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1
Introduction
The United States is poised to begin building its first offshore wind energy
power plants. Several projects have been proposed or are under develop-
ment, primarily along the Eastern Seaboard and the Great Lakes. In April
2010, the Cape Wind project, to be located off the Massachusetts coast,
became the first to be approved by federal and state authorities.
Central to the project approval process is the Department of the Inte-
rior’s Minerals Management Service (MMS), recently renamed the Bureau
of Ocean Energy Management, Regulation, and Enforcement (BOEMRE).
The Energy Policy Act of 20051 assigned it responsibility for the orderly,
safe, and environmentally responsible2 development of renewable energy
resources in U.S. federal waters, also known as the outer continental shelf
(OCS)3,4 (see Box 1-1). BOEMRE has exclusive jurisdiction over non-
hydrokinetic projects on the OCS.
On April 29, 2009, BOEMRE published a final rule, codified at
30 CFR 285,5 governing renewable energy project activities on the
OCS. Figure 1-1 lays out the regulatory process stipulated by the rule.
The regulations require submission of several documents for BOEMRE
approval of a proposed facility. Chief among them are three reports
covering facility design, fabrication, and installation. The BOEMRE
1 P.L. 109-58, Section 388.
2 74 FR 81, p. 19638.
3
On June 8, 2010, MMS was renamed the Bureau of Ocean Energy Management, Regulation, and
Enforcement. For convenience, this report uses the latter name in referring to this organization,
despite the fact that some of the actions discussed took place before the name change.
4
The term “outer continental shelf ” refers to those submerged lands, subsoil, and seabed that belong
to the United States and lie seaward of state water boundaries (http://www.boemre.gov/
AboutBOEMRE/ocsdef.htm, accessed Dec. 19, 2010).
5
Excerpts from this rule are given in Appendix B of this report.
5
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6 Structural Integrity of Offshore Wind Turbines
BOX 1-1
Regulatory Timeline for Renewable Energy
Development on the U.S. OCS
2005 The Energy Policy Act of 2005, Section 388, authorizes
MMS to do the following, among other things:
• Act as the lead agency for federal offshore renewable
energy and alternative uses of offshore public lands
(also known as the OCS);
• Ensure consultation with states and other stakeholders;
grant easement, leases, or rights-of-way for renewable
energy–related uses of the federal OCS; and
• Pursue appropriate enforcement actions in the event
that violations occur.
2007 In November, MMS issued the final programmatic envi-
ronmental impact statement (PEIS) in support of the
establishment of a program for authorizing renewable and
alternative use activities on the OCS. The final PEIS exam-
ined the potential environmental effects of the program
on the OCS and identified policies and best management
practices that could be adopted for the program.
In December, the Record of Decision was released, affirm-
ing that MMS would proceed with establishment of the
Renewable Energy Program for the OCS on the basis of the
analysis presented in the PEIS.
2007 In November, MMS announced an interim policy for
authorizing the installation of offshore data collection
and technology testing facilities on the OCS. The policy
was designed to jump-start baseline data collection efforts
in advance of final regulations.
(On June 23, 2009, five exploratory leases were granted
for renewable wind energy resource assessment on the
OCS offshore Delaware and New Jersey.)
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Introduction 7
2009 On April 9, MMS signed a memorandum of understand-
ing with the Federal Energy Regulatory Commission
(FERC). The memorandum clarified that MMS has exclu-
sive jurisdiction with regard to the production, transporta-
tion, or transmission of energy from nonhydrokinetic
renewable energy sources, including wind and solar. FERC
has exclusive jurisdiction to issue licenses for the con-
struction and operation of hydrokinetic projects, includ-
ing wave and current, but companies will be required first
to obtain a lease through MMS.
2009 On April 29, MMS published a final rule (30 CFR Part 285,
74 FR 81, pp. 19638–19871) establishing a regulatory
framework for leasing and managing renewable energy proj-
ect activities on the U.S. OCS. The regulations are intended
to encourage orderly, safe, and environmentally responsi-
ble development of renewable energy sources on the OCS.
Subpart G covers the technical reports that must be sub-
mitted on the final design, fabrication, and installation of
facilities. It also lays out a third-party verification process
that requires use of a “certified verification agent” (CVA)
to verify and certify that projects are designed, fabricated,
and installed in conformance with accepted engineering
practices and with the submitted reports.
The regulations specify that part of the CVA’s responsibil-
ity in the design phase is to conduct an independent assess-
ment to ensure that the facility is designed to withstand the
environmental and functional load conditions appropri-
ate for the intended service life at the proposed location.
