The vocabulary of wind performance.

Practitioner definitions across performance and output, losses and faults, operations and maintenance, and the data behind them.

A working vocabulary for the teams accountable for a fleet's production: what each term means, where the industry uses it loosely, and how it appears in SCADA data. Every definition links to the terms it depends on, so a concept can be followed rather than looked up one word at a time.

Wind performance vocabulary, defined as operators use it.

Availability, capacity factor, performance ratio, and losses all mean slightly different things depending on who is selling. A written definition is the cheapest form of honesty available to a vendor, because it can be held against the product afterwards.

These are therefore practitioner definitions rather than marketing ones. Where a term has a precise meaning it is given, and where the industry genuinely disagrees, that is stated.

Each definition links to the terms it depends on, which is what makes the set usable rather than merely alphabetical.

Three ways in.

You have met a term and want it defined

Use site search or the category sections below. Every definition opens with a one-line answer before it explains anything.

You are comparing performance claims

Start with the terms that decide whether two figures are comparable at all: availability, capacity factor, and how a loss is attributed.

You are planning maintenance

The condition and failure-mode terms explain what a predictive alert is actually detecting, and what it is not.

Performance & Output

Capacity factor

The energy a turbine actually produced over a period, divided by what it would have produced running at rated power the whole time.

Annual energy production

The total energy a turbine or site delivers over a year, and the figure almost every commercial decision in wind is ultimately measured against.

Power curve

The relationship between wind speed and power output for a turbine - the manufacturer's version is a specification, and the real one is measured.

Availability

The share of time a turbine was able to operate, distinguishing hours lost to faults and maintenance from hours with no usable wind.

Rated power

The maximum continuous electrical output a turbine is designed to deliver, reached at rated wind speed and held flat above it.

Cut-in and cut-out wind speed

The wind speeds at which a turbine starts generating and at which it shuts down to protect itself, defining the operating window.

Air density

The mass of air passing through the rotor, which scales available power directly and varies with altitude, temperature, and humidity.

P50 and P90

Exceedance probabilities for an energy yield estimate: the production a site is expected to beat half the time, and the more conservative figure it should beat nine years in ten.

Losses & Faults

Yaw misalignment

A persistent offset between where a turbine points and where the wind is actually coming from, quietly costing energy without raising a fault.

Pitch misalignment

A blade set at a different angle from its neighbors, or all three set away from optimum, costing output and unbalancing the rotor.

Blade erosion

Progressive roughening and material loss along the leading edge of a blade, caused by rain, hail, and particulates, which degrades aerodynamic performance.

Wake effect

The slower, more turbulent air left behind an upwind turbine, which reduces output and increases loading on the machines downwind of it.

Turbulence intensity

How much the wind speed fluctuates around its mean, expressed as a ratio, and a primary driver of both fatigue loading and power curve scatter.

Icing losses

Production lost when ice accretes on blades, degrading their aerodynamic profile and often forcing a protective shutdown.

Gearbox failure

The loss of a turbine's gearbox, historically the most expensive single failure in onshore wind and the classic target for early detection.

Underperformance

A turbine producing less than it should in the conditions it actually experienced, as distinct from producing less than a neighbor or less than last year.

Unplanned downtime

Hours a turbine is stopped by something nobody scheduled - a fault, a failure, or a grid event - and the most expensive kind of hour a fleet has.

Fault code

The status and alarm identifiers a turbine controller emits, which record what the machine noticed - not everything that was wrong with it.

Operations & Maintenance

Curtailment

Output deliberately held below what the wind would allow - for grid limits, negative prices, noise rules, or wildlife protection.

Predictive maintenance

Servicing equipment when evidence says it is degrading, rather than on a fixed schedule or after it has already failed.

Condition monitoring

Tracking the mechanical health of a turbine's drivetrain from vibration, temperature, and oil data, to detect degradation before it becomes failure.

Operations and maintenance

The ongoing cost and activity of running a wind farm - scheduled service, repairs, spares, access, and the people who do it.

Availability warranty

A contractual guarantee that turbines will be available for a stated share of the time, with defined exclusions and liquidated damages if the target is missed.

Vessel mobilization

Bringing a crew transfer or jack-up vessel to an offshore wind farm - the access constraint that dominates offshore maintenance economics.

Lifetime extension

Operating a wind farm beyond its original design life, justified by an engineering assessment of how much fatigue the structures have actually accumulated.

Repowering

Replacing or substantially upgrading turbines on an existing site to raise output, using the land, grid connection, and permits already in place.

Data & Modeling

SCADA data

The operational record a turbine already produces - power, wind speed, temperatures, and status codes, usually averaged into ten-minute intervals.

Nacelle anemometer

The wind sensor mounted on top of the nacelle, behind the rotor - the turbine's own view of the wind, and a measurement it distorts.

Meteorological mast

A free-standing tower carrying calibrated wind instruments, used as the reference measurement for resource assessment and power performance testing.

IEC 61400-12

The international standard defining how a turbine's power performance is measured, so that a warranted power curve means the same thing to both parties.

Normal behavior model

A model trained on a turbine's own healthy operating history to predict what a channel should read, so that deviation from it becomes the signal.

Anomaly detection

Identifying operating behavior that departs from an established pattern, without needing labeled examples of the failures being looked for.

Loss attribution

Accounting for the gap between the energy a site could have produced and what it delivered, assigning each portion to a specific, named cause.

A more intelligent approach to sustainable energy.

See how OpenTurbine can help your team understand performance, anticipate operational issues, and make better decisions across your wind assets.

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