DOE OE Global Energy Storage Database Energy Storage Terms Glossary
ENERGY STORAGE GLOSSARY OF TERMS
Term Definition Examples
–A–
Alternating current (AC) is an electric current which
Alternating Current
periodically reverses direction, in contrast to direct
(AC)
current (DC) which flows in only one direction.
Area control error is the difference between scheduled
Area Control Error
and actual electrical generation within a control area on
(ACE)
the power grid.
Automatic Automatic generation control is a system for adjusting
Generation Control the power output of multiple generators at different
(AGC) power plants in response to changes in the load.
Automated metering infrastructure describes an
integrated system of smart meters, communications
Automated Metering
networks, and data management systems that enable
Infrastructure (AMI)
two-way communication between utilities and
customers.
APU Ancillary Power Unit
–B–
Battery Energy A battery energy storage system is a rechargeable battery
Storage System system that stores energy to be used at a later time.
(BESS)
Benefit Stream Frequency
The benefit stream(s) affected by this policy.
Affected Regulation
An energy
storage system
is used to re-
start turbines
A black start is the process of restoring a power station
of a generation
Black Start to operation without relying on the external electric
facility after a
power transmission network.
large blackout
causes
generators to
go offline.
–C–
Capital Expenditure The total up-front capital expense of the system stated in
2000000
(CAPEX) dollars.
CCGT Combined-cycle gas turbine
Compressed Air Energy Storage is a way to store energy
Compressed Air using compressed air. Surplus power is used to compress
Energy Storage air using a rotary compressor and then stores the energy
(CAES) in a chamber. When the power is needed, it is released
from the chamber and passed through an air turbine that
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DOE OE Global Energy Storage Database Energy Storage Terms Glossary
Term Definition Examples
generates electricity from the flow of high pressure air.
A project that is Contracted is under signed contract to
Contracted
be built, however construction has not yet begun.
–D–
Debt Provider The primary debt provider in the project.
The person or organization responsible for organizing
Developer the development and implementation of the energy
storage project.
Demand response is a change in the power consumption
Demand Response
of an electric utility customer to better match the demand
(DR)
for power with the supply.
Depth of discharge is an alternative method to indicate a
battery’s state of charge; it is the complement to the
Depth of Discharge battery’s state of charge. Depth of discharge is usually
(DOD) expressed using units of A h (e.g, 0 is full and 50 A h is
empty) or percentage points (100 % is empty and 0 % is
full).
Direct current (DC) is an electric current which flows in
Direct Current (DC) one direction only, in contrast to alternating current
(AC).
Duration at Rated The amount of time (in HH:MM) the storage system can
02:30
Power output at its rated power capacity.
–E–
The U.S. Energy Information Administration (EIA) is a
principal agency of the U.S. Federal Statistical System
Energy Information responsible for collecting, analyzing, and disseminating
Administration energy information to promote sound policymaking,
(EIA) efficient markets, and public understanding of energy
and its interaction with the economy and the
environment.
Can be used to
eliminate
demand
charges,
Electric Bill Energy storage used by end-use customers in a variety of
charge during
Management facets to reduce electric bills.
off-peak to
reduce peak
consumption,
etc.
Smooth the
Electric Bill Energy storage used by end-use customers in a number output of solar
Management w/ of facets, and in conjunction with renewable generation panels to
Renewables resources, to reduce electric bills. eliminate the
risk of high
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DOE OE Global Energy Storage Database Energy Storage Terms Glossary
Term Definition Examples
demand
charges during
peak hours
when the solar
drops off.
Electric Energy Time Energy time shift involves storing energy during low
Shift price times, and discharging during high price times.
Depending on the circumstances in a given electric
supply system, energy storage could be used to defer
Electric Supply
and/or to reduce the need to buy new central station
Capacity
generation capacity and/or to ‘rent’ generation capacity
in the wholesale electricity marketplace.
Generation capacity that may be offline, or that
comprises a block of curtailable and/or interruptible
Electric Supply loads, and that can be available within 10 minutes.
Reserve Capacity - Unlike spinning reserve capacity, non-spinning reserve
Non-Spinning capacity is not synchronized with the grid (frequency).
Non-spinning reserves are used after all spinning
reserves are online.
Generation capacity that is online but unloaded and that
can respond within 10 minutes to compensate for
Electric Supply
generation or transmission outages. ‘Frequency-
Reserve Capacity -
responsive’ spinning reserve responds within 10 seconds
Spinning
to maintain system frequency. Spinning reserves are the
first type used when a shortfall occurs.
Stands for "Engineering, Procurement, Construction" -
DBR
EPC Identifies the entity or entities that performed any or all
Construction
of these services for the project.
Electromagnetic compatibility (EMC) is the ability of
electrical equipment and systems to function acceptably
in their electromagnetic environment, by limiting the
Electromagnetic
unintentional generation, propagation and reception of
Compatibility (EMC)
electromagnetic energy which may cause unwanted
effects such as electromagnetic interference (EMI) or
even physical damage in operational equipment.
EOC Executive Oversight Committee
ESHB Energy Storage Handbook
ESTF Energy Storage Test Facility
EV Electric Vehicle
–F–
Frequency regulation involves moment-to-moment
Frequency
reconciliation of the supply of electricity and the demand
Regulation
for electricity. The reconciliation is done every few
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DOE OE Global Energy Storage Database Energy Storage Terms Glossary
Term Definition Examples
seconds. So at any given moment, if electricity demand
exceeds supply then the supply is increased to meet
demand. And, if demand is less than supply then the
supply is decreased.
–G–
G&T generation and transmission
The level at which an energy resource (such as
Transmission;
generation or storage) connects to the grid. An energy
Grid Interconnection Secondary
resource could be connected at Transmission, Primary
Distribution
Distribution, or Secondary Distribution levels.
GST Grid Storage Technologies
GW gigawatts
– H–
hr hour
Hz hertz
–I–
The installed cost includes all equipment, delivery,
installation, interconnection, and step- up transformation
costs. For this benchmarking work it was assumed a site
was available; however no land costs, permitting, and
Installed Cost ($/kW)
project planning costs were included. These costs are
comparable to the installed costs of a combustion turbine
(CT) or combined-cycle gas turbine (CCGT) for up-front
capital and financing requirements.
An investor owned utility is a business organization
Investor Owned providing and managing a utility as a private enterprise
Utility (IOU) rather than a function of a government or utility
cooperative.
An independent power producer (IPP) or non-utility
Independent Power generator (NUG) is an entity, which is not a public
Producer (IPP) utility, but which owns facilities to generate electric
power for sale to utilities and end users.
The ISO or RTO that manages the grid where the energy
storage system is installed, if applicable. In the areas
ISO/RTO
where an ISO is established, it coordinates, controls, and
(Independent System
monitors the operation of the electrical power system, CAISO;
Operator/Regional
usually within a single US State, but sometimes NYISO
Transmission
encompassing multiple states. RTOs typically perform
Organization)
the same functions as ISOs, but cover a larger
geographic area.
–J–
No “J” Terms
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DOE OE Global Energy Storage Database Energy Storage Terms Glossary
Term Definition Examples
–K–
A kilowatt is a unit of power, expressed as one thousand
kW
watts.
A kilowatt hour is a unit of energy, expressed as one
kWh
thousand watts being used for an hour.
–L–
Lead-acid is one of the oldest and most developed
battery technologies. They remain popular because they
Lead Acid / Pb-acid can produce high or low currents over a wide range of
Battery temperatures, they have a good shelf life and life cycles,
and they are relatively inexpensive to manufacture and
purchase.
The levelized cost of capacity is the $/kW-yr. revenue
per kW of discharge capacity needed to cover all life-
Levelized Cost of
cycle fixed and variable costs and provide the target rate
Capacity (LCOC)
($/kW-yr.) of return based on financing assumptions and ownership
types. This metric is primarily of interest for comparing
to capacity resources, such as a CT.
The LCOE is the $/MWh revenue for delivered energy
needed to cover all Life- cycle fixed and variable
Levelized Cost of
costs,and provide the target rate of return based on
Energy (LCOE)
($/MWh) financing assumptions and ownership types. This metric
is primarily of interest for energy resources such as
renewables or baseload fossil generation.
Lithium batteries are primary batteries that have metallic
lithium as an anode. These types of batteries are also
Lithium (Li) Battery referred to as lithium-metal batteries. They stand apart
from other batteries in their high charge density (long
life) and high cost per unit.
A load management system is a system which balances
the supply of electricity on a network with the electrical
load by adjusting or controlling the load as opposed to
Load Management
the output. Load management allows utilities to reduce
System (LMS)
demand for electricity during peak usage times, which
can in turn reduce costs by eliminating the need for
peaking power plants.
Load following resources’ output changes in response to
the changing balance between electric supply (primarily
Load Following generation) and end user demand (load) within a specific
region or area, over timeframes ranging from minutes to
a few hours.
A load-serving entity is an industry term for a utility /
Load-serving Entity
electric company. Load-serving entities provide electric
(LSE)
service to end-users and wholesale customers.
–M–
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DOE OE Global Energy Storage Database Energy Storage Terms Glossary
Term Definition Examples
MMBtu one million Btu (british thermal units)
A mega volt-ampere reactive (var) is a unit of
Mega Volt-ampere measurement of reactive power. Reactive power exists in
reactive (MVAR) an AC circuit when the current and voltage are not in
phase.
A megawatt is a unit of power, expressed as one million
Megawatt (MW)
watts.
A megawatt hour is a unit of energy, expressed as one
Megawatt (MWh)
million watts being used for an hour.
–N–
A sodium–sulfur battery is a type of molten-salt battery
constructed from liquid sodium (Na) and sulfur (S). This
type of battery has a high energy density, high efficiency
of charge/discharge and long cycle life, and is fabricated
Sodium-Sulfur (NaS) from inexpensive materials. The operating temperatures
of 300 to 350 °C and the highly corrosive nature of the
sodium polysulfides, primarily make them suitable for
stationary energy storage applications. The cell becomes
more economical with increasing size.
The National Electrical Code (NEC), or NFPA 70, is a
National Electrical
regionally adoptable standard for the safe installation of
Code (NEC)
electrical wiring and equipment in the United States.
The nickel–cadmium battery (NiCd battery or NiCad
Nickel-cadmium
battery) is a type of rechargeable battery using nickel
(NiCd)
oxide hydroxide and metallic cadmium as electrodes.
The National Institute of Standards and Technology
(NIST) is a physical sciences laboratory, and a non-
National Institute of
regulatory agency of the United States Department of
Standards and
Commerce. Its mission is to promote innovation and
Technology (NIST)
industrial competitiveness. NIST's activities are
organized
–O–
O&M Operations and Maintenance
OEM original equipment manufacturer
–P–
The system
performed at a
capacity factor
of 90% during
Any performance statistics or results available on the the year of
Performance
project. 2010. Other
examples of
performance
statistics
include: -
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DOE OE Global Energy Storage Database Energy Storage Terms Glossary
Term Definition Examples
Round Trip
Efficiency
(RTE) -
Ramping Rate
- Greenhouse
Gas Emissions
- Noise
(decibels) -
Availability -
Number of
maintenance
visits
Power conversion A power converter is an electrical or electro-mechanical
system / Power device for converting electrical energy. It may be
conditioning system converting AC to or from DC, or the voltage or
(PCS) frequency, or some combination of these.
A plug-in electric vehicle (PEV) is any vehicle that can
be recharged from an external source of electricity, such
Plug-in Electric
as wall sockets, and the electricity stored in the
Vehicle (PEV)
rechargeable battery packs drives or contributes to drive
the wheels.
A plug-in electric hybrid vehicle is any vehicle that can
Plug-in Hybrid
be recharged from an external source of electricity, while
Electric Vehicle
also supporting traditional sources of fuel such as
(PHEV)
gasoline or diesel.
Pumped-storage hydroelectricity (PSH), or pumped
hydroelectric energy storage (PHES), is a type of
Pumped
hydroelectric energy storage used by electric power
Hydroelectric
systems for load balancing. The method stores energy in
Energy Storage
the form of gravitational potential energy of water,
(PHES)
pumped from a lower elevation reservoir to a higher
elevation.
PSLF Positive Sequence Load Flow
The Present Value of Life-cycle Costs includes the
Present Value of installed costs (above) and all ongoing fixed and variable
Life-cycle Costs operating costs over useful life. The present value of the
($/kW Installed) annual costs is divided by the kW of energy storage
system discharge capacity installed.
The Present Value of Life-cycle Costs described above
Present Value of divided by usable kWh of energy storage capacity
Life-cycle Costs installed. Both of the Present Value of Life-cycle Costs
($/kWh Installed) metrics can be compared against estimates of present
value benefits or revenues to estimate cost-effectiveness.
In the United States, a utilities commission, utility
Public Utility
regulatory commission (URC), public utilities
Commission (PUC)
commission (PUC), or public service commission (PSC)
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DOE OE Global Energy Storage Database Energy Storage Terms Glossary
Term Definition Examples
is a governing body that regulates the rates and services
of a public utility, such as an electric utility.
PV Photovoltaic or present value
–Q–
No “Q” terms
–R–
Changing the loading level of a Generating Unit in a
constant manner over a fixed time (e.g., Ramping up or
Ramping
Ramping down). Such changes may be directed by a
computer or manual control.
The total possible output from the energy storage
Rated Power 600kW
system, expressed in kW.
A flow battery, or redox flow battery (after reduction–
oxidation), is a type of electrochemical cell where
Redox Flow Battery
chemical energy is provided by two chemical
(RFB)
components dissolved in liquids contained within the
system and separated by a membrane.
A regional transmission organization in the United States
is an electric powertransmission system operator (TSO)
Regional that coordinates, controls, and monitors a multi-state
Transmission electric grid. The transfer of electricity between states is
Organization (RTO) considered interstate commerce, and electric grids
spanning multiple states are therefore regulated by the
Federal Energy Regulatory Commission (FERC).
Using an
energy storage
system to
capture excess
energy
generated by
Centralized or distributed Electric Energy Time Shifting
Renewable Energy grid-connected
specifically related to the uncontrollable nature of
Time-shift wind and solar
renewable generation.
farms during
low demand
times in order
to dispatch it
during high
demand times.
Use of storage to mitigate rapid output changes from
renewable generation due to: a) wind speed variability
Renewables Capacity affecting wind generation and b) shading of solar
Firming generation due to clouds. It is important because these
rapid output changes must be offset by other
“dispatchable” generation.
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DOE OE Global Energy Storage Database Energy Storage Terms Glossary
Term Definition Examples
–S–
Electric
The benefits provided by the energy storage system.
Energy Time-
Services reference individual benefits and may come
Shift;
from direct market participation or reduced/deferred cost
Renewables
Service/Use Case relative to the status quo. Use Cases are groups of (or
Capacity
sometimes individual) services that are provided by a
Firming;
single energy storage system. If possible, select from our
Frequency
pre-determined set values.
Regulation
Supervisory Control and Data Acquisition is a control
system architecture comprising computers networked
Supervisory Control data communications and graphical user interfaces (GUI)
and Data Acquisition for high-level process supervisory management. It allows
(SCADA) industrial organizations to control industrial processes
locally or at remote locations, and to monitor, gather,
and process real time industrial data.
State of charge is the level of charge of an electric
State of charge battery relative to its capacity. The units of SoC are
(SOC) percentage points (0% = empty; 100% = full). The units
of SoC are percentage points (0% = empty; 100% = full).
A static synchronous compensator (STATCOM), also
known as a static synchronous condenser (STATCON),
Static Synchronous is a regulating device used on alternating current
Compensator electricity transmission networks. It is based on a power
(STATCOM) electronics voltage-source converter and can act as either
a source or sink of reactive AC power to an electricity
network.
A static VAR compensator is a set of electrical devices
for providing fast-acting reactive power on high-voltage
Static VAR electricity transmission networks. SVCs are part of the
Compensator (SVC) Flexible AC transmission system device family,
regulating voltage, power factor, harmonics and
stabilizing the system.
