Moving Toward Cost-Competitive, Commercial Floating Wind EnergyUS Offshore Wind 2018

Garrett BarterNational Renewable Energy LaboratoryJune 7, 2018

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Executive summary and outline: Six key points1. There is an abundant deep water offshore wind

energy resource near coastal demand centers that:

– Can only be fully tapped with floating wind technology– Has the potential to be the same (or lower) cost with

fewer siting conflicts than fixed-bottom technology

2. Different regions and depths will require different floating technology solutions

– Shallow mooring technology has to mature at transitional depths to overcome the marginal risk preference of fixed-bottom turbines

– Lease areas in floating-friendly depths are needed soon to make floating offshore wind a reality by 2025‒2030

3. There is an opening for US leadership in floating technology and market maturation

4. Floating offshore wind energy is a complex system and well-suited to a systems engineering approach:– Whether viewed by its physics, economics, or

operational complexity

5. There are a number of system-friendly technology and design opportunities that:– Can significantly reduce the total lifecycle cost (i.e.,

levelized cost of energy [LCOE]) of floating wind power plants

6. There is an opportunity for the wind industry to evolve to offer vertically integrated, system-focused products:– Which is similar to aerospace “prime” contractors*The U.S. Department of Energy (DOE), National Renewable Energy Laboratory (NREL), and the other national laboratories will demonstrate the benefit of this approach.

Covered by Walt Musial Focus

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The Need for Multidisciplinary Analysis and Optimization (MDAO)

Floating offshore wind energy is a complex system, whether viewed by its physics, economics, or logistics, and is well suited to a systems engineering approach

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• Iterative design approach is a byproduct of industry expertise, power purchase agreements, and financing agreements– Companies need to leverage their expertise and protect their intellectual property

• Growth of wind industry over the past 20 years is a testament to the success of the “Iterative” approach

• Floating wind turbines can be designed in this paradigm, but they will be more costly than necessary.

Current offshore turbine design is more “Iterative” than “Integrated” because of market realities

Iterative Design ParadigmTurbine Iteration

Adapted from offshore oil and gas platforms

Adapted from fixed-bottom turbine design

Adapted from fixed-bottom turbine design

Developer Iteration

Operations & Maintenance

Balance of stationArray effectsController

designSubstructure

designTurbine design

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Physical and economic complexities make the floating challenge well-suited to system-focused solutions

Given the complexity of:• Physics – aerodynamic and hydrodynamic loading on a

compliant structure• Logistics – manufacturing, operational expenditures (OpEx),

installation, and assembly• Economics – over 50 types of costs are impacted.

A multidisciplinary, systems-focused approach is needed!

Floating Wind LCOE BreakdownSource: Mone et al. (2017)

There are many physical phenomena involved in floating wind energy and capturing all of the interactions is an extreme challenge.

78% of LCOE does not come from the turbine (but is impacted by its design)*BOS: balance of station

Illustration by Al Hicks, NREL

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MDAO Framework• Union of all disciplines and costs into a single

simulation framework– Enables optimization and tradespace exploration

MDAO Benefits and Output• Accelerates engineer’s exploration of the

tradespace and discovery of hybrid innovations• Prior expertise is essential to achieve credible

objectives– Optimization does not replace the engineer!

Floating Wind MDAO Tool Requirements• Integrated design: Design systems holistically,

considering the turbine, tower, controller, and floater as one integrated system

• Lifetime cost accounting: Consider cost impact of all factors including manufacturing, installation, operation, maintenance, and decommissioning.

MDAO allows for linking engineering design decisions to the LCOE balance sheet, but will require tool and expertise development

Integrated paradigm: Multidisciplinary analysis and optimization (MDAO)

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Shifting to computer-based systems engineering tools does not replace the value of experience or standards

• Optimization (even in conceptual design) is the last step in narrowing the design tradespace

• Must use experience to help guide the optimization and focus tradespace exploration

• Experience is the best tool in determining a new technology’s/ design’s cost reduction potential

• Experience is also embedded into code design, assumptions, and cost models.

Design Trade Space

Safe Operation Predictable Performance

Cost-Competitive Potential

Consensus Standards

Intelligent Design Criteria / Constraints (Experience)

Systems Optimization

Mature Cost-Competitive

Floating Wind Systems

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NREL has brainstormed a shortlist of design considerations that will yield the most cost-efficient solutions

•Regulatory compliance•Maximize energy production

•Minimize platform motion and loading

•Weight minimization (and low center of gravity)

•Design standardization–Mass-produced–Independent of water depth

or sea state

•Scalability–Neutral or advantageous

cost scaling from 5 to 15 MW

•Manufacturability–Economical (simple parts)–Transportable to assembly

locations

•Deployability–Use common ports–Commission at quayside–Tow-out with tugs

•Maintainability–Minimize specialized vessel

and labor hours at sea

•Corrosion control–Minimize long-term effects

of ocean environment

•Decommissioning

Design Trade Space

Safe Operation Predictable Performance

Cost-Competitive Potential

Consensus Standards

Intelligent Design Criteria / Constraints (Experience)

