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How to certify in wind energy – risk mitigation on a new level October 2017 - Introduction to the new Service Specifications for project, type and component certification of wind turbines and power plants including a full overview on standards and recommended practices The Service Specification applying to type certification of wind turbines as well as for component certification was published in summer 2016, the one for project certification of power plants at the end of 2015. The experiences gathered from certification projects in on- and offshore wind realised over the last three decades have been taken into account for these new service specifications or certification schemes and programs. Correspondingly the project, type and component certification schemes have been adapted to meet market needs and expectations. But in course of the update of the whole scheme much more effort was taken to get to the next level of certification and standardization while keeping the consistency of DNV GL certification solutions provided to wind industry for more than 30 years; beyond modules and elements of certification this includes all technical aspects laid down in standards and recommended practices. Keywords: Onshore Wind, Offshore Wind, Project Certification, Type Certification, Component Certification, Service Specification, Standard, Recommended Practice

Certification along the project life-cycle The pressure on reduction of cost of energy is high in the wind energy sector. Focusing on reducing costs increases the risk for safety, quality and reliability. Hence, the independent evaluation of a third party is of an even higher importance to ensure the highest level of safety, quality and reliability for wind power plants. The service specification DNVGL-SE-0441 identifies modules and elements for type and component certification of onshore and offshore wind turbines and serves as a: 

facilitator to identify and apply relevant technical standards

guidance for engineers from concept to serial production

description to meet state-of-the-art requirements for modern wind turbines, and beyond

common communication platform for describing the scope and extent of activities performed for certification of a wind turbine and its components

contractual basis for certification of wind turbines and components

The conceptual and prototype stages of the development process are covered considering technology qualification and risk analysis. The interface to project certification is addressed through

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the introduction of a new Type Certificate which will be site / product specific, covering the full lifecycle of the wind turbine. The lifetime of a wind farm is typically 20 years. The cost reduction pressure in the power sector makes it vital to consider increasing their design lifetime to 25 or 30 years. Such power plant design lifetime can be chosen and it is advisable to take it into consideration at the start of a project through all relevant phases. The certification services are adjusted to follow the development phases of wind turbine or component from concept to serial production and beyond, see Figure 1. These development phases may be supported during the wind turbine development by respective certification deliverables.

Statement of  Feasibility

Prototype Certificate

Provisional Type  Certificate

Type Certificate

Site Specific  Type  Certificate

Type Certificate  Renewal

Life Extension

Decom‐ missioning

Figure 1: Certification services aligned with the development process

The new Service Specification SE-0441 is divided into four main sections: 

Section 1 includes the introduction to the service specification.

Section 2 gives an overview of the certification scheme and its certification modules.

Section 3 gives a detailed description of the certification scheme and its modules.

Section 4 describes the final deliverables as well as the maintenance of the certificates.

The completely new and revised document system is organized according to a three-level document hierarchy, with these main features: 

Principles and procedures related to certification services are separated from technical requirements and are presented in service specifications (SE). Service specifications present the scope and extent.

Technical requirements are issued as self-contained standards (ST). Standards are issued as neutral technical standards to enable their use by national authorities, as international codes and as company or project specifications.

Associated product documents are issued as recommended practices (RP). Recommended practices provide interpretation of safe engineering practice for general use by industry.

Design and certification of electrical installations The DNV GL standard DNVGL-ST-0076 “Design of electrical installations for wind turbines” provides principles and technical requirements for design and construction of electrical installations for wind turbines onshore and offshore. The standard can be applied as part of the technical basis for

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carrying out certification of offshore wind turbines and it is also intended to cover the requirements implied when using IEC-related certification schemes. All systems and components mentioned therein and listed below can undergo a component certification as per DNVGL-SE-0441. The standard is applicable to the design of electrical components and electrical systems for the complete wind turbine, including main components, cable systems and, control and protection systems. Electrical installations shall be so designed that: 

the maintaining of normal operational conditions will be ensured without recourse to any emergency source of electrical power

the operation of emergency equipment required for machinery and personal safety will be ensured under various defined emergency conditions

the safety of personnel and installations from electrical hazards will be ensured and risks of injury to human life will be reduced to a minimum

the equipment and installations will reach the expected life times

sufficiently high reliability is reached for the entire system.

The standard ST-0076 covers: 

rotating electrical machines

power transformers (dry-type and liquid-immersed)

frequency converters

high voltage switchgear

back-up power supply systems

low-voltage switchgear, controlgear and switchboards including safety-related parts

cables, lines and accessories

lightning protection, earthing and bonding

electrical pitch and yaw drives

selection and interconnection of electrical equipment

electrical control and protection systems

testing, installation, commissioning and maintenance

corrosion protection

fire protection

extreme environmental conditions, offshore applications

ventilation and cooling

grid parallel and island operations

Newly (and in parallel documents) introduced is the flexible proof that grid codes are met. Maximum acceptance of certificates is crucial herein. Applying the new Service Specification for the certification of grid code compliance (DNVGL-SE-0124) together with the respective standard (DNVGL-ST-0125) ensures application of latest knowledge for grid connection and integration.

