Quick summary

This glossary of terms guide gives you quick access to Offshore Wind Terminology so you always know what people are talking about.

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Annual Energy Production (AEP)This is the amount of energy generated in a year, usually measured in GWh (Giga Watt Hours). Gross AEP gives you total energy generated excluding any losses. For simulation work this is the predicted Gross AEP, and will be based on the power curve. Net AEP has losses removed. Examples of losses are unexpected WTG downtime, electrical losses in cables and transmission systems etc
Array cable (also known as Inter-array cable (IAC))The electrical cables that connect individual WTG’s to each other, and to the central offshore substation. The voltage level is usually either 33kV or 66kV
AvailabilityThe actual percentage of time that the WTG or the wind farm is available to produce power. It does not necessarily mean that the WTG produces power because of the intermittency of the wind. This percentage is often built into Service and Maintenance agreements, and can be expressed in either a time based, or a yield based percentage.
Balance of Plant (BoP)A “catch-all” term for anything that is not the WTG. This can include the foundations, electrical systems, and onshore assets
ConsentPlanning permission to construct the wind farm
Capacity factorThe “rated capacity” is the maximum power the WTG produces. The capacity factor is ratio between this and the actual energy it produced (or is predicted to produce)
CAPEX – Capital expenditureAll expenses to develop and build a wind farm until the day that the wind farm is completed and handed over to the organisation overseeing operation and maintenance. There will be a significant milestone in the project plan and contracts for this
Crew Transfer vessel (CTV)A type of boat that is used to transfer technicians and other members of staff to offshore work activities from shore or transferring from another larger vessel located in the area
DECEX – Decommissioning expenditureAt the end of the project there needs to be a plan for the decommissioning and safe removal of all structures and assets. This is the cost associated with this job
EIA – Environmental impact assessmentActivities relating to Consent, where a number of studies need to be performed on the impact of the proposed wind farm on the environment. For example, impact of piling during installation, impact on fishing, visual impact from shore, bird and bat studies etc
EPCI – Engineer, procure, construct and installA general term for a contractor who has a wide scope in terms of design and construction. For example, an EPCI contractor might be responsible for the design and construction of everything apart from the procurement and installation of the WTG’s
Export CableElectrical cable connecting the offshore substation to the onshore substation. Usually runs at a high voltage e.g. 220kV
FEED – Front end engineering designUsually a defined phase of project development where the engineering issues are defined and studied. Various scenarios are developed before procurement
FID – Final investment decisionThe developer decides whether to commit to the project or not. Previous to this, all consents, subsidy agreements contracts with major component suppliers have been agreed, if not yet signed and fully committed
Jacket foundationAn alternative to a monopile foundation, often using a lattice structure on 3 or 4 legs
LCOE – Levelised cost of energyA financial indicator for the income required where the project breaks even, when taking into account the WACC (weighted average cost of capital). Often a figure in $/£/€ per mWh is generated, where electricity needs to be generated at that price or lower otherwise the wind farm is not feasible
MWh – Megawatt hourCommonly used measure of power alongside MW (unit of energy)
Monopile foundationUsually a cylindrical tube that is hammered into the seabed to provide the support for the WTG on top
OSS – Offshore substationAn offshore structure mounted on a monopile or jacket. The array cables all feed into here from the WTG’s and a separate export cable runs to shore or to a large collector station. It can also house transformers, AC to DC converters, reactive power compensators and backup generators
OFTO – Offshore transmission ownerUsually associated with UK projects, the offshore transmission assets need to sold off under the direction of the UK’s Ofgem (Office of Gas and Electricity Markets)
OPEX – Operational expenditureAll costs associated with operation and maintenance of the wind farm including any service agreements, from project handover (after construction) to the end of the lifetime of the wind farm
O & M – Operation and maintenanceThis is the phase after construction, and after the project is handed over. The wind farm will probably initially operate under a service agreement with the wind turbine supplier, where they will maintain the WTG assets for an annual fee. The foundations and other electrical systems also need to be maintained, and marine traffic needs to be coordinated
SOV – Service operation vesselThis is basically a larger CTV that also provides offshore accommodation and other storage facilities to support ongoing offshore activities. It might have DP (dynamic positioning) so that a “walk to work” system can be used to transfer personnel from the SOV to the wind turbine access platform
SCADA – Supervisory Control and Data AcquisitionThis is a monitoring and control system for the wind farm. Key and critical sensors can be observed and alarm signals will alert technicians of any faults. There will be one system for the WTG’s and maybe other separate SCADA systems that monitor other parts of the wind farm. For example, ICCP corrosion systems, offshore substation, bird detection systems etc could run as separate systems
TP – Transition pieceThe top part of the foundation that connects the monopile (or other structure) to the tower. It is usually attached to the substructure with a bolting system, grouting, or a combination of both
WACC – Weighted average cost of capitalThe cost of borrowing or the return the owner wishes to receive over the lifetime of the project
Wind Turbine Generator (WTG)The main components of a wind turbine generator which include the blades, hub, nacelle and tower. The tower might be in 3 or more sections