Gillian Smith, DNV-GL. Decommissioning of Offshore Wind Installations

Decommissioning of Offshore Wind Installations
delivered by Gillian Smith, DNV-GL

In the last two years, the first few offshore wind projects have been dismantled and others are approaching the end of their design lives. In contrast the decommissioning activities of the offshore oil and gas sector began over 30 years ago and a large body of experience and specialised techniques has been developed and continues to evolve. With care, the offshore wind sector can benefit greatly from this extensive experience, whilst keeping aware of distinct difference between the two sectors. This paper describes decommissioning techniques available at present, lessons learned that are transferable from the oil and gas sector, and some potential future developments.

The volume of offshore wind decommissioning will ramp up slowly, mirroring the build rate, with turbine sizes and site conditions becoming more challenging. By 2035 it Is estimated that 2 GW will be decommissioned each year, representing 500 turbines. The main techniques transferable from oil and gas decommissioning are in sub-sea cutting methods.

The main difference is the much higher share of cost in O&G decommissioning related to well-plugging, cleaning and safe dismantling of the topside given the greater risk of pollution, in contrast, offshore wind decommissioning essentially comprises marine removal operations. Key lessons are the need to design for decommissioning and to keep meticulous records throughout the life of a project. Looking ahead, likely developments are identified in methods for foundation removal, re-use and recycling, onshore infrastructure and clarifications on the extent that components may be left in place.

At the end of 2016, there were approximately 3,600 offshore wind turbines in Europe providing 13 GW capacity [1], compared with just 60 MW capacity In 2000. In the last two years, several early projects have already been decommissioned, for example Yttre Stengrund, Lely, Hooksiel and Vindeby.

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