National Grid Reserve Service

In order to balance the supply and demand of electricity on short timescales, the UK National Grid has contracts in place with generators and large energy users to provide temporary extra power, or reduction in demand. These reserve services are needed if a power station fails for example, or if forecast demand differs from actual demand. National Grid has several classes of reserve services, which in descending order of response time are: Balancing Mechanism (BM) Start-Up, Short-Term Operating Reserve, Demand Management and Fast Reserve.[1][2]

National Grid Frequency Response

This is a service that large power users such as steel works, cold stores, large water pumping stations, can offer to the UK National Grid. These contractors have frequency sensitive relays fitted to the incoming breakers, and these disconnect the load if the system frequency falls beyond a pre-set figure (49.7 Hz). These loads are shed for a contracted period of at least 30 minutes. Within this period Standing Reserve (Reserve Service) diesels of similar capacity (i.e., around 660 MW total) start up, and enable the Frequency Service loads to be re-connected and the relays re-armed.

Frequency Service is designed to cope with the loss of two 660 MW sets in quick succession. There is about 2.25 GW of such Frequency Service loads available in the UK to cover a peak demand of about 60 GW.

If the total Reserve Service payments, about 2250 MW × £7,000 = £15.75 million are divided by the total kWh delivered by the National Grid to all customers, approximately 0.3 trillion kWh then this amounts to a total cost of about 0.005p/kWh.

Similar arrangements operate in the United States and France and all other large power grids.[3]

Short Term Operating Reserve (STOR)

At some times of the day National Grid needs access to sources of extra power, in the form of either generation or demand reduction, to be able to deal with actual demand being greater than forecast demand and/or unforeseen generation unavailability. These additional power sources which are available to National Grid are referred to as ‘Reserve’ and comprise synchronised and non-synchronised sources. National Grid procures the non-synchronised requirement primarily by contracting for Short Term Operating Reserve, which is provided by a range of service providers by means of standby generation and/or demand reduction.

The need for STOR varies depending on the time of year, the time of week and time of day, being a function of the system demand profile at that time. To reflect this, National Grid splits the year into a number of Seasons, for both Working Days (including Saturdays) and Non-Working Days (Sundays and most Bank Holidays), and specifies the periods in each day that Short Term Operating Reserve is required. These periods are referred to as Availability Windows.

Short-Term Operating Reserve is a contracted Balancing Service, whereby the service provider delivers a contracted level of power when instructed by National Grid, within pre-agreed parameters. The main, minimum capability requirements for the service are as follows:

  • Minimum Contracted MW capability = 3MW.
  • Contracted MW must be achievable no later than 240 minutes after instruction from National Grid.
  • Contracted MW must be deliverable for no less than 2 hours.

The service can be provided by both BM and non-BM participants. Utilisation of the service from BM participants is via the Balancing Mechanism. For non-BM service providers, a bespoke monitoring and dispatch system, STOR Dispatch, is installed (formerly known as SRD - Standing Reserve Dispatch).

There are two forms of payment that National Grid will make as part of the service:

  1. Availability Payments. Where a service provider makes its unit/site available for the STOR service within an Availability Window, National Grid will pay for that availability on a £/MW/h basis.
  2. Utilisation Payments. Where National Grid instructs delivery of STOR from a unit/site, then it will pay for the energy delivered on a £/MWh basis. (This includes the energy delivered in ramping up to and down from the Contracted MW level). For BM service providers this payment will be effected through the Balancing Mechanism.

STOR is subject to a number of restrictions and conditions which include a minimum capacity threshold of 3MW. Above this capacity it is possible to tender directly to National Grid for the provision of STOR services or via the assistance of an agent. Prospective providers can choose to use an Agent to administer their tender process and, on their behalf, submit STOR Tenders to National Grid. National Grid perceives the role of an Agent as essentially a “go-between”, interfacing with both the prospective Reserve Provider and National Grid. National Grid is willing to deal with Agents provided that no part of the tender process or contracting process is hindered. Using an Agent (or not) does not affect evaluation of STOR Tenders.

