In the coming years, an important number of offshore wind turbines will reach the end of their initially planned service life. In a wind turbine end-of-life scenario, owners can decide between extending the life of the asset, repowering the site or decommissioning. This decision-making process is affected by important sources of uncertainty, especially in offshore environments. The limited experience makes the decommissioning procedure challenging, as it is still largely unexplored. This work assesses the current state of knowledge about the challenges surrounding the decommissioning process of an offshore wind farm. The four main challenges encountered are identified and analysed in detail, namely the regulatory framework, the overall planning of the process, the logistics and vessels’ availability, and the environmental impacts confronted. Ultimately, this paper aims at stimulating the dialogue among stakeholders and raising the awareness of adequately regulating and preparing the upcoming decommissioning of offshore wind farms in Europe.
This paper explores the state of the knowledge regarding the decommissioning process of offshore wind farms in Europe. From the limited existing experiences, it is clear that wind turbine end-of-life scenarios and particularly, decommissioning, are affected by high uncertainties. In addition, the complexity of the offshore environment, the high variability between projects, and lack of experience makes planning and risk identification essential for the successful decommissioning of these projects. As a result, the major challenges encountered during this process are identified and individually analysed, namely the regulations, the planning of the process, the vessels’ availability and the environmental impacts.
The decommissioning phase of offshore wind farms currently lack a specific regulatory framework. This negatively affects concepts such as liabilities, but strongly impacts other fields like the planning of the process and the resulting environmental impacts. Offshore wind farm owners lack specific guidelines that could help ease their decommissioning planning, that should ideally be included as part of the development phase. With regards to the environmental impacts, the absence or limited dedicated maritime regulations may lead to decisions that can harmfully disturb the marine environment. As a result, the elaboration of specific regulations and guidelines is strongly recommended including precise liabilities for the owners. Concerning the planning, the ideal guidelines should help the owners with the decision about what needs to be done, estimating the decommissioning costs and ensuring that potential technical modifications arisen over time are adequately monitored and considered in the initial plan. The availability of appropriate vessels is also found as a potential bottleneck; decommissioning programmes might compete with new installation activities, operation and maintenance procedures or decommissioning oil and gas facilities, which all require similar vessel characteristics. Again, anticipation is key to ensure adherence to planned duration and costs, together with reduced risks. Finally, the environmental impacts of a partial removal of the asset together with a proper recycling strategy could be the ideal combination for achieving a sustainable decommissioning. Approaches for blade recycling could as well diminish the wind energy carbon footprint and make the process even more sustainable.
Further research should aim at tackling the challenges identified. The assessment of the uncertainty affecting the whole decommissioning process should also become a priority, to allow a proper scheduling, to minimise expenditures and to mitigate risks. Certainly, the decommissioning phase, such as other wind turbine end-of-life scenarios, is affected by important sources of uncertainty. Nevertheless, the complexity of the offshore environment, the diversity of the site characteristics and the limited experience compared to onshore, makes the decommissioning of offshore wind farms more critical. Furthermore, possibilities for blade recycling need to be explored to achieve more sustainable alternatives.