The regulations also specify that part of the CVA’s respon-
sibility in the fabrication and installation phases is to use
good engineering judgment and practices in conducting
an independent assessment of fabrication and installation
(continued on next page)
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8 Structural Integrity of Offshore Wind Turbines
BOX 1-1 (continued)
Regulatory Timeline for Renewable Energy Development on the U.S. OCS
activities. The CVA is also to ensure that these activities are
conducted according to the approved applications.
2009 On August 3, MMS published its “Guidelines for the Min-
erals Management Service Renewable Energy Framework,
July 2009.” The guidelines are divided into six chapters,
covering qualification requirements; definitions; and lease
and grant conveyance, administration, and payments.
The guidelines state that five additional chapters will be
“posted at a later date.” One of them, Chapter 9, will
“explain the requirements for facility design, fabrication,
and installation.” Chapter 10 will cover requirements for
environmental and safety management, inspection, and
facility assessment. Chapter 11 will discuss decommis-
sioning requirements.
2010 MMS decided that, rather than publishing the five chapters
above as part of the “Guidelines for the Minerals Manage-
ment Service Renewable Energy Framework,” it would
develop separate guidelines for each topic and issue them as
“Notices to Lessees” (personal communication, J. Cushing,
BOEMRE, Oct. 1, 2010).
SOURCE: MMS n.d.
regulations set out in great detail what must be included in these reports—
for example, structural drawings, a summary of the environmental data
used in the design, a complete set of design calculations, a geotechnical
report, the industry standards proposed for use in fabrication, and details
on the offshore equipment to be used for installation.6 However, the reg-
6
The list is not complete. See 30 CFR 285 for details.
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Introduction 9
FIGURE 1-1 Approval process for offshore wind turbines set forth in 30 CFR 285.
(There is also a noncompetitive path.) [NOTE: The Coastal Zone Management
Act (CZMA) consistency provision (15 CFR 930) requires that federal agency
activities be consistent with the enforceable policies of a coastal state’s federally
approved coastal management program. COP = construction and operations
plan, RE = renewable energy, and SAP = site assessment plan. SOURCE: Presenta-
tion to the committee by John Cushing, BOEMRE.]
ulations do not specify standards or detailed requirements that the facil-
ity must meet for BOEMRE to approve the reports.
Instead, the regulations require that a third party, a “certified verifica-
tion agent” (CVA),7 conduct an independent assessment of the facility
design on the basis of “good engineering judgment and practices” and cer-
tify to BOEMRE that the facility is designed to withstand the environmen-
tal and functional load conditions appropriate for the intended service life
at the proposed location. According to the regulations, the CVA must also
certify to BOEMRE that project components are fabricated and installed
7
In some circumstances, BOEMRE may waive the requirement to use a CVA (see Appendix B).
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10 Structural Integrity of Offshore Wind Turbines
in accordance with “accepted engineering practices” and with the approved
reports and operating plans.
Standards and guidelines for the design, fabrication, installation, and
operation of offshore wind turbines8 have been developed by interna-
tional bodies as well as by individual companies and countries, predom-
inantly in Europe (see Chapter 3). However, none of these standards or
guidelines has been accepted by U.S. agencies, nor has the United States
developed its own. Standards and guidelines exist for other offshore
activities in U.S. waters, such as oil and gas development and waterborne
shipping. Other relevant standards cover items such as the environment
and workplace health and safety. But BOEMRE has not specified any cri-
teria that offshore wind turbine projects must meet to secure approval.
STUDY CHARGE AND SCOPE
In the absence of such standards and guidelines for the United States,
BOEMRE asked the National Research Council (NRC) to review its
approach to overseeing the development and safe operation of wind
turbines on the OCS, with a focus on structural safety. The charge to
the study committee is given in Box 1-2.
The committee’s scope was limited to structural safety, in accordance
with discussions with the sponsor at the first committee meeting.9 Hence,
although the term “Structural and Operating Safety” appears in the com-
mittee’s title, the committee limited its treatment of operational safety to
those aspects that could be affected by structural design, fabrication, and
installation. It included within its scope the design, fabrication, and instal-
lation of subsea cables. As illustrated in Figure 1-2, the committee char-
acterized its scope as “from design to commissioning.”
One caveat is that structural integrity cannot be considered in isolation.
In complex engineering systems such as wind turbines, there are non-
structural components and systems whose failure and malfunctioning
8
In this report, “wind energy turbine generators” are often referred to simply as “wind turbines.”
A set of wind turbines is often referred to as a “wind farm.” One or more turbines, when consid-
ered together with the rest of the equipment involved in transferring electricity from the turbines
to shore, can also be referred to as a “wind farm” or, alternatively, a “wind energy power plant.”
