Erneuerbare Energien

Lifetime Extension for Wind Turbines

Services for continued operation of wind turbines

Services for continued operation of wind turbines

Continued operation of wind turbines after 20 years

Life cycle of wind turbines: make the most of your wind turbine’s extended lifetime potential

The probability of relevant damage due to material fatigue increases drastically after a wind turbine comes to the end of its design life. However, this does not necessarily mean the turbine has to be withdrawn from operation and decommissioned. In practical terms, many turbines still have reserves after the usual 20-year design life, which can be used for continued operation. Identification of these reserves can help to unlock additional potential for energy generation beyond the 20-year period for owners and operators of wind parks.

Once lifetime extension of a turbine after 20 years has been identified as an interesting option, diverse aspects need to be considered for its realisation. Type certification is used as a basis for verifying and evaluating fundamental safety with respect to the design life of the wind turbine model. This and other factors must take maintenance and operation requirements and the appropriate wind and climate conditions at the chosen site into consideration. When the operational design life reaches its end, an expert analysis for continued operation must be prepared to identify and confirm the remaining reserves for extension of the wind turbine life.

Analysis and evaluation for the continued operation of wind turbines – Our lifetime extension services for wind turbine operators and owners

TÜV SÜD’s expert analysis for continued operation establishes the basis for any application to authorities and insurance companies for continued operation of your wind turbine. Our expert analysis for continued operation is based on internationally recognised standards as well as the requirements of the BWE (Bundesverband Windenergie e.V. - German Wind Association) and DIBt:2012.

Procedure of the expert analysis for continued operation:

  1. Inspection of the wind turbine by our expert engineers: examination of the technical condition of the turbine as well as evaluation of damage and potential for further damage
  2. Determination of loads throughout the turbine’s operating life: analysis of site-specific wind conditions over the years and their effects on the turbine
  3. Analysis and calculations: computer estimate of turbine loads under site-specific conditions as well as design conditions, determination of available reserves of the turbine components and determination of the remaining period before essential replacement of components

After completion of our structural integrity analyses and evaluations, a detailed evaluation report is created that transparently presents the boundary conditions for safe continued operation of the turbine. For potential future turbine transactions, the evaluation report can additionally be used as a basis for a valuation and/or rating of the turbine and its condition. The evaluation report contains information including:

     - Potential period of continued operation

     - Required replacement of components and parts

     - Required recurring inspections of foundations, tower, machinery and rotor blades in
       the continued operation period

Why choose TÜV SÜD – Expert analysis for continued operation

TÜV SÜD’s expert analysis for continued operation offers wind park operators and owners various advantages:

     - They receive a clearly understandable and detailed evaluation report, which delivers a
       transparent basis for decision-making over continued operation of their wind turbine

     - The TÜV SÜD evaluation report for continued operation can be used to apply for
       extension of the operating approval by the authorities or to maintain insurance validity
       during the continued operation period

     - TÜV SÜD is an accredited certification body for wind turbines (IEC 61400 series, IECRE
       and others) and issues evaluation reports for continued operation which are
       recognised by all relevant authorities, insurance companies and other parties
       worldwide for extension of operating approval for your wind turbines

Exploit the maximum potential for continued operation of your wind turbine– with TÜV SÜD’s expertise and know-how! Our experienced wind turbine experts provide detailed information about the available services on request.

Any questions? – Read our FAQs:


  • How exactly is the evaluation process for continued operation of a wind turbine structured?

    In detail, preparation of an expert analysis for continued operation of a wind turbine is subdivided into three parts. An evaluation report is drawn up based on the results of the analyses performed. If desired, multiple turbines at a single site can be analysed together and the results presented in a combined evaluation report.

    1. Practical part: Inspection of turbine

      In the practical part, the current technical condition of the wind turbine is inspected and recorded. This on-site inspection by an expert engineer is taken as a basis for determining whether the condition of the turbine is sufficient to allow continued operation beyond its design life. Cracks, loose bolts and other issues related to single components are often discovered. Certain turbine types have well-known design-related issues, which are additionally considered at the inspections on site.

      Critical factors for potential continuation of operation are the condition of the components in the main load path, e.g. foundations, tower, machine carrier and hub, as well as other load-bearing structures and rotor blades. Additionally, all other safety-relevant parts and components are examined during the inspections, e.g. lightning protection system (LPS), pitch drives (where applicable for older turbines) and electric and electronic systems.

      A well-maintained wind turbine usually does not show serious issues. Nevertheless, when serious issues that directly impact on the structural integrity of the wind turbine are detected, immediate shutdown of the wind turbine operation is recommended to protect both the wind turbine itself and the surrounding infrastructure and population. Minor issues or damage which can easily be fixed by simple maintenance measures are more frequently discovered during the inspections. On the turbine itself, these could be damage from weathering or corrosion, or damaged coatings or worn-out wiring. Where the rotor blades are concerned, small cracks or surface pitting are common.

    2. Wind conditions: Determination of wind conditions at the site

      Detailed knowledge of the wind conditions at the site throughout the turbine’s operating life is an essential basis for exact estimation of the turbine loads and the remaining margins. In this process, the site-specific wind data and the operation data (SCADA data) of the wind turbine are evaluated and the turbine documentation is reviewed. This enables mean wind speeds, extreme wind events and turbulence intensities to be tracked over the turbine’s operating life. These detailed data are subsequently used to calculate the loads on the wind turbine over the operating life in the third, analytical part.

