More and more wind farms are now being situated offshore, where wind resources are stronger and wind turbines present less of an issue in terms of visual interference with surrounding landscape. DNV is the leading provider of project certification for offshore wind projects around the world.
Offshore wind farms
DNV certified the first offshore wind turbines installed in 1991 in Denmark. Since that time, DNV has certified and is in the process of verifying more than 40 offshore wind farm projects ranging from 5 megawatts to 1 gigawatt. To guide these activities, DNV has developed standards for offshore structures, DNV-OS-J101, and is accredited by the Dutch Accreditation Agency. Some of the major offshore wind farms being certified by DNV include London Array (1 GW), Greater Gabbard (500 MW) and Thanet Offshore Wind Farm (300 MW) in the UK and Horns Rev (369 MW) in Denmark.
Why project certification?
In some countries, project certification is a requirement of national agencies for offshore wind projects. However, even when not required by regulation, most project owners pursue project certification in order to gain additional assurance in the design and implementation of their offshore wind project. Due to the size of the investments required for offshore wind farms, third-party verification services are a significant benefit for owners, investors, and insurance providers as a means of reducing risk and protecting investments.
During the project design stage, project certification provides an additional benefit by identifying potential issues and thus minimizing the need for design changes at later stages of the project
Project certification
DNV’s scheme for project certification of offshore wind farms consists of six phases. A Type Certificate of the wind turbine is required as a prerequisite. DNV’s project certification scheme is consistent with the IEC’s project certification scheme for offshore wind project.
Phase I-II
In general, Phases I and II cover the steps for achieving final design verification, which include site-specific approval of the integrated structural systems consisting of wind turbine, foundation and soil. The site-specific approval includes verification of external conditions such as soil, wind and wave conditions.
In addition to review of design documentation, independent analyses can be carried out for critical details. For that purpose DNV has access to several commercial finite element program systems and aeroelastic codes. Structural design verification could cover wind turbine foundations and other structures such as offshore substations.
Phase III-V
Phases III-V involve all the follow-up verification and on-site inspections in connection with the implementation of the project. This includes manufacturing and installation surveys of support structures, substations and wind turbines and commissioning of these.
Manufacturing surveys take place at the fabrication site. The survey for welded structures is based on a review of welding procedures, welder’s qualifications, procedures for Non-Destructive Testing, NDT inspection findings, etc.
Each project phase will be completed with a statement of compliance and after completion of Phases I through V the DNV Project Certificate will be obtained.
Phase VI
Operations and maintenance surveillance of the wind farm is required in order to maintain the Project Certificate. During this phase it is confirmed that the wind farm project is operated and maintained in conformity with the relevant manuals.
DNV recommends beginning certification early in the project development process, preferably at the time data are collected for soil, wind and wave site specific investigations. Involvement by DNV at the early stages of a project helps to ensure that the information required for later certification is collected.
Basis for certification
The basis for the project certification is proposed to be the DNV Offshore Standard, Design of Offshore Wind Turbine Structures, DNV-OS-J101.
Accreditation
DNV has been accredited by DANAK to provide project certification services.