As the wind industry works towards meeting installed offshore wind capacity targets, there is a key, sometimes overlooked element that has the potential to create significant setbacks: end-of-life management. While most countries involved in offshore wind power are organizing leasing rounds to allocate maritime space to project developers, those countries with a more mature wind market must also consider that they will lose capacity due to wind farms reaching the end of their lifetime in the coming years. This key point could be the element that prevents countries from achieving their targets.
Let’s take Denmark as an example using analysis from Spinergie’s Market Intelligence solution. Denmark currently has 13 fully commissioned offshore wind farms within its waters and two (Vesterhav Nord and Syd) constructed but awaiting commissioning. One wind farm has already been decommissioned in the Danish sector: the 5 MW capacity / 11 turbine Vindeby project. Spinergie’s analysis, which assumes a 25-year lifespan for a wind farm, indicates that the country is on track to lose 3 GW to aging wind farms by 2050. This will impact Denmark’s chances of reaching its 2050 capacity target of 35 GW - which it is on track to miss by more than 16 GW.
Here, we examine the options available to developers when assessing the end of a wind farm’s lifecycle and how decommissioning will impact the overall market during the run-up to capacity target deadlines.
Wind Farm End-of-Life Scenarios: options available in offshore wind
The end-of-life phase of the wind farm lifecycle must be considered during the development stage in anticipation of having a plan in place when assets are no longer safe or operational. Currently, installed turbines have an expected lifespan of 25 years (on average), with this expected to increase to 30 years by the end of the 2020s. There are three main options available to developers for the final stage:
- Removal: either full or partial. All offshore wind turbines and associated infrastructures, such as foundations and cables, are removed in full removal. For partial removal, only part of the structure (turbines and some parts of the foundation) is taken away to keep the area safe for vessels. The remaining parts become host to marine species as a habitat created due to the reef effect.
- Repower: again, this can be either full or partial. All old generating assets are replaced with next-generation technology for a full repower. In partial repowering, only part of the old generating assets will be replaced with next-generation, low-cost, high-output technology. This operation was performed for the first time at the Bockstigen project in Sweden in 2018. It extended the wind farm's lifetime by 15 years, with the 550-kW turbines replaced by 660-kW turbines.
- Life Extension: the life of the turbine is extended by conducting minor and low-cost repairs. It’s important also to note that such repairs would need to be undertaken more frequently than previously, as the asset is older and more fragile.
Case Study: wind farm removals in Europe
Five decommissioning campaigns have been observed in Europe for wind farms built before 2001. With an average life span of 18 years, these projects were mostly small, with a maximum 2 MW capacity turbines, with Vindeby having the most at 11. Despite these narrow parameters, they have provided important insight into the best way to remove offshore wind-generating assets. Additionally, all five of these wind farms have provided rare examples of removals.
Decommissioning the 13-year-old Blyth wind farm was the first example in the UK sector - both as a wind farm project and as a decommissioning. Permitting authorities required the removal of the wind farm. One of the two Vestas V66-2MW turbines was recycled, while the other was used for training at the Port of Blyth.
The Decommissioning Scope: Developer RWE decommissioned the two-turbine Blyth wind farm in 2019 with Fugro jackup Excalibur contracted to undertake the work scope. The net duration per turbine was 11.6 days. After removing the blades, nacelles, and tower, Excalibur was used to cut the foundation 0.5 meters below the sea floor using a water-jetting tool. The remaining socket was filled with ballast stone.
Utgrunden: The 2000-built Utgrunden wind farm was located off the east coast of Sweden just above the Yttre Strengrund wind farm. Decommissioned at 18 years old, Vattenfall had taken the decision as the seven 1.5 MW Enron turbines had exceeded their operational lifetime.
The Decommissioning Scope: Vattenfall contracted Ziton jackup Wind Pioneer for the 2018 decommissioning scope at Utgrunden. In removing the seven installations, the rotor was removed while still connected to the blades before the nacelles and the tower were removed. Finally, cutting technology was used to remove the subsea structures. Cable Layer Pleijel was used four years later to remove the remaining cables. The net duration per turbine removal at Utgrunden was 5.6 days.
