Functional Requirements for Electric Energy Storage Applications on the Power System Grid 1022544 Functional Requirements for Electric Energy Storage Applications on the Power System Grid 1022544 Technical Update, May 2011 EPRI Project Manager W. Steeley ELECTRIC POWER RESEARCH INSTITUTE 3420 Hillview Avenue, Palo Alto, California 94304-1338 ▪ PO Box 10412, Palo Alto, California 94303-0813 ▪ USA 800.313.3774 ▪ 650.855.2121 ▪ askepri@epri.com ▪ www.epri.com DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIES THIS DOCUMENT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS AN ACCOUNT OF WORK SPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCH INSTITUTE, INC. (EPRI). 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REFERENCE HEREIN TO ANY SPECIFIC COMMERCIAL PRODUCT, PROCESS, OR SERVICE BY ITS TRADE NAME, TRADEMARK, MANUFACTURER, OR OTHERWISE, DOES NOT NECESSARILY CONSTITUTE OR IMPLY ITS ENDORSEMENT, RECOMMENDATION, OR FAVORING BY EPRI. THE FOLLOWING ORGANIZATIONS, UNDER CONTRACT TO EPRI, PREPARED THIS REPORT: Norris Energy Consulting Company Technology Transition Corporation Electric Power Research Institute (EPRI) This is an EPRI Technical Update report. A Technical Update report is intended as an informal report of continuing research, a meeting, or a topical study. It is not a final EPRI technical report. NOTE For further information about EPRI, call the EPRI Customer Assistance Center at 800.313.3774 or e-mail askepri@epri.com. Electric Power Research Institute, EPRI, and TOGETHERSHAPING THE FUTURE OF ELECTRICITY are registered service marks of the Electric Power Research Institute, Inc. Copyright © 2011 Electric Power Research Institute, Inc. All rights reserved. ACKNOWLEDGMENTS The following organizations, under contract to the Electric Power Research Institute (EPRI), prepared this report: Norris Energy Consulting Co. 123 Clear Creek Ct. Martinez, CA 94553 Principal Investigator B. Norris Technology Transition Corporation 1211 Connecticut Ave NW, Suite 600 Washington, DC 20036 Principal Investigators J. Serfass E. Wagner EPRI 3420 Hillview Ave. Palo Alto, CA 94303 Principal Investigators H. Kamath A. Maitra W. Steeley A. Tuohy This report describes research sponsored by EPRI. EPRI acknowledges the work group leaders, who provided valuable guidance and leadership to this project. Our gratitude goes out to the following: Eva Gardow, FirstEnergy Service Company Mike Grant, Duke Energy Tom Walker, American Electric Power Dale Bradshaw, National Rural Electric Cooperative Association’s Cooperative Research Network George Gurlaskie, Progress Energy Florida We would also like to thank the many unnamed individuals who participated in numerous conference calls and webinars and provided countless questions and comments that helped refine this report. This publication is a corporate document that should be cited in the literature in the following manner: Functional Requirements for Electric Energy Storage Applications on the Power System Grid. EPRI, Palo Alto, CA: 2011. 1022544. iii PRODUCT DESCRIPTION This report describes functional requirements of energy storage connected to the power grid for several applications. The applications of interest include grid management at the substation and on the distribution system and storage to integrate larger scale variable renewable energy installations. The requirements developed in this project provide a common basis for manufacturers and utilities to consider the general needs of storage in these applications. They also provide a basis for utilities to develop storage equipment specifications in specific locations with specific grid, load, environmental and other characteristics. Results and Findings This report provides functional requirements for three key energy storage applications: substation-based storage, distributed energy storage systems, and energy storage to integrate renewables. Energy storage to integrate renewables is divided into three subcategories: solar photovoltaic ramping support, wind ramping support, and load- and resource-shifting applications. The requirements for each application include details on the use cases and operating modes, power output and duration, system ratings and effectiveness, physical requirements, communications and data flow, and operational and safety issues. Challenges and Objectives Energy storage is receiving increasing attention from utility engineers and regulators for its potential to solve a variety of technical challenges in the management of electric power. However, utilities, vendors, and regulators must develop a common ground on which to base their understanding of energy storage application requirements. This report presents a set of functional requirements for energy storage systems connected to the electric power system to be used in specific ways (use cases and operating modes). By steering procurement and development efforts consistent with these requirements, utilities and developers can work with a common understanding to develop the most effective storage solutions to utility problems. Application, Value, and Use This report will provide significant value to energy storage manufacturers and system integrators by communicating grid requirements for each of the energy storage applications. The report will help utility system planners who are considering the role that energy storage can have on the management of the grid and the temporal differences between economic energy supply and customer energy needs. The report provides generalized requirements for storage systems, independent of the technologies of interest, suitable for helping engineering and procurement personnel develop the more detailed specifications required in a procurement action. This report also will help power system operators communicate with the developers of large-scale wind and solar farms and also the developers of energy storage systems, so that they can each bring their value to the operation of the electric grid and, therefore, bring value to the electric consumer. Recommendations for further study have been included in the report. Many of the recommendations relate to the need for data and information to assist in development of storage operating modes and value propositions. v EPRI Perspective This project is one element of the Electric Power Research Institute (EPRI) Energy Storage Program to accelerate the grid-readiness of energy storage systems by 2015. Other related projects include the analytics to support the business case for energy storage systems (see the EPRI report Electricity Energy Storage Technology Options: A White Paper Primer on Applications, Costs and Benefits [1020676]) and research reports on testing, evaluation, and demonstration of storage systems for grid and application readiness. Widespread use of storage will require a coordinated effort by technology developers and utilities to ensure that systems are designed to adequately address utility needs. Utilities must understand the technical and cost characteristics of the various technologies being advanced by developers. System providers must offer energy storage systems that meet those requirements. It is that latter objective that has been the central motivation of this project. The project has brought together all the stakeholders—including utilities, manufacturers, and system operators—to document some of the basic requirements for storage owned and operated by utilities. The project operated under the guidelines that the functional requirements were to be technology neutral, that the economic justification of the applications would not be addressed, that the functional requirements were not to be detailed technical specifications, and finally, that not all storage applications envisioned could be included. This report focuses on the applications of high priority identified by the utility participants. All the included applications represent energy storage systems that would be controlled and operated by the utility and located on the utility side of the meter. To be most effective, the functional requirements that the participants have developed must be reviewed periodically to take advantage of utility and manufacturer experience being gained. Approach The project created a public, open source approach by including high-level energy storage stakeholders, including representatives from utilities, renewable energy project developers, equipment developers and manufacturers, regulators, independent system operators, power pools, and government and educational institutions. After a first draft of application requirements were developed, the project was opened up for public comments and received increasingly detailed input from stakeholders through public webinars, while application-specific work groups refined their individual functional requirements. Keywords Distributed energy storage system (DESS) Energy storage Functional requirements Renewables integration Substation-based storage vi ABSTRACT Energy storage on the electric power system is becoming an increasingly important tool in managing the evolving transmission system and the integration of large-scale, intermittent solar and wind generation. Electric utilities are evaluating and deploying energy storage technologies to serve a variety of applications to address the challenges posed by these fundamental changes. The needs differ from utility to utility. This report, developed by the Electric Power Research Institute (EPRI), Norris Energy, and Technology Transition Corporation, with the support of more than 100 utilities and other stakeholders, provides functional requirements for three key energy storage applications: substation-based storage, distributed energy storage systems, and energy storage to integrate renewables, which itself is divided into three subcategories, each describing a different set of circumstances—solar photovoltaic ramping support, wind ramping support, and load and resource shifting applications. The requirements for each application include details on the use cases and operating modes, power output and duration, system ratings and effectiveness, physical requirements, communications and data flow, and operational and safety issues. These sets of functional requirements present guidelines for utilities and equipment developers and manufacturers. Using this report as a basis for developing more detailed specifications allows both parties to better understand energy storage application needs. vii EXECUTIVE SUMMARY Project Description Energy storage is receiving increasing attention from utility engineers and regulators for its potential to address a variety of technical challenges in the management of electric power. Utilities face the need to economically serve uncertain peak load growth at substations, the desire to provide enhanced reliability and resilience in adaptive Smart Grids, and the need to use highly variable and unpredictable renewable energy sources. All these needs could potentially be addressed using storage technologies. Widespread use of storage will require the coordinated effort of technology developers and utilities to ensure that systems are designed to adequately address utility needs. On one hand, utilities need a better understanding of the technical and cost attributes of the various technologies being advanced by the developers. On the other hand, developers need a better understanding of the prospective uses and requirements of utilities. It is that latter objective that has been the central motivation of this project. The project has brought together representatives from all stakeholder groups—including utilities, manufacturers, and system operators—to document some of the basic requirements for storage owned and operated by utilities. The requirements vary depending on location—transmission, substation, and distribution—and the specific challenges addressed, such as peak load management or enhancing the flexibility of the bulk grid to enable the integration of large-scale renewables. In the process, a set of functional requirements for energy storage systems to be used in specific ways (use cases and operating modes) was developed. By steering procurement and development efforts consistent with these requirements, utilities and developers can work with a common understanding to develop the most effective storage solutions to utility problems. Rationale for Energy Storage The current and anticipated challenges facing the electric grid include the following: Variable renewable energy generation (primarily wind energy) is rapidly growing in its overall contribution to the resource mix, requiring a more flexible grid system that can accommodate its uncertain, partly dispatchable output. Variability in solar photovoltaic (PV) power output due to the diurnal solar cycle, passing clouds, and other events can lead to ramping effects and unpredictable load management at the system level. Likewise, variations in wind power output, whether short-term (seconds) or longer term (minutes), can affect distribution voltage (in those cases where wind is connected at the distribution level) and might create a requirement for additional regulation and ramping support at the system level. State renewable portfolio standards, which require that a specified minimum fraction of the electricity supplied in a state be generated from renewable energy sources, will likely result in substantial increases in the penetration of these sources on the grid in the coming 10 to 20 years. ix Bidirectional power flow created by distributed energy resources presents a challenge for distribution systems with voltage regulation and protection schemes originally designed for one-way power flow. Smart Grid designs call for additional distribution automation and sophistication, such as islanding and self-healing designs aimed at improving user reliability. Limited transmission capacity threatens to force existing clean-energy wind resources to be curtailed during peak production times, but expansion of transmission capacity presents regulatory and environmental challenges. Utilities seek new ways to extend the useful life of existing capital assets to defer investment in capital upgrades, maintaining reliable power at a reasonable cost to users while accounting for uncertainty in load growth. Energy storage has the potential to address all these concerns. Objective and Scope This project sought to develop a set of functional requirements for energy storage systems to be used in specific ways (use cases and operating modes). The goal is for utilities and developers to work with a common understanding to develop the most effective storage solutions to utility problems. The project scope adhered to the following guidelines: The process and this report were based entirely on utility requirements for specific applications and not on the capabilities of underlying storage technologies. Although certain energy storage technologies might operate better in one application or area than another, it is not the purpose of this project to evaluate the suitability of specific storage technologies. Economic analysis of the applications was not performed. The process and this report address only high-level functional requirements and are not intended to serve as complete technical specifications for procurement. The ultimate list of requirements, including specific standards and other utility-specific requirements, will have to be specified by the utilities through its normal procurement process. Not all storage applications were included. Other variations, such as storage for the exclusive purpose of frequency regulation or seasonal energy storage, are possible, but they are not included in the scope of this project. This report focuses on a few high-priority applications identified by the utility participants. Energy storage at the customer side of the meter is not considered in this project. The project focuses, instead, on opportunities in utility system management. Approach and Methodology This project was based on stakeholder review of draft application requirements and stakeholder advice on how to refine the requirements to produce this report. The project began with a draft application requirement document. Following internal reviews, the Electric Power Research Institute (EPRI) conducted a series of webinars and work group calls with stakeholders to obtain their comments and suggestions for the developing document. Over the course of this project, more than 100 companies have participated in varying capacities (see Appendix D). This report is the result of six work group conference calls, nine webinar meetings, and off-line inputs received directly from the participants. x Requirements The project focused on three essential energy storage applications that serve different functions on the electric grid. These applications vary in categories such as location on the electric grid, capacity, operating modes and use cases, and the required duration of energy storage. These applications are not intended to represent a comprehensive list of all energy storage applications but rather focus on the applications of primary interest to the participating utilities. An overview of the three key systems is shown in the following two tables. Table 1 is an overview of the first two applications, substation-based storage and distributed energy storage systems (DESS). Table 2 describes the third application, storage to integrate renewables, with its three sub-cases. Table 1 Matrix for Substation-Based Storage and Distributed Energy Storage Systems Applications Application Substation-Based Storage (see Section 2) 1–20 MW 2–6 hours Includes both stationary and transportable Distributed Energy Storage System (DESS) (see Section 3) 25–200 kW (individual unit rating) Single-phase (25–75 kW) Three-phase (up to 200 kW) Use Cases / Operating Modes (See Note) Interconnection Point Notes Peak load management is controlled using substation/feeder real-time load signals. Peak load management Frequency regulation Distribution voltage (4kV–34kV) Capacity market (regional transmission organization [RTO] or independent system operator [ISO]) Substation or feeder Frequency regulation controlled using signals from ISO. Although not currently in effect, a capacity market controlled using signals from ISO is a future option. Voltage regulation/reactive power support Peak load management is controlled using substation/feeder real-time load signals. Peak load management Backup power/islanded grid operation Voltage regulation/reactive power support Secondary (customer) voltage Utility side of meter May operate as island Frequency regulation (may require aggregation) Capacity market (RTO/ISO) Frequency regulation controlled using signals from ISO. May be used in capacity markets. Reactive power dispatch based on local voltage. If only frequency regulation is desired, duration may be as low as 15 minutes. 