保持电网的可靠性—来自可再生能源整合研究的经验教训.pdf

NREL is a national laboratory of the U.S.Department of Energy Office of Energy Efficiency&Renewable Energy Operated by the Alliance for Sustainable Energy,LLC This report is available at no cost from the National Renewable Energy Laboratory(NREL)at www.nrel.gov/publications.Contract No.DE-AC36-08GO28308 Technical Report NREL/TP-5C00-89166 April 2024 Maintaining Grid Reliability Lessons from Renewable Integration Studies Paul Denholm,Ilya Chernyakhovskiy,and Lauren Streitmatter National Renewable Energy Laboratory NREL is a national laboratory of the U.S.Department of Energy Office of Energy Efficiency&Renewable Energy Operated by the Alliance for Sustainable Energy,LLC This report is available at no cost from the National Renewable Energy Laboratory(NREL)at www.nrel.gov/publications.Contract No.DE-AC36-08GO28308 National Renewable Energy Laboratory 15013 Denver West Parkway Golden,CO 80401 303-275-3000 www.nrel.gov Technical Report NREL/TP-5C00-89166 April 2024 Maintaining Grid Reliability Lessons from Renewable Integration Studies Paul Denholm,Ilya Chernyakhovskiy,and Lauren Streitmatter National Renewable Energy Laboratory Suggested Citation Denholm,Paul,Ilya Chernyakhovskiy,and Lauren Streitmatter.2024.Maintaining Grid Reliability Lessons from Renewable Integration Studies.Golden,CO:National Renewable Energy Laboratory.NREL/TP-5C00-89166.https:/www.nrel.gov/docs/fy24osti/89166.pdf.NOTICE 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 the U.S.Department of Energy Office of Policy.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.Cover Photos by Dennis Schroeder:(clockwise,left to right)NREL 51934,NREL 45897,NREL 42160,NREL 45891,NREL 48097,NREL 46526.NREL prints on paper that contains recycled content.iii 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 communications support was provided by Amy Brice,Liz Breazeale,Madeline Geocaris.Helpful review and comments were provided by Paul Donohoo-Vallett,Bahram Barazesh,Patrick Brown,Jaquelin Cochran,Jeffery Dennis,Jason Frost,Trieu Mai,Glenda Oskar,Sohum Pawar,Gian Porro,Eric Rollison,Mark Ruth,Paul Spitsen,and Ryan Wiser.iv This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.Table of Contents 1 Introduction.1 1.1 Three Key Issues To Maintaining Bulk System Reliability With Increased Wind and Solar.1 1.2 Summary of Findings.2 1.3 How Have We Studied the Evolving Grid?.3 1.4 Study Geography.4 1.5 Studies Considered.5 2 Meeting the Ramp:Lessons From Variability Studies.7 3 Meeting the Demand:Lessons From Resource Adequacy Studies.10 4 Keeping the Grid Moving:Lessons From Frequency Stability Studies.13 4.1 Frequency Stability Summary of the Issue and Study Approach.13 4.2 Study Findings.13 5 From Study to Practice:Where Are We Now and Where Are We Going?.16 5.1 Incorporating High Levels of Variable Generation in Utility Planning.16 6 Conclusions.18 1 This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.1 Introduction In 2023,clean energy resources(including renewables and nuclear power)provided about 41%of electricity in the United States,with more than 16%of total generation provided by wind and solarcalled“variable”renewable energy sources because of their daily and seasonal fluctuations in availability(U.S.Energy Information Administration 2024).The bulk power system,which supplies and transmits electricity,maintained high reliability throughout the year,showing that grid reliability is achievable as deployment of wind and solar has increased.Wind and solar contributions to the nations electricity mix are projected to grow significantlyGagnon et al.(2024)project that wind and solar could provide more than 60%of national electricity generation by 2035 under existing polices.Maintaining high reliability in the bulk power system while increasing renewable resource deployment is a critical priority for electric grid planners,operators,and regulators.The U.S.Department of Energy(DOE)and other organizations have sponsored numerous research studies over the last two decades to examine the effect of increased wind and solar deployment on grid reliability,including a number of studies that examine grids deriving more than 50%of annual energy from wind and solar.Here,we discuss key findings from both the research body of knowledge and real-world practice related to grid reliability,and we demonstrate how to plan for and achieve continued reliability in the future as wind and solar deployment increase.1.1 Three Key Issues To Maintaining Bulk System Reliability With Increased Wind and Solar Maintaining bulk system reliability requires balancing the supply of electricity with demand at various timescales,from less than a second to hours,days,and beyond.1 Maintaining reliability with increased deployment of wind and solar at scale presents issues that can be summarized into three general categories:1.Responding to short-term variability of wind and solar generation.The fluctuation of variable renewable energy supply was one the first concerns with wind and solar deployment.Output from these resources can vary over multiple timescales from seconds to hours with limited predictability.This variability and uncertainty can impact how the system is operated,so there has been considerable effort to study ways to mitigate these impacts.2.Ensuring enough generation to meet demand during all hours of the year.Grid planners traditionally focused on meeting demand during peaks,like hot summer afternoons and cold winter nights.But with the growth of wind and solar,focus has shifted to maintaining an adequate mix of resources to meet demand in all hours,particularly where renewables are expected to replace traditional fossil-fueled generators.1 For additional discussion of the concept of power system reliability(including formal definitions of reliability elements),see North American Electric Reliability Corporation(2013).2 This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.Planning is further complicated by the impact of new loads from electrification,which can also shift the timing of peak demands.3.Maintaining stability in the event of a grid disturbance.One aspect of grid stability that relates to the deployment of wind and solar is frequency stability,or the ability to avoid large changes in frequency after a generator or transmission line failure.The concern is associated with the loss of traditional system inertia as renewable resources like wind and solar displace fossil-fueled resources,whose operating characteristics inherently provide inertia.2 1.2 Summary of Findings Dozens of studies address various aspects of reliability with the increased deployment of renewable energy resources in regions across the United States.The studies examine contributions from renewables that range from 30%to 100%of total generation and show that these systems can achieve a desired level of reliability if appropriate measures are taken to change how the grid is planned and operated.These measures can be summarized in four categories:1.Short-term variability and