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PD IEC TS 61400 — Wind Turbine Availability Assessment Technical Specification Series (Production-Based Availability and Wind Power Station Availability)
Wind Turbines / Wind Energy Generation Systems — Production-Based Availability and Availability for Wind Power Stations (2014/2016 Editions)
🌬️ PD IEC TS 61400 is the BSI-adopted IEC/TS 61400 series on availability assessment for wind turbines. The two parts in this batch are Part 26-2, which defines production-based availability for wind turbines, and Part 26-3, which gives the information model and calculation for availability of wind power stations. Both are handled by BSI Technical Committee PEL/88 (Wind turbines). Unlike traditional time-based availability that only counts “operable hours”, this series is built around actual energy output, providing a unified, auditable methodology for availability contracts, settlement, and assessment between turbine manufacturers, owners, insurers, and regulators.
💡 The difference between time-based and production-based availability is a common source of contractual disputes in the wind industry: a turbine that is “98% available in time” can lose far more than 2% of generation if all its outages fall in high-wind, high-yield periods. This series is designed to remove that ambiguity.
1. Series Composition and Framework 📌
| Standard | Title | IEC Edition | Core Content |
|---|---|---|---|
| PD IEC/TS 61400-26-2:2014 | Wind turbines — Part 26-2: Production-based availability for wind turbines | IEC TS 61400-26-2 (Ed.1.0, 2014-06) | Production-based availability definition, information model, potential energy determination |
| PD IEC/TS 61400-26-3:2016 | Wind energy generation systems — Part 26-3: Availability for wind power stations | IEC TS 61400-26-3 (Ed.1.0, 2016-08) | WPS and BOP information models, service categories, availability calculation |
⚠️ This series covers only the themed availability rules (the 26-x sub-series); design, loads, noise and other topics are in 61400-1, -2, -11 etc. Use it together with the full IEC 61400 series, not in isolation.
2. Part 26-2: Production-Based Availability ⚡
PD IEC/TS 61400-26-2:2014 assigns each interval of operating time to predefined information categories and computes availability from potential energy production versus actual energy production:
- Information model: defines “information available” and “information unavailable” states and their priority ordering, so a given interval is counted only once.
- Allocation of production terms: assigns production terms to categories, clarifying which states count as available and which as loss.
- Mean-value based information: rules for time-averaged and power-averaged data where point-by-point recording is not possible.
- Entry and exit points: boundary conditions for state transitions, ensuring a consistent counting basis.
- Potential energy production: Annex A gives possible determination methods, such as back-calculation from the power curve, wind resource data, and available periods.
Thus production-based availability becomes “the proportion of potentially generatable energy actually produced”, directly reflecting energy availability and suited to production-warranty contracts and loss allocation.
3. Part 26-3: Availability for Wind Power Stations 🏭
PD IEC/TS 61400-26-3:2016 extends the view from a single turbine to the whole wind farm and is a milestone document for international wind-industry availability statistics:
- Wind power station (WPS) vs. balance of plant (BOP): clearly separates the wind-generating station itself from collection, substation, and export auxiliary facilities, with availability computed separately.
- Services: decomposes availability by service, covering every stage of providing electrical power from the station to the grid.
- Information categories and priority: extends the available/unavailable framework and defines priority ordering to form a unified state tree.
- Detailed state classification: rules for fine-grained states such as OPERATIVE, IN SERVICE, FULL PERFORMANCE, and PARTIAL PERFORMANCE.
- Statistics and reporting: provides consistent definitions for whole-station and per-turbine availability, supporting worldwide cross-comparison.
✅ A further value of this series is “same-definition dialogue”: once manufacturers and owners adopt the same information model, availability figures become comparable rather than misleadingly different, giving a credible basis for international wind asset valuation.
4. Summary of Key Technical Points 🔧
| Topic | Key Content | Document |
|---|---|---|
| Information model | Available/unavailable classification and priority | 26-2 / 26-3 |
| Availability basis | Production-based availability definition | 26-2 |
| Potential energy | Power-curve back-calculation, wind-resource methods (Annex A) | 26-2 |
| Station-level statistics | WPS vs. BOP separation, service categories | 26-3 |
| State refinement | OPERATIVE / IN SERVICE / FULL / PARTIAL PERFORMANCE | 26-3 |
| Statistical consistency | Entry/exit points, mean-value information, priority handling | 26-2 / 26-3 |
5. Engineering Practice 🛠️
- 🔍 Availability contracts: cite this series in power purchase agreements (PPA) and O&M contracts so availability is verifiable and auditable.
- 🔧 Loss analysis: split generation loss by information category (fault, grid curtailment, planned maintenance, adverse weather) to locate availability bottlenecks.
- 📊 Asset valuation: use production-based rather than time-based availability for wind farm valuation and refinancing due diligence.
- 📋 O&M optimisation: use state-classification results to optimise maintenance windows, scheduling planned outages in low-wind periods to improve energy availability.
6. Frequently Asked Questions ❓
❓ Q: What is the difference between time-based and production-based availability?
A: Time-based availability counts only “operable time proportion”, ignoring wind strength; production-based availability uses potential energy as the denominator and actual energy as the numerator, better reflecting real generation-capacity loss, so it is preferred in contracts and settlement.
A: Time-based availability counts only “operable time proportion”, ignoring wind strength; production-based availability uses potential energy as the denominator and actual energy as the numerator, better reflecting real generation-capacity loss, so it is preferred in contracts and settlement.
❓ Q: What counts as “information available” versus “information unavailable”?
A: Information available is the time when enough data exists to judge turbine/station state; information unavailable is when data is missing and state cannot be determined. Both are counted separately, and priority rules ensure a moment falls into only one category.
A: Information available is the time when enough data exists to judge turbine/station state; information unavailable is when data is missing and state cannot be determined. Both are counted separately, and priority rules ensure a moment falls into only one category.
❓ Q: Why does Part 26-3 separate WPS and BOP?
A: Wind farm output depends not only on turbines but also on collection lines, substations, and export facilities. Separating them clarifies responsibility — owners and O&M contractors typically answer for different parts — and supports grid-side assessment.
A: Wind farm output depends not only on turbines but also on collection lines, substations, and export facilities. Separating them clarifies responsibility — owners and O&M contractors typically answer for different parts — and supports grid-side assessment.
🔍 Q: How is potential energy production determined?
A: Common methods include back-calculation from measured wind speed and the manufacturer power curve, interpolation from nearby met masts, or modelling from historical generation. Annex A gives several possible methods and their applicability; the method should be fixed before contract signature to avoid later dispute.
A: Common methods include back-calculation from measured wind speed and the manufacturer power curve, interpolation from nearby met masts, or modelling from historical generation. Annex A gives several possible methods and their applicability; the method should be fixed before contract signature to avoid later dispute.