2–4 hours Note: Use cases are listed in order of decreasing priority. Products need not meet all use cases. xi Table 2 Matrix for Energy Storage to Integrate Renewables Application Solar PV Ramping Support (see Section 4) Power up to several megawatts (TBD by utility site) 1 second to 20 min (TBD by utility) Wind Ramping Support (see Section 4) 1–100 MW 2–15 minutes Life equivalent to 10,000 full energy cycles Load or Resource Shifting (see Section 4) Kilowatts to many hundreds of megawatts 2–10 hours Use Cases/Operating Modes Interconnection Point Accommodate rapid power swings that would otherwise create disturbances on systems where highpenetration levels of solar PV systems are found Better manage the variability of solar active power output. Distribution voltage (4kV–34kV) Accommodate variable wind farm output so that ramp rates (MW/min) are kept within a desirable range Provide net load ramping support for the grid at large Maintain local transmission and distribution system voltage Notes Distribution voltage (4kV–34kV) Transmission voltage (>34kV) Provide frequency regulation Reactive power controlled based on local voltage. (This function is accomplished by the power electronics accompanying the storage.) If local benefits for control area or a specific distribution feeder are required (as for a single wind farm), storage system must be co-located with the variable generation. If bulk power system benefits are desired, storage system can be located anywhere on the grid. Provide low-voltage ridethrough (LVRT) for wind farm (if required) LVRT support is built-in to most modern wind turbines. Store energy generated during off-peak demand periods to serve loads during peak demand periods May be directly coupled and sized to local renewable resource or sized and operated independently. Participate in capacity markets as dispatchable energy and reserves Distribution voltage (4kV–34kV) Transmission voltage (>34kV) Provide ancillary services May also serve to reduce ramp rates from variable wind farm output and dampen solar PV ramping. Substation–based storage applications (see Section 2) provide primarily peak load management and frequency regulation services at the substation, could be either stationary or portable, and provide power in the range of 1–20 MW for 2–6 hours. Distributed energy storage systems (DESSs) (see Section 3) and include applications near the customer for management of small groups of loads. The primary uses of these systems are peak load management, backup power, and regulation services. The systems would be rated in the range of 25–200 kW for 2–4 hours of discharge duration and would be located on the utility side of the meter. xii Energy storage to integrate renewables (see Section 4) addresses issues that arise due to increasing amounts of renewables on the grid. This application is divided into the following three categories, each with a different set of circumstances. Solar PV ramping support applications, which provide power for short periods of time (a few seconds up to 20 minutes) to mitigate power swings on the system. Wind ramping support applications, which can improve the flexibility of the transmission and distribution system to accommodate rapid changes in power generation from wind farms by providing buffer capacity for short periods of time. Load and resource shifting applications, in which energy is shifted from peak generation hours to peak load hours. These storage systems will require up to 10 hours of energy. They could be deployed in a wide range of power ratings, from a few kilowatts to many hundreds of megawatts (potentially even gigawatts) depending on where they are connected to the power delivery network. Systems could be designed to address other applications, as well, to obtain a better return on the upfront capital investment. Recommendations The following additional work is required to further define the functional requirements for these applications (see Section 5): Collection and sharing of data. The application of the functional requirements presented in this report would be enhanced by detailed operating data on wind and solar generation and other system characteristics that will impact the specifications for equipment being applied. It is also important that the information sharing in this project be continued among utilities, storage equipment suppliers, wind and solar developers, and related institutions so that the equipment being developed and purchased continues to improve in its applicability to grid management issues and opportunities. Utilities and others are encouraged to share their data, challenges, issues, and case studies for inclusion in possible revisions of this report. System sizing for solar PV ramping application. Utilities that use storage to accommodate solar PV ramping events must determine the power and energy requirements for the storage system based on local conditions. The means for determining optimal sizing is not yet well understood. The factors might include local meteorological characteristics, the local installed capacity of solar PV, the relative spacing of the individual solar PV systems, the existing voltage regulation available, and the local distribution system (such as wire sizes). In addition, solar PV models have only recently been integrated into distribution load flow models. Additional work needs to be done in this area. The degree to which storage is necessary to accommodate variability is similarly unclear for all the renewable applications described in this report. Solar PV control algorithms. Although the reactive power capabilities that might be included in a grid-connected energy storage system can be used to regulate voltage, it is not clear how to dispatch the active power capabilities for this purpose. The details of the dispatch model must be developed. For example, storage can be used to charge and discharge to limit the rate of change of power on the line at the point of storage interconnection. The algorithm might be dependent on local distribution impedance. Wind plant LVRT. The application of using storage for LVRT for wind plants is not yet well understood. Most modern wind plants provide LVRT as a matter of course, obviating the xiii need for storage in this application. The operating modes and design requirements, if any, must be better defined. Solar PV and wind duty cycles. For both the solar PV ramping and wind ramping applications, the required cycle life is not yet well understood. On a given day, the cycle requirements are expected to be dependent on the number of generators in the fleet (more generators reduce aggregate variability), their physical placement, local meteorological conditions, the local power system design, and the timing of generator output relative to loads. Additional work is necessary to model storage operation needed to maintain stability and, thereby, define cycling requirements. Communication protocol details. The details of communication protocols for all the applications described in this report must be further delineated. Definition and standardization of these protocols will simplify the process for both suppliers and utilities. Defining functional requirements for other energy storage applications. This report describes three key storage applications, excluding a number of additional applications. Further work is needed to define functional requirements for commercial and industrial (C&I) power quality, C&I power reliability, C&I energy management, residential energy management, and residential backup. xiv CONTENTS 1 INTRODUCTION ....................................................................................................................1-1 Current Developments Affecting the Electricity Grid ............................................................1-1 Potential Uses for Electric Energy Storage ....................................................................1-1 Electric Energy Storage Options and Technology Neutrality .........................................1-2 Defining Functional Requirements .......................................................................................1-3 What is a Functional Requirement Versus a Technical Specification? ..........................1-3 EPRI’s Role in Energy Storage ......................................................................................1-4 This Project ..........................................................................................................................1-4 The Basics .....................................................................................................................1-4 Objective and Scope ......................................................................................................1-5 Approach and Process...................................................................................................1-8 2 SUBSTATION-BASED STORAGE ........................................................................................2-1 Overview ..............................................................................................................................2-1 Description of Application...............................................................................................2-1 Use Cases and Operating Modes ........................................................................................2-2 Performance Ratings ...........................................................................................................2-3 System Definition ...........................................................................................................2-3 Auxiliary Loads...............................................................................................................2-3 System Rating Practices ................................................................................................2-3 Storage System Effectiveness .............................................................................................2-4 Storage Efficiency ..........................................................................................................2-4 Performance Curve ........................................................................................................2-4 Physical Characteristics .......................................................................................................2-4 Size ................................................................................................................................2-4 Transportation Standards...............................................................................................2-4 Rigging and Harnessing.................................................................................................2-5 Status Lights and Alarms ...............................................................................................2-5 Environmental Conditions ..............................................................................................2-5 Electrical Interface................................................................................................................2-5 Standards.......................................................................................................................2-5 Disconnect Breaker........................................................................................................2-5 Contactor........................................................................................................................2-5 Communications, Control, and Data Management ..............................................................2-6 Communications Method ...............................................................................................2-6 Communications Protocol ..............................................................................................2-6 Integrated Interface ........................................................................................................2-6 Operational Data ............................................................................................................2-6 Event-Triggered Data.....................................................................................................2-7 xv Data Access ...................................................................................................................2-7 Installation and Maintenance ...............................................................................................2-7 Safety ...................................................................................................................................2-7 3 DISTRIBUTED ENERGY STORAGE SYSTEMS—UTILITY PAD MOUNT...........................3-1 Overview ..............................................................................................................................3-1 Description of Application...............................................................................................3-1 Use Cases and Operating Modes ........................................................................................3-2 System Rating Practices ......................................................................................................3-3 System Definition ...........................................................................................................3-3 Auxiliary Loads...............................................................................................................3-3 Operation As a Current Source or Voltage Source ........................................................3-3 System Rating Practices ................................................................................................3-3 System Effectiveness...........................................................................................................3-4 Standby Efficiency..........................................................................................................3-4 Storage Efficiency ..........................................................................................................3-4 Speed of Response........................................................................................................3-5 Performance Curve ........................................................................................................3-5 Physical Characteristics .......................................................................................................3-5 Size ................................................................................................................................3-5 Transportation Standards...............................................................................................3-5 Rigging and Harnessing.................................................................................................3-5 Status Lights and Alarms ...............................................................................................3-5 Environmental Conditions ..............................................................................................3-6 Electrical Interface................................................................................................................3-6 Standards.......................................................................................................................3-6 Disconnect Breaker........................................................................................................3-6 Communications, Control, and Data Management ..............................................................3-6 Communications Method ...............................................................................................3-6 Communications Protocol ..............................................................................................3-6 Integrated Interface ........................................................................................................3-6 Operational Data ............................................................................................................3-7 Event-Triggered Data.....................................................................................................3-7 Data Access ...................................................................................................................3-7 Installation and Maintenance ...............................................................................................3-7 Safety ...................................................................................................................................3-7 4 ENERGY STORAGE TO INTEGRATE RENEWABLES........................................................4-1 