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By using these not only the proof that grid code compliance (GCC) is given and that grid codes are met but as well know-how to receive the release from the relevant system operator, utility or network authority is transferred. The benefits result in a win-win-situation for all parties involved: 

Manufacturers of generating units can have proof of evidence independent from any grid code, with a scope defined according to the GCC-features (Appendix of the GCC-Standard) by applying no specific GCC class (“without GCC-class”).

System operators will benefit when they want to see their individual requirements met. This is possible when requiring the strongest GCC class I for a project certificate (PC I).

Equipment manufacturers benefit by asking for an Equipment Certificate in GCC class II, covering many countries and many grid codes, taking into account a standardized but limited scope.

Design and certification of rotor blades The DNV GL standard DNVGL-ST-0376 „Rotor blades for wind turbines“ provides principles and technical requirements for rotor blades for wind turbines onshore and offshore. This standard can be applied as part of the technical basis for carrying out type certification of wind turbines or component certification of rotor blades. The standard is applicable to all types of wind turbines and rotor blades, even though many requirements have been formulated specifically for blades made from fibre-reinforced plastics for operation on horizontal axis wind turbines. It is applicable to the structural and functional design, and manufacturing, of rotor blades for wind turbines, including requirements for materials, testing, repair and operation. Rotor blades shall be designed so that: 

the maintaining of normal operational conditions will be ensured

the safety of personnel and installations will be ensured and risks of injury to human life will be reduced to a minimum

the rotor blades will reach the expected life time

sufficiently high reliability is reached for the entire system.

Newly introduced is the test pyramid including its options for future rotor blade tests. In many cases, it may be appropriate or even necessary to supplement material coupon tests and full scale blade tests by further testing on an intermediate level. When certifying a rotor blade for compliance with the present standard, such intermediate level testing may be applied as part of the design verification process, by using test results as design values in structural verification analyses, and as partial substitute for full scale blade testing. Manufacturing inspections and surveillance are important part of the certification process nowadays. The inspections shall be based on witnessing as much of the manufacturing process for the blade in question which is realistically possible. The intention of the inspections being, to gain

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sufficient confidence that quality management, works office/area and shop floor documentation and procedures used by the concerned manufacturing site staff being inspected, conform to the approved component certified design documentation and that the design can be repeatedly transferred into production. This standard gives guidance and provides the full scope of manufacturing inspections.

Design and certification of structures The full overview on support structures is to be found in DNVGL-ST-0126 “Support structures for wind turbines”. Offshore substations are covered by DNVGL-ST-0145. The standard DNVGL-ST-0126 is a fully updated standard for onshore and offshore wind turbine support structures. It offers pragmatic design approaches and can for example be used for design of steel and concrete towers, gravity-based concrete foundations, together with steel foundations such as monopile foundations, jacket structure foundations and suction bucket foundations. The standard contains as well requirements to materials, execution, operations and maintenance (O&M) related to the design. This is done by inclusion of guidance text, or for example by reference to material and execution standards. Examples of new guidelines for steels structures are: 

lattice towers design requirements

inspection requirements for the fabrication phase (inspection classes vs. structural member categories) with respect to fatigue-critical details when well proven track record for production exists.

Examples of new guidelines for concrete structures are: 

crack control requirements

fatigue design for concrete and reinforcement with new available methods

requirements for qualification of grout material.

Examples of new guidelines for geotechnical design are: 

detailed assessment of impact from dynamic loading as an alternative to gapping check for gravity-based foundations

new safety system considerations with respect to single element of failure

suction bucket design requirements

requirements for application of “observational method” for geotechnical design.

After use of the standard for more than 18 months, maintenance of it started in 2017. The document will go for hearing of the revised edition soon.

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Figure 2: Wind turbine components with definitions as covered by DNVGL-SE-0126

Full scheme with innovations For all standards all requirements specified therein shall be fulfilled. However deviations from these requirements or the application of alternative means of complying with these requirements, may be acceptable after consultation and agreement. It is key that an equivalent level of safety and reliability can be demonstrated while applying alternative methods, tests, analysis or solutions. Starting with the publication of the electrical engineering standard exactly two years ago, the meanwhile famous rotor blade standard was published at the end of 2015. Finally a year ago the standard for loads was published. With that the last piece of the puzzle for the full scheme for onand offshore wind energy went to the public. The documents on control and protection systems, offshore support structures (see below) or extreme temperatures and icing complete the full scheme. The final documents on machinery components and mechanical engineering as well as offshore cables are implemented already. They are all glued together by the service specifications for component, type and project certification and can be amended with documents on e.g. lifetime extension, corrosion protection, tropical cyclones, met masts, fire and condition monitoring systems or shop and laboratory approvals. Even companies providing trainings or education as well as those doing maintenance and repairs can get their programs and services certified applying the respective service documents. The latest revision of all DNV GL documents can be found in the ”rules and standards” pages on the website

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The main differentiators of this certification scheme to other existing schemes are: 

more guidance and descriptions to facilitate application

all wind turbine relevant topics addressed in one service specification (SE)

all wind turbine development phases are supported by the certification scheme / program

certification may be tailored by adding multiple optional services, e.g. based on additional SE

