We need to ensure that the decommissioning of wind turbines has a sustainable impact, writes Catherine Leaf, senior managing consultant, Ramboll.
With a target of net-zero carbon to meet by 2050, renewable energy, including wind power, will prove invaluable as we continue phasing out fossil fuels. As the challenges posed by decommissioning oil and gas platforms in the North Sea become increasingly apparent, the wind industry must observe closely.
With offshore wind farms maturing roughly five years earlier than oil and gas platforms, interweaving effective decommissioning planning into construction is a necessity.
There are approximately 500 fixed and subsea oil and gas production systems, as well as 5,000 wells and 3,000 pipelines hosted by the UK Continental Shelf (UKCS). Around 10% of these structures have been decommissioned since 2014, spending over £1billion each year and the trade association OGUK estimates a further £15billion spent over the next decade on decommissioning UK assets. Plugging and abandonment account for almost 50% of the cost, while elements that will also relate to offshore wind decommissioning, including pipeline de-energising and onshore waste management, contribute for 3% and 2% respectively.
Without the same hazardous waste management challenges posed by oil and gas decommissioning, offshore wind farm decommissioning is much less financially taxing. In fact, recent estimates put the upper cost of decommissioning the UK offshore wind stock at £3.6billion. However, despite the lower financial cost, the wider challenges decommissioning will bring for the wind industry should not be ignored. As decommissioning projects are set to rise over the next ten years, with existing offshore wind farm stock reaching maturity, the sustainability of decommissioning methods must be considered.
Keeping the end in sight
One key consideration is the need to plan for decommissioning from the beginning. When the North Sea oil platforms were first deployed 50 years ago, there was little consideration of their removal. This lack of forward planning is now the primary cause of the issues now facing operators, with the OSPAR Convention requiring them to leave behind a clear seabed.
Without technology able to readily remove gravity-based structures safely and sustainably, operators’ ability to meet the OSPAR requirements is uncertain. In addition, the International Maritime Organisation’s guidelines advise that man-made structures should not enter waters unless they can be removed. Importantly, the wind industry is deploying scores of offshore wind turbines that require installation supported by large diameter monopiles but the technology needed for removing these installations is not currently readily available.
Although there now exists a regulatory requirement, via the Energy Act of 2004, to prepare a decommissioning programme (DP) at the development stage for offshore renewable energy installations and for decommissioning, restoration and aftercare strategies for onshore development, DPs are often vague and assume that technology will have caught up with the engineering challenges associated with decommissioning. This jars with the principles of sustainable construction and could cause future problems.
Staying in the loop
Wind farms are likely to be modified, upgraded and repowered where economically viable, as well as see a change of operator, during their lifetime. Therefore, records of modifications must be updated regularly, with each update made for ensuring a sustainable removal process.
Legislation now requires operators to comply with the principles of the waste hierarchy and with focus increasingly on designing for reuse, the need for a circular economy is gaining traction. As stakeholders and investment partners in the energy industry expect sustainable practices at the decommissioning stage, wind turbines have the advantage over oil and gas structures, as their simpler design enables greater sustainable decommissioning processes.
In Eastern Europe, the reuse of component parts from decommissioned onshore wind farms is already established. There have also been positive reuse schemes in small communities, such as the Isle of Gigha, Scotland, which in 2004 bought three second-hand Vestas machines. However, as the existing offshore wind stock ages and O&G decommissioning gears up there is a need to consider market forces: there will be a limited number of yards able to manage waste and a large amount of recycled materials entering the market, thus lowering the value of materials.
A few years ago, Decom North Sea (DNS) released a study assessing the options for managing steel from oil and gas decommissioning. Although recycling over disposing was preferable, findings showed that recycling still posed a high energy demand and due to the absence of UK-based steel mills, provided little benefit to the UK economy.
However, the importance of collaborating across the decommissioning industry for encouraging effective reuse and recycling markets was made clear, and earlier this year the Scottish government awarded DNS funding to develop a design competition that considers ways to reuse steel from decommissioned oil and gas assets. This could be hugely beneficial to design and installation plans for future wind turbines.
Ultimately, decommissioning strategies must be integrated into design and installation plans from the beginning and long-term sustainable impact must be considered to adhere to the principles of a circular economy. With a simpler design model equipped with the lessons learnt from the oil and gas sector, the wind industry has the chance to spearhead effective and sustainable ways to decommission wind farm infrastructure.