Overview ..............................................................................................................................4-1 Solar Photovoltaic Ramping Support ...................................................................................4-1 Overview ........................................................................................................................4-1 Use Cases and Operating Modes ..................................................................................4-2 xvi Performance Ratings .....................................................................................................4-2 System Effectiveness.....................................................................................................4-3 Physical Characteristics .................................................................................................4-3 Electrical Interface..........................................................................................................4-4 Communications, Control, and Data Management ........................................................4-5 Installation and Maintenance .........................................................................................4-5 Safety .............................................................................................................................4-6 Wind Ramping Support ........................................................................................................4-6 Overview ........................................................................................................................4-6 Use Cases and Operating Modes ..................................................................................4-7 Performance Ratings .....................................................................................................4-8 System Effectiveness.....................................................................................................4-9 Physical Characteristics .................................................................................................4-9 Electrical Interface........................................................................................................4-10 Communications, Control, and Data Management ......................................................4-10 Data Access .................................................................................................................4-11 Installation and Maintenance .......................................................................................4-11 Safety ...........................................................................................................................4-12 Load and Resource Shifting...............................................................................................4-12 Overview ......................................................................................................................4-12 Use Cases and Operating Modes ................................................................................4-13 Performance Ratings ...................................................................................................4-14 System Effectiveness...................................................................................................4-14 Physical Characteristics ...............................................................................................4-15 Electrical Interface........................................................................................................4-16 Communications, Control, and Data Management ......................................................4-16 Installation and Maintenance .......................................................................................4-17 Safety ...........................................................................................................................4-17 5 RECOMMENDATIONS FOR FUTURE WORK ......................................................................5-1 Collection and Sharing of Data ............................................................................................5-1 System Sizing for Solar Photovoltaic Ramping Application .................................................5-1 Solar Photovoltaic Control Algorithms..................................................................................5-1 Wind Plant Low-Voltage Ride-Through................................................................................5-1 Solar Photovoltaic and Wind Duty Cycles............................................................................5-1 Communication Protocol Details ..........................................................................................5-2 Defining Functional Requirements for Other Energy Storage Applications .........................5-2 6 REFERENCES .......................................................................................................................6-1 A APPLICABLE CODES AND STANDARDS ......................................................................... A-1 B APPLICABLE PARAMETERS FOR SPECIFICATIONS...................................................... B-1 xvii C ABBREVIATIONS, ACRONYMS, AND TERMINOLOGY .................................................... C-1 D PARTICIPANTS.................................................................................................................... D-1 xviii LIST OF FIGURES Figure 1-1 Overview of Energy Storage Use Cases ..................................................................1-2 Figure 1-2 Overview of Siting of Energy Storage Applications ..................................................1-3 Figure 2-1 Block Diagram of Substation–Based Storage Applications ......................................2-2 Figure 3-1 Block Diagram of Distributed Energy Storage System Applications.........................3-2 Figure 4-1 Block Diagram of Solar Photovoltaic Ramping Support Applications .......................4-2 Figure 4-2 Block Diagram of Ramping Applications ..................................................................4-7 Figure 4-3 Block Diagram of Load and Resource Shifting Applications ..................................4-13 xix LIST OF TABLES Table 1-1 Matrix for Substation-Based Storage and Distributed Energy Storage Systems Applications................................................................................................................................1-6 Table 1-2 Matrix for Energy Storage to Integrate Renewables .................................................1-7 xxi 1 INTRODUCTION Current Developments Affecting the Electricity Grid The electric power grid is quickly evolving into a smarter, more sophisticated delivery system that incorporates new renewable, distributed generation, end-use, and communications and control systems. The changes will provide many benefits, such as the ability to respond to public policy goals, increase the diversity of generation options, and provide consumers with more choices; however, the challenges are several, including the following: Variable renewable energy generation with limited dispatchability is rapidly growing in its overall contribution to the resource mix. Variability in solar photovoltaic (PV) power output due to the diurnal solar cycle, passing clouds, and other events can lead to ramping events and unpredictable load management at the system level. Likewise, variations in wind power output, whether short term (seconds) or longer term (minutes), may affect distribution voltage (in those cases in which wind is connected at the distribution level) and might create a requirement for additional regulation and ramping support at the system level. State renewable portfolio standards, which require that a specified minimum fraction of the electricity supplied in a state be generated from renewable energy sources, will likely result in substantial increases in the penetration of these sources on the grid in the coming 10–20 years. Bidirectional power flow created by distributed energy resources presents a challenge for distribution systems with voltage regulation and protection schemes originally designed for one-way power flow. Smart Grid designs call for additional distribution automation and sophistication, such as islanding and self-healing designs aimed at improving user reliability. Limited transmission capacity threatens to force existing clean energy wind resources to be curtailed during peak production times, but expansion of new transmission capacity presents regulatory and environmental challenges. Utilities seek new ways to extend the useful life of existing capital assets to defer investment in capital upgrades and maintain reliable power at a reasonable cost to users while accounting for uncertainty in load growth. Potential Uses for Electric Energy Storage In principle, all these issues can be addressed with appropriately designed grid-connected storage systems. Storage can be sized from the kilowatt range up to thousands of megawatts. It can be designed to discharge from subcycle durations up to many days. Storage can be controlled locally or remotely and can be designed for extremely fast reaction in response to control signals. Storage can both absorb and inject active power and can be coupled with power electronics that can absorb and inject reactive power. 1-1 Depending on the utility requirements, storage systems can provide voltage and frequency regulation, load and resource shifting, ramping, and dispatchability. They can be designed for the needs of distribution and/or transmission systems and for single-purpose or multi-purpose operation (see Figure 1-1). 1000 Power Rating (MW) 100 Load Leveling Ramping Energy Arbitrage Spinning Reserve System Stability Renewables - Wind - Solar VAR Support 10 Frequency Regulation Power Quality 1.0 Temporary Power Interruptions Peak Peak Shaving Shaving T&D Deferral and T&D Deferral Transmission Conjunction Management Remote Island Applications Village Power Applications 0.1 0.1 Cycle 10 Cycle 15 Second 15 Minutes 1 Hour 5 Hour Energy Discharge Time (Axis Not To Scale) Source: Electric Power Research Institute Figure 1-1 Overview of Energy Storage Use Cases Electric Energy Storage Options and Technology Neutrality A wide range of technologies that have the potential to meet these application needs have been or are being developed, including the following: Electrical. Capacitors, supercapacitors, and superconducting magnetic energy storage systems Electrochemical. Battery systems, flow batteries, and hydrogen with fuel cells Mechanical. Pumped hydroelectric energy storage, compressed air energy storage, flywheel energy storage, and hydraulic accumulators 1-2 The process and this report were based entirely on utility requirements for specific applications, and not on the capabilities of underlying storage technologies. Although certain energy storage technologies might operate better in one application or area than another, it is not the purpose of this project to evaluate the suitability of specific storage technologies. To the extent possible, the descriptions of the functional requirements in this report are applicable across all possible technologies. However, on occasion, there are references to requirements that are expected to be relevant only to specific technologies. For example, the capacity of electrochemical batteries might degrade over time, so the rating of systems must account for this possibility, and this is addressed. Such references are provided merely for comparability and clarity; they are not intended to represent recommendations about the suitability of a given storage option. Figure 1-2 illustrates possible siting options for energy storage applications. Source: Electric Power Research Institute Figure 1-2 Overview of Siting of Energy Storage Applications Defining Functional Requirements What is a Functional Requirement Versus a Technical Specification? This report is the result of a consensus process among participating utilities (with input from developers, independent system operators, government and private institutions) as a means of communicating basic requirements and uses for storage as they pertain to identified needs. It is not intended to serve as a procurement specification. For developers, the report will provide insight into the needs and basic system requirements that their products will be called on to 1-3 deliver. For the utilities, the report will serve to facilitate the development of specific procurement documents based on the existing knowledge base for energy storage. Such a utility procurement document would include much more specific information that is not covered in this report. For example, although this document does reference a few key standards (see Appendix A), most utilities would likely reference additional requirements that are specific to their procurement practices (see Appendix B). Utilities might also elect to simplify the requirements, for example, by reducing the number of operating modes. In this report, performance requirements are suggested, subject to more precise determination by the buying utility. Accordingly, the verb form used in these functional requirements is, in many cases, should or may rather than shall or must. When used in a purchase specification, the verbs in these suggested requirements should be modified appropriately to declare a requirement. EPRI’s Role in Energy Storage The Electric Power Research Institute (EPRI) and its member companies have done considerable research and analysis of the benefits of energy storage within the utility distribution system. Much of this progress will enable energy storage to be a fundamental component and benefit to the creation of the Smart Grid. The U. S. Department of Energy defines the Smart Grid as an automated, widely distributed energy delivery network, characterized by a two-way flow of electricity and information, that is capable of monitoring and responding to changes in everything from power plants to customer preferences to individual appliances. This advanced network will make it possible to lower the high cost of meeting peak demand and will support the incorporation of distributed and renewable energy sources [1]. Many utilities and other stakeholders believe that the development and implementation of energy storage at the distribution level is critical to creation of the Smart Grid. One utility that has taken a leadership role in the development and implementation of distributed energy storage specifications is American Electric Power (AEP). AEP has circulated for public comment a set of specifications defining a concept for distributed energy storage called community energy storage. In 2009, AEP and EPRI engaged in a stakeholder review process using these open source specifications as a starting point, developing a set of broader functional requirements based on stakeholder input. This input included a broad range of comments from potential users, manufacturers, and systems developers. Four webcasts were held, and many stakeholders contributed. The AEP community energy storage specifications are procurement documents; therefore, they contain many technical details specific to AEP’s requirements [2]. The functional requirements in this report are intended to be more general so that they apply all utilities that have typical applications (that is, use cases and operating modes) for energy storage systems. This Project The Basics EPRI developed this project to bring together stakeholders in the development of stationary energy storage systems, solicit their input, and develop application requirements for energy 1-4 storage system solutions in transmission, substation, and distribution applications and for integration of large-scale renewables into power system operations. The project team believes that the application of energy storage to improve the flexibility of the grid to accommodate the penetration of renewable energy potentially has the greatest benefit to renewable energy project developers and power system operators alike. Energy storage can have value for specific customer installations, such as allowing a solar array to serve off-peak or nighttime loads. This project does not address customer-sited storage—only utility-sited storage on the utility system—although a system could be located near a customer facility and it could address the unique grid impact of a small group of customers. These functional requirements were developed through the consensus of utilities and other stakeholders that have participated in the process. Objective and Scope The objective of this project was to develop a set of functional requirements for energy storage systems to be used in specific ways (use cases and operating modes). The objective is for utilities and developers to work with a common understanding to develop the most effective storage solutions to utility problems by steering procurement and development efforts consistent with these requirements. The project scope consisted of adhering to the following set of guidelines. The process and this document were based entirely on utility requirements and not on the capabilities of underlying storage technologies. Although certain energy storage technologies might operate better in one application or area than another, it is not the purpose of this project to evaluate the suitability of specific storage technologies. Economic analysis of the applications was not performed. The process and this report address only high-level functional requirements and are not intended to serve as a complete technical specification for procurement. The ultimate list of requirements, including specific standards and other utility-specific requirements, will have to be specified by the utilities through its normal procurement process. Not all storage applications were included. Other variations, such as storage for the exclusive purpose of frequency regulation or seasonal energy storage, are possible, but they are not included in the scope of this project. This report focuses on a few high-priority applications identified by the utility participants. Energy storage at the customer side of the meter was not considered in this project. The project focuses, instead, on opportunities in utility system management. Tables 1-1 and 1-2 are provided to summarize how each application fits into the overall list of functional requirements being developed. These matrices are not intended to list all possible applications. Rather, they are intended to describe systems, their uses, and technical requirements as configured in each section. 