demand and energy requirements of the end-use customers at all times, taking into account scheduled and reasonably expected unscheduled outages of system elements” (1). This includes meeting peak demand during periods of hot or cold weather, during periods of low VRE output, during scheduled or unscheduled plant outages, or during extreme weather. 2 This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications. This discrepancy increases the challenge of communicating the potential role and opportunities for storage of various durations, especially when considering the economics of different technologies that may provide difference services. Regulatory and market frameworks will likely need to evolve to accommodate this reality. However, the lack of a simple uniform definition provides an opportunity to educate key stakeholders about the critical importance of evaluating resource adequacy with increased deployment of renewables and multiple storage technologies. 2 First Things First: Defining “Duration” of Energy Storage First, it is important to establish the definition of storage “duration.” This document takes the perspective of the end user of a stationary storage device, including grid planners, operators, and utilities. From this perspective, duration has a fairly straightforward definition summarized by the U.S. Energy Information Administration (2): The duration of a battery is the length of time that a storage system can sustain power output at its maximum discharge rate, typically expressed in hours. The energy capacity of the battery storage system is defined as the total amount of energy that can be stored or discharged by the battery storage system. It is important to emphasize that we interpret both energy and duration as measuring the usable energy and duration available to the plant or system operator, net of energy held back to maintain minimum and maximum state of charge or other factors. This means that the amount of usable energy stored is equal to the net power rating multiplied by the duration. For example, a 1-MW (AC rating) battery with 4 hours of duration has 4 MWh of usable stored energy that can be delivered to the grid. The “gross” storage capacity needed to achieve the net capacity is a separate factor determined by the manufacturer or developer to ensure that the net duration is available to the end user. The use of net vs. gross capacity for defining duration has significant precedent. Pumped storage hydropower plants, which represent the vast majority of energy storage deployed to date, are traditionally measured by the amount of stored water that can actually be used, accounting for the minimum and maximum levels of both the lower and upper reservoir, as opposed to the total amount of water in the reservoir. 2 Note that this definition describes only the amount of energy stored, not how long it will be stored before use. 3 However, the two quantities are potentially related as durations increase, as devices with the capacity to store multiple days of energy will likely need to store this energy for multiple days (or longer)