Power Curve Working Group Overview

Peter StuartSenior Technical Manager

Tuesday 06th October 2014

1

Power Curve Working Group Power Curve Working Group MotivationMotivation

What does the PCWG aim to do?

3

• The power curve working group (PCWG) formed to answer a specific question:

What power will a wind turbine generate in the full range of atmospheric conditions seen in the ‘real world’?

Wind Speed

Pow

er

Is a power curve based on just wind speed and density the ‘whole truth’?

Power Curve

Turbine Performance in the Real World

• The real world has…

4

high wind speed

high turbulence

low wind shear

high wind shear

low wind speed

low turbulence

• and many combinations of the above (on same site at different times)…

• Wind conditions change all the time, and so does turbine performance.

Wind Speed

Tu

rbu

len

ce

in

ten

sit

y

Measured Power Deviation Matrix: Deviation vs TI and Wind Speed

Power Curve Working Group: Who are we?

5

RES, VattenfallCrown EstateDong, IberdrolaSSE, RWEEDF, EON, ESBI, Mainstream, Scottish Power

DNV GLNatural PowerAWS True PowerSgurrWind GuardBarloventoAnemos-JacobPrevailing

VestasSenvionGESuzlonSiemensNordex

The power curve working group (PCWG) is a balanced and broad industry group encompassing Developers, Consultants, Manufacturers and Academics/Researches.

NRELDTULLNJIWESCIRCEORE Catapult

Openness is a key principal: Proceedings of all meetings publically available at: http://www.ewea.org/events/workshops/resource-assessment-2013

LeosphereRomowindZephIRVaisala

The group aims to examine ways of improving understanding of wind turbine energy yield in ‘real world’ conditions.

Understanding the Problem Understanding the Problem and Each Otherand Each Other

Statement of the problem

7

• The power function of a wind turbine is dependent on wind speed, density, vertical wind shear, vertical wind veer, turbulence intensity, directional variation and inflow angle.

Pow

er

Wind Speed

Density

Wind Shear

Wind Veer

Turbulence

Power Function

Inflow Angle

8

Corrections should be applied for ‘real world’ conditions which are different to those for which a power curve is representative. These corrections fall into two categories:

Type A: Adjustments made to reflect changes in the energy available for conversion across the rotor in a ten minute period due to ‘non-standard conditions’.

Type B: Adjustments made to reflect changes in the conversion efficiency due to ‘non-standard conditions’.

Nomenclature: Types of Correction

Available Energy

Turbine Behaviour

Nomenclature: Types of Correction

9

• Proxy methods: relate production to a parameter which is broadly associated with changes in performances. Acknowledge that the underlying mechanisms may not be identified, but pursue regardless if methods demonstrably improve predictions. e.g. production loss based on low turbulence intensity.

• Analytical/physical methods: apply methods based on understanding of underlying physics/statistics. May involve use of additional measurements such as LiDAR e.g. Rotor Equivalent Wind Speed and Turbulence Correction defined in 61400-12-1.

Common Understanding in Practice

10

Measured Power Deviation Matrix: Deviation vs TI and Wind Speed

Recent PCWG discussion:‘There is a gap between the proxy and analytical methods, in particular in the low wind speed & low turbulence quadrant. Type B effects are suspected as the reason for the difference’

Round Robins: Understanding Round Robins: Understanding the Methods We Already Havethe Methods We Already Have

Round Robin Exercises

12

• The PCWG has held a series of round robins aims at improving common understanding of methods define in 61400-12-1:

• Rotor Equivalent Wind Speed

• Turbulence Correction (Turbulence Renormalisation)

• Equivalent Wind Speed Including Veer

• Site Specific Power Curves (coming soon)

• The Round Robins have been invaluable in prompting detailed discussion in how best to apply these methods.

• The final product of the round robins is a publically available ‘consensus analysis’.

Round Robin: Application of REWS Method

13

Pretty good agreement!

Round Robin: Application of Turbulence Correction Method

14

Not so good agreement!

Round Robins

15

• The disagreement in the Turbulence Correction Method demonstrated that people find this method relatively difficult to apply.

Dropbox\PowerCurveWorkingGroup\Consensus Analysis

• To address this issue a consensus implementation of the Turbulence Correction has been developed.

• The consensus analysis uses a pure excel implementation of the turbulence correction method (Excel array formulas)

• A ‘guided tour’ of the consensus analysis was presented at the September 2014 PCWG meeting.