1-5 Table 1-1 Matrix for Substation-Based Storage and Distributed Energy Storage Systems Applications Application Substation-Based Storage (see Section 2) 1–20 MW 2–6 hours Includes both stationary and transportable Distributed Energy Storage System (DESS) Use Cases / Operating Modes (See Note) Interconnection Point Notes Peak load management is controlled using substation/feeder real-time load signals. Peak load management Frequency regulation Distribution voltage (4kV–34kV) Capacity market (regional transmission organization [RTO] or independent system operator [ISO]) Substation or feeder Frequency regulation controlled using signals from ISO. Although not currently in effect, a capacity market controlled using signals from ISO is a future option. Voltage regulation/reactive power support Peak load management is controlled using substation/feeder real-time load signals. Peak load management (see Section 3) Backup power/islanded grid operation 25–200 kW (individual unit rating) Voltage regulation/reactive power support Single-phase (25–75 kW) Frequency regulation (may require aggregation) Three-phase (up to 200 kW) Capacity market (RTO or ISO) Secondary (customer) voltage Utility side of meter May operate as island Frequency regulation controlled using signals from ISO. May be used in capacity markets. Reactive power dispatch based on local voltage. If only frequency regulation is desired, duration may be as low as 15 minutes. 2–4 hours Note: Use cases are listed in order of decreasing priority. Products need not meet all use cases. 1-6 Table 1-2 Matrix for Energy Storage to Integrate Renewables Application Solar PV Ramping Support (see Section 4) Power up to several megawatts (TBD by utility site) 1 second to 20 min (TBD by utility) Wind Ramping Support (see Section 4) 1–100 MW 2–15 minutes Life equivalent to 10,000 full energy cycles Use Cases/Operating Modes Accommodate rapid power swings that would otherwise create disturbances on systems where highpenetration levels of solar PV systems are found Interconnection Point Better manage the variability of solar active power output. Distribution voltage (4kV–34kV) Accommodate variable wind farm output so that ramp rates (MW/min) are kept within design limits Provide net load ramping support for the grid at large Maintain local transmission and distribution system voltage Distribution voltage (4kV–34kV) Transmission voltage (>34kV) Provide frequency regulation Kilowatts to many hundreds of megawatts 2–10 hours Reactive power controlled based on local voltage. (This function is accomplished by the power electronics accompanying the storage.) If local benefits for control area or a specific distribution feeder are required (as for a single wind farm), storage system must be co-located with the variable generation. If bulk power system benefits are desired, storage system can be located anywhere on the grid. LVRT support is built-in to most modern wind turbines. Provide low-voltage ridethrough (LVRT) for wind farm (if required) Load or Resource Shifting (see Section 4) Notes Store energy generated during off-peak demand periods to serve loads during peak demand periods Participate in capacity markets as dispatchable energy and reserves Distribution voltage (4kV–34kV) Transmission voltage (>34kV) May be directly coupled and sized to local renewable resource or sized and operated independently. May also serve to reduce ramp rates from variable wind farm output and dampen solar PV ramping. Provide ancillary services In many cases, the working groups avoided the tendency to list all possible uses and focused instead on the one or two most likely uses given the size, location, and other characteristics of the system. In addition, the working groups recognized that some pairs of uses are mutually exclusive. For example, capacity allocated to longer-duration load following might not be simultaneously allocated to instantaneous frequency regulation. In such cases, the use cases are listed in order of priority. 1-7 It is true, however, that some equipment intended to serve one of the applications might also provide benefits described in another application. For example, storage designed for substation support might also provide local utility assistance useful for handling short-term ramps from a big box store’s solar system. Approach and Process This project began with EPRI drafting a strawman application requirement, followed by an internal review, and a webinar with EPRI members to provide initial review of the strawman document. A series of webinars were conducted for review of the document by increasing numbers of utility and non-utility stakeholders. Stakeholders were identified through either prior engagement in energy storage activities, a position of significance for the project, or project members who were already involved. Participants were encouraged to join one or more application work groups. Five work groups were formed to scrutinize the functional requirements of each of the applications in preparation for application-specific webinars. Throughout the project, participants were encouraged to submit comments, additions, and specific wording to the project group for inclusion. Over the course of this project, more than 100 companies have participated in varying capacities (see Appendix D). This report is the result of six work group conference calls, nine webinar meetings, and a number of off-line inputs received directly from utility companies, vendors, independent system operators, regulators, government agencies, and universities. 1-8 2 SUBSTATION-BASED STORAGE Overview Description of Application Substation-based storage systems provide utility-controlled energy storage for any or all of the following: Peak load management Frequency regulation and area control Generation capacity Reactive power support Critical load support during outage (islanding) Systems should generally have a maximum power rating of 1–20 MW (charging and discharging) and the ability to store 2–6 hours of energy for on-demand delivery to the power grid. For frequency regulation and capacity markets, systems may be able to provide energy for shorter time periods. For peak load management to provide substation grid support, the minimum practical storage size is believed be about 1 MW for 2–6 hours, for 15-kV class distribution systems. For 25-kV and 35-kV classes, the minimum practical size of a unit is probably 4 MW. Products can be modular. Systems would connect at distribution voltage at the substation or feeder. Systems can also serve the purpose of renewable integration (see Section 4). Systems include stationary units and transportable units. Stationary units are physical assets sited at the substation or distribution feeder, with a useful service live of about 15 years. Transportable units are physical assets that also have a service life of about 15 years but that may be easily relocated from site to site as utility needs change, typically on a seasonal basis. They may be installed with minimal site preparation in a period of approximately one day and removed in approximately one day, with standard utility equipment such as cranes and lifts. Scheduled maintenance is expected, including replacement of a storage device (such as energy storage). Replacement schedules and costs must be understood in the purchasing decision. Figure 2-1 illustrates a typical substation-based storage application. 2-1 Utility Substation or Feeder Transformer (Optional) Disconnect Aux. Loads (Optional) Contactor Energy Storage and Power Conditioning Figure 2-1 Block Diagram of Substation–Based Storage Applications Use Cases and Operating Modes Systems may be capable of serving multiple purposes, each represented by a control mode. These modes could all be supported within the system capabilities and self-protection requirements. Modes may include the following: Load follow mode. The system ideally could discharge at varying levels according to a control signal. The system ideally would calculate the required discharge relative to a remotely set threshold value. Frequency regulation mode. The system ideally could charge or discharge in response to signals received approximately every second. The system ideally would seek to maintain a target state of charge (such as 50%) over the long run while supporting frequency or area control. (Although the utilities participating in this project considered load following, for peak load management, to be the primary application, systems that provide only frequency regulation, for either transmission or distribution, are also possible. Constant power charge mode. The system could charge at a fixed kilowatt power level. Constant power discharge mode. The system could discharge at a fixed kilowatt power level. Reactive power mode. Systems may be designed to source or sink reactive power. This function could be part of power charge or power discharge mode. 2-2 Self-directed charge mode. The system could charge according to its own optimum method to reach a defined ready state at a defined time. Self-maintenance mode. The system is free to perform its own conditioning, as needed. Standby mode. The system may neither charge nor discharge but only draw necessary auxiliary load. Contactors are closed. Shutdown mode. The system may open its contactors to prevent interaction with the grid. (Nominal auxiliary load contactors may continue to serve these loads.) Islanding mode. Upon sensing a loss of power from the utility, the system will shut down. If an outage persists for a predetermined time (to be determined by the utility), the system may come back to serve loads to be determined by the utility. A block diagram for a system designed to operate in this mode would differ from Figure 2-1. Performance Ratings System Definition Systems interconnect with the utility at distribution voltage (that is, the voltage of the substation or feeder) and include step-down transformers (if necessary), a main disconnect breaker, a contactor, and all power conditioning and auxiliary systems necessary to support their operation. Auxiliary Loads All auxiliary loads necessary to operate and protect the system, such as controls, cooling systems, fans, pumps, and heaters, are considered auxiliary loads internal to the system. System Rating Practices Systems should be rated, in both power and energy, as measured at the interface of the system and the utility. All system loads and losses, including wiring losses, power conditioning losses, auxiliary loads, and chemical or ionic losses could be considered internal to the system, and ratings are net of these loads and losses. In cases where auxiliary loads (such as cooling systems) are periodic in nature, ratings could be described for conditions in which these loads are active in the worst-case conditions (or, alternatively, provide sufficient supplementary information so that ratings under these worst-case conditions may be easily determined). System net power ratings may be defined in either kWAC or MWAC for a nominal constant discharge of 4 hours. Additional power ratings, such as pulse power capabilities, may also be specified. System net energy ratings may be defined in either kWhAC, MWhAC, or hours at rated power that is sustainable for a nominal discharge time. System reactive power capabilities should be specified in kvar, Mvar, or power factor. When islanded, systems should be able to cope with momentary overload and support in-rush currents at 2.5 to 3 times the normal ratings for 2–3 seconds and also be able to maintain constant voltage under changing customer loads. 2-3 Storage System Effectiveness Storage Efficiency Storage efficiency is defined as follows: kWhout kWhin Equation 2-1 Where: kWhout is the total ac energy delivered by the storage system to the grid across the standard duration of discharge from fully charged to fully discharged at its rated continuous power capacity. kWhin is the total energy delivered from the grid to the storage system over a full 24-hour daily cycle (the charging energy). The measurement of reported storage efficiency should begin and end with the system at a full state of charge. This measurement would be performed using only the remote operating modes available to the system operator, with no manual intervention. Performance Curve The system should have an estimated calendar life of at least 15 years and 1500 full energy cycles. If the life of the product is expected to deteriorate with time or use, the system should be designed so that the full energy requirements are met at the end of the expected lifespan under expected usage conditions. If the product lifetime is sensitive to depth of discharge, the product should be sized so that the energy requirements are met at a given depth of discharge at the end of life and that this depth of discharge is selected to meet the required cycle life according to manufacturer recommendations. For lifetime assessment, it would be beneficial to have a graph that displays the distinction between depth of discharge and required number of cycles. Physical Characteristics Size Systems should be designed to minimize footprint and volume. For example, systems would ideally be less than 500 ft2/MWh and include space needed to maintain and install the system. 2 Systems would preferably not exceed 2000 ft or 15–20 feet in height. Other siting restrictions should be clearly stated. Transportation Standards Systems should be transportable at normal speeds over all North American interstate highways and railways, and meet all U.S. Department of Transportation (USDOT) hazardous materials and other regulations. For example, systems should be designed so that turn radii and bridge 2-4 clearances are met when transported on lowboy trailers. System components (such as electrolyte) may be shipped separately, as needed, and assembled at the site. Rigging and Harnessing Systems should be installable using standard industry rigging equipment, such as cranes and lifts, and include provisions for installation in the system design. Status Lights and Alarms Systems should be equipped with meaningful status lights and light-emitting diode (LED) panels to operate the system and, at minimum, provide easy access to mode and ac power (charging or discharging) information. Audible alarms should be included as necessary to ensure safety, such as for chemical leaks. Environmental Conditions Systems should be designed to meet normal utility standards regarding ambient temperature ranges, humidity ranges, air quality, emissions (sulfur oxides [SOx], nitrogen oxides [NOx], and other air emissions if applicable), seismic, audible noise (similar to power transformers), electromagnetic interference (EMI), fire protection (National Fire Protection Association [NFPA] standards), and flood protection (specified by utilities in the procurement process). Supplier must provide sufficient information specific to their particular product to facilitate utility personnel training and communications with emergency response and environmental agencies. Material safety data sheets (MSDSs) should be provided as applicable. Sample codes and standards are listed Appendix A. Electrical Interface Standards Systems should meet nationally recognized standards for safety, electrical design, interconnection, harmonics, dc injection, and insulation. Utilities are not required to meet Underwriters Laboratories (UL) standards for equipment on the utility side of the meter. However, UL and other relevant interconnection standards may be required by the utilities for safety or protection of the grid. (For example, standards that address system response to grid disturbances, such as UL 1741, may be required.) Disconnect Breaker The disconnect breaker must be capable of breaking the full rated power of the system and operated either manually or remotely. The utility may require that this device accommodate short-circuit and basic impulse level ratings. Contactor The system should have a contactor, the operation of which is dependent on the mode. Auxiliary loads ideally would be served internally to the system, so that all power draw ideally would be through the contactor, unless required by the utility. 