The certification and testing of wind turbines is very important to provide assurance to all entities involved in wind energy projects: wind park operators, banks, government agencies, etc. People usually comprehend certification as the examination of companies, operators or products according to certain criteria. In the Wind Energy sector certification of products and manufacturers is a standard. The certification (of conformity) is a task done by independent institutions (or persons), which document that a result, procedure or service is in accordance with a certain standard or another certain normative document [1].
An overview of the main elements of such certifications is shown in figure 1.
Figure 1 – Typical elements of a type certification [3]
The most important part of the wind turbine type certification is the design assessment, which generally is executed in two steps. The first step comprehends the testing of the operation and security concepts and also the design load and load calculations. The second step of the design evaluation conformity compares the results of the first step with the relevant guidelines and standards [2].
The type testing objective is to provide data needed to verify aspects which are vital to safety and therefore need additional experimental verification, and aspects which cannot be reliably evaluated by analysis. The type testing comprises safety & function tests, dynamic behaviour tests, load measurements, blade tests and other component tests [3].
The objective of the manufacturing evaluation is to assess if the specific manufactured wind turbine is in conformity with the design specifications. This evaluation shall include an examination of the quality system, an assessment of the implementation with regard to the design documentation and surveillance and auditing. These elements together shall assure that the technical requirements identified in the design documentation are correctly implemented in the manufacturing procedures, that all quality checkpoints with the process of manufacture identified in the design process are included and that the surveillance or auditing is sufficient to assure that conformity is maintained in the ongoing manufacturing process [3].
In the characteristic measurements performance related characteristics of the wind turbine type is established. The type characteristics measurements comprise power performance tests, power quality tests and acoustic noise measurements [3]
The foundations of the certification are the above mentioned standards and normative documents. Here should be distinguished wind energy specific norms and general norms, which may also be applied to wind turbines. Besides a certification of the product and the manufacturer there is sometimes an additional project specific test, especially when the local conditions are not covered by the general certification scheme [1].
The specific wind turbine standards used to perform these evaluations may be of international, regional or national levels. National standards are found in Denmark, Germany and the Netherlands. The International Electrotechnical Commission (IEC) has published a series of international standards. The IEC standards, which have the reference number 61400 and are entitled Wind Turbine Generator Systems, have already been adopted by several countries around the world or are used as the foundation for the development of national standards. Table 1 shows the standards already available and standards which are still under development by IEC.
| Part | Title | Status | Publication Date |
| 1 | Design requirements (Ed. 3.0) | Available | 2005-08 |
| 2 | Design requirements for small wind turbines (Ed. 2.0) | Available | 2006-03 |
| 3 | Design requirements for offshore wind turbines | Work in Progress | - |
| 4 | Design and specifications of gearboxes | Work in Progress | - |
| 11 | Acoustic noise measurement techniques (Ed. 2.0) | Available | 2002-12 |
| 12 | Wind turbine power performance testing | Available | 2005-12 |
| 13 | Measurement of mechanical loads | Available | 2001-06 |
| 14 | Declaration of apparent sound power level and tonality values | Available | 2005-03 |
| 21 | Measurement and assessment of power quality characteristics of grid connected wind turbines | Available | 2001-12 |
| 22 | Certification of wind turbines – Rules and Procedures | Work in Progress | - |
| 23 | Full-scale structural testing of rotor blades | Available | 2001-04 |
| 24 | Lightning protection | Available | 2002-07 |
| 25 | Communications for monitoring and control of wind power plants | Work in Progress | - |
Table 1 – IEC wind turbine standards [4]