• An excel consensus analysis of the Rotor Equivalent Wind Speed Method is also available in DropBox.

Inner-Outer Range ProposalInner-Outer Range Proposal

Stakeholder Interaction: Inner and Outer Range Concept

17

Shear

Tur

bule

nce

Inner Range

Performance = 100% (on average)

Outer Range

Performance < 100% (on average)

• The inner-out range concept has been proposed as a pragmatic framework for offering a ‘two-tier’ performance warranty.

18

Stakeholder Interaction: Inner and Outer Range Concept

• AEPReference(u): The reference AEP per wind speed bin. • AEPmeasured(u): The measured AEP per wind speed bin.• F(u): The fraction of data in the outer range per wind speed.• R: (Warranty level in Outer Range) / (Warranty level in Inner Range)

• Proposal document is publically available at: http://www.ewea.org/events/workshops/wp-content/uploads/2014/03/PCWG-Inner-Outer-Range-Proposal-Dec-2013.pdf

• The proposal has already been used contractually by some working group members.

Inner-Outer Range ProposalInner-Outer Range Proposal

• The first release of the (Version 0.5.0) of the PCWG Open Source Analysis tool is now available to download.

• The code is provided without warranty under the terms of the MIT software license (see attached for more details). The tool itself can be downloaded at: https://sourceforge.net/projects/pcwg/files

• The tool has been benchmarked against the Excel Consensus Analysis of the working group Round Robin Exercises.

• The tool is open source and working group members are encouraged to contribute. Those interested can access the project source code on GitHub: https://github.com/peterdougstuart/PCWG

20

PCWG Open Source Analysis Tool

21

PCWG Tool: Calculation of Power Curve Deviation Matrices

• Example Analysis of combined dataset of 5 turbines of the same type

Deviation before Turb CorrectionDeviation after Turb Correction

Data SharingData Sharing

• The PCWG currently has 5 datasets which have been supplied to the group by its members.

23

Data Sharing

• The existing datasets have been invaluable, but much more could be achieved if more data was available.

• If you have any data which you can share please get in touch!

• In particular analysis like the power deviation matrices require a substantial amount of data to generate something meaningful.

• The ideal dataset is a power performance test dataset with both masts and LiDARs.

• Traditional mast based power performance datasets are also highly useful.

What Next & ConclusionsWhat Next & Conclusions

What Next for the PCWG

1. Publication of companion document for Turbulence Correction Consensus Analysis i.e. a guide to applying this method.

2. Site Specific Power Curves Round Robin

3. Publication of document expressing the ideal format for communicating power curve information.

4. New features in Open Source Analysis Tool e.g. site calibration module.

5. Innovative data sharing exercise: find new ways to bring data together

6. Examine correction methods for other parameters e.g. inflow angle

7. Drill into ‘gap’ between proxy and analytical methods (Type B effects).

25

Conclusions

• The PCWG has been formed to find practical approaches to deal with the issue of turbine performance in real world conditions.

26

• The PCWG has reached a consensus that the power function of a wind turbine is dependent on wind speed, density, vertical wind shear, vertical wind veer, turbulence intensity, directional variation and inflow angle.

• The PCWG is exploring corrections for ‘real-world’ wind conditions and new methods of stake holder interaction in order to give a more realistic expectation of turbine performance.

• Further collaboration between manufacturers, developers and consultants is required to improve communication of power function information and explore corrections for real world conditions.

• This is an issue the industry has the power to solve!

• These corrections will help the wind industry further improve/refine the accuracy of its energy yield predictions and thus improve investor confidence.

27

Time

Power Curve Working Group Roadmap

Dec 2012

Definition

Meeting 1

Define what’s the problem we are trying to solve.

Solution / Evolution

Meeting 2

Identify possible solutions

Round Robin 1

Mar 2013

Meeting 3

May 2013

Apr - May 2013

Conclusion

Trial solutions

Feedback on solutions.

Compare experiences & lessons leant.

Identify refined and/or alternative solutions

Jun – Sep 2013

Round Robin 2

Meeting 4

Trial refined solutions

Feedback on refined solutions.

Dec 2013

Is problem is solved?

Jun2014

Publically disseminate presentations and minutes

Should problem be redefined?

Iterate solutions as required…

Final Meeting

Finalise conclusions

Publication of journal paper by working group.

Publication of guideline document.

Current Status