2-5 Communications, Control, and Data Management Communications Method Systems may be communication agnostic and incorporate open systems communication architecture. Communications Protocol The system may require any of several communications options, such as cellular, mesh node, Wi-Fi, and WiMAX. Selection between communications options will depend on the utility. Also, the control interface protocol will be specified by the utility. Typical control interface protocols such as the Distributed Network Protocol 3 (DNP3; serial or Internet protocol [IP]) and International Electrotechnical Commission (IEC) 61850 may be specified by the utility. Integrated Interface Systems may be required to be designed in conformity with the Smart Grid Interoperability Standards [3], to the extent applicable at their current level of development. Specifically, systems may be required to be consistent with the energy storage interconnection guidelines and the Energy Storage and Distributed Energy Resources (ES-DER) Use Cases [4]. Utilities will generally require monitoring and control through their operations centers. Systems may be operated in various utility-defined modes and are preferably capable of responding appropriately to load signals as described in this report. Systems can include the necessary communication and telemetry hardware, and may support communications protocols, to effectively provide the required services. Types of control include the following: Load-following signals provide an analog of load measured at the location of interest, such as the substation serving the local area loads, in intervals of 1–10 minutes. The system responds by discharging power proportionate to the load that exceeds a specified constant threshold. Frequency regulation signals are provided by the RTO or ISO, typically in intervals of 1–5 seconds. The system responds by charging or discharging at a power level proportional to the signal level. Capacity signals are received from a power market (such as an ISO), in intervals of 10–60 minutes, that indicate the system’s discharge power level. The system could also provide relevant status information, such as state of charge and measured power, for feedback to the utility control system. The system might also have a liquid crystal display (LCD) or similar local control capability, with additional control capabilities and diagnostics. Operational Data Systems could have the provision for storing key operational data in a time-sequenced flat data file. At a minimum, systems should store energy received and energy delivered in minute-byminute, time-stamped data bins. 2-6 Event-Triggered Data Systems could also store events, such as changes in operational mode, received commands, faults, and shutdowns. Each event could be time stamped. Data Access All data could be downloadable, either remotely or locally via a standard computer port or wireless connection. All data could be exportable in a nonproprietary format. Installation and Maintenance Systems should be designed to allow installation, operation, and maintenance by utility-qualified substation and distribution personnel and contractors. Adequate documentation and training should be provided. Systems should require only standard shop and electrical tools, lifts, and cranes, or specialty tools should be supplied with the systems. Subsystems, such as power electronics modules or energy storage banks (ac or dc connections), may be classified by the supplier as nonserviceable in the field, provided that these subsystems may be removed and replaced by utility personnel. All consumable or degradable parts, such as air filters, should be classified by replacement interval. Safety Systems should be able to protect themselves from internal failures and utility grid disturbances. Therefore, systems should be self protecting for ac or dc component system failures. In addition, systems should be able to protect themselves from various types of grid faults and other abnormal conditions on the grid. Systems should reflect the safety standards of the utility. For example, utility and local fire personnel should be notified of particular safety issues and the appropriate response in case of an emergency. Systems should be designed to minimize risk of injury to the workforce and public during installation, maintenance, and operation. Systems should be designed to minimize the risk of damage to the environment, including land contamination or disturbance (footprint), water contamination or diversion, and air emissions. Systems should not require that a utility develop a spill containment plan or provide additional safety equipment. Systems could be designed to be recycled through known processes. Disconnects could be lockable and have a visible break. 2-7 3 DISTRIBUTED ENERGY STORAGE SYSTEMS— UTILITY PAD MOUNT Overview Description of Application Utility pad-mounted DESSs are utility-controlled electrical energy storage units that can be used to provide the following: Peak load management (may be used for transmission and distribution asset deferral) Increased customer reliability (backup power) Voltage regulation and reactive power support Frequency regulation (may require aggregation to meet minimum size requirements) Generation capacity to the RTO or ISO Systems could be designed with a power rating of 25–200 kW (charging and discharging) and to store 2–4 hours of dispatchable energy to the grid, as needed, unless the system serves only voltage regulation purposes, in which case it may store 15+ minutes of dispatchable energy. To enhance the voltage regulation capabilities, systems may be designed with reactive power ratings as specified by the utility. Systems can be located anywhere along the distribution feeder on secondary (customer-level) voltages but on the utility side of the meter. Systems can operate in island mode, as necessary, and support the loads of one or more utility customers, depending on sizing. The system may also serve the purpose of renewable integration (hybrid option) as described in Section 4. Figure 3-1 illustrates a typical DESS application. 3-1 Distribution Transformer Bypass (N/O) Disconnect Breaker Aux. Loads (Optional) Bypass (N/C) Energy Storage and Power Conditioning To customers Figure 3-1 Block Diagram of Distributed Energy Storage System Applications Use Cases and Operating Modes Systems could be capable of serving multiple purposes, each represented by a control mode. These modes could all be supported within the system capabilities and self-protection requirements. Modes include the following: Peak load management mode. The system could discharge at varying levels according to a control signal. The system could calculate the required discharge relative to a remotely-set threshold value. Frequency regulation mode. The systems, when operated as a group, could charge or discharge in response to signals received approximately every second. The system could seek to maintain a target state of charge (such as 50%) over the long run while supporting frequency. Constant power charge mode. The system could charge at a fixed kilowatt power level. Constant power discharge mode. The system could discharge at a fixed kilowatt power level. 3-2 Reactive power mode. Systems may be designed to source or sink reactive power. This function could be part of power charge or power discharge mode. Self-directed charge mode. The system could charge according to its own optimum method to reach a defined ready state at a defined time. Self-maintenance mode. The system is free to perform its own conditioning, as needed. Standby mode. The system should neither charge nor discharge but only draw necessary auxiliary load. Contactors are closed. Shutdown mode. The system may open its contactors to prevent interaction with the grid. (Nominal auxiliary load contactors may continue to serve these loads.) Islanding mode. The systems could detect abnormal utility conditions or open contactor and serve customers in an island (refer to IEEE P1547.4). When the utility is restored, it could resynchronize and reconnect. – Quick transition mode. The system may respond quickly (for example, subcycle) and automatically to island mode. – Intended or adjustable time-delayed transition mode. The system may delay (for example, minutes) the switch to island mode to allow other grid systems to react before islanding. System Rating Practices System Definition In addition to specifications for the storage system, procurement documentation should contain specifications for all switchgear and auxiliary loads necessary to support its operation (see Figure 3-1). Auxiliary Loads All auxiliary loads necessary to operate and protect the system, such as controls, cooling systems, fans, pumps, and heaters, should be considered auxiliary loads internal to the system. Operation As a Current Source or Voltage Source When synchronized with the utility and operating as a current source, the system may be capable of discharging stored energy to either the customer load or the utility, depending on the relative size of the load to the discharge power. In the extreme case, when customer load is zero, all energy may flow to the utility. If operating in island mode and as a voltage source, all energy flows to the customer loads. System Rating Practices Systems may be rated in terms of net delivered power and energy. With two interconnection points (the utility and the customer load), the net power is the total outflow power, less the total inflow power. For example, if the power delivered to the load is 50 kW and the power delivered from the utility is 30 kW, the net delivered power is 20 kW. 3-3 All system loads and losses, including wiring losses, losses through the contactor/static switch, power conditioning losses, auxiliary loads, and chemical or ionic losses are considered internal to the system and ratings are net of these loads and losses. In cases where auxiliary loads (such as cooling systems) are periodic in nature, ratings may be described for conditions in which these loads are active in the worst-case conditions (or, alternatively, provide sufficient supplementary information so that ratings under these worst-case conditions may be easily determined). System net power ratings may be in kWAC for a nominal constant discharge of 4 hours. Additional power ratings, such as pulse power capabilities, may also be specified. System net energy ratings may be in either kWhAC or hours at rated power that is sustainable at the nominal discharge time. System reactive power capabilities should be specified in kvar or power factor. When islanded, systems should be able to cope with momentary overload and support in-rush currents at 2.5 to 3 times the normal ratings for 2–3 seconds and also be able to maintain constant voltage under changing customer loads. System Effectiveness Standby Efficiency Standby efficiency may be specified and defined as the ac energy delivered from the storage system to the load over 24 hours, divided by the energy delivered to the storage system from the grid over the same period, during which no charge or discharge operation of the storage system is performed other than as necessary for maintaining full charge and readiness. For example, if heaters or pumps are operated during the 24-hour period, these would reduce the standby efficiency because they would require the utility to supply their energy. To test the standby efficiency, the load may be a constant resistive load at 1/10 the system power rating. Storage Efficiency Storage efficiency is defined as follows: kWhout kWhin Equation 3-1 Where: kWhout is the total ac energy delivered by the storage system to the grid across the standard duration of discharge from fully charged to fully discharged at its rated continuous power capacity. kWhin is the total energy delivered from the grid to the storage system over a full 24-hour daily cycle (the charging energy). 3-4 The measurement of reported storage efficiency should begin and end with the system at a full state of charge. This measurement may be performed using only the remote operating modes available to the system operator, with no manual intervention. Speed of Response Specifications may define maximum transition time between detection of utility disturbance and the islanded support of connected loads. This transition time would include detection, switching, and storage ramp-up to steady-state power. Performance Curve The system should have an estimated calendar life of at least 15 years. If the life of the product is expected to deteriorate over time, the following requirements apply: For peak load management, the system ideally has an estimated cycle life of at least 2250 cycles at full energy discharge. If required by the utility for frequency regulation, the system should, in addition, have an estimated cycle life of at least 150,000 cycles at 10% depth of discharge. If the product is sensitive to depth of discharge, the manufacturer could state the limitations and the product should be sized so that the depth of discharge corresponds to the required cycle life. For lifetime assessment, it would be beneficial to have a graph that displays the distinction between depth of discharge and required number of cycles. Physical Characteristics Size Systems should be designed to minimize footprint and volume. Other siting restrictions should be clearly stated. Transportation Standards Systems should be transportable at normal speeds over all North American interstate highways and railways, and meet all USDOT hazardous materials and other regulations. For example, systems should be designed so that turn radii and bridge clearances are met when transported on lowboy trailers. System components (such as electrolyte) may be shipped separately, as needed, and assembled at the site. Rigging and Harnessing Systems should be installable using standard industry rigging equipment, such as cranes and lifts, and include provisions for installation in the system design. Status Lights and Alarms Systems should be equipped with meaningful status lights and LED panels to operate the system and, at minimum, provide easy access to mode and ac power (charging or discharging) 3-5 information. Audible alarms should be included as necessary to ensure safety, such as for chemical leaks. Environmental Conditions Systems should be designed to meet normal utility standards regarding ambient temperature ranges, humidity ranges, air quality, emissions (SOx, NOx, and other air emissions if applicable), seismic, audible noise (similar to power transformers), EMI, fire protection (NFPA standards), and flood protection (specified by utilities in the procurement process). Supplier must provide sufficient information specific to their particular product to facilitate utility personnel training and communications with emergency response and environmental agencies. MSDSs should be provided as applicable. Sample codes and standards are listed Appendix A. Electrical Interface Standards Systems should meet nationally recognized standards for safety, electrical design, interconnection, harmonics, dc injection, and insulation. Utilities are not required to meet UL standards for equipment on the utility side of the meter. However, UL and other relevant interconnection standards may be required by the utilities for safety or protection of the grid. (For example, standards that address system response to grid disturbances, such as UL 1741, may be required.) Disconnect Breaker The disconnect breaker should be lockable and have a visible break. It should be capable of breaking the full rated power of the system and operated manually. The utility will have full access and control over this device. Communications, Control, and Data Management Communications Method Systems may be communication agnostic and incorporate open systems communication architecture. Communications Protocol The system may require any of several communications options, such as cellular, mesh node, Wi-Fi, and WiMAX. Selection between communications options will depend on the utility. Also, the control interface protocol will be specified by the utility. Typical control interface protocols such as (DNP3, serial or IP) and IEC 61850 may be specified by the utility. Integrated Interface Systems may be required to be designed in conformity with the Smart Grid Interoperability Standards [3], to the extent applicable at their current level of development. Specifically, systems may be required to be consistent with the energy storage interconnection guidelines and the 3-6 Energy Storage and Distributed Energy Resources (ES-DER) Use Cases [4]. Utilities will generally require monitoring and control through their operations centers. Systems should be operated in various utility-defined modes and could be capable of responding appropriately to load signals as described in this report. Systems could include the necessary communication and telemetry hardware, and could support communications protocols, to effectively provide the required services. For example, in the load-following mode, the system could respond to a time-varying discharge power level request sent by the utility and representing the substation or load. The system could also provide relevant status information, such as state of charge and measured power, for feedback to the utility control system. The system could also have an LCD or similar local control capability, with additional control capabilities and diagnostics. Operational Data Systems could have provisions for storing key operational data in a time-sequenced flat data file. At a minimum, systems should store energy received and energy delivered in minute-by-minute, time-stamped data bins. Event-Triggered Data Systems could also store events, such as changes in operational mode, received commands, faults, and shutdowns. Each event could be time stamped. Data Access All data could be downloadable, either remotely or locally, via a standard computer port or wireless connection. All data could be exportable in a nonproprietary format. Installation and Maintenance Systems should be designed to allow installation, operation, and maintenance by utility-qualified substation and distribution personnel and contractors. Adequate documentation and training should be provided. Systems should require only standard shop and electrical tools, lifts, and cranes, or specialty tools should be supplied with the systems. Subsystems, such as power electronics modules or energy storage banks (ac or dc connections), may be classified by the supplier as nonserviceable in the field, provided that these subsystems may be removed and replaced by utility personnel. All consumable or degradable parts, such as air filters, should be classified by replacement interval. Safety Systems should be able to protect themselves from internal failures and utility grid disturbances. Therefore, systems should be self protecting for ac or dc component system failures. In addition, systems should be able to protect themselves from various types of grid faults and other abnormal conditions on the grid. 3-7 Systems should reflect the safety standards of the utility. For example, utility and local fire personnel should be notified of particular safety issues and the appropriate response in case of an emergency. Systems should be designed to minimize risk of injury to the workforce and public during installation, maintenance, and operation. Systems should be designed to minimize the risk of damage to the environment, including land contamination or disturbance (footprint), water contamination or diversion, and air emissions. Systems should not require that a utility develop a spill containment plan or provide additional safety equipment. Systems should preferably be designed to be recycled through known processes. Disconnects could be lockable and have a visible break. 