The first part covers all aspects of the safety and control concept as well as the load assumptions and load calculations. The load calculations for wind turbines are to be based on aeroelastic codes using stochastic wind fields and modal or finite element analysis techniques. In the case of offshore wind turbines the loads have to contain both the aeroelastic and the fluid-structure interaction of the submerged part. The latter may have a considerable influence on the structural response for certain types of foundations or underwater structures.

During the second part of the Design Assessment all components (rotor blades, hub and nacelle cover, machinery components, tower, foundation and electrical installations) of the system are being examined on the basis of the previously approved loads and the relevant standards and regulations. Besides no IEC standards or other national and international regulations for design and assessment of these components GL Renewables Certification's Guidelines are applied in most cases. In general all available national and international guidelines can be applied.

At the end of the Design Assessment manuals and procedures for transport, erection, start-up, commissioning, operation and maintenance are checked for suitability, completeness and compliance with the assumptions in the design documentation. Rotor blade testing forms an integral part of the design assessment of the blade, so does component testing of gearboxes or electrical components. Lightning Protection will be assessed under the scope of the electrical installations. The Design Assessment can be carried out on four different levels: A-, B, C- and D-Design Assessment.

C- and D-Design Assessment

Within the C-Design Assessment (for prototypes of wind turbines), a plausibility check of the prototype will be performed on the basis of the design documentation. This type of Design Assessment can be used to erect the prototype of a wind turbine. It is based on a load assessment and a complete plausibility check of the rotor blades, the main components as well as of the tower and foundation. Depending on national or local regulations the complete assessment of tower and foundation might be necessary. The final step will be the issue of a Statement of Compliance for the C-Design Assessment which is valid for test operation comprising a maximum of 2 years or 4000 equivalent hours at full load. The D-Design Assessment covers the same aspects as the C-Design Assessment, but leaves out the relation to a specific site and prototype. The main focus here is a first plausibility check of the turbine concept. After this period the B-Design Assessment shall be obtained at latest.

A- and B-Design Assessment

A- or B-Design Assessment is the next step in certification. Both assessments consist of a complete examination of the design analyses with all required material and component tests and are completed with the commissioning witnessing of one of the first wind turbines of the assessed type. Following completion, the certification body will issue a Statement of Compliance for the A- or B-Design Assessment. The B-Design Assessment may contain items that are outstanding, if these are not directly safety-relevant. Furthermore it has a validity period of one year. This period can be used to fulfil the missing requirements for the A-Design Assessment which may not contain any outstanding items and does not expire unless the design is modified. The examination of a foundation is optional within the scope of the A- or B-Design Assessments. The submission of documents for the Implementation of design related requirements in Production and Erection (IPE), which is part of Type Certification, is of advantage to be carried out within the Design Assessment to reduce the total time of Type Certification.

After a successful assessment the Statement of Compliance for the Design Assessment and the respective Certification Reports on load assumptions, safety system, rotor blades, machinery components, tower and foundation, electrical installations, hub and nacelle cover as well as commissioning witnessing will be issued.