Systems Optimization

Mature Cost-Competitive

Floating Wind Systems

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OptimizationObjective

Optimization objective is LCOE, the full lifecycle cost of the whole plant, to (try to) capture the entire value chain• Capture the entire

lifecycle cost in LCOE– CapEx is the capital

expenditures (sum of balance-of-station and turbine capital cost)

– OpEx are the annual operational expenditures

– FCR is the fixed charge rate to annualize CapEx

– AEP is the net annual energy production

• LCOE isn’t perfect– Only captures costs, not

revenue– Would like to capture the

“value chain” for the developer. Plant Cost

of Energy

Balance-of-Station Costs

Plant Layout and Energy Production

Grid Integration

Community and Environmental

Impacts

Operational Expenditures

Complex Wind Inflow

Turbine Capital Costs

Turbine Design and Performance

𝑳𝑳𝑳𝑳𝑳𝑳𝑳𝑳 =𝑭𝑭𝑳𝑳𝑭𝑭 ∗ 𝑳𝑳𝑪𝑪𝑪𝑪𝑳𝑳𝑪𝑪 + 𝑳𝑳𝑪𝑪𝑳𝑳𝑪𝑪

𝑪𝑪𝑳𝑳𝑪𝑪Analysis modules for LCOE calculation

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Turbine• Two/three blades• Up/downwind• Horizontal and

vertical-axis turbines

• Multirotor• Controls

Platform• Ballast• # of columns• Plates• Ship shaped• Pontoons• Multiple turbines

Mooring• Catenary• Taut• Fiber/rope• Turret

Anchors• Drag• Suction• Torpedo• Gravity

Tower• Steel• Concrete• Composite

Drivetrain• One/multistage

gearbox• Direct drive• Superconducting• Hydraulic

Assembly• Quayside/on-site• Crane selection

Electrical• Array cable

voltage• Substation

technology• Grid

interconnection

Operation and Maintenance (O&M)• Vessel selection• Quayside/on-site

Plant• Controls• Layout• Anchors• DC interconnects

Optimization will help mix and match “Building Blocks” together and refine parameters to create viable designs

Partial List of Building Blocks Three-bladed, downwind

rotor

Direct drive

Composite tower

Three-column semisubmersible

with central turbine and truss

Three catenary mooring lines

Drag anchors

66-kV array cable

Service op. vehicle

Turbine Building Block

System Optimization• Iterate on design

variables• Minimize objective

(LCOE)• Apply constraints• Assign LCOE

“score” to building block combination

• Repeat.

Candidate System Sampled from Building Blocks

Tower Building Block

O&M Building Block

Platform Building Block

Electrical Building Block

Mooring Building Block

Anchor Building Block

Building Block: An architecture, design feature, or technology that can be combined together to form a wind energy system

Drivetrain Building Block

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LCOE

Uncertainty quantification

Mixed-integer

optimization

Analytic gradients

Adjoint methods

Multifidelity modeling

Optimization under

uncertainty

Concepts that will be especially useful for floating applications include:• Uncertainty quantification

– Uncertainty comes from inexact models, approximate data, and other sources

– Need to put error bars on outputs

• Optimization under uncertainty– How to make design choices that take into account

uncertainty

• Multifidelity modeling– Low-fidelity models may be useful for broad

tradespace exploration but might miss some constraints because of complicated physics

• Mixed-integer operation– Account for both continuous design parameters

(e.g., hub height) and discrete parameters (e.g., number of mooring lines)

Some advanced optimization/mathematics techniques will be helpful

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Technologies Well-Suited for System Integration

There are a number of system-friendly technology and design opportunities that can significantly reduce the total lifecycle cost (i.e., LCOE) of floating wind plants

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Each of the classical “archetype” substructures have trade-offs

Spar

SemisubmersibleTension leg

platform

Illustration by Joshua Bauer, NREL

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In the “Wild West” of alternative floating substructure ideas, there is no clear winner (yet), but many promising ideas

saitec offshoreSATH

GICON

Principle Power Inc WindFloat

SBM Offshore

AerodynEngineeringSCD nezzy

Stiesdal TetraSpar

Many of these designs combine elements from the three archetypes to compound the “pros” and reduce the “cons.”

