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
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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
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Electric Power Research Institute, EPRI, and TOGETHERSHAPING 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:


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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.
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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):
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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
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
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
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