Construction
Once the project is approved and finance is in place, the developer will hand over responsibility for the site to the lead contractor, who will handle the construction process. The developer will also have to arrange for any work to allow the wind farm to connect to the local distribution or transmission network. If an Environmental Management Plan has been agreed (depending on the nature, size and location of the site), it will be implemented at the earliest opportunity. The construction process generally takes 6-12 months, depending on the size of the project. The local community can be kept informed of progress using an information board system, or an announcement in the local newspaper.
Commissioning
Once construction is complete and grid connections have been made, the wind farm will be ready for commissioning. This will involve ‘switching on’ the turbines for the first time, allowing wind-generated electricity to flow to the grid for the first time. Developers will often organise a ceremony to celebrate the completion of the project.
Operation & Maintenance
Developers have responsibility for the operation of their wind energy project throughout its lifetime and the public should be notified of any changes of operation. Maintenance activities will need to take place regularly for individual turbines and associated infrastructure to ensure maximum performance.
Decommissioning / Repowering
At the end of their working lives (usually 20 years), the wind turbines will usually be removed and the materials recycled. The site may then be ‘repowered’, where new turbines are installed in their place, or fully decommissioned. Repowering offers the potential for significant increases in output from existing sites, as the latest technology will be installed. However, in some cases the original planning consent may stipulate that the site is decommissioned. The developer may then choose to apply for planning permission to repower the site, or be forced to decommission it. This would require removal of the foundations and restoration of the site as close as possible to its previous condition.
Alternating current (AC)- Flow of electricity that constantly changes direction between positive and negative sides. Electricity produced in the UK moves in current that shifts direction at a rate of 50 times per second (50 Hertz, 50Hz).
Base load- The minimum load experienced by an electric utility system over a given period of time.
Baseload capacity - Generating equipment operated to serve loads 24-hours per day (eg. nuclear power plants).
BETTA– the British Electricity Transmission and Trading Arrangements introduced in April 2005, extending NETA to Scotland.
Capacity- The maximum load a generating unit, generating station, or other electrical apparatus is rated to carry.
Capacity factor - The ratio of the electrical energy produced by a generating unit relative to the electrical energy that could have been produced at continuous full power operation during the same period of time. The Capacity Factor for wind energy in the UK is typically between 20% and 40%.
Capacity value– Sometimes referred to as capacity credit, this is an expression of the percentage of conventional generation that can be displaced by wind generation. The capacity value may be equal to the capacity factor at low levels of wind penetration, but will be lower as penetration increases.
CCGT- Combined cycle gas turbine; modern gas powered electricity generating technology. Conservation- A foregoing or reduction of electric usage for the purpose of saving natural energy resources and limiting peak demand in order to ultimately reduce the capacity
requirements for plant and equipment. Current (electric)- Flow of electrons in an electric conductor.
Demand (electric)- The rate at which electrical energy is delivered to or by a system. Demand is expressed in kW, kVA, or other suitable units at a given instant or over any designated period of time.
Defra- Department of Environment, Food and Rural Affairs
Distributed generation (embedded
generation)- A distributed generation system involves small amounts of generation located on a utility's distribution system for the purpose of meeting local (substation level) peak loads and/or displacing the need to build additional (or upgrade) local distribution lines.
DTI- Department of Trade and Industry Distribution- The system of wires, switches, and transformers that serve neighbourhoods and businesses; classified as 132,000 volts and below in England and Wales (132kV is considered to be part of the Transmission Network in Scotland). A distribution system reduces the voltage from high-voltage transmission lines (275,000 volts or 400,000 volts) to a level that can be distributed to homes or businesses; 132,000V, 33,000V, 11,000V, 3,300V, 440V.
Distribution system- That part of the electric system that delivers electrical energy to consumers.
DSO, DNO- Distribution System (or Network) Operator.
Embedded generation– see distributed generation
Energy- This is broadly defined as the capability of doing work. In the electricity industry, energy is more narrowly defined as electricity supplied over time, normally expressed in kilowatt-hours. Energy consumption- The amount of energy consumed in the form in which it is acquired by the user. The term excludes electrical generation and distribution losses.
Energy efficiency- Programmes that reduce energy consumption whilst maintaining a given level of output.
Energy mix- the distribution or proportion of different energy sources within the total energy supply.
Energy resources- Everything that could be used by society as a source of energy. Energy source- A source that provides the power to be converted to electricity e.g. hydro, solar, wind, biomass, fossil fuel, nuclear fuel. Energy use- Energy consumed during a specified time period for a specific purpose (usually expressed in kWh).
Generation (Electricity)- Process of producing electric energy by transforming other forms of energy.
Generator- Machine used to convert mechanical energy into electrical energy. Gigawatt (GW)- The unit of electrical power equal to one thousand-million watts, or one thousand megawatts.
Grid- Matrix of an electrical distribution system, the National Grid in the UK.
Installed capacity- The total generating units' capacities in a power plant or on a total utility system. The capacity can be based on the nameplate rating or the declared net (dependable) capacity (DNC).
Intermittent resources- Resources whose output depends on some other factor that cannot be controlled by the utility e.g. wind or sun. Thus, the capacity varies by day and by hour.
Kilowatt (kW)- The electrical unit of power equal to 1,000 watts.
Kilowatt-hour (kWh)- The basic unit of electric energy equal to one kilowatt of power supplied to or taken from an electric circuit for one hour.
Load- The amount of electric power delivered or required at any specified point or points on a system. Load originates primarily at the power consuming equipment of the customer.
Load factor- The ratio of the average load supplied to the peak or maximum load during a designated period. Similar to capacity factor, but more often used when describing conventional plant.
