Energy Storage Glossary

Courtesy of:  Energy Storage Association (ESA)

  • 10

    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.

  • 128

    Adiabatic

    See: Diabatic

    Of, relating to, or being a reversible thermodynamic process that occurs without gain or loss of heat and without a change in entropy. 

  • 134

    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.

  • 135

    Alberta Electric System Operator

    Acronym(s): AESO

    Agency 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.

  • 136

    Allowance for funds used during construction

    Acronym(s): AFUDC

    AFUDC 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.

    Source: ESA Technical Working Group
  • 139

    Alternating current

    Acronym(s): AC

    Flow 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
  • 138

    American National Standards Institute

    Acronym(s): ANSI

    The organization responsible for approving U.S. standards in many areas, including computers and communications. Standards approved by this organization are often called ANSI standards.

  • 140

    Amp hours

    See: Ampere hours
    Source: ESA Technical Working Group
  • 141

    Ampere hours

    See: Current

    A 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
  • 142

    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.)

  • 16

    ANSI

    See: American National Standards Institute
  • 143

    Area control error

    Acronym(s): ACE

    The instantaneous difference between a Balancing Authority

  • 144

    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.

    Source: ESA Technical Working Group
  • 145

    Automatic generation control

    Acronym(s): AGC

    Equipment that automatically adjusts generation in a Balancing Authority Area from a central location to maintain the Balancing Authority

  • 146

    Available transfer capability

    Acronym(s): ATC

    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.

  • 147

    Average cost

    The revenue requirement of a utility divided by the utility.

  • 143

    Area control error

    Acronym(s): ACE

    The instantaneous difference between a Balancing Authority

  • 144

    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.

    Source: ESA Technical Working Group
  • 145

    Automatic generation control

    Acronym(s): AGC

    Equipment that automatically adjusts generation in a Balancing Authority Area from a central location to maintain the Balancing Authority

  • 146

    Available transfer capability

    Acronym(s): ATC

    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.

  • 147

    Average cost

    The revenue requirement of a utility divided by the utility.

  • 148

    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.

    Source: ESA Technical Working Group
  • 149

    Balancing authority

    Acronym(s): BA

    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.

  • 150

    Balancing authority area

    Acronym(s): BAA

    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.

  • 151

    Base load

    The minimum amount of electric power delivered or required over a given period at a constant rate.  

  • 152

    Baseload generation

    Electricity generation designed/intended to operate constantly almost all of the time.

    Source: ESA Technical Working Group
  • 153

    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.

    Source: ESA Technical Working Group and AA Portable Power Corp.
  • 154

    Battery electric vehicle

    Acronym(s): BEV

    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.

    Source: ESA Technical Working Group
  • 155

    Battery electricity storage

    Acronym(s): BES

    Large scale battery systems connected to the electrical grid for both power and energy Storage

    Source: ESA Technical Working Group
  • 156

    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.  

  • 157

    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.

  • 158

    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.  

  • 159

    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.

  • 160

    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.

  • 161

    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.

    Source: ESA Technical Working Group
  • 162

    California Public Utilities Commission

    Acronym(s): CPUC

    CPUC regulates investor-owned utility companies (IOUs) and sets the rates customers pay for electricity.  

  • 163

    Capacity

    See: Power

    The rate at which equipment can either generate, convert or transfer energy.

    Source: ESA Technical Working Group
  • 164

    Capacity emergency

    A capacity emergency exists when a Balancing Authority Area

  • 165

    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.

    Source: ESA Technical Working Group
  • 166

    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.

    Source: ESA Technical Working Group
  • 167

    Capital expenditures

    Acronym(s): CAPEX

    All costs associated with design, purchase, installation/construction and financing of investments in/purchase of capital equipment.

    Source: ESA Technical Working Group
  • 168

    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.

  • 169

    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.

  • 170

    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.

    Source: ESA Technical Working Group
  • 171

    Charge

    The process of injecting energy to be stored into the storage system.

    Source: ESA Technical Working Group
  • 172

    Charge rate

    The rate at which storage can be charged.

    Source: ESA Technical Working Group
  • 173

    Circuit recloser

    See: Recloser
    Source: ESA Technical Working Group
  • 174

    Coalition to Advance Renewable Energy through Bulk Storage

    Acronym(s): CAREBS

    CAREBS promotes energy storage and provides a policy voice for the energy storage community.

  • 175

    Cogeneration

    Generation of useful electric and heat energy using the same conversion system (e.g. internal combustion engine, combustion turbine or fuel cell).

    Source: ESA Technical Working Group
  • 176

    Combined cooling, heating and power

    See: Cogeneration
    Acronym(s): CCHP
    Source: ESA Technical Working Group
  • 177

    Combined cycle gas turbine

    Acronym(s): CCGT

    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.

  • 178

    Combined heat and power

    See: Cogeneration
    Acronym(s): CHP
    Source: ESA Technical Working Group
  • 179

    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).

  • 180

    Conservation voltage

    See: Conservation voltage reduction
  • 181

    Conservation voltage reduction

    Acronym(s): CVR

    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.

  • 182

    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.  

    Source: ESA Technical Working Group
  • 183

    Constant-voltage charge

    For batteries; a charging process during which the voltage applied to a battery’s terminals is constant.

    Source: ESA Technical Working Group
  • 184

    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.

  • 187

    Contingency

    The unexpected failure or outage of a system component, such as a generator, transmission line, circuit breaker, switch or other electrical element.

  • 188

    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)  

  • 189

    Contract path

    An agreed upon electrical path for the continuous flow of electrical power between the parties of an Interchange Transaction.

  • 191

    Control performance standard

    Acronym(s): CPS

    The reliability standard that sets the limits of a Balancing Authority

  • 192

    Cost-of-service

    The total cost incurred by the utility to generate, transmit and deliver electricity and to provide customer service.

    Source: ESA Technical Working Group
  • 193

    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.

  • 194

    Critical peak pricing

    Acronym(s): CPP

    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).

    Source: ESA Technical Working Group
  • 195

    Current

    See: Electric current
    Source: ESA Technical Working Group
  • 196

    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.

    Source: ESA Technical Working Group
  • 197

    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.

  • 198

    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.

    Source: ESA Technical Working Group
  • 199

    Cutoff voltage

    See: End-point voltage

    Voltage at the end of useful discharge.

  • 200

    Cycle

    See: Cycle life

    One sequence of storage charging and discharging. Also known as charge-discharge cycle.

    Source: ESA Technical Working Group
  • 201

    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.

    Source: ESA Technical Working Group
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