9 “Background Information and Study Goals,” presentation to the committee by John Cushing,
BOEMRE, July 28, 2010.
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Introduction 11
BOX 1-2
NRC Committee on Offshore Wind Energy
Turbine Structural and Operating Safety
Statement of Task
The study will provide guidance to MMS on the direction and
intent of its proposed approach to overseeing the development
and safe operation of offshore wind turbines. The study will pro-
vide findings regarding:
Task I. Standards and Practices: The applicability and ade-
quacy of existing standards and practices for the design,
fabrication, and installation of offshore wind turbines.
Task II. Role of Certified Verification Agents (CVAs): The
expected role of the CVA in identifying standards to be
used (including determining the compatibility—the
acceptability of mixing and matching—of standards
from different sources), and the expected role of the
CVA in conducting monitoring and onsite inspections
to verify compliance with the standards.
Task III. CVA Qualifications: The expected experience level,
technical skills and capabilities, and support equip-
ment and computer hardware/software needed to be
considered a qualified CVA.
The focus of the study will be limited to the safety of structural
and operational characteristics of offshore wind turbines, includ-
ing turbine design, fabrication, and installation.
can trigger or result in structural overload or failure. Chapter 3 notes how
these interactions are accounted for.
As shown in Figure 1-1, the environmental hazards associated with
the establishment and operation of offshore wind energy facilities are
covered through the National Environmental Policy Act (NEPA) process.
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12 Structural Integrity of Offshore Wind Turbines
FIGURE 1-2 Scope of this study. (SOURCE: Generated by the committee.)
These hazards include effects on birds, other wildlife, and the seabed.
BOEMRE will prepare environmental assessments (EAs) or environmen-
tal impact statements (EISs), as required by NEPA, for offshore wind proj-
ect proposals.
This report does not review the environmental hazards that are assessed
in EAs or EISs. As noted earlier, the committee’s charge is limited to con-
sideration of hazards resulting from structural failures.
COMMITTEE APPROACH
The committee’s first task was to assess the applicability and adequacy of
existing standards and practices for the design, fabrication, and installa-
tion of offshore wind turbines.
In response to this charge, the committee reviewed standards and
guidance documents (the latter encompassing rules, guidelines, recom-
mended practices, and other similar documents) that have been devel-
oped by classification societies (nongovernmental organizations and
private companies), industry associations, and European governments. It
identified some of the deficiencies in these standards and documents that
would have to be remedied if they were to be applied in the United States.
As discussed in Chapter 3, the committee found that many existing
standards and guidance documents could appropriately be applied in
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Introduction 13
the United States but that no one set was complete. All have deficiencies
in their coverage (for example, storms and hurricanes on the Atlantic
coast and in the Gulf of Mexico) or their analysis methods that would
have to be remedied before they could be used in the United States.
To respond fully to its charge, however, the committee believed that it
had to do more than review existing standards and guidance and indicate
their deficiencies. Other reports have identified at least some of the defi-
ciencies, and the committee has drawn on these reports for its assessment.
The committee’s view was that, to provide BOEMRE with useful feedback,
the committee should offer its perspectives on how BOEMRE might rem-
edy those deficiencies. It believed that it should step back and examine not
only the mechanics of remedying the deficiencies but also the underlying
philosophies that could guide the development of additional standards or
guidance documents for offshore wind turbines in the United States.
In applying this broader perspective, the committee reviewed the
approaches to oversight of offshore wind turbines taken by European
countries. It noted that current standards and guidance in Europe
range from very detailed and prescriptive to high-level and less pre-
scriptive. The committee also reviewed how the safety of engineered
structures is overseen in other U.S. industries—oil and gas production,
waterborne shipping, and buildings. It noted that regulation in these
industries has been moving away from a detailed, prescriptive model
and toward a more performance-based model.
As discussed in Chapter 4, the committee’s consensus is that
performance-based oversight is the most effective approach to reme-
dying deficiencies in standards and practices for offshore wind instal-
lations. This approach will help to fulfill two government objectives:
• The safe, orderly, and environmentally responsible development of
renewable energy on the OCS, which is the charge of BOEMRE; and
• The broad exploitation of the offshore wind resource, which is an objec-
tive of the U.S. Department of Energy and is in line with the adminis-
tration’s stated priorities.