3-8 4 ENERGY STORAGE TO INTEGRATE RENEWABLES Overview Although there are other storage applications to integrate renewable energy systems (such as grid voltage support and wind short-term power fluctuations), the scope of this project focused on the following three main applications that the participating utilities determined to be most important: Solar PV ramping support applications, which provide power for short periods of time (a few seconds up to 20 minutes) to accommodate power swings that would otherwise create disturbances on the system. Wind ramping support applications, which help accommodate variable wind farm output so that system ramp rates are kept within a desirable range for the power delivery system, by providing buffer capacity of 1–100 MW of energy for up to 15 minutes. Load and resource shifting applications, which are intended to serve loads occurring during peak periods with energy generated and stored during off-peak demand times. To do this, the storage units will require up to 10 hours of energy. They could be deployed in a wide range of power ratings, from a few kilowatts to many hundreds of megawatts (potentially even gigawatts). Systems could be designed to address other applications as well, to obtain a better return on the upfront capital investment. Solar Photovoltaic Ramping Support Overview Description of Application Solar PV ramping support systems provide short-term utility-controlled electrical energy storage to accommodate power swings that would otherwise create disturbances on systems where high penetration levels of solar PV systems are found on distribution feeder circuits, especially during times of low loads. Systems could be designed up to several millivolt amperes of reactive power and active power determined by the utility site, sized according to the local circuit needs and storing up to 20 minutes of energy. Systems are located on distribution voltages. Figure 4-1 illustrates a typical solar photovoltaic ramping support application. 4-1 Distribution Line Transformer (Optional) Disconnect Aux. Loads (Optional) Line Voltage and Current Measurements Contactor Energy Storage and Power Conditioning Figure 4-1 Block Diagram of Solar Photovoltaic Ramping Support Applications Use Cases and Operating Modes Systems could be capable of operating in a solar PV ramping mode. Systems could source or sink reactive and/or active power to regulate local voltage. Reactive power settings may be set based on local voltage readings. In this mode, charging and recharging occurs alternately in such a way to maintain a target state of charge. Performance Ratings System Definition Systems interconnect with the utility at distribution voltage (4–34kV) and include current and potential transformers, a transformer (if required), a disconnect breaker, controls, and all power conditioning and auxiliary systems necessary to support its operation. Smart control should be provided as needed. Auxiliary Loads All auxiliary loads necessary to operate and protect the system, such as controls, cooling systems, fans, pumps, and heaters, are considered auxiliary loads internal to the system. System Rating Practices Systems may be rated, in both power and energy, as measured at the interface of the system and the utility. All system loads and losses, including wiring losses, power conditioning losses, 4-2 auxiliary loads, and chemical or ionic losses are considered internal to the system, and ratings are net of these loads and losses. In cases where auxiliary loads (such as cooling systems) are periodic in nature, ratings could be described for conditions in which these loads are active in the worst-case conditions (or, alternatively, provide sufficient supplementary information so that ratings under these worst-case conditions may be easily determined). System net power ratings may be in kWAC that is sustainable at a constant level for the nominal discharge time. Additional power ratings, such as pulse power capabilities, may also be specified. System net energy ratings may be in either kWhAC or hours at rated power that is sustainable at the nominal discharge time. System reactive power capabilities should be specified in kvar or power factor. System Effectiveness Storage Efficiency Storage efficiency is of secondary importance for this application. Manufacturers are free to define efficiency in any appropriate manner. Performance Curve The system may have an estimated calendar life of ideally at least 15 years. If the life of the product is expected to deteriorate over time, it would also have a cycle life as determined by the utility to support voltages based on local installed solar PV capacity and line loading. Units would be operated most often when solar PV capacity is high, lines are lightly loaded, and solar irradiance is variable. Although the understanding of the cycle requirements under this application is limited, cycle life may be equivalent to 5000 full energy cycles. Actual operation is expected to be partial charge/discharge cycles. If the product is sensitive to depth of discharge, the manufacturer could state the limitations, and the product should be sized so that the depth of discharge corresponds to the required cycle life. For lifetime assessment, it would be beneficial to have a graph that displays the distinction between depth of discharge and required number of cycles. Physical Characteristics Pole-Top and Ground-Mounted Installations Systems may be designed for installation on utility poles (similar to capacitor banks). Systems may otherwise be designed for ground-mounted installation. Systems with small footprint and volume are preferable. Transportation Standards Systems should be transportable at normal speeds over all North American interstate highways and railways, and meet all USDOT hazardous materials and other regulations. For example, 4-3 systems should be designed so that turn radii and bridge clearances are met when transported on lowboy trailers. System components (such as electrolyte) may be shipped separately, as needed, and assembled at the site. Rigging and Harnessing Systems should be installable using standard industry rigging equipment, such as cranes and lifts, and include provisions for installation in the system design. Status Lights and Alarms Systems should be equipped with meaningful status lights and LED panels to operate the system and, at minimum, provide easy access to mode and ac power (charging or discharging) information. Audible alarms should be included as necessary to ensure safety, such as for chemical leaks. Environmental Conditions Systems should be designed to meet normal utility standards regarding ambient temperature ranges, humidity ranges, air quality, emissions (SOx, NOx, and other air emissions if applicable), seismic, audible noise (similar to power transformers), EMI, fire protection (NFPA standards), and flood protection (specified by utilities in the procurement process). Supplier must provide sufficient information specific to their particular product to facilitate utility personnel training and communications with emergency response and environmental agencies. MSDSs should be provided as applicable. Sample codes and standards are listed Appendix A. Electrical Interface Standards Systems should meet nationally recognized standards for safety, electrical design, interconnection, harmonics, dc injection, and insulation. Utilities are not required to meet UL standards for equipment on the utility side of the meter. However, UL and other relevant interconnection standards may be required by the utilities for safety or protection of the grid. (For example, standards that address system response to grid disturbances, such as UL 1741, may be required.) Disconnect Breaker The disconnect breaker may be capable of breaking the full rated power of the system and operate manually. Breakers on pole-top installations may be operable using a standard hot stick. Contactor The system may have a contactor, the operation of which is dependent on mode. Auxiliary loads could be served internally to the system, so that all power draw could be through the contactor, unless required by the utility. 4-4 Communications, Control, and Data Management Communications Method Systems may be communication agnostic and incorporate open systems communication architecture. Communications Protocol The system may require any of several communications options, such as cellular, mesh node, Wi-Fi, and WiMAX. Selection between communications options will depend on the utility. Also, the control interface protocol will be specified by the utility. Typical control interface protocols such as (DNP3, serial or IP) and IEC 61850 may be specified by the utility. Integrated Interface Systems may be required to be designed in conformity with the Smart Grid Interoperability Standards [3], to the extent applicable at their current level of development. Specifically, systems may be required to be consistent with the energy storage interconnection guidelines and the Energy Storage and Distributed Energy Resources (ES-DER) Use Cases [4]. Systems may be remotely monitored and controlled. Remote control could be limited to power on/off, and local control (when on) may be automated based on local voltage and current conditions. Reactive power of storage device (source and sink) is to be a utility-configurable function of local voltage. The system may also have an LCD or similar readout capability, with locally settable options and diagnostics. Operational Data Systems may have the provision for storing key operational data in a time-sequenced flat data file. At a minimum, systems could store energy received and energy delivered in minute-byminute, time-stamped data bins. Event-Triggered Data Systems may also store events, such as changes in operational mode, received commands, faults, and shutdowns. Each event may be time stamped. Data Access All data may be downloadable, either remotely or locally, via a standard computer port or wireless connection. All data may be exportable in a nonproprietary format. Installation and Maintenance Systems should be designed to allow installation, operation, and maintenance by utility-qualified substation and distribution personnel and contractors. Adequate documentation and training should be provided. Systems should require only standard shop and electrical tools, lifts, and cranes, or specialty tools should be supplied with the systems. 4-5 Subsystems, such as power electronics modules or energy storage banks (ac or dc connections), may be classified by the supplier as nonserviceable in the field, provided that these subsystems may be removed and replaced by utility personnel. All consumable or degradable parts, such as air filters, should be classified by replacement interval. Safety Systems should be able to protect themselves from internal failures and utility grid disturbances. Therefore, systems should be self protecting for ac or dc component system failures. In addition, systems may be able to protect themselves from various types of grid faults and other abnormal conditions on the grid. Systems should reflect the safety standards of the utility. For example, utility and local fire personnel should be notified of particular safety issues and the appropriate response in case of an emergency. Systems should be designed to minimize risk of injury to the workforce and public during installation, maintenance, and operation. Systems should be designed to minimize the risk of damage to the environment, including land contamination or disturbance (footprint), water contamination or diversion, and air emissions. Systems should not require that a utility develop a spill containment plan or provide additional safety equipment. Systems could be designed to be recycled through known processes. Disconnects could be lockable and have a visible break. Wind Ramping Support Overview Description of Application Ramping support systems provide short-term utility or third-party wind farm–controlled electrical energy storage to accomplish the following: Accommodate variable wind farm output so that ramp rates (MW/min) are kept to within limits defined by system operators Provide net load ramping support for the grid at large Maintain local transmission and distribution system voltage Provide frequency regulation services (when not limiting wind intermittency and ramp rate) Provide LVRT for the wind farm (if required) Systems will be designed with a power rating in the 1–100 MW power levels, sized according to the requirements of the local wind farm design and wind regime, and to store 2–15 minutes of energy. Systems designed to provide support to a particular wind farm must be located at or close to the wind farm, whereas systems designed for providing ramping support to the bulk grid can be located anywhere. These systems can be connected at distribution or transmission 4-6 voltages. When the energy storage system is being used to perform ramping, it may not be able to provide frequency regulation, and vice versa. Figure 4-2 illustrates a typical ramping application. Transmission Line Substation Transformer Distribution Bus System Interconnection Point Disconnect Line Voltage and Power Measurements Aux. Loads (Optional) Contactor Energy Storage and Power Conditioning Figure 4-2 Block Diagram of Ramping Applications Use Cases and Operating Modes Systems will be capable of operating either one or two control modes. Each of these modes will be independent of the others. Systems are not required to operate modes simultaneously. Modes are the following: Ramp rate limiter. This mode uses real-time power measurements from the wind farm/transmission interface to limit the rate of change of power (positive or negative) to specific limits. When wind farm output rises rapidly, the system will charge; when wind farm output falls, the system will discharge, as necessary, to meet the interconnection ramp rate requirements. This will benefit the wind farm operations by reducing curtailment and will also reduce the effect of high wind ramp rates on the bulk system. This mode requires that the storage system be co-located with the wind farm. 4-7 Ramping support for the grid. This mode uses dispatch signals from the ISO or RTO to provide or absorb energy to provide additional flexibility to the grid as a whole, rather than to an individual wind farm. This application does not require that the storage be co-located with a wind farm. Voltage regulation. This mode is to source or sink reactive power based on the real-time local transmission voltage. Frequency regulation. The system could charge or discharge in response to signals received approximately every second. The system could seek to maintain a target state of charge (such as 50%) over the long run, while supporting frequency. LVRT. Provide LVRT for wind farm (if necessary). This function is provided through the power electronics associated with the storage system, rather than the storage itself. Most modern wind generation technology incorporates power electronics that can address LVRT without additional support. Performance Ratings System Definition Systems include current and potential transformers, a step-up transformer, a disconnect breaker, controls, and all power conditioning and auxiliary systems necessary to support its operation. Auxiliary Loads All auxiliary loads necessary to operate and protect the system, such as controls, cooling systems, fans, pumps, and heaters, are considered auxiliary loads internal to the system. System Rating Practices Systems shall be rated, in both power and energy, as measured at the interface of the system and the utility. All system loads and losses, including wiring losses, power conditioning losses, auxiliary loads, and chemical or ionic losses are considered internal to the system and ratings are net of these loads and losses. In cases where auxiliary loads (such as cooling systems) are periodic in nature, ratings shall be described for conditions in which these loads are active in the worst-case conditions (or, alternatively, provide sufficient supplementary information so that ratings under these worst-case conditions may be easily determined). System net power ratings shall be in kWAC or MWAC that is sustainable at a constant level for the nominal discharge time. Additional power ratings, such as pulse power capabilities, may also be specified. System net energy ratings may be in either kWhAC, MWhAC, or hours at rated power for a manufacturer-specified nominal discharge time. System reactive power capabilities should be specified in kvar, Mvar, or power factor. 