Trends, Technical Risks, and Opportunities in Partial Repowering Alex Byrne

March 1, 2017 AWEA OMS Conference

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Traditional wind turbine lifecycle

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Repower

Extended life

DecommissionEnd of design lifeStart of operation

Inject gearboxes, blades, labor, cranes, effort to keep turbines running

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Benefit of repowering is to use of newer technology – why wait until turbines are facing obsolescence?

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Full repowering: remove entire turbine and replace with new technology

Partial repowering: keep some portion of turbine and replace some portion with new technology

Studies have shown full repowering generally not attractive until after year 20 unless there are incentives– May 2016, IRS clarified criteria for project upgrades

to qualify for PTC– Investments must be 4x retained value– Calculations made per turbine pad– Business case highly project and turbine specific

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Aging fleet: 12% of US turbines are more than 10 years old

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What does partial repowering mean?

No formal definition of ‘partial’ Some options include:– Full nacelle and rotor replacement– Replacement of rotor, various drivetrain, ancillary

components and controls Tower and foundation likely to remain Tower replacement conceivable but may not result in

economically viable approach Large increases in rotor size (>20% increase) could result

in loads exceeding capacity in tower and foundations 20% rotor size increase ~ 10 to 20% energy boost

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Risks and benefits relative to new construction

Structural and foundation risks Energy risk Environmental and permitting concerns Contractual risks Electrical balance of plant impacts

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Site conditions and structural reliability risk

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Design load capacity (IEC)

20 yrs original turbine

site loading

20 yrs repower turbine

site loading

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ation

!

10 yrs original

site load

20 yrs repower site load

10 yrs original site load

20 yrs repower site load

With partial repowering, some components will operate beyond their design life

Careful analysis of site conditions and fatigue loading is critical

Benign vs aggressive siting influences risk

Certification status of repowered turbines: still a question

Controls and material innovations in recent years reduce loads

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Towers and foundations

Foundations– New foundation loads must be assessed– Foundations older than 10 years may not have been

designed for fatigue– Assess current site and soil conditions– Review operating history of turbine for extreme events– Refurbishment might be possible, but costly

Towers– Non-destructive testing at key load points and welds– Evaluate fatigue, harmonics and tip clearance– New/old interface compatibility & adapters– Risk-based inspections

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Structural reliability risk challenges and mitigates

Analytical estimation of consumed life is uncertain– Without certification of repowered turbine, structural

risk likely higher than with new construction Inspection and repair plans / reserves help mitigate

this elevated risk Risk based inspections (RBI)– Inspect at an optimized interval to: – Maintain risk of failure below a target– Catch cracks before they are critical– Mitigate risk of continued operation of used

components in spite of uncertainty

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RBI conceptually

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Energy assessment: often lower uncertainty

DNV GL has seen 2-3% reduction in uncertainty in long term AEP

Why? Historic operating data provides better knowledge of:– Environmental and BOP loss factors – Grid curtailment and other interconnection

issues – Wake effects– Long term wind resource– Wind speed variation across site

Possible reduction in inter-turbine spacing– Impact on loads?– Sector management impact on energy?

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Contractual, environmental and permitting

Environmental: – Larger rotor: – Avian and wildlife review – Sound, shadow, and other setbacks

– Increased tip height: Changes to FAA approvals Local or state permitting and review processes –triggering new review

process? Contractual: – New turbine supply & installation agreement– New warranties– Interconnection Agreement –limitations or necessary changes?– Offtake agreements – min/max limits, term, rates, etc.– O&M agreements – Changes due to new turbines, parts, responsibilities

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Electrical Balance of Plant

Risks: – Turbine and plant capacity may change– Additional years of operation

Mitigation: – Evaluate equipment capacity and remaining

life of existing equipment– Pad transformers and cables– Medium voltage cables and overhead

conductors– Turbine grounding– Transmission– Interconnection

– Substation:– Main power transformers– Feeder circuit breakers– Main breakers– Reactive power compensation– Surge arresters

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Conclusions

We’ve seen a lot of interest in partial repowering including safe harbor activities in 2016 NextEra and BP have been public about their plans to repower Potential benefits can be compelling, but are site specific: – Increased energy – Increased reliability– Requalification for PTC

Risks must be assessed/mitigated:– Reliability of used components especially tower and foundation– Undersiting and improved controls can be leveraged– Risk based inspections to limit exposure to failure

– Environmental, permitting, contracts re-opened– Electrical BoP capacity and life

DNV GL white paper on partial repowering available at www.dnvgl.com/publications

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SAFER, SMARTER, GREENER

www.dnvgl.com

Thank you!

Alex ByrneAlex.Byrne@DNVGL.com206-387-4253