The benefits of applying these service specifications can be: 

independent approval of the wind turbine and component to reduce own risk in developing and designing

building of trust in the design and construction

reducing costs by early detection of non-conformities

confidence in technical integrity

confirmation of requirements as stated by project developers, investors, operators, manufacturers, governmental and non-governmental organizations

prove by an independent body to meet the national and international acknowledged stateof-the-art and to ease market entry

utilize statements and certificates for authorization by governmental institutions

prove to investors or insurer that third party approval is successfully performed

securing sustainable energy production throughout life-cycle

minimizing technical risks

document stepwise the maturity of the wind turbine development project

mitigate risks to environment and people

Component certification as a term used in this article covers e.g. major and minor components, systems, single parts or assemblies used in a wind turbine or attached to it; that could be e.g. specific components such as rotor blade, generator, gearbox, brake, coupling, main bearing, nacelle frame or tower, systems such as pitch system, yaw system, fire protection or condition monitoring system as well as parts such as bolts and tower internals. The mandatory certification modules comprise design, manufacturing and testing at different stages of the wind turbine development process. The specifications together with referred standards and recommended practices represent a completely revised and expanded version of the GL-IV-1 “Guideline for the Certification of Wind Turbines”, Edition 2010 and GL-IV-2 “Guideline for the Certification of Offshore Wind Turbines”, Edition 2012; both with a history of 30 years. The world’s latest and most integral service specification on project certification of wind power plants is DNVGL-SE-0190 published at the end of 2015. It’s a fully revised certification scheme taking as first the control station and current market developments into account. No other scheme is comparably holistic and at the same time applicable to individual on- and offshore wind power projects.

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Figure 3: On- and offshore wind power plant assets according to DNVGL-SE-0190

The experiences gained and lessons learned from European offshore wind power projects in recent years were taken into account during development of this new service specification (SE). The SE has been developed based on industry input, feedback received and project experiences gained over decades. The full life cycle and all assets of a wind power plant are now addressed and reference is made to all relevant standards. Providing better guidance for developers, owners and contractors during the whole life cycle of the offshore wind power plant, from concept to operation, lifetime extension to decommissioning and repowering was a goal throughout the whole process of development of this SE. Implementing an optional asset related certification procedure for offshore wind turbines, substations, power cables and control stations laid in the focus of it. New optional phases such as concept, lifetime extension, decommissioning and repowering were included to maximise the risk mitigation opportunities. This new scheme allows flexible split into phases and assets related certifications, and to add optional service elements based on individual needs and preferences. It helps mitigating risks at an effective stage during different certification phases. Manufacturing surveillance aspects have been fully revised to acknowledge different efforts and use synergies to reduce costs. Since issuing its first wind certification standard in 1986, DNV GL continuously worked together with the industry to develop up to date certification schemes tailored to the demands of the advancing renewables market. Standards are the basis for the state of the art, but to really solve the challenges it is necessary to have an early and strong collaboration with well experienced actors in the wind industry business. And it requires consistency DNV GL is demonstrating in this industry sector for more than 30 years; the maintenance plan for all service documents is already prepared for the next 5 years to ensure availability of all documents mentioned and published to serve market needs.

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If you are interested in finding out more about our service documents for renewable sectors, please feel free to contact:

Mike Wöbbeking Director and Service Area Leader, Renewables Certification, DNV GL - Energy +49 40 36149 3307

Contributing authors: Fabio Pollicino, Service Line Leader Project Certification Christer Eriksson, Service Line Leader Type Certification Tobias Gehlhaar, Principal Engineer Matthias-Klaus Schwarz, Head of Section Morten Søgaard Andersen, Principal Specialist

Document code DNVGL-SE-0441 DNVGL-SE-0190 DNVGL-SE-0436 DNVGL-SE-0439 DNVGL-SE-0077 DNVGL-SE-0124 DNVGL-SE-0263 DNVGL-SE-0448 DNVGL-ST-0076 DNVGL-ST-0126 DNVGL-ST-0361 DNVGL-ST-0376 DNVGL-ST-0437 DNVGL-ST-0438 DNVGL-ST-0125 DNVGL-ST-0262 DNV-RP-A203 DNVGL-RP-0175 DNVGL-RP-0363 DNVGL-RP-0416 DNVGL-RP-0440

Title Type and component certification of wind turbines Project certification of wind power plants Shop approval in renewable energy Certification of condition monitoring Certification of fire protection systems for wind turbines Certification of grid code compliance Certification of lifetime extension of wind turbines Certification of service and maintenance activities in the wind energy industry Design of electrical installations for wind turbines Support structures for wind turbines Machinery for wind turbines Rotor blades for wind turbines Loads and site conditions for wind turbines Control and protection systems for wind turbines Grid Code Compliance Lifetime extension of wind turbines Technology Qualification Icing of wind turbines Extreme temperature conditions for wind turbines Corrosion protection for wind turbines Electromagnetic compatibility of wind turbines

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How to certify in wind energy  
How to certify in wind energy  

Introduction to the new Service Specifications for project, type and component certification of wind turbines.