Commissioned in 1991 as a pilot project to test the viability of offshore wind, the Vindeby wind farm, located offshore southeast Denmark, was decommissioned after 26 years. The decision to decommission was taken “partly because the consent was expiring” and “that all gears needed considerable refurbishment,” according to Ørsted’s Lars Bie Jensen interviewed in 2017. As many materials as possible were recycled during the decommissioning process.
The Decommissioning Scope: The 11-turbine project was decommissioned in 2017, with the Danish port of Nyborg used as the logistics base and SSE jackup Sound Prospector used for removal operations. The blades, nacelles, and tower were dismantled individually while the tripod foundations were broken down on-site using hydraulic demolition shears before later collection. The process took 8.2 net days (effective vessel days to perform the removal on site) per turbine.
A further two wind farms make up the five decommissioned in total. The 15-year-old Yttre Strengrund wind farm, which lay off the east coast of Sweden, was fully decommissioned by January 2016. In a statement, Vattenfall said that due to the fact the turbines were an early model, with only 50 produced, they had “difficulty in obtaining spare parts, and the high costs of refurbishing turbines and gearboxes contributed to the fact that it was not economically justifiable to replace the turbines.”
Finally, Nuon’s decision to dismantle the Lely wind farm, which was located off the Dutch coast, came after one of the four turbines lost its rotor head and blades due to metal fatigue in 2014. While the remaining turbines had not suffered the same metal fatigue, the decision was still taken to decommission as the 20-year-old wind farm was approaching the end of its lifecycle.
Lessons learned from decommissioning offshore wind farm projects
As may be expected, the smaller the lifetime of offshore assets, the sooner the question of end-of-life management needs to be addressed. For assets with a projected 25-year lifespan, which is a plausible scenario for older installations, a first surge in turbine decommissioning is anticipated between 2026 and 2030.
This anticipated surge in wind farm decommissioning is primarily due to the likely end-of-life timing for the first large-scale projects installed in the early 2000s. A key case in point is Vattenfall’s 80-turbine Horns Rev 1 offshore Denmark, commissioned in 2002. Another larger-scale project, RWE’s Scroby Sands in the UK sector, recently experienced a significant failure in one of its 30 turbines. It is expected to reach the end of its 25-year operating lifespan in 2029. It was commissioned in 2004.
In the mid-2010s, numerous large-scale projects were initiated, including RWE's Gwynt y Mor (comprising 160 turbines) and Orsted's West of Duddon Sands (with 108 turbines). These installations will approach their operational end in the late 2030s, necessitating proactive end-of-life management planning to guarantee the availability of suitable vessels.
Furthermore, as the number of turbines and their installed capacity continues to grow, the demand for jack-up vessels will inevitably arise if the decommissioning route is chosen. These vessels are likely to be sourced from the existing Operations and Maintenance (O&M) fleet, adding additional pressure to vessel supply and potentially creating bottlenecks in the future.
The above chart indicates the steep growth in the number of turbines that will be decommissioned up to 2040 - at the same time, the industry will be under pressure to find the vessel supply to meet the installation and O&M demand.
This analysis shows that decommissioning considerations are pivotal in assessing a country's ability to meet its capacity targets by the 2050 deadline. As demand picks up, so too does the end-of-life phase of wind farms become increasingly significant, and it is likely to be a factor in some countries failing to meet their targets.
By drawing from the experiences of projects that have already been decommissioned, developers can refine their strategies, streamline the process, and mitigate potential challenges. Properly evaluating the available decommissioning options is essential for making informed decisions about how the end-of-life process will impact the industry. This is especially true concerning supply chain considerations such as port availability and jackup vessel supply.
Additional reporting by Yvan Gelbart and Sarah McLean
For further analysis of the supply chain issues facing the offshore wind market, read our white paper: What is Driving Global Wind Demand and Are Global Capacity Targets Attainable?
Interested in finding out more about how Spinergie can help wind developers plan their offshore wind projects through every stage of the life cycle? Contact us for a demo today.