EOLink

EquinorHywind

UMaine VolturnUS

IDEOL

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Pros• Lighter rotor nacelle assembly means lighter

substructure, lower material cost– Lighter rotor (20%‒25%)– Higher tip speeds mean lower torque, lighter

drivetrains• More resiliency to high sea states• Installation and O&M advantages

– Rotor assembly on ground– Easier compliance with height-limited transport (e.g.,

bridge underpass, Federal Aviation Administration regulations, and so on)

– Easy helipad access

Cons• Less solidity means larger chords, heavier single blades• Greater dynamic imbalance requires a teeter or

independent pitch controller• Higher tip speed means:

– Higher loads on some components– Noise concerns.

Rotor Building Blocks: Two blades would have system benefits down through the substructure as well as O&M advantages

Source: Ming Yang

Source: 2B Energy

Ming Yang SCD 6.5 MW (China)

Envision Energy 3.6 MW (China)

Source: Rick Damiani, NREL

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Rotor Building Blocks: Downwind rotors have system-level benefits

𝛾𝛾

Source: Annoni et al. (2017)

Increased power capture• Nacelle blockage accelerates

inflow to rotor plane

Wind plant flow control• Wake steering with tilt may be more effective than yaw• Upwind turbines cannot tilt due to tower strike• Has not been explored on floating platform yet

Centrifugal

GravityThrust

NetForce

NetForce

TipClearance

Wind

Lighter, flexible blades• Upwind blades must be stiff to prevent tower strike• Downwind blades can be lighter and allowed to flex• May even align with the net force vector, eliminating

bending moment

UpwindTurbine

DownwindTurbine

Source: Rick Damiani, NREL

Semipassive yaw• Weather-vane-like dynamics

increases yaw stability• Relaxes demands on yaw motor and

control system• Has not been proven yet.

Source: Equinor

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• Reducing weight throughout the load path will be critical for cost reduction– Lowering the CG will also be critical to reducing tower-top motion– Weight reduction above the waterline leads to mass/cost reduction

below the waterline as well

• Many opportunities for weight reduction– Greater use of carbon fiber composites in tower, blades, hubs, and

nacelles– Switch to superconducting, direct-drive generators– Switch to “generative” designs and additive manufacturing

• Many of these opportunities are more expensive per kilogram, but require fewer kilograms– Difficult trade-off to make intuitively

• Will need a system-level engineering tool to determine sensitivities and make cost-benefit trade-offs.

Many other component building blocks offer weight reduction with a cost premium: How to make the cost-benefit trade-off?

Suprapower superconducting direct-drive generator

S Sanz et al 2014

Generative Design Concept

Autodesk Research “Dreamcatcher” image courtesy Autodesk, Inc. © 2018

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• Design features for system-level benefits might not be a new technology or architecture

• Design features can also minimize costs of (majority of the total LCOE):– Manufacturing– Assembly– Installation– O&M

• Experience is critical to taking advantage of these opportunities– Can be difficult to develop sufficiently

detailed cost and process models of these activities

– Would be easy for an optimizer to miss these cost reduction opportunities.

Design choices can reduce the manufacturing, assembly, installation, and O&M costs, which are the biggest cost drivers

• A large portion of the LCOE (62%) for a floating turbine is attributed to the BOS costs and OpEx

• These attributes are heavily influenced by design choices

• Attributes that are derived from experience and lead to cost-effective solutions

• Might be difficult for an optimizer to capture these benefits

Source: Mone et al. (2017)

• Maximize energy production• Minimize platform motion and

loading• Weight minimization• Regulatory compliance• Design standardization

• Manufacturability• Deployability• Maintainability• Scalability• Corrosion control• Decommissioning

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Taking assembly into account in the designOff-center turbine alleviates crane boom and loading requirements

Principle Power Inc WindFloat

IDEOL

Small draft allows for: • Wide port availability• Quayside assembly that minimizes costly specialized vessel

and labor hours at sea• Usage of land-based crawler cranes (cheapest option).

Source: GICON

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Turbine and Platform• Compliance with common port facilities• Towable designs eliminate need for

customized vessels– Some designs have different towed and

operational configurations (e.g., TetraSpar) • Horizontal transport of turbines would open

up new solutions as well– Have to design drivetrain and bearings for this

load case

Mooring and Anchors• DNV-GL: Built-in support for winches

simplifies mooring line tensioning (also, may be eliminating need for specialized vessels)

• Gravity anchors simplify anchor installation and mooring line connection

• As turbine size grows, may need new mooring architectures or materials for manufacturing and vessel compliance.

Taking transport and installation into account in the design

Windflip- horizontal assembly and transport of spar

GICONSBM OffshoreWindFlip

Horizontal transport example

Gravity anchors example

TetraSpar “Transformer” platform

Source: Stiesdal Offshore Technology A/S

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• Heavy maintenance will still be required over the lifetime of a floating turbine, for example:– DNV-GL: At least 1‒2 events over a 20- to 25-year lifetime

• Quayside maintenance strategy (for major events) design requirements include:– A towable platform design– Electrical and mooring lines designed for easy disconnection– Plant cabling designed to continue power production from

other turbines in string

• In-situ repair strategy design requirements include:– Plant cabling designed to continue power production from

other turbines in string– Tower design that supports self-climbing cranes to simplify

marine operations and vessel requirements

• INNWIND project proposed a front-mounted generator to simplify the more labor-intensive drivetrain maintenance operations.