    3. Analytical part: Calculation of turbine loads and margins of components

      The information collected concerning the wind conditions at the site forms the basis for the final analytical part and calculations in the expert analysis for continued operation. These calculations, which are related to load simulations, take the requirements of the IEC 61400-1 standard (and also DIBt:2012 and others if necessary) as well as the original design conditions into consideration. The resulting time series can be summarised to give damage equivalent loads (DEL) for all relevant components and parts. The continued operation time is calculated on the basis of these values, taking into account the load level under design conditions for the relevant components in the main load path.
  • What documents have to be provided by wind turbine operators?

    When an expert analysis of continued operation and evaluation report are drawn up, various operation and (energy) production data for the wind turbine are considered together with the evaluation reports as part of the Type Certificate. The analysis process further takes into account any documentation related to the erection, commissioning and operating approval of the wind turbine together with its conditions and requirements, as well as maintenance, repair and inspection reports.

    The outlined documents and data can only be provided by the operator and owner of the wind turbine. To ensure an efficient workflow, these should be provided before the start of evaluation. If further documents are required they will be requested by our expert engineers in the course of the evaluations. If data or documents are not available, TÜV SÜD will work to find reliable alternative solutions and approaches to clarify the relevant areas in order to be able to issue an evaluation report for continued operation.

  • Economic situation

    When a wind turbine moves into a period of continued operation, it is usually no longer covered by the regular payment schemes set up by governments and authorities worldwide. The point of departure from the payment scheme often, but not always, coincides with the (common) 20-year design life of a wind turbine. Some newer turbines have a longer design life, while some national renewable energy schemes do not guarantee payments for 20 years. Some wind parks may even fall outside any national scheme because a PPA was concluded or a different situation applies.

    Assuming the very common situation that a wind turbine has left the national payment scheme and the design life has expired, the energy generated very often has to be sold at currently available market prices. The original prices per kWh at the time of erection and commissioning of the turbine are usually no longer reached. Measures to maintain an optimised energy price during production (e.g. operation of turbine only when high energy prices are guaranteed) are possible, but require the support of the chosen grid operator and energy seller.

    In addition to the efforts made in producing the expert analysis of continued operation, further actions, e.g. replacement of components, may be required for the turbine, either immediately or after a few years of operation.

    Even if the economic situation of turbine operation in the continued operation period is characterised by decreasing income and earnings, there might still be identifiable potential savings. This mainly involves savings related to rent (e.g. when rental contracts come up for extension, an earnings-related variable rent may be feasible that would save rent in the continued operation periods and potentially offer the lessor a later option to increase rents if repowering with larger turbines becomes possible). Insurance payments as well as maintenance and other service provision might offer further potential for savings, considering that none of them would generate any further earnings if the turbine was dismantled.

    The extent to which continued operation of a wind turbine makes sense and is economically viable must be judged on a case-by-case basis. Beside pure economics, it also depends on the owner and operator’s expectations of income. An additional attraction for some operators might be to secure a site for repowering (on the basis of a changed legal situation in the future) while initially keeping the existing turbine operating on a decreased income and replacing it by a much larger turbine later.

    When an operator decides not to continue operating a wind turbine for economic reasons, a last alternative to dismantling is the sale of the turbine to another operator specialising in continued operation.

    Financial considerations may mean shutdown and dismantling for many older wind turbines. TÜV SÜD’s services can help to extend the operating life of your wind turbine and keep your turbine available as a renewable energy source. Just ask our experts for details.

  • Continued operation, sale, repowering or dismantling?

    The decision as to which of the four options is suitable for which operator and which turbine at which site must be founded on detailed analysis. Irrespective of the most attractive option for you, TÜV SÜD supports you along the whole life cycle throughout every phase of operation of your wind turbine.

    Continued operation and the related necessity of setting up new contracts and dealing with other issues needing clarification might seem to involve enormous efforts at first glance. Nevertheless, this option is often actually the one with the least effort and fewest changes: the turbine still remains in operation and the number of involved parties (authorities, insurance etc.) is still low compared to the other options.

    An expert analysis for continued operation is often also required when the turbine is sold. Furthermore, detailed Due Diligence Checks are necessary. If desired, we can also offer our services for this.

    If dismantling of the turbine is the chosen option, many other topics will need clarification; additionally, heavy equipment is necessary.

    In repowering, old turbines are replaced by a lower number of newer turbines with increased nominal power and efficiency. This usually results in increased hub heights and rotor diameters. In sum, higher annual energy production by the wind park is usually possible afterwards. In addition to the dismantling operations involved, planning and preparation for the erection of the new turbines often goes on in parallel, sometimes resulting in individual synergy effects. Replacement of a single turbine by a larger one with greater annual energy production and higher efficiency is often reasonable and feasible. Due to the political boundary conditions in many countries worldwide, not many wind parks can currently be repowered feasibly and cost-effectively. With an eye to local ongoing political debate, continued operation of a wind turbine or wind park could be worth considering – even if only moderately economically viable – with the hope of changes to political boundary conditions in the near future.

  • When is continued operation possible and reasonable ?

    In the situations described above, the question might arise as to what fundamental boundary conditions need to be fulfilled for continued operation of a wind turbine to become a viable option.

    In summary, continued operation of a wind turbine may be feasible in principle if

       - A positive evaluation report for continued operation is available

       - Continued operation is economically viable

       - There are no opposing legal interests

       - Repowering is not possible or economically viable

    Continued operation is most likely to be possible when the wind turbine

       - Has not faced any extreme events (strong hurricanes, “storm of the century”)

       - Is located in a wind park with >5D in main wind direction

       - Has undergone regular service and maintenance together with appropriate corrective
         actions and repairs

       - Was inspected regularly as part of recurring inspections and the last inspection report
         does not show any serious faults (report in 18th or 19th year of operation)



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