Technology / Engineering guide
Wind Turbine Availability, Downtime & Missing Records
An availability percentage needs a definition of the service, period and included states. Separate equipment availability, data completeness and energy results before using a number to compare turbine performance or project operation.
Make the numerator and denominator visible.
Classify the represented periods and retain unknown intervals before calculating or comparing an availability indicator.
01 / Different indicators
State which availability question the number answers.
Equipment availability concerns a defined service or operating condition; data availability concerns usable records.
Equipment availability concerns a defined service or operating condition; data availability concerns usable records. Energy production describes another outcome. A complete dataset can record an unavailable turbine, while missing telemetry need not establish that generation stopped.
The public scope of IEC 61400-26-1 identifies an information model for time-based and production-based indicators. The reference provides reporting context, not a calculation made for MARSTON or a claimed product availability.
02 / Time basis
Define the period and included categories.
State the calendar interval, turbine or equipment group and the service being considered.
State the calendar interval, turbine or equipment group and the service being considered. Identify the included categories, entry and exit definitions, and the records used to classify time. A denominator described only as operating hours leaves important interpretation questions unresolved.
Specify how simultaneous indications are resolved so one interval is not counted twice. Scheduled work, faults, external restrictions and other categories need the definitions agreed for the reporting purpose. This page does not prescribe a contractual category scheme.
03 / Missing records
Keep unknown states separate from established downtime.
If an interval cannot be classified from applicable evidence, retain it as unknown under the adopted reporting method.
If an interval cannot be classified from applicable evidence, retain it as unknown under the adopted reporting method. An absent log entry is not automatically a stop, successful operation or zero output. State any method used to recover classification from other records.
Report data coverage separately when it affects the indicator. Do not remove unknown intervals without explaining the denominator change. The data-quality guide covers file handling; this page concerns the conclusion permitted by the available states.
04 / Worked example
Show the effect of the stated denominator.
In a hypothetical 100-hour record, suppose 90 hours are classified available, 5 unavailable and 5 unknown.
In a hypothetical 100-hour record, suppose 90 hours are classified available, 5 unavailable and 5 unknown. The available share of the full represented period is 90%. Among the 95 classified hours, the available fraction is 90/95, approximately 94.7%.
Those are explicitly defined illustrative fractions, not an IEC-compliant metric, contractual result or MARSTON record. Reporting the second figure without its classified-hours denominator would conceal the unknown period. The example does not decide how a real project should categorise those hours.
05 / Production basis
Separate time fractions from energy consequences.
Equal-duration interruptions can coincide with different resource and output conditions.
Equal-duration interruptions can coincide with different resource and output conditions. A time-based indicator therefore does not alone describe an energy effect. A production-based assessment needs an applicable reference and method for any energy that was expected but not delivered.
Keep measured energy distinct from estimated lost production and state the assumptions for the latter. Do not turn low generation during a low-resource period into proof of technical unavailability. The energy-assessment guide covers the wider projection inputs.
06 / Reporting record
Compare like definitions and retain event evidence.
A useful report includes the adopted definition, represented period, category totals, unknown coverage and supporting event references.
A useful report includes the adopted definition, represented period, category totals, unknown coverage and supporting event references. Identify changes in classification rules between reporting periods. A trend assembled using different denominators may answer a different question from the original one.
For a MARSTON project, request records and definitions applicable to the supplied configuration and required service. No annual availability, uptime guarantee or downtime target is promised here. Commercial acceptance needs agreed terms and evidence rather than a generic percentage.
Continue the review with Wind Turbine Yaw Power Consumption & Net Energy Accounting.
Continue the review with Average Wind Speed & Wind-Speed Distributions.
Continue the review with Wind Turbine Factory & Site Acceptance: Evidence Planning.
Continue the operating-record review with the distinctions among MTBF, failure rate and availability.
General background: IEC 61400-26-1 public scope: time- and production-based availability. These references explain industry concepts; they are separate from the applicable MARSTON product and project documents.
Prepare the information for this review.
Use the checklist to organise the project information. Mark unavailable items and retain document references.
| Review item | Information to provide | Purpose |
|---|---|---|
| Indicator definition | Equipment service, data coverage or production purpose | State the question being answered. |
| Period & scope | Calendar interval and assessed equipment | Define the represented population. |
| State categories | Definitions, transitions and concurrent-state rules | Allocate time consistently. |
| Unknown periods | Unclassified duration and any recovery method | Retain missing evidence. |
| Reported result | Numerator, denominator, category totals and references | Make comparison transparent. |
Engineering questions.
Is data availability the same as turbine availability?
No. Usable records and the equipment’s defined service condition are different questions.
Does missing telemetry establish downtime?
Not by itself. Retain the unknown state or applicable classification evidence.
Can unknown intervals simply be excluded?
Any exclusion changes the basis. State the method, denominator and missing coverage explicitly.
Does a time-based percentage describe lost energy?
Not alone. A production-based assessment needs a defined reference and relevant resource or output conditions.
Is the 94.7% example a MARSTON figure?
No. It is a clearly hypothetical fraction using a stated classified-hours denominator.
What supports a fair availability comparison?
A common service definition, period, classification rules, denominator and visible unknown coverage with supporting records.
Technical enquiry
Bring your project information to the discussion.
An availability percentage needs a definition of the service, period and included states. Share the available information and the equipment scope you want reviewed in a technical quotation.