uncertainty in renewable generation can be managed cost-effectively by increasing grid flexibility.Many grid flexibility options have been deployed,including changing how the power system is scheduled,balancing supply and demand over larger regions,using energy storage and other quick-ramping resources,and employing new operating reserve approaches.2.Demand for electricity during all hours of the year can be met through a portfolio approach.A portfolio approach aggregates variable renewable deployment with dispatchable resources like energy storage,existing and new fossil resources,and new“clean firm”technologies.Studies highlight the benefits of combining solar and storage to meet summer peaks.These studies also demonstrate that significant renewable resource contributions and deep decarbonization can occur as existing(and new)fossil resources transition from sources that provide energy during many hours of the year to resources that operate primarily during periods of low wind or solar output.Systems studies that approach or reach 100%clean energy demonstrate how clean firm technologies can replace existing fossil resources that are acting primarily as capacity resources.3.Increased utilization of power electronics supports frequency stability.Frequency stability studies have demonstrated that grids can maintain reliable operation with greatly increased use of wind and solar.Along with energy storage,wind and solar resources use power electronics that can react very quickly to faults and provide frequency support to the gridwhich can offset the decline in inertia.2 While this list covers most of the important issues evaluated in renewable integration and reliability studies,it is not comprehensive.There are other important issues that have been studied and some that require further study.These include voltage control and stability,system strength,transient stability,and fault current.These issues are not discussed further in this report.3 This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.4.Expanded transmission networks are central to increasing reliability.Capacity expansion and chronological operational studies generally conclude that increased utilization of existing transmission and new transmission expansion are needed to cost-effectively achieve high contributions of wind and solar across the United States.This includes building out local transmission networks to access the best renewable energy resources as well as expanding transmission capacity between balancing areas and interconnections to move power from where it is available to where it is most needed.This also acts to reduce variability of the aggregated supply of renewable resources across various timescales.These findings have been incorporated into current utility practices,which has led to instantaneous contributions of wind and solar of over 80%in several regions of the United States(Millstein,OShaughnessy,and Wiser 2023).Current utility plans now incorporate various approaches to achieving increased economic deployments of wind and solar while maintaining reliability standards.1.3 How Have We Studied the Evolving Grid?Dozens of studies have been performed that examine one or more of the three key issues using a variety of tools and approaches,but they have some common elements.3 They generally start with establishing the scenarios to be studied,including the generation mix in some future year.The scenarios can be developed manually or by using a capacity expansion model that identifies the optimal(least-cost)mix of resources that can meet the target grid conditions.4 Once the future resource mix and study conditions are established,a variety of tools may be used,depending on the study goal:Variability studies are used to evaluate how the mix of generation,storage,and transmission resources can respond to variations in supply from wind and solar.5 Many of the earliest studies were designed to examine the avoided costs that result from reduced output from fossil-fueled plants.They often focus on the impact of variability on the existing fossil-fueled generation fleet to ensure the system can react quickly enough and provide adequate levels of operating reserves.The studies also often examine the impact on power plant costs as the plants spend more time varying output and more frequently stop and start.Variability studies use a production cost model that simulates the chronological operation of the grid at an hourly(or sub-hourly)resolution and calculates the cost of operating the system.6 These studies typically evaluate reliability over a single year using historical weather patterns.Resource adequacy studies evaluate the probability that there will be unserved energy(power outages)that might result from some combination of insufficient supply of 3 A more detailed description of study methods is provided in Katz and Chernyakhovskiy(2020).4 Capacity expansion models are not unique to renewable studies.They have been used as part of utility planning processes for decades.For additional discussion see Murphy and Weiss(1990)and Cole et al.(2017).5 While production cost models typically do not simulate the more rapid variations in supply in the regulation time frame,they do ensure adequate reserves can respond to more rapid variation.6 These tools use detailed datasets that include individual generator performance and how fast they can vary output.4 This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.generation resources or higher-than-average demand.7 These studies often include additional consideration of forecasted changes to demand patterns due to energy efficiency and electrification of end uses.The studies perform chronological simulations over at least one year of future grid conditions,examining in detail the potential shortfall of supply and potential mitigation measures during periods of high demand and during periods of lower renewable energy supply,often using the same production cost models as variability studies.However,resource adequacy studies may also use additional tools that consider uncertainty in resources over longer time periods and a broader set of possible weather conditions(or use a single tool that combines both chronological simulations with the probabilistic component).Frequency stability studies examine the ability of the grid to maintain system frequency within a tolerance.Unlike the previous studies that examine one or more full years,these studies typically only consider a few moments in time,often those where the system may be particularly vulnerable to a fault,such as periods where many thermal generators have been turned off and there is less inertia on the grid.They use a class of tool known as a power flow model to simulate the dynamic operation of the grid immediately following a fault and can identify conditions where frequency stability may be compromised.8 It is important to note that most studies are iterative in naturethey often discuss reliability concerns,identify one or more potential solutions,and evaluate the so