The alternative option for sites that either don’t have the 3MW minimum capacity at a single location or would rather defer the operational responsibilities to a specialised third party service provider. The role of an Aggregator is to develop and operate multiple sites (STOR Sub Sites) and offer these to National Grid as single STOR Site(s). This role is specifically different to that of an Agent. Whilst an Aggregator can be an asset owner, typically an Aggregator will act on the behalf of one or more third party asset owners to submit “composite” STOR Tenders to National Grid. National Grid therefore perceives the role of an Aggregator as essentially a “Reserve Provider”, holding the STOR Contract itself whilst managing the necessary interfaces with the various individual asset owners.

The prices tendered by a potential provider will determine their position in the operational merit order and affect the number of events, operating hours and payment levels they will receive.

Other National Grid measures

The above measures happen routinely and without any interference with normal supplies to consumers. There are other similar arrangements which are used only as a last resort since they do involve disconnecting consumers. If Frequency Response and spinning reserve fails to control grid frequency and it falls too far, then the fans feeding combustion air into power station boilers begin to deliver at inadequate draft/pressure since they are synchronous, and the output of all power-stations in the grid, goes into irreversible decline. To prevent this, frequency sensitive relays on entire substations trip out, disconnecting entire customer areas on a pre-determined schedule.

This continues until, as a last resort, large areas can be switched out manually.

See also


  1. ^ National Grid. "National Grid: Reserve Services". Retrieved 2011-08-01.
  2. ^ See Claverton Energy Group web site - "Commercial Opportunities for Back-Up Generation and Load Reduction via National Grid, the National Electricity Transmission System Operator (NETSO) for England, Scotland, Wales and Offshore."
  3. ^ ENTSO-E Operation Handbook, Policy 1 (2009): Load-Frequency Control and Performance

External links

Ancillary services (electric power)

Ancillary services are the services necessary to support the transmission of electric power from seller to purchaser given the obligations of control areas and transmitting utilities within those control areas to maintain reliable operations of the interconnected transmission system.

Ancillary services are the specialty services and functions provided by the electric grid that facilitate and support the continuous flow of electricity so that supply will continually meet demand. The term ancillary services is used to refer to a variety of operations beyond generation and transmission that are required to maintain grid stability and security. These services generally include, frequency control, spinning reserves and operating reserves. Traditionally ancillary services have been provided by generators, however, the integration of intermittent generation and the development of smart grid technologies have prompted a shift in the equipment that can be used to provide ancillary services.

Availability-based tariff

Availability Based Tariff (ABT) is a frequency based pricing mechanism applicable in India for unscheduled electric power transactions. The ABT falls under electricity market mechanisms to charge and regulate power to achieve short term and long term network stability as well as incentives and dis-incentives to grid participants against deviations in committed supplies as the case may be.

Cost of electricity by source

The distinct ways of electricity generation can incur significantly different costs. Calculations of these costs can be made at the point of connection to a load or to the electricity grid. The cost is typically given per kilowatt-hour or megawatt-hour. It includes the initial capital, discount rate, as well as the costs of continuous operation, fuel, and maintenance. This type of calculation assists policymakers, researchers and others to guide discussions and decision making.

The levelized cost of energy (LCOE) is a measure of a power source that allows comparison of different methods of electricity generation on a consistent basis. It is an economic assessment of the average total cost to build and operate a power-generating asset over its lifetime divided by the total energy output of the asset over that lifetime. The LCOE can also be regarded as the average minimum price at which electricity must be sold in order to break-even over the lifetime of the project.

Demand response

Demand response is a change in the power consumption of an electric utility customer to better match the demand for power with the supply. Until recently electric energy could not be easily stored, so utilities have traditionally matched demand and supply by throttling the production rate of their power plants, taking generating units on or off line, or importing power from other utilities. There are limits to what can be achieved on the supply side, because some generating units can take a long time to come up to full power, some units may be very expensive to operate, and demand can at times be greater than the capacity of all the available power plants put together. Demand response seeks to adjust the demand for power instead of adjusting the supply.

Utilities may signal demand requests to their customers in a variety of ways, including simple off-peak metering, in which power is cheaper at certain times of the day, and smart metering, in which explicit requests or changes in price can be communicated to customers.