Structural failures in offshore wind farms pose lower risk to human
health and the environment than do structural failures in oil and gas
platforms. In the committee’s view, however, successful exploitation of
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14 Structural Integrity of Offshore Wind Turbines
offshore wind energy will require not only that turbines operate with
low risk to human health and the environment but also that they prove
highly reliable (to avoid negative perceptions of the industry) and become
economically competitive with other sources of electricity. The com-
mittee sees performance-based oversight as the regulatory model most
compatible with fostering innovation, which it views as key in devel-
oping a viable U.S. industry and bringing down the cost of electricity
generated from offshore wind.
During its work, the committee was cognizant of the rapid pace at
which offshore wind projects were being proposed for specific sites and
of the work in several states to develop regulatory structures for projects
in state waters. It recognized the need for the federal government to spec-
ify, fairly soon, how it will evaluate the acceptability of proposed projects
for the OCS, so that project developers will have sufficient information
to move their projects forward and to attract the necessary financing.
The committee also noted that, although BOEMRE is concerned with
projects outside of state waters, federal guidance would also be of help to
states as they develop their criteria for approving projects in state waters.
In recognition of BOEMRE’s need to act quickly in specifying the
requirements that proposed projects on the OCS must meet, the com-
mittee has set out interim measures that could be implemented soon as
well as options for longer-term approaches to oversight.
In carrying out its charge, the committee met three times. At its first
two meetings, it received briefings on the development of standards for
offshore wind energy in Europe and on current industry efforts to develop
consensus standards for the United States. Representatives from non-
governmental organizations, industry associations, and one state pro-
vided perspectives from stakeholders on the development of offshore
wind energy. The committee was also able to take advantage of an NRC
workshop on offshore wind energy that was held on March 25–26, 2010.10
ORGANIZATION OF THE REPORT
Box 1-3 provides definitions for some key concepts that are used exten-
sively in Chapters 3 and 4. Chapter 2 provides a brief overview of the
motivation for the United States in developing offshore wind energy. It
10 See http://www.trb.org/MarineBoard/MarineBoard.aspx.
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Introduction 15
BOX 1-3
Key Concepts: Verification, Certification,
and Classification
Verification. Verification is the process of determining whether
a design, procedure, measurement, or other activity follows a
specified standard, guideline, design basis, or other definition
as specified for a project. Verification can apply to design, fabri-
cation, or installation. For instance, if the intent is that a project’s
turbines be designed according to the International Electro-
technical Commission 61400-3 standard, a verifier would assess
whether the requirements of that standard were followed and were
correctly applied, good practice was followed, and no significant
deficiencies were evident. A verifier may perform independent cal-
culations or tests.
Certification. Certification of a design, fabrication, or installation
implies a higher level of responsibility on the part of the reviewer
than does verification. To certify a design, for instance, indepen-
dent design calculations or testing would likely be performed by
the certifier as a check, rather than the certifier simply assessing
whether the design was in accordance with the specified standard
and design basis and whether the resulting design is accurate.
The term “certification” was likely derived from the statutory
requirement in the United Kingdom that an offshore oil and gas
facility receive a “certificate of fitness” from an appointed certi-
fying authority on the basis of an independent assessment of the
design, method of construction, and operations manual and
associated surveys carried out by surveyors appointed by the
certifying authority.
Classification. Nongovernmental organizations and private com-
panies that establish and maintain technical rules and guidelines
for the design, construction, and operation of ships and offshore
structures are commonly known as “classification societies.”
(continued on next page)
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16 Structural Integrity of Offshore Wind Turbines
BOX 1-3 (continued)
Key Concepts: Verification, Certification, and Classification
As used in relation to a classification society, classification is a
variation on the concept of certification. The difference is that
the classification society is evaluating the design, fabrication, or
installation with reference to its own rules or guidelines rather
than an externally developed standard or guideline.
then reviews offshore wind energy production worldwide and describes
the technologies involved in current offshore turbine generators.
The next two chapters address the first element of the committee’s
charge (Task I). Chapter 3 reviews existing standards, the differences
among them, and the work under way to identify deficiencies and develop
new standards. Chapter 4 sets out the regulatory philosophies underlying
various oversight regimes and how they might be incorporated into stan-
dards and guidance for application in the United States. Chapter 5 targets
the second part of the committee’s charge (Task II) by reviewing the role
of third-party oversight and CVAs. Chapter 6 assesses the qualifications
needed by CVAs (Task III).
The final chapter summarizes the committee’s key findings and recom-
mendations for structural and operating safety of offshore wind energy
turbine generators.
REFERENCE
Abbreviation
MMS Minerals Management Service
MMS. n.d. The Role of MMS in Renewable Energy. Fact sheet. http://www.mms.gov/
offshore/renewableenergy.
