Background It typically takes 6 months to 1 year for the renewable energy produced by an offshore wind turbine to displace the carbon emissions required to build and maintain the wind farm [1].
Whilst an offshore wind turbine designed for a minimum 20 year lifetime offsets far more emissions than it produces, there is a drive within the industry to make offshore wind a truly zero-emission source of electricity.
Offshore wind turbines are maintained using marine gas oil powