Energy Storage Glossary
Courtesy of: Energy Storage Association (ESA)
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Adequacy
The ability of the electric system to supply the aggregate electrical demand and energy requirements of the end-use customers at all times, taking into account scheduled and reasonably expected unscheduled outages of system elements.
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Adiabatic
See: DiabaticOf, relating to, or being a reversible thermodynamic process that occurs without gain or loss of heat and without a change in entropy.
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Adverse reliability impact
The impact of an event that results in frequency-related instability; unplanned tripping of load or generation; or uncontrolled separation or cascading outages that affects a widespread area of the Interconnection.
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Alberta Electric System Operator
Acronym(s): AESOAgency responsible for the safe, reliable and economic planning and operation of the Alberta Interconnected Electric System (AIES). Provides 1. open and non-discriminatory access to Alberta’s interconnected power grid for generation and distribution companies and large industrial consumers of electricity, 2. contracts with transmission facility owners to acquire transmission services and 3. with other parties; provide fair and timely access to the system, 4. develop and administer transmission tariffs, 5. procure ancillary services to ensure system reliability and 6. manage settlement of the hourly wholesale market and transmission system services.
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Allowance for funds used during construction
Acronym(s): AFUDCAFUDC is an accounting practice whereby the costs of debt and equity funds used to finance plant construction are credited on the statement of income and charged to construction in progress on the balance sheet.
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Alternating current
Acronym(s): ACFlow of electricity whose polarity/voltage changes (alternates) between positive and negative. The majority of power produced by electric utilities in the U.S. the form of current that alternates at a rate of 60 cycles per second (Hz), also known as the fundamental frequency. In Europe and elsewhere the fundamental frequency is 50 Hz.
Source: ESA Technical Working Group -
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American National Standards Institute
Acronym(s): ANSIThe organization responsible for approving U.S. standards in many areas, including computers and communications. Standards approved by this organization are often called ANSI standards.
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Amp hours
See: Ampere hoursSource: ESA Technical Working Group -
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Ampere hours
See: CurrentA unit of measurement of the amount of current that can or does flow over a given amount of time. See also current.
Source: ESA Technical Working Group -
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Ancillary service
Those services that are necessary to support the transmission of capacity and energy from resources to loads while maintaining reliable operation of the Transmission Service Provider’s transmission system in accordance with good utility practice. (From FERC order 888-A.)
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ANSI
See: American National Standards Institute
Area control error
The instantaneous difference between a Balancing Authority
Asset utilization
The extent to which an asset is used relative to the maximum amount of use that is possible. For example, an asset that could be used throughout he entire year and that is only used during half of the year has an asset utilization of 50%. Another relevant metric for electric utility assets is kWh generated, transmitted or delivered per kW of (asset) rated capacity.
Automatic generation control
Equipment that automatically adjusts generation in a Balancing Authority Area from a central location to maintain the Balancing Authority
Available transfer capability
1. A measure of the transfer capability remaining in the physical transmission network for further commercial activity over and above already committed uses. It is defined as Total Transfer Capability less existing transmission commitments (including retail customer service), less a Capacity Benefit Margin, less a Transmission Reliability Margin. 2. The amount of additional [transmission] capability available in the transmission network to accommodate additional requests for transmission services.
Average cost
The revenue requirement of a utility divided by the utility.
Area control error
The instantaneous difference between a Balancing Authority
Asset utilization
The extent to which an asset is used relative to the maximum amount of use that is possible. For example, an asset that could be used throughout he entire year and that is only used during half of the year has an asset utilization of 50%. Another relevant metric for electric utility assets is kWh generated, transmitted or delivered per kW of (asset) rated capacity.
Automatic generation control
Equipment that automatically adjusts generation in a Balancing Authority Area from a central location to maintain the Balancing Authority
Available transfer capability
1. A measure of the transfer capability remaining in the physical transmission network for further commercial activity over and above already committed uses. It is defined as Total Transfer Capability less existing transmission commitments (including retail customer service), less a Capacity Benefit Margin, less a Transmission Reliability Margin. 2. The amount of additional [transmission] capability available in the transmission network to accommodate additional requests for transmission services.
Average cost
The revenue requirement of a utility divided by the utility.
Backup Power (Reliability)
This electric service reliability application focuses on the need for back-up power systems at Commercial and Industrial facilities. Usually, the facilities use a combination of batteries for ride-through of momentary outages and then have a diesel generator for longer duration outages.
Balancing authority
The responsible entity that integrates resource plans ahead of time, maintains load-interchange-generation balance within a balancing authority area (BAA), and supports Interconnection frequency in real time.
Balancing authority area
The collection of generation, transmission, and loads within the metered boundaries of the Balancing Authority. The Balancing Authority maintains load- resource balance within this area.
Base load
The minimum amount of electric power delivered or required over a given period at a constant rate.
Baseload generation
Electricity generation designed/intended to operate constantly almost all of the time.
Battery
1. Two or more electric cells connected together electrically. In common usage, the term “battery” is also applied to a single cell, such as a household battery. 2. A system comprised of identical electrochemical cells.
Battery electric vehicle
A battery electric vehicle (BEV) is a type of electric vehicle (EV) that uses chemical energy stored in rechargeable battery packs. BEVs useelectric motors and motor controllers instead of internal combustion engines (ICEs) for propulsion.
Battery electricity storage
Large scale battery systems connected to the electrical grid for both power and energy Storage
Bilateral transaction
A transaction between two willing parties who negotiate an agreement. For example, the sale of electricity from an Independent Power Producer (IPP) to utility customers and other large customers is often the result of a bi-lateral transaction.
Black start
Black start service is the ability of a generating unit to start without an outside electrical supply, or is the demonstrated ability of a generating unit with a high operating factor to automatically remain operating at reduced levels when disconnected from the grid. Black start service is necessary to help ensure the reliable restoration of the grid following a blackout.
Black start capability plan
A documented procedure for a generating unit or station to go from a shutdown condition to an operating condition delivering electric power without assistance from the electric system. This procedure is only a portion of an overall system restoration plan.
Bulk electric system
As defined by the Regional Reliability Organization, the electrical generation resources, transmission lines, interconnections with neighboring systems, and associated equipment, generally operated at voltages of 100 kV or higher. Radial transmission facilities serving only load with one transmission source are generally not included in this definition.
Burden
Operation of the Bulk Electric System that violates or is expected to violate a System Operating Limit or Interconnection Reliability Operating Limit in the Interconnection, or that violates any other North American Electric Reliability Corporation (NERC), Regional Reliability Organization, or local operating reliability standards or criteria.
C rate
1. A charge rate that, under ideal conditions, is equal to the energy storage capacity of an electricity storage device divided by 1 hour. For example, a storage device that can store 5 kiloWatt-hours of electric energy has a C rate of five kiloWatts, also known as a C rate of 1. And, a C rate of 5 means energy storage divided by 12 minutes. 2. 1 C is the charge rate necessary to charge a battery in one hour. 10 C charges in 6 minutes and 0.1 C charges in 10 hours. 3. C rate is the charge rate a) for a specific storage device/system or type, b) under ideal conditions, c) that is equal to the energy storage capacity of the device divided by 1 hour. For example, a storage device that can store 5 kiloWatt-hours of electric energy has a C rate of five kiloWatts, also known as a C rate of 1. A C rate of 5 for the same system means energy storage capacity of five kilowatt-hours divided by 12 minutes whereas a C Rate of 1/5 would indicate discharge of a 5 kiloWatt-hour storage device divided by five hours.
California Public Utilities Commission
CPUC regulates investor-owned utility companies (IOUs) and sets the rates customers pay for electricity.
Capacity
The rate at which equipment can either generate, convert or transfer energy.
Capacity emergency
A capacity emergency exists when a Balancing Authority Area
Capacity factor
A value indicating the average percentage of full capacity used over a given period of time. For example, a generating facility which operates at an average of 70% of its normal full capacity over a measured period has a capacity factor of 0.7 for that period.
Capacity firming
Use of storage to provide energy to fill-in when variable generation (i.e. solar and wind) output is below the generator’s rated power output; done to provide constant power output.
Capital expenditures
All costs associated with design, purchase, installation/construction and financing of investments in/purchase of capital equipment.
Cascading
The uncontrolled successive loss of system elements triggered by an incident at any location. Cascading results in widespread electric service interruption that cannot be restrained from sequentially spreading beyond an area predetermined by studies.
Cascading outage
The uncontrolled successive loss of bulk electric system facilities triggered by an incident (or condition) at any location resulting in the interruption of electric service that cannot be restrained from spreading beyond a pre- determined area.
Characteristic voltage
The inherent voltage at which the storage system operates. For electrochemical batteries; the inherent voltage of individual cells, which is driven by the underlying chemical reaction(s) within the cell.
Charge
The process of injecting energy to be stored into the storage system.
Charge rate
The rate at which storage can be charged.
Circuit recloser
Coalition to Advance Renewable Energy through Bulk Storage
CAREBS promotes energy storage and provides a policy voice for the energy storage community.
Cogeneration
Generation of useful electric and heat energy using the same conversion system (e.g. internal combustion engine, combustion turbine or fuel cell).
Combined cooling, heating and power
Combined cycle gas turbine
Combined cycle gas turbine plants utilize more than one cycle to generate electricity with waste heat used to make steam, generating additional electricity through a steam turbine.
Combined heat and power
Competitive power supplier
An entity that owns and/or operates one or more independent power facilities that are not regulated under the traditional terms. These suppliers are regulated and monitored by the Federal Energy Regulatory Commission (FERC).
Conservation voltage
Conservation voltage reduction
Operation of T&D equipment at the minimum allowable voltage to improve energy efficiency and/or to reduce peak demand. Most CVR schemes contain two fundamental components: reactive power compensation and voltage optimization. Reactive power compensation is achieved through the operation of shunt capacitors in order to maintain the power factor at the substation transformer within a prescribed band. Voltage optimization is achieved through the operation of substation voltage regulators in order to regulate the voltage at specific end of line points within a prescribed range.
Constant-current charge
1. For batteries; a charging process during which the electric current into the battery is constant. 2. For batteries; a charging process during which the electric current into the battery is constant. Charging is stopped when the battery is fully charged and constant-voltage charging is used.
Constant-voltage charge
For batteries; a charging process during which the voltage applied to a battery’s terminals is constant.
Constrained facility
A transmission facility (line, transformer, breaker, etc.) that is approaching, is at, or is beyond its System Operating Limit or Interconnection Reliability Operating Limit.
Contingency
The unexpected failure or outage of a system component, such as a generator, transmission line, circuit breaker, switch or other electrical element.
Contingency reserve
1. The provision of capacity deployed by the balancing authority to meet the disturbance control standard (DCS) and other North American Electric Reliability Corporation (NERC) and regional reliability organizations’ contingency requirements. 2. Reserves set aside to support the transmission system in the case of the worst foreseeable contingency event (often referred to as N-1)
Contract path
An agreed upon electrical path for the continuous flow of electrical power between the parties of an Interchange Transaction.
Control performance standard
The reliability standard that sets the limits of a Balancing Authority
Cost-of-service
The total cost incurred by the utility to generate, transmit and deliver electricity and to provide customer service.
Critical assets
Facilities, systems, and equipment which, if destroyed, degraded, or otherwise rendered unavailable, would affect the reliability or operability of the Bulk Electric System.
Critical peak pricing
A program involving “high” or “very high” prices (relative to normal prices) that are assessed during “critical peak” periods (when demand is at or near supply).
Current
Current density
The amount of current per unit area such as the amount of current flowing through a wired per unit of cross sectional area of the wire that is perpendicular to flow of current. Current density is a vector quantity whose direction is the same as the direction of current flow.
Curtailment
1. A reduction in the scheduled capacity or energy delivery of an Interchange Transaction. 2. A temporary reduction in customer load that occurs or that is imposed because demand exceeds the capacity.
Customer facility charge
An charge that is part of an end-use customer’s electricity bill that may be used to cover—among other utility costs— cost to maintain utility facilities and infrastructure needed to provide electric service to the respective customer. Charges may include, for example, T&D equipment, accounting, meter reading and site-specific services. Facility charges may also be a way to combine several small fixed-cost charges associated with maintaining a customer’s energy account.
Cutoff voltage
Cycle
One sequence of storage charging and discharging. Also known as charge-discharge cycle.
Cycle life
The number of charge-discharge cycles after which storage becomes inoperable or unusable for a given application. In practice, storage may be inoperable or unusable when it can still deliver a portion of its initial rated energy and/or power rating.