Energy dictionary

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  • a

  • AFRR

  • Aggregators
    Organisations or commercial businesses that pay disparate users and producers of electricity for slow or rapid reductions and increases in demand or supply to and from the grid and aggregate the result into packaged quantities that are of sufficient size to be attractive to power System Operators.  

  • Ancillary services
    A range of adjustments to electricity supply into and out of grid to keep the power system stable and sustain a reliable supply of high quality electricity. Adjustments are automatic and manual. They are controlled by power System Operators who call on generators to provide grid support services in a market driven or command and control process. There is no globally standard nomenclature for the various ancillary services.

  • Arbitrage
    The buying of low cost energy on a power system with the purpose of selling it elsewhere or at another time in expectation of making profit. Owners of storage facilities require a sufficiently large spread between the price at which they buy electricity and the price at which they sell it to make arbitrage worthwhile.

  • Automatic Frequency Restoration Reserve

  • b

  • Balancing
    Ensuring a match between power demand and power supply, without which electricity systems cannot maintain stability

  • Balancing market
    A short-term market that enables power generators to make bids to increase or decrease the output of their plant

  • Balancing Services
    Measures to balance supply and demand by reductions or increases in power output from generating plant. There are several types of balancing service delivered on various timescales, from seconds to hours. They fall into two basic categories, automatic or manual. Most of the rapid response services are provided automatically.

  • Baseload
    The minimum load (demand from consumers) on an electricity network

  • Black start
    Power stations or storage facilities that are able to start up independently without the need for electricity supply from a grid connection

  • Bulk power supply
    The provision of electricity for consumption by society. By far the largest market for sales of all electricity generated.

  • c

  • Congestion
    Also known as grid bottlenecks and network congestion. Electricity networks become congested when more electricity threatens to flow into them than the capacity of the wires or transformers to absorb and transport it to customers.

  • Curtailment
    The throttling back of power, usually at the request of the System Operator, because a sector of the electricity transmission system is congested and would otherwise be overloaded (see Congestion)

  • d

  • Demand side management
    Also called demand response. A system service, energy users are paid to reduce (sometimes increase) power demands to facilitate balancing of the system. Users can receive payment from aggregators of demand side response or directly from the System Operator

  • e

  • Enhanced Frequency Response
    Ultra rapid delivery of active power output in one second or less in response to a grid frequency deviation. A relatively new service. Some System Operators now hold specific auctions for "enhanced frequency response", with battery storage providers competing for contracts. Batteries are particularly well suited to injecting near instantaneous bursts of power into the grid as needed. Development of cheaper batteries is making enhanced frequency response from batteries affordable. They can potentially deliver the power more rapidly than generating units.

  • f

  • FCR
    Measures that include primary regulation, primary reserve and frequency response

  • Flexibility
    Measures that enable electricity systems to respond to the continuous variations in consumer demand and power supply, including the supply from some renewable energy sources.

  • Frequency Containment Reserve
    Measures that include primary regulation, primary reserve and frequency response

  • Frequency Response
    Provided by power generators whose output increases or decreases automatically in response to changes in frequency falls below or exceeds the target (50 Hz in Europe, parts of Africa and Asia and 60 Hz in North America). Also referred to as simply "response". Most primary frequency response services have timescales around ten seconds and secondary frequency response timescales around 30 seconds. Enhanced frequency response is within one second.

  • g

  • Grid bottlenecks

  • i

  • Inertia
    The energy stored in an electricity system by virtue of the kinetic energy of the rotating generators

  • Interconnector
    Transmission lines linking sectors of the grid that are controlled by different System Operators. Power systems can be divided into sectors within a country, be contained to an area surrounded by water, or span international borders.

  • m

  • Manual Frequency Restoration Reserve

  • Manual Reserves
    Also referred to as manual frequency restoration reserve (MFRR). Reserves that are called on by the System Operator to restore system frequency or balance supply and demand.

  • MFRR

  • p

  • Peak shaving
    Various mechanisms for reducing the peaks in demand that require bringing more generation online. Peaking plant only sell power occasionally (to cover peaks in demand) and must cover their capital and running costs with high charges, which make their electricity the most expensive to procure. Reducing peaks in demand reduces the average price of electricity to the consumer and the spread between high and low prices that can make arbitrage profitable. (see arbitrage)

  • Primary Regulation
    Also referred to as frequency containment reserve (FCR). Measures that include primary regulation, primary reserve and frequency response.

  • Primary Reserve Market
    In Europe refers to a reserve market forged from a coupling of the primary reserve markets of Germany, Belgium, the Netherlands, Switzerland and Austria to make up a combined market of over 800 MW, expected to grow to 900 MW in 2020, according to PA Consulting Group. Weekly tenders for the reserve needed provide long-term cash security, a disincentive to participation by battery energy storage systems.

  • r

  • Reactive Power
    Reactive power exists in alternating current power systems when current and voltage are not in phase. It exists as a consequence of current passing through most machines and other devices. In most electrical systems, the current lags behind the voltage, due to the presence of motors and other inductive loads, but capacitive loads have the opposite effect and the current leads the voltage. Synchronous generators can provide "lagging" or "leading" power and are used to bring current and voltage in phase. Some wind turbines can performe the corrective function.

  • Regulating Power
    The power used to assist in the restoration of system frequency, up or down.

  • Reserves
    A generic term for increases and decreases of power supplied to the grid (for a fee) as requested by the System Operator.

  • Response

  • s

  • Secondary Regulation
    Also known as secondary response and automatic frequency restoration response (AFRR). Measures that may be needed to restore system frequency after primary regulation has provided the initial action.

  • Secondary Reserve Market
    A commercial market for secondary regulation. See Secondary regulation

  • Short Term Operating Reserve

  • Spinning Reserve
    The provision of extra or reduced power under instruction from the System Operator, with a notice period of around 30 minutes, also referred to as short term operating system

  • Standing Reserve
    The provision of extra or reduced power under instruction from the System Operator, with a notice period typically two to four hours

  • System Operator
    The body whose responsibility it is to ensure that system demand and supply are kept in balance

  • v

  • Voltage Support
    Measures needed to keep system voltage and reactive power levels within statutory or technical limits. The support may be provided by ensuring that there is adequate generation within a particular area or be the use of static devices such as synchronous compensators