Losses- The general term applied to energy (kWh) and capacity (kW) lost in the operation of an electric system. Losses occur principally as energy transformations from kWh to waste-heat in electrical conductors and apparatus.
Megawatt (MW)-One million watts. A large coal-fired power station in the UK typically has an installed capacity of between 2,000 MW and 4,000 MW
Megawatt-hour (MWh)- One thousand kilowatt-hours or one million-watt hours.
NETA- the New Electricity Trading Arrangements introduced in March 2001 for England and Wales, and governed by the Balancing and Settlement Code (see BSC). Now superseded by BETTA.
Off-peak- Periods of relatively low system demands.
OFGEM- the Office of Gas and Electricity Markets; the energy regulator for the GB gas and electricity sectors.
Outage- Time during which service is
unavailable from a generating unit, transmission line, or other facility.
Payback- The length of time it takes for the savings received to cover the cost of
implementing the technology.
Peak- Periods of relatively high system demands.
Peak demand- Maximum power used in a given period of time.
Phase- One of the characteristics of the electric service supplied or the equipment used.
Practically all residential customers have single- phase service at 240 volts. Large commercial and industrial customers typically have three- phase service from 440 volts upwards. Plant- A facility containing prime movers, electric generators, and other equipment for producing electric energy.
Power- The rate at which energy is transferred. Power plant- A generating station where electricity is produced.
Production- The act or process of generating electric energy.
Pumped storage- A facility designed to generate electric power during peak load periods with a hydroelectric plant using water pumped into a storage reservoir during off-peak periods.
Regulation- An activity of government to control or direct economic entities by rulemaking and adjudication.
Reliability- Electric system reliability has two components - adequacy and security. Adequacy is the ability of the electric system to supply the aggregate electric demand and energy
requirements of the customers at all times, taking into account scheduled and unscheduled outages of system facilities. Security is the ability of the electric system to withstand sudden disturbances such as electric short circuits or unanticipated loss of system facilities. Renewable energy- the term used to cover those energy flows that occur naturally and repeatedly in the environment, it includes all energy derived from the sun (solar, wind, ocean, and hydro power, plus biomass), and
geothermal sources.
Energy that is capable of being renewed by the natural ecological cycle, generally wind, wave, tidal, solar, hydro, biomass.
Renewables Obligation- support mechanism aimed at increasing the percentage of
renewable energy generation on the national grid. The Renewables Obligation works by placing an obligation on electricity suppliers to source an increasing percentage of supply from renewables. Separate obligations apply in Scotland and Northern Ireland.
Reserve capacity- Capacity in excess of that required to carry peak load.
ROCs- Renewable Obligation Certificates; the tradable ‘currency’ of the RO.
Running and quick-start capability- Generally refers to generating units that can be available for load within a 30-minute period.
Scheduled outage- An outage that results when a component is deliberately taken out of service at a selected time, usually for the purposes of construction, maintenance, or testing.
Spinning reserve- Reserve generating capacity running at zero load.
Substation- A facility used for switching and/or changing or regulating the voltage of electricity. Service equipment, line transformer
installations, or minor distribution or
transmission equipment are not classified as substations.
Supplier- A person or corporation, generator, broker, marketer, aggregator or any other entity, that sells electricity to customers, using the transmission or distribution facilities of an electric distribution company.
System (Electric)- Physically connected generation, transmission, and distribution facilities operating as a single unit. Terawatt (TW)- One thousand gigawatts Therm-
Transformer- A device for changing the voltage of alternating current.
Transmission- The act or process of transporting electric energy in bulk.
Transmission and distribution (T&D) losses- Losses that result from the heating effect of current as it flows through wires to travel from the generation facility to the customer. Because of losses, the electricity produced by the utility is greater than the electricity that shows up on the customer bills.
Transmission and distribution (T&D) system- An interconnected group of electric transmission lines and associated equipment for the
movement or transfer or electrical energy in bulk between points of supply and points at which it is transformed for delivery to the ultimate customers.
Transmission lines- Heavy wires that carry large amounts of electricity over long distances from a generating station to places where electricity is needed. Transmission lines are held high above the ground on tall towers called transmission towers.
Transmission network- the electricity
transmission system operating at voltages above 132kV (in England and Wales) and including 132kV in Scotland)
TSO, TNO– (Electricity) Transmission System (or Network) Operator
Upgrade- Replacement or addition of electrical equipment resulting in increased generation or transmission capability.
Utility- A regulated vertically-integrated
electricity company. "Transmission utility" refers to the regulated owner/operator of the transmission system only. "Distribution utility" refers to the regulated owner/operator of the distribution system which serves retail customers.
Volt– the unit of electrical potential. It is the electromotive force which, if steadily applied to a circuit having a resistance of one ohm, will produce a current of one ampere.
Volt-amperes- The volt-amperes of an electric circuit; the mathematical product of the volts and amperes. Equals the power in a direct current circuit.
Voltage- Measure of the force of moving electrical energy.
Watt- The electrical unit of power or rate of doing work. One horsepower is equivalent to approximately 746 watts.
Watt-hour- One watt of power expended for one hour.
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14 Figures from BWEA website at: http://www.bwea.com/map/index.html
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24 Garrad Hassan (2005). Data kindly provided from the GH Forecaster. http://www.garradhassan.com
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37 Harrison, L, 2004. Wind economics set to beat gas in Ireland. Windpower Monthly, December 2004.
38 German Energy Agency, 2005. Planning of the grid integration of wind energy in Germany offshore and onshore up to the year 2020.
39 Oxera, 2004. Security of supply, energy investment requirements and cost implications. Report for Centrica
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44 DEFRA (2004). Energy Efficiency: The Government’s Plan For Action. Available at:
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48 Data obtained from RESTATS service provided by Future Energy Solutions for the DTI. Public data available at:
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