4-8 System Effectiveness Storage Efficiency Storage efficiency is of secondary importance for this application. Manufacturers are free to define efficiency in any appropriate manner. Performance Curve The cycle requirements for this application are not well understood at this time. Systems would typically be designed to meet ramping requirements over a period of 15 years. The actual cycle count will depend on wind regime, aggregation effects of nearby turbines, and control area ramping resources and requirements, as represented in the wind farm interconnection requirements. One estimate might be that systems would charge and discharge the energy equivalent of 2 full cycles per day on average over the year, or approximately 10,000 cycles. This would correspond to 20,000 cycles at 50% of storage capacity and 100,000 cycles at 10% of capacity. Systems will provide for both absorption and release of energy to control high ramp rates caused by the abrupt increase or reduction in wind farm power, respectively. Because the magnitudes of these events are not regular, the energy content of each cycle is not expected to be regular. Therefore, the systems will need to be able to deliver a wide range of controllable power levels independent of the state of charge. To simplify the life requirements, systems may be specified in terms of equivalent complete energy cycles, such as 10,000 full energy cycles. Systems that degrade in energy delivery capability over time would be specified in terms of the energy available corresponding to the end of life, although the initial energy may also be included. For example, a 10-MWh energy storage system would be understood to deliver 10 MWh after 15 years of expected cycling. If such a system was capable of delivering 15 MWh initially, that figure may also be indicated. For lifetime assessment, it would be beneficial to have a graph that displays the distinction between depth of discharge and required number of cycles. Physical Characteristics Size Systems should be designed to minimize footprint and volume. As an example, systems would 2 ideally be less than 500 ft /MWh and include space needed to maintain and install the system. Other siting restrictions should be clearly stated. Transportation Standards Systems should be transportable at normal speeds over all North American interstate highways and railways, and meet all USDOT hazardous materials and other regulations. For example, systems should be designed so that turn radii and bridge clearances are met when transported on lowboy trailers. System components (such as electrolyte) may be shipped separately as needed and assembled at the site. 4-9 Rigging and Harnessing Systems should be installable using standard industry rigging equipment, such as cranes and lifts, and include provisions for installation in the system design. Status Lights and Alarms Systems should be equipped with meaningful status lights and LED panels to operate the system and, at minimum, provide easy access to mode and ac power (charging or discharging) information. Audible alarms should be included as necessary to ensure safety, such as for chemical leaks. Environmental Conditions Systems should be designed to meet normal utility standards regarding ambient temperature ranges, humidity ranges, air quality, emissions (SOx, NOx, and other air emissions if applicable), seismic, audible noise (similar to power transformers), EMI, fire protection (NFPA standards), and flood protection (specified by utilities in the procurement process). Supplier must provide sufficient information specific to their particular product to facilitate utility personnel training and communications with emergency response and environmental agencies. MSDSs should be provided as applicable. Sample codes and standards are listed Appendix A. Electrical Interface Standards Systems should meet nationally recognized standards for safety, electrical design, interconnection, harmonics, dc injection, and insulation. Utilities are not required to meet UL standards for equipment on the utility side of the meter. However, UL and other relevant interconnection standards may be required by the utilities for safety or protection of the grid. (For example, standards that address system response to grid disturbances, such as UL 1741, may be required.) Disconnect Breaker The disconnect breaker shall be capable of breaking the full rated power of the system and operate manually. Contactor The system shall have a contactor, the operation of which is dependent on mode. Auxiliary loads will be served internally to the system, so that all power draw will be through the contactor, unless required by the utility. Communications, Control, and Data Management Communications Method Systems may be communication agnostic and incorporate any appropriate open systems communication architecture. 4-10 Communications Protocol The system may require any of several communications options, such as cellular, mesh node, Wi-Fi, and WiMAX. Selection between communications options will depend on the utility. Also, the control interface protocol will be specified by the utility. Typical control interface protocols such as (DNP3, serial or IP) and IEC 61850 may be specified by the utility. Integrated Interface Systems may be required to be designed in conformity with the Smart Grid Interoperability Standards [3], to the extent applicable at their current level of development. Specifically, systems may be required to be consistent with the energy storage interconnection guidelines and the Energy Storage and Distributed Energy Resources (ES-DER) Use Cases [4]. Systems will be controlled remotely by the utility, the RTO or ISO, or the wind farm control center, depending on ownership and jurisdiction. Local measurements of the transmission voltage and overall wind farm power output will be sent to the system control. The system will also provide relevant status information, such as state of charge and measured power, for feedback to a central control system at either the utility or wind farm operations center. The system will also have an LCD or similar local control capability, with additional control capabilities and diagnostics. Operational Data Systems shall have the provision for storing key operational data in a time-sequenced flat data file. At a minimum, systems should store energy received and energy delivered in minute-byminute, time-stamped data bins. Frequency response applications will require more frequent samples. Event-Triggered Data Systems shall also store events, such as changes in operational mode, received commands, faults, and shutdowns. Each event shall be time stamped. Data Access All data shall be downloadable, either remotely or locally, via a standard computer port or wireless connection. All data must be exportable in a nonproprietary format. Installation and Maintenance Systems should be designed to allow installation, operation, and maintenance by utility-qualified substation and distribution personnel and contractors. Adequate documentation and training should be provided. Systems should require only standard shop and electrical tools, lifts, and cranes, or specialty tools should be supplied with the systems. Subsystems, such as power electronics modules or energy storage banks (ac or dc connections), may be classified by the supplier as nonserviceable in the field, provided that these subsystems may be removed and replaced by utility personnel. All consumable or degradable parts, such as air filters, should be classified by replacement interval. 4-11 Safety Systems should be able to protect themselves from internal failures and utility grid disturbances. Therefore, systems may be self protecting for ac or dc component system failures. In addition, systems may be able to protect themselves from various types of grid faults and other abnormal conditions on the grid. Systems should reflect the safety standards of the utility. For example, utility and local fire personnel should be notified of particular safety issues and the appropriate response in case of an emergency. Systems should be designed to minimize risk of injury to the workforce and public during installation, maintenance, and operation. Systems should be designed to minimize the risk of damage to the environment, including land contamination or disturbance (footprint), water contamination or diversion, and air emissions. Systems should not require that a utility develop a spill containment plan or provide additional safety equipment. Systems could be designed to be recycled through known processes. Disconnects could be lockable and have a visible break. Load and Resource Shifting Overview Description of Application Load and resource shifting systems provide long-term storage for utilities or third parties (such as wind farms and solar PV plant operators) to accomplish the following: Store energy generated during off-peak demand periods, to serve loads during peak demand periods Participate in capacity markets as a dispatchable energy resource Provide ancillary services Systems may be designed with a power rating appropriate to the renewable generation, whether at the kilowatt level, hundreds of megawatts, or even gigawatts. Large systems would be limited in size only by transmission capacity. Systems may have the capability of storing up to 10 hours of energy depending on needs. (Some have much longer storage durations, including even seasonal storage.) Systems will primarily be located on transmission and distribution voltages but may also be located on secondary distribution voltages. The system may also serve the purpose of providing solar PV ramping and wind ramping support, as defined in the previous two sections. Figure 4-3 illustrates a typical load and resource shifting application. 4-12 Utility Renewable Resource (Optional) Transformer (As Required) Disconnect Aux. Loads (Optional) Contactor Energy Storage and Power Conditioning Figure 4-3 Block Diagram of Load and Resource Shifting Applications Use Cases and Operating Modes These use cases are in order of priority of utility need. Systems may support one or more of the following, depending on utility needs: Store energy generated during off-peak demand periods to serve loads during peak demand times. The system would charge when low-cost generation (renewable or otherwise) is available off-peak and discharge this energy during on-peak periods. Participate in capacity markets as a dispatchable resource. The system would charge and discharge in response to control signals that match contractual obligations in the capacity market. Provide ancillary services. The system could respond to frequency regulation or other signals to provide ancillary services. 4-13 Performance Ratings System Definition Systems include a transformer (if required), a disconnect breaker, controls, and all power conditioning and auxiliary systems necessary to support its operation. Auxiliary Loads All auxiliary loads necessary to operate and protect the system, such as controls, cooling systems, fans, pumps, and heaters, are considered auxiliary loads internal to the system. System Rating Practices Systems are rated, in both power and energy, as measured at the interface of the system and the utility. All system loads and losses, including wiring losses, power conditioning losses, auxiliary loads, and chemical or ionic losses are considered internal to the system, and ratings are net of these loads and losses. In cases where auxiliary loads (such as cooling systems) are periodic in nature, ratings may be described for conditions in which these loads are active in the worst-case conditions (or, alternatively, provide sufficient supplementary information so that ratings under these worst-case conditions may be easily determined). System net power ratings should be in kWAC or MWAC that is sustainable at a constant level for the nominal discharge time. Additional power ratings for other applications (such as pulse power), may also be specified. System net energy ratings may be in either kWhAC, MWhAC or hours at rated power discharge for the nominal discharge time. System reactive power capabilities should be specified in kVA, Mvar, or power factor. Systems may be required to provide the ability to source or sink reactive power, depending on the needs of the utility. System Effectiveness Storage Efficiency Storage efficiency is defined as follows: kWhout kWhin Equation 4-1 Where: kWhout is the total ac energy delivered by the storage system to the grid across the standard duration of discharge from fully charged to fully discharged at its rated continuous power capacity. 4-14 kWhin is the total energy delivered from the grid to the storage system over a full 24-hour daily cycle (the charging energy). The measurement of reported storage efficiency should begin and end with the system at a full state of charge. This measurement would be performed using only the remote operating modes available to the system operator, with no manual intervention. Performance Curve The system may have an estimated calendar life of ideally at least 15 years. If the life of the product is expected to deteriorate over time, the system shall be able to provide 3000 cycles (cycles correspond to full discharge and full charge power for the nominal discharge time). If the product is sensitive to depth of discharge, the manufacturer could state the limitations and the product should be sized so that the depth of discharge corresponds to the required cycle life. For lifetime assessment, it would be beneficial to have a graph that displays the distinction between depth of discharge and required number of cycles. Physical Characteristics Size Systems should be designed to minimize footprint and volume. As an example, systems would ideally be less than 500 ft2/MWh and include space needed to maintain and install the system. Other siting restrictions should be clearly stated. Transportation Standards Systems should be transportable at normal speeds over all North American interstate highways and railways, and meet all USDOT hazardous materials and other regulations. For example, systems should be designed so that turn radii and bridge clearances are met when transported on lowboy trailers. System components (such as electrolyte) may be shipped separately as needed and assembled at the site. Rigging and Harnessing Systems should be installable using standard industry rigging equipment, such as cranes and lifts, and include provisions for installation in the system design. Status Lights and Alarms Systems should be equipped with meaningful status lights and LED panels to operate the system, and at minimum provide easy access to mode and ac power (charging or discharging) information. Audible alarms should be included as necessary to ensure safety, such as for chemical leaks. Environmental Conditions Systems should be designed to meet normal utility standards regarding ambient temperature ranges, humidity ranges, air quality, emissions (SOx, NOx, and other air emissions if applicable), 4-15 seismic, audible noise (similar to power transformers), EMI, fire protection (NFPA standards), and flood protection (specified by utilities in the procurement process). Supplier must provide sufficient information specific to their particular product to facilitate utility personnel training and communications with emergency response and environmental agencies. MSDSs should be provided as applicable. Sample codes and standards are listed Appendix A. Electrical Interface Standards Systems should meet nationally recognized standards for safety, electrical design, interconnection, harmonics, dc injection, and insulation. Utilities are not required to meet UL standards for equipment on the utility side of the meter. However, UL and other relevant interconnection standards may be required by the utilities for safety or protection of the grid. (For example, standards that address system response to grid disturbances, such as UL 1741, may be required.) Disconnect Breaker The disconnect breaker should be lockable and have a visible break. It should be capable of breaking the full rated power of the system and operate manually. The utility will have full access and control over this device. Contactor The system could have an automatically operated contactor. Auxiliary loads ideally would be served internally to the system, so that all power draw ideally would be through the contactor, unless required by the utility. Communications, Control, and Data Management For small systems, the following may not be required. Communications Method Systems may be communication agnostic and incorporate open systems communication architecture. Communications Protocol The system may require any of several communications options, such as cellular, mesh node, Wi-Fi, and WiMAX. Selection between communications options will depend on the utility. Also, the control interface protocol will be specified by the utility. Typical control interface protocols such as (DNP3, serial or IP) and IEC 61850 may be specified by the utility. Integrated Interface Systems may be required to be designed in conformity with the Smart Grid Interoperability Standards [3], to the extent applicable at their current level of development. Specifically, systems may be required to be consistent with the energy storage interconnection guidelines and the 4-16 Energy Storage and Distributed Energy Resources (ES-DER) Use Cases [4]. Utilities will generally require monitoring and control through their operations centers. The system may also be required to provide relevant status information, such as state of charge and measured power, for feedback to the utility control system. The system may also require an LCD or similar local control capabilities and diagnostics. Operational Data Systems may require a provision for storing key operational data in a time-sequenced flat data file. At a minimum, systems should store energy received and energy delivered in minute-byminute, time-stamped data bins. Event-Triggered Data Systems may also be required to store events, such as changes in operational mode, received commands, faults, and shutdowns. Each event would be time stamped. Data Access All data would be downloadable, either remotely or locally via a standard computer port or wireless connection. All data would be exportable in a nonproprietary format. Installation and Maintenance Systems should be designed to allow installation, operation, and maintenance by utility-qualified substation and distribution personnel and contractors. Adequate documentation and training should be provided. Systems should require only standard shop and electrical tools, lifts, and cranes, or specialty tools should be supplied with the systems. Subsystems, such as power electronics modules or energy storage banks (ac or dc connections), may be classified by the supplier as nonserviceable in the field, provided that these subsystems may be removed and replaced by utility personnel. All consumable or degradable parts, such as air filters, should be classified by replacement interval. Safety Systems should be able to protect themselves from internal failures and utility grid disturbances. Therefore, systems may be self protecting for ac or dc component system failures. In addition, systems should be able to protect themselves from various types of grid faults and other abnormal conditions on the grid. Systems should reflect the safety standards of the utility. For example, utility and local fire personnel should be notified of particular safety issues and the appropriate response in case of an emergency. Systems should be designed to minimize risk of injury to the workforce and public during installation, maintenance, and operation. Systems should be designed to minimize the risk of damage to the environment, including land contamination or disturbance (footprint), water contamination or diversion, and air emissions. 