Lifetime Extension

Objectives

The task works on the exchange of knowledge on methods for estimating the accumulated damage of wind turbine components after operating the turbines for a certain number of years, and how to perform lifetime extension decisions. The activities of 2025 were focused on the following topics representing the work-packages of the task: 1) Integrating economic reliability and risk, 2) Data-driven life estimation, and 3) Preparing for a sustainable future (2050).

The first topic focuses on writing a review paper about the barriers to performing lifetime extensions of offshore wind farms, primarily located in the North Sea region of Europe. This is because this is the location of the oldest offshore wind farms. A series of interviews has been conducted with stakeholders in the offshore wind sector, and the main takeaway is that the lack of clear legislation and specification of decision-making authority on offshore wind lifetime extension is seen as the largest challenge.

The second topic focuses on technical methods for evaluating accumulated damage and estimating the remaining useful life of a wind farm asset. Task members contribute with academic works to illustrate the methods in relation to the recent IEC TS 61400-28:2025 on life extension[2]. A review paper is in progress.

The last topic has focused on fleet evolution models to describe the expected decommissioning of wind turbines in mainly European countries, where sufficiently detailed registers of the fleets are available. Secondly, the possibility of recommending a +50 year design lifetime of future wind turbine assets has been discussed, and a review paper is in progress.

Participation

The list of participants of the task is 14, representing seven countries and involving five companies in 2025 as shown in table 1.

Progress, Results, and Impact in 2025

The research activities of 2025 have been focused on 3 main topics:

1. The collection of information on the status of lifetime extension of offshore wind and the identification of barriers to obtaining lifetime extension of offshore wind farms.
2. The collection of information on minimal technical requirements to obtain lifetime extension and methods for estimating the consumed life of wind farms.
3. Identification of possible scenarios of lifetime extension towards 2050 and discussions on targets for future design lifetime of wind turbine assets.

The first topic focused on interviews conducted with stakeholders in the offshore wind sector. The intention was to identify barriers to performing lifetime extensions of offshore wind farms across legal, technical, and economic dimensions.

While the interviews were being processed and interpreted, other inputs to the discussion appeared. The IEC Technical Specification 61400-28 IEC TS 61400-28:2025 "Wind energy generation systems - Part 28: Through-life management and life extension of wind power assets" [2] was published in 2025 and provided insights into the technical requirements needed to perform lifetime extensions. The IEC 61400-28 describes the technical aspects that must be examined to estimate the Remaining Useful Lifetime (RUL) of wind farms.

Concrete examples of lifetime extension of offshore windfarms were seen for the first time in Denmark in 2025 with 5 lifetime extensions of offshore wind farms and allowed for 10-25 years of addition operation [3]. Figure 1 illustrates the offshore wind farms of Denmark and the farms obtaining lifetime extension are marked with rings. The lifetime extensions of the Danish Wind farms were based on the guideline from the Danish Energy Agency (DEA) [4] and the interview with the stakeholder of the offshore wind sector showed that a common legal framework on lifetime extension of offshore wind farms is seen as the main barrier for performing lifetime extension in the North Sea region. Thus, the main recommendation of the review paper [1] is to attempt to create a common European legal framework that will allow cross-national lifetime extension projects to be coordinated in order to reduce the cost.

The second topic was focused on the technical methods, which can be used to evaluate the remaining useful life of wind turbines as part of a lifetime extension decision. This has been an ongoing process of the task and it has been identified that it is difficult to obtain public available measurements from wind turbine in order to perform public benchmark comparison of the methods. Thus, the focus was changed to providing academic examples of estimates of the remaining useful lifetime of a wind turbine in relation to the IEC 61400-28 technical Specification. A review paper on the methods for evaluating remaining useful lifetime is in progress.

The third topic is focused on estimating the future fleet capacity of countries and regions by determining the current rate of decommissioning as obtained from national databases of operating and decommissioned wind turbines. The work originated by describing the expected decommissioning of the Danish [5] and then the German [6] fleet. More recent investigations have shown that the European wind turbine fleet reaches an average age of 32 years when 50 % of a turbine installation year has been decommissioned [7]. A similar model was used in the task to create a study of the potential decommissioning of the Irish wind turbine fleet towards 2100 and was presented at a joint workshop between IEA task 42, 45 and 60 at the SEAI in Dublin in June 2025. A review paper on predicting the decommissioning rate of the European turbine fleet is in progress. Methods to prolong the lifetime of steel structures for wind energy are also reported in the review.

Next Steps

The Task is approaching the end of the second phase and a follow up activity can be to assist the work needed to raise the current IEC Technical Specification 61400-28(IEC TS 61400-28:2025) "Wind energy generation systems - Part 28: Through-life management and life extension of wind power assets" to a full standard within the next 5 year. The IEA TCP Wind holds representatives of energy agencies from many counties around the world and interdisciplinary discussions could facilitate the formulation of the final standard of the IEC 61400-28.

References

1. M. Henkel, B. R. Faria, K. Robbelein, M. Moattari, R. Harris, H. Johansson, A. B. Abrahamsen, L. Ziegler, C. Devriendt and J. S. Nielsen (2026). Review of Current Lifetime Extension Practices for Offshore Wind Turbines. Submitted to Renewable and Sustainable Energy Reviews
2. Technical Specification IEC TS 61400-28:2025. Wind energy generation systems - Part 28: Through-life management and life extension of wind power assets. Link.
3. Danish Energy Agency (2026). Existing offshore wind farms. Link. lifetime extension
4. Danish Energy Agency (2026). Vejledning om ansøgnings- og tilladelsesprocessen for repowering og forlængelse af elproduktionstilladelse af bestående elproduktionsanlæg på havet. Link.
5. A.B. Abrahamsen, J. Beauson, K.W. Lund, E.S. Madsen, D.P. Rudolph and J.P. Jensen (2024). Method for estimating the future annual mass of decommissioned wind turbine blade material in Denmark. Wind Energy. 2024;27(2):165‐178. Link.
6. K.J. Kramer, A.B. Abrahamsen, J. Beauson, U.E. Hansen, N.-E. Clausen, A.P.M. Velenturf and M. Schmidt (2024). Quantifying circular economy pathways of decommissioned onshore wind turbines: The case of Denmark and Germany. Sustainable Production and Consumption, Volume 49, 2024, Pages 179-192. Link.
7. L. Mc Govern, E. Tapoglou, and A. Georgakaki (2025), Material streams from wind energy decommissioning to 2050, Publications Office of the European Union, Luxembourg, 2025, JRC139814. Link.