Taking operation and maintenance into account in the design

Source: Lagerwey https://www.lagerwey.com/blog/2017/08/30/lagerwey-test-climbing-crane-eemshaven

Source: Asger et al. (2017)

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Bringing a System Focus to the Wind Industry

There is an opportunity for the wind industry to evolve to offer vertically integrated, system-focused products

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How to transform the market from “Iterative” to “Integrated”?

Iterative Design Paradigm

Integrated Design Paradigm

What does transformation look like?

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Prime Contractor System Design and Integration: Boeing

Both aircraft and wind turbines use a global supply chain network, but aerospace prime contractors own the whole system

System Integration: Deepwater Wind

JacketGulf Island Fabrication

BladesLM Windpower

NacelleGE

VesselsFred. Olsen WindcarrierMontco Offshore

CablesLS Cable

DrivetrainGE supply chain

Source: Deepwater WindSource: Boeing

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• Floating offshore wind system design will requiredesign authority over the entire plant and product

• Multiple possible pathways toward this goal include:– Focused expansion– Close partnerships– Mergers and acquisitions

• As a young market for offshore wind, the UnitedStates would be a good “field test”

• NREL and DOE can help transition technology toindustry and start to build close partnerships– Not interested in picking “winners.”

Multiple possible pathways toward wind prime contractors; DOE/Labs can help reduce risk

Early-Stage Research Concepts and Partnerships (Lab/Industry/University)

Low Cost Sharing• Strategic planning• Model capability gap

analysis• Fundamental tool

development• Sensitivity, trade-off, and

scaling studies

Precommercial Product Development

Moderate Cost Sharing• Advanced capability

development across toolsuite

• Detailed prototype design• Standards agreement• Risk reduction of future

deployments

Commercial Development

High Cost Sharing• Field validation• Field demonstration• Commercial productintegration

DOE-Lab Technology Transition Plan

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5. Showcased system-friendly buildingblocks that could significantly reducefloating LCOE

Recap of (new) key points

6. Opportunity for industry to offervertically integrated systems,maybe with prime contractortemplate

4. Floating offshore wind energyis well-suited to a systemsapproach

www.nrel.gov

This work was authored by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding provided by U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Wind Energy Technologies Office. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.

Thank you

NREL/PR-5000-71659

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References

Annoni, J., A. Scholbrock, M. Churchfield, and P. Fleming. 2017. “Evaluating Tilt for Wind Plants,” American Control Conference (ACC), 2017. https://ieeexplore.ieee.org/document/7963037/.

Asger Bech Abrahamsen, Dong Liu, and Henk Polinder. “Direct drive superconducting generators for INNWIND.EU wind turbines” Deliverable D 3.11. Superconducting generators. August 31, 2017.

Hall, Matthew, Brad Buckham, and Curran Crawford. 2013. “Evolving offshore wind: A genetic algorithm-based support structure optimization framework for floating wind turbines.” 2013 MTS/IEEE OCEANS - Bergen: 1-10.

Mone, C., M. Hand, M. Bolinger, J. Rand, D. Heimiller, and J. Ho. 2017. 2015 Cost of Wind Energy Review (Technical Report). NREL/TP-6A20-66861. National Renewable Energy Laboratory (NREL), Golden, CO (US). https://www.nrel.gov/docs/fy17osti/66861.pdf.

Sanz, S., T. Arlaban, R. Manzanas, M. Tropeano, R. Funke, P. Kováč, Y. Yang, H. Neumann, and B. Mondesert. "Superconducting light generator for large offshore wind turbines." In Journal of Physics: Conference Series, vol. 507, no. 3, p. 032040. IOP Publishing, 2014. http://iopscience.iop.org/article/10.1088/1742-6596/507/3/032040/pdf

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Parking Lot

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Existing work in literature gives an example of how this might be done for the substructureParameterize platform geometry• Position of platform in water• Number of columns and their

spacing• Diameter, wall thickness for

each column• Supporting internal stiffeners• Ballast properties• Connecting truss members• Number of mooring lines• Mooring line length, diameter

A B

CD

EF F

Couple with full turbine engineering and plant economics for greatest benefit!

Optimize over candidate geometries• Heuristic algorithm to

respect multiple local minima

• Mixed-integer support for geometry parameterization

Rotor + drivetrain +

controller

Tower

Platform

Mooring lines

Anchors

Electrical cabling

O&M strategy

Source: Hall et al. (2013)