–T–
T&D transmission and distribution
Thermal Energy Storage allows excess thermal energy to
be stored and used later. Storage media include water or
ice-slush tanks, masses of native earth or bedrock
Thermal Energy accessed with heat exchangers by means of boreholes,
Storage (TES) deep aquifers contained between impermeable strata;
shallow, lined pits filled with gravel and water and
insulated at the top, as well as eutectic solutions and
phase-change materials.
TOU time of use
Transmission In many areas, transmission systems are becoming
Congestion Relief congested during periods of peak demand, driving the
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DOE OE Global Energy Storage Database Energy Storage Terms Glossary
Term Definition Examples
need and cost for more transmission capacity and
increased transmission access charges. Additionally,
transmission congestion may lead to increased use of
congestion charges or locational marginal pricing (LMP)
for electric energy. Storage can be used to avoid
congestion-related costs and charges. In this application,
storage systems are installed at locations that are
electrically downstream from the congested portion of
the transmission system. Energy is stored when there is
no transmission congestion, and discharged (during peak
demand periods) to reduce transmission capacity
requirements.
Energy storage used for transmission support improves
T&D system performance by compensating for electrical
anomalies and disturbances such as voltage sag, unstable
Transmission
voltage, and sub-synchronous resonance. The result is a
Support
more stable system with improved performance
(throughput). Benefits from transmission support are
highly situation-specific and site-specific.
A Transmission System Operator (TSO) is an entity
Transmission System entrusted with transporting energy in the form of natural
Operator (TSO) gas or electrical power on a national or regional level,
using fixed infrastructure.
The T&D Upgrade Deferral benefit is related to the use
of a relatively small amount of modular storage to: a)
defer the need to replace or to upgrade existing T&D
equipment or b) to increase the equipment’s existing
service life (life extension). Storage for T&D equipment
Transportable
life extension is especially compelling for the aging fleet
Transmission and
of underground circuits which are quite expensive to
Distribution (T&D)
replace or to upgrade. Those circuits’ life can be
Upgrade Deferral
extended by: a) reducing the number of ground faults
and/or b) reducing loading such that operating
temperature is reduced, which reduces degradation of the
insulation. Transportable systems can be moved to where
they are needed most on the grid.
–U–
An uninterruptible power supply or uninterruptible
power source (UPS) is an electrical apparatus that
provides emergency power to a load when the input
Uninterruptible power source or mains power fails. A UPS differs from
Power Supply (UPS) an auxiliary or emergency power system or standby
generator in that it will provide near-instantaneous
protection from input power interruptions, by supplying
energy stored in batteries, supercapacitors, or flywheels.
– V–
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DOE OE Global Energy Storage Database Energy Storage Terms Glossary
Term Definition Examples
VAR reactive power and volt-ampere reactive
Vented lead acid batteries are commonly called
Vented lead acid “flooded” or “wet cell” batteries because this type of
(VLA) battery “vents” hydrogen continuously during normal
float operation.
A valve-regulated lead-acid battery (VRLA battery)
sometimes called sealed lead-acid (SLA) or maintenance
Valve-regulated free battery, is a type of lead–acid battery. They are
Lead-acid (VRLA) widely used in large portable electrical devices, off-grid
Battery power systems and similar roles, where large amounts of
storage are needed at a lower cost than other low-
maintenance technologies like lithium-ion.
A volt is a unit of electromotive force, the difference of
Volts (V) potential that would drive one ampere of current against
one ohm resistance.
To manage "reactance" at the grid system level, grid
system operators rely on an ancillary service called
‘voltage support’. The purpose of voltage support is to
offset reactive effects so that grid system voltage can be
Voltage Support
restored or maintained. "Reactance" occurs because
equipment that generates, transmits, or uses electricity
often has or exhibits characteristics like those of
inductors and capacitors in an electric circuit.
–W–
No “W” terms
–X–
No “X” terms
–Y–
No “Y” terms
–Z–
The zinc–bromine flow battery is a type of hybrid flow
Zinc-Bromine battery. A solution of zinc bromide is stored in two
(ZnBr2) Flow tanks. When the battery is charged or discharged the
Battery solutions (electrolytes) are pumped through a reactor
stack and back into the tanks.
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