Energy Storage Glossary

The instantaneous difference between a Balancing Authority

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

The revenue requirement of a utility divided by the utility.

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.

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

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.

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

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.

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.

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.

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

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.

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

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.

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

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

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.

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).

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.

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

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

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

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

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).

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.

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.

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