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Operated by the Alliance for Sustainable Energy, LLC

This report is available at no cost from the National Renewable Energy

Laboratory (NREL) at www.nrel.gov/publications.

Contract No. DE-AC36-08GO28308

SWAY/NREL Collaboration on 

Offshore Wind System Testing 

and Analysis

Cooperative Research and 

Development Final Report

CRADA Number: CRD-11-459

NREL Technical Contact: Amy Robertson

CRADA Report

NREL/TP-5000-63650

February 2015
NOTICE

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This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Cooperative Research and Development Final Report

In accordance with Requirements set forth in Article XI, A(3) of the CRADA document, this 

document is the final CRADA report, including a list of Subject Inventions, to be forwarded to 

the Office of Science and Technical Information as part of the commitment to the public to 

demonstrate results of federally funded research.

Parties to the Agreement: SWAY AS

CRADA Number: CRD-11-459

CRADA Title: SWAY / NREL Collaboration on Offshore Wind System Testing and Analysis

Joint Work Statement Funding Table Showing DOE Commitment:

Estimated Costs NREL Shared Resources

Task 1 $ 534,200.00

Task 2 $ 200,000.00

TOTALS $ 734,200.00

Abstract of CRADA Work:

This Shared Resources CRADA defines collaborations between the National Renewable Energy 

Laboratory and SWAY. Under the terms and conditions described in this CRADA agreement, 

NREL and SWAY will collaborate on the SWAY 1/5th-scale floating wind turbine 

demonstration project in Norway. NREL and SWAY will work together to obtain measurement 

data from the demonstration system to perform model validation.

Summary of Research Results:

From this collaboration between NREL and SWAY, NREL had the opportunity to install 

additional measurement equipment on the SWAY floating wind turbine, thus building experience 

at NREL in working with measurement systems in an offshore environment. While NREL has a 

lot of experience in testing land-based wind systems and is gaining experience in offshore testing 

through the MHK program, this project constituted our first experience in the testing of wind 

turbine systems offshore. As such, much was learned from this project to inform future efforts in 

this area. Some of the lessons learned include the usefulness of certain sensors and instruments in 

a marine environment; how to install and work with instruments in an offshore environment; the 

difficulties in integrating separate data acquisition systems, which can be an issue for offshore 

wind systems where the support structure built by one company is mated to a wind turbine built 

by a different company; and the need for well-defined processes to develop a test program. A big 

lesson was learned after the sinking of the SWAY 1:5 scale model on the need for all 

components of a down-scaled model subjected to a real and full scale offshore environment to be 

water-tight.
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This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Through the collaboration, NREL obtained the measurements from the SWAY system on the 

metocean conditions, loads, and motion, and used these to validate a coupled aero-hydro-elastic 

model of the system. The validation work provided SWAY with a better understanding of the 

performance of their system, and NREL with a better understanding of the unique dynamics of 

the SWAY system (a tethered spar), and the ability for the FAST tool to model the system 

behavior. Some difficulties encountered in this process included the lack of knowledge of 

measurement units; drift in sensor measurements and lack of continuous calibration; failure of 

some sensors; corruption of the wave measurement due to close-shore interaction; uncertainty in 

the tide level; and the inability of FAST to easily model the change in tide level. The findings of 

this work were summarized in a technical paper to be published at NREL.

Subject Inventions Listing:

N/A

Report Date:

January 15, 2015

Responsible Technical Contact at Alliance/NREL:

Amy Robertson

Name and email address of POC at company:

Eystein Borgen, Eystein.Borgen@swayturbine.com

This document contains NO confidential, protectable, or proprietary information.