Since the start of the wind turbine industry in the 1980s independent certification by third parties has played an important role in minimising the number of errors in design and providing additional confidence to manufacturers, developers, owners, finance, insurance and the authorities

Type certification
Type certification is offered according to the following certification schemes:

• IEC WT 01
• DNV
• Danish
• Dutch.

Authorities in several countries throughout the world recognize these schemes.

The DNV and Danish certification schemes are based on the IEC WT 01 certification system. The Dutch scheme is based on NVN 11400-0.

The IEC WT 01 system described in IEC System for conformity testing and certification of wind turbines is based on modules. Each of the modules is concluded by a well defined statement or certificate.

The Wind Turbine Type Certificate is issued when the four mandatory modules are completed:

• Design evaluation
• Type testing
• Manufacturing evaluation
• Final evaluation.

The Wind Turbine Type Certificate may also include the following optional modules:

• Foundation design evaluation
• Type characteristic measurements (acoustic noise, design evaluation, power quality).

Design evaluation
The design evaluation is normally carried out as a review of the design documentation submitted by the manufacturer. In addition to documentation review, independent analysis will normally be carried out. Independent load calculations are made using an aerolastic program different from the one used by the manufacturer. For this purpose DNV has two advanced aeroelastic programs available, FLEX5 and HAWC developed by Risø DTU, the Danish National Laboratory for Sustainable Energy.

Independent gear rating calculations are carried out by the DNV program NV5053. This program was developed based on the DNV classification note 41.2. If required, FEM analysis is carried out for critical components. DNV and Risø DTU have access to several commercial FEM program systems.

Type testing
Type testing is carried out in order to prove the wind turbine performance with respect to power production. Furthermore, safety and function testing and measurements are carried out to verify the load calculations and the blade design. Type testing will normally comprise:

• Safety and function tests
• Load measurements
• Power performance measurements
• Static and fatigue blade tests.

Normally, accredited institutes carry out the main parts of these tests.

Manufacturing evaluation
Manufacturing evaluation comprises:

• Quality system evaluation
• Manufacturing inspection.

The evaluation of the quality system is covered in the Danish and the Dutch certification schemes by requiring the manufacturer to operate a certified quality system according to ISO 9001. In IEC WT 01 there are no requirements for a certified quality system. In that case DNV Wind Turbine Certification will perform an audit for verification of compliance with the requirements in the ISO 9001 standard.

For the manufacturing inspection a survey of the manufacturing of one turbine of the type will be carried out.

Issue of the Type Certificate
A final verification report and Type Certificate will be issued when the wind turbine type subject to type certification is found to comply with the applicable code/standards/requirements.

Maintenance of the Type Certificate
The validity period of a wind turbine Type Certificate is specified in the certificate and is typically between one and five years. Annual surveys of randomly chosen specimens of each type of turbine are carried out during the validity period of the Type Certificate. The purpose of this survey is verification of the manufacturer’s design procedures, their maintenance and implementations in relation to the design procedures and design parameters initially approved by DNV.

Accreditation
DNV has been accredited by Dutch Accreditation Council RvA to provide Project Certification services.

DNV wind energy
A unit in technical co-operation with Risø DTU.