4-17 Systems should not require that a utility develop a spill containment plan or provide additional safety equipment. Systems would ideally be designed to be recycled through known processes. Disconnects could be lockable and have a visible break. 4-18 5 RECOMMENDATIONS FOR FUTURE WORK Collection and Sharing of Data The application of the functional requirements presented in this report would be enhanced by detailed operating data on wind and solar ramping events and other system characteristics that will impact the specifications for equipment being applied. It is also important that the information sharing in this project be continued among utilities, storage equipment suppliers, wind and solar developers, and related institutions so that the equipment being developed and purchased continues to improve in its applicability to grid management issues and opportunities. Utilities and others are encouraged to share their data, challenges, issues, and case studies for inclusion in possible revisions of this report. System Sizing for Solar Photovoltaic Ramping Application Utilities that use storage for mitigating solar PV power ramping events will need to be able to determine the power and energy requirements based on local conditions. The means for determining optimal sizing is not well understood. The factors may include local meteorological attributes, the local installed capacity of solar PV, the relative spacing of the individual solar PV systems, the existing voltage regulation equipment, and the local distribution system topology (such as wire sizes and lengths). In addition, solar PV models are only recently being integrated into distribution load flow models. Additional work must be done in this area. This issue of acceptable levels of variability related to sizing may be relevant not only to solar PV systems but to all applications described in the report. Solar Photovoltaic Control Algorithms Although the reactive power capabilities that may be included in a grid-connected energy storage system can be used to regulate voltage, it is not clear how to dispatch the active power capabilities for this purpose. The details of the dispatch model must be further developed. For example, storage can be used to charge and discharge to limit the rate of change of power on the line at the point of interconnection. In addition, the algorithm may depend on local distribution impedances. Wind Plant Low-Voltage Ride-Through The application of using storage for LVRT for wind plants is not well understood. The operating modes and design requirements must be better defined. Solar Photovoltaic and Wind Duty Cycles For both the solar PV ramping support and wind ramping support applications, the required cycle life is not well understood. On a given day, the cycle requirements are expected to depend on the 5-1 number of generators in the fleet (more generators reduce aggregate variability), their physical placement, local meteorological conditions, the local power system design, and the timing of generator output relative to loads. Additional work is necessary to model storage operation needed to maintain stability and, thereby, define cycling requirements. Communication Protocol Details The details of communication protocols for all the applications described in this document must be further delineated. By defining and standardizing these protocols, the process for both suppliers and utilities will be simplified. Defining Functional Requirements for Other Energy Storage Applications This report describes three key storage applications, excluding a number of additional applications. Further work is needed to define functional requirements for commercial and industrial (C&I) power quality, C&I power reliability, C&I energy management, home energy management, and home backup. 5-2 6 REFERENCES 1. U. S. Department of Energy. The Smart Grid: An Introduction. http://www.oe.energy.gov/1165.htm. Accessed May 25, 2011. 2. American Electric Power. Functional Specification For Community Energy Storage (CES) Unit, Rev. 2.2. December 2009. http://www.aeptechcenter.com/ces/docs/ CESUnitSpecifications_rev2_2.pdf. Accessed May 25, 2011. 3. U. S. Department of Commerce, National Institute of Standards and Technology. NIST Framework and Roadmap for Smart Grid Interoperability Standards, Release 1.0. NIST Special Publication 1108. January 2010. http://www.nist.gov/public_affairs/releases/ upload/smartgrid_interoperability_final.pdf. Accessed May 25, 2011. 4. U. S. Department of Commerce, National Institute of Standards and Technology. Priority Action Plan 7: Key Energy Storage and Distributed Energy Resources (ES-DER) Use Cases. April 2010. http://collaborate.nist.gov/twiki-sggrid/pub/SmartGrid/PAP07Storage/ Key_ES-DER_Use_Cases_v2.doc#_Toc258244283. Accessed May 25, 2011. 6-1 A APPLICABLE CODES AND STANDARDS The following codes and standards can be used by utilities as references: ANSI/IEEE Std C2-2007 TM, National Electrical Safety Code ANSI C57.12.25-1990, Pad-Mounted Transformer Requirements ANSI C57.12.28-2005, Pad-Mounted Equipment Enclosure Integrity ANSI Z535–2002, Product Safety Signs and Labels Community Energy Storage (CES), Storage Unit Functional Specification, Revision 2.2, 12/09/2009 FCC Sections 15.109 and 15.209, Federal Communications Commission, Code of Federal Regulations, Radiated Emission Limits, General Requirements IEC 61850, Standard on the Design of Electrical Substation Automation IEEE 519-1992TM, IEEE Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems IEEE 1547-2003 (R 2008)TM, IEEE Standard for Interconnecting Distributed Resources with Electric Power Systems IEEE P1547.1, Standard For Conformance Test Procedures for Equipment Interconnecting Distributed Resources with Electric Power Systems IEEE P1547.2, Application Guide for IEEE Std. 1547, Standard for Interconnecting Distributed Resources with Electric Power Systems IEEE P1547.3, Guide for Monitoring, Information Exchange, and Control of Distributed Resources Interconnected With Electric Power Systems IEEE P1547.4, Draft Guide for Design, Operation, and Integration of Distributed Resource Island Systems with Electric Power Systems IEEE P1547.5, Draft Technical Guidelines for Interconnection of Electric Power Sources Greater than 10 MVA to the Power Transmission Grid IEEE P1547.6, Draft Recommended Practice For Interconnecting Distributed Resources With Electric Power Systems Distribution Secondary Networks IEEE P1547.7, Draft Guide to Conducting Distribution Impact Studies for Distributed Resource Interconnection IEEE P1547.8, TBD (for example, expanded use of Std 1547) IEEE C37.90.2-2004 TM, IEEE Standard Withstand Capability of Relay Systems to Radiated Electromagnetic Interference from Transceivers IEEE C37.90.1-2002 TM, IEEE Standard for Surge Withstand Capability (SWC) Tests for Protective Relays and Relay Systems (ANSI) IEEE C62.41-1991(R 1995) TM, IEEE Recommended Practice on Surge Voltages in LowVoltage AC Power Circuits A-1 IEEE C62.41.1-2002 TM, IEEE Guide on the Surges Environment in Low-Voltage (1000 V and Less) AC Power Circuits IEEE C62.41.2-2002 TM, IEEE Recommended Practice on Characterization of Surges in Low-Voltage (1000 V and Less) AC Power Circuits IEEE C62.45-2002 TM, IEEE Recommended Practice on Characterization of Surges in LowVoltage (1000 V and Less) AC Power Circuits National Fire Protection Association (NFPA) Standards National Institute of Standards and Technology (NIST) Special Publication 1108 Standard System for the Identification of the Hazards of Materials for Emergency Response Smart Energy Profile (SEP) Standard System for Communication with Demand Side Management Equipment UL 1741, UL Standard for Inverters, Converters, Controllers and Interconnection System Equipment for Use With Distributed Energy Resources UL 1778, Underwriters Laboratory’s Standard for Uninterruptible Power Systems (UPS) for up to 600V A.C. Uniform Building Code, Applicable to seismic rating (such as up to 5% peak acceleration with 10% probability of being exceeded in 50 years) U.S. Department of Transportation, Pipeline and Hazardous Materials Transportation Law (HMR; 49 CFR Parts 171–180) A-2 B APPLICABLE PARAMETERS FOR SPECIFICATIONS The following topics may be addressed in detail in the technical specifications of a utility procurement: Scope Electrical Requirements and Connections o Ratings Alternating current voltage Basic impulse level Power and energy Efficiency Parasitic losses Inrush capability Ampacities Self discharge Voltage stability o Interface and alternating current terminations o Surge protection Enclosure o Filters o Maintenance access o Size o IEEE standards o Nameplate o Signage and safety placards o Direct current connections Control Functions o Modes o Loss of power o Communications Environmental o Operating temperatures o Humidity o Storage and transport temperatures o Altitude o Seismic requirements Harmonics, noise and EMI emissions o Acceptable limits o IEEE standards Protection o Fusing and sensing B-1 o Response to faults o Breaker operations Communications o Options o Protocols Factory acceptance testing Alarms and status indictors Standards and code compliance Commercial terms o Warrantees o Documentation o Maintenance services o Supplier qualifications o Inspections o Insurance and bonding requirements o References o Licenses o Delivery terms o Quality assurance/quality control program o Factory acceptance testing o Field commissioning o Legal terms B-2 C ABBREVIATIONS, ACRONYMS, AND TERMINOLOGY This appendix defines abbreviations, acronyms, and special terms used in this report. ac alternating current ANSI American National Standards Institute C&I commercial and industrial, referring to utilities’ commercial and industrial customers or loads compressed air energy storage an energy storage system that accumulates comparatively large amounts of energy generated during off-peak periods to be released during peak load periods to meet higher demand. dc direct current DESS distributed energy storage system, an energy storage system in which small (25–200 kW) distributed energy storage units are connected to secondary transformers that serve a few houses or small commercial loads EMI electromagnetic interference IEC International Electrotechnical Commission IEEE Institute of Electrical and Electronics Engineers ISO independent system operator, an organization formed at the direction or recommendation of the Federal Energy Regulatory Commission. In the areas where an ISO is established, it coordinates, controls, and monitors the operation of the electrical power system. kvar kilovar, a unit of reactive power kWAC kilowatts, alternating current kWhAC kilowatt hours, alternating current MSDS material safety data sheet Mvar megavar, a unit of reactive power MWAC megawatts, alternating current MWhAC megawatt hours, alternating current NFPA National Fire Protection Association C-1 LVRT low-voltage ride-through, a required capability of an electric device in case of temporarily reduced voltage in the grid, either due to a fault or load changes PV photovoltaic renewable portfolio standards mechanisms to increase renewable energy generation using a cost-effective, market-based approach that is administratively efficient for states; a renewable portfolio standard requires electric utilities and other retail electric providers to supply a specified minimum amount of customer load with electricity from eligible renewable energy sources RTO regional transmission organization, an organization that is responsible for moving electricity over large interstate areas; an RTO coordinates, controls, and monitors an electricity transmission grid that is larger with much higher voltages than the typical power company’s distribution grid; RTOs typically perform the same functions as ISOs, but cover a larger geographic area superconducting magnetic energy storage an energy storage device using a magnetic field in a superconducting environment UL Underwriters Laboratories, an independent product safety certification organization that has been testing products and writing widely recognized industry standards (UL Standards for Safety) for more than a century Wi-Fi a trademark of the Wi-Fi Alliance; a term used to describe wireless local area network products that are based on the IEEE 802.11 standards WiMAX Worldwide Interoperability for Microwave Access, a telecommunications protocol that provides fixed and mobile Internet access C-2 D PARTICIPANTS Representatives of the following organizations participated in various capacities in this research project: Advanced Energy Conversion Aerospace & Defense AEYCH LLC Altairnano Ameren American Electric Power American Leaders American Superconductor American Wind Power & Hydrogen Amphenol American Superconductor Corporation American Public Power Association Amy Stern Consulting Arizona Public Service Asea Brown Boveri - ABB BAE Systems Ballard Power Systems Baltimore Gas and Electric BC Hydro Beacon Power Corporation Beckett Corporation Bloomberg New Energy Finance Boston-Power BP Solar BrightSource Burns and Roe Business Solutions Caithness Corporation California Energy Commission Clean Energy Group City College of New York Customized Energy Solutions Clarkson University Commercial Energy Horizons Consolidated Edison of NY Cool Systems CPS Energy Dairyland Power Cooperative Delaware County Electric Cooperative Delmarva Power Department of Energy Dresser-Rand DTE Energy Duke Energy Energy Central Exide Technologies Federal Energy Regulatory Commission (FERC) FirstEnergy Service Company First Solar Fluidic Energy FuelCell Energy G4 Synergetics General Compression General Electric Energy General Microgrids Grasslands Renewable Energy Great River Energy Hawaiian Electric Company Hydro One Hydrogenics Ice Energy ICG Aeolian Energy Idaho National Laboratory (INL) Idaho Power Ideal Power Converters Inertia Energy Group Inertia Engineering Kansas City Power & Light Kenjiva Energy Systems KEMA /KEMA Powertest Los Angeles Dept. Water & Power Long Island Power Authority MegaWatt Storage Farms Mehta Associates Meridien Solar MidAmerican Energy Company Midwest ISO D-1 R. W. Beckett Corp. Reiser Law Office RPI Center for Future Energy Systems Sacramento Municipal Utility District (SMUD) Salt River Project Samsung SDI America San Diego Gas & Electric Sandia National Labs Schneider Electric Sentech Siemens Smart Grid Implementation Group Snohomish County Public Utility District Southern California Edison Statoil Hydrogen Technologies Steffes Corporation Tecknowledgey Tenaska Power Services Tri-State G & T Tennessee Valley Authority (TVA) Ultralife Corporation University of Connecticut WindSoHy Xcel Energy Xylene Power Yale University Younicos AG ZEM Zinc Air Modtech Corp. National Renewable Energy Lab (NREL) National Rural Electric Cooperative Association (NRECA) Navigant Consulting New Generation New Technology New York ISO New York State Energy Research and Development Authority (NYSERDA) New York State Foundation for Science, Technology and Innovation (NYSTAR) NextEnergy NorthEast Transportation Electrification Alliance NTEA Oak-Mitsui Orange & Rockland Utilities Paper Battery Company Patrick Energy Services PG&E Corporation PJM Interconnection PNM Resources Powergetics Primus Power Progress Energy / Progress Energy Florida Project for Sustainable FERC Energy Policy Protium Energy Technologies Proton Energy Systems Public Utilities Commission of Ohio Public Utilities Commission of Texas D-2 Export Control Restrictions The Electric Power Research Institute Inc., Access to and use of EPRI Intellectual Property is granted with the specific understanding and requirement that responsibility for ensuring full compliance with all applicable U.S. and foreign export laws and regulations is being undertaken by you and your company. 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