The customer may adjust power demand by postponing some tasks that require large amounts of electric power, or may decide to pay a higher price for their electricity. Some customers may switch part of their consumption to alternate sources, such as on-site diesel generators.

In many respects, demand response can be put simply as a technology-enabled economic rationing system for electric power supply. In demand response, voluntary rationing is accomplished by price incentives—offering lower net unit pricing in exchange for reduced power consumption in peak periods. The direct implication is that users of electric power capacity not reducing usage (load) during peak periods will pay "surge" unit prices, whether directly, or factored into general rates.

Involuntary rationing, if employed, would be accomplished via rolling blackouts during peak load periods. Practically speaking, summer heat waves and winter deep freezes might be characterized by planned power outages for consumers and businesses if voluntary rationing via incentives fails to reduce load adequately to match total power supply.

Dinorwig Power Station

The Dinorwig Power Station (; Welsh: [dɪˈnɔrwɪɡ]), known locally as Electric Mountain, is a pumped-storage hydroelectric scheme, near Dinorwig, Llanberis in Snowdonia national park in Gwynedd, northern Wales. The scheme can supply a maximum power of 1,728-megawatt (2,317,000 hp) and has a storage capacity of around 9.1-gigawatt-hour (33 TJ).

Load management

Load management, also known as demand side management (DSM), is the process of balancing the supply of electricity on the network with the electrical load by adjusting or controlling the load rather than the power station output. This can be achieved by direct intervention of the utility in real time, by the use of frequency sensitive relays triggering the circuit breakers (ripple control), by time clocks, or by using special tariffs to influence consumer behavior. Load management allows utilities to reduce demand for electricity during peak usage times (peak shaving), which can, in turn, reduce costs by eliminating the need for peaking power plants. In addition, some peaking power plants can take more than an hour to bring on-line which makes load management even more critical should a plant go off-line unexpectedly for example. Load management can also help reduce harmful emissions, since peaking plants or backup generators are often dirtier and less efficient than base load power plants. New load-management technologies are constantly under development — both by private industry and public entities.

National Grid (Great Britain)

In the electricity sector in the United Kingdom the National Grid is the high-voltage electric power transmission network serving Great Britain, connecting power stations and major substations and ensuring that electricity generated anywhere on it can be used to satisfy demand elsewhere. The network covers the great majority of Great Britain and several of the surrounding islands. It does not cover Ireland; Northern Ireland is part of a single electricity market with the Republic of Ireland.

The GB grid is connected as a wide area synchronous grid nominally running at 50 hertz. There are also undersea interconnections to other grids in northern France (HVDC Cross-Channel), Northern Ireland (HVDC Moyle), the Isle of Man (the AC Isle of Man to England Interconnector), the Netherlands (DC BritNed) and the Republic of Ireland (the DC EirGrid).

On the breakup of the Central Electricity Generating Board in 1990, the ownership and operation of the National Grid in England and Wales passed to National Grid Company plc, later to become National Grid Transco, and now National Grid plc. In Scotland the grid was already split into two separate entities, one for southern and central Scotland and the other for northern Scotland, connected by interconnectors. The first is owned and maintained by SP Energy Networks, a subsidiary of Scottish Power, and the other by SSE. However, National Grid plc continues to be the transmission system operator for the whole GB grid.

Renewable Electricity and the Grid

Renewable Electricity and the Grid: The Challenge of Variability is a 2007 book edited by Godfrey Boyle which examines the significance of the issue of variability of renewable energy supplies in the electricity grid.

Reserve service

Reserve service may refer to the following:

A military reserve force

The National Grid Reserve Service in the United Kingdom


STOR may refer to:

Short Term Operating Reserve, see National Grid Reserve Service

STØR, American furniture chain

Variable renewable energy

Variable renewable energy (VRE) is a renewable energy source that is non-dispatchable due to its fluctuating nature, like wind power and solar power, as opposed to a controllable renewable energy source such as dammed hydroelectricity, or biomass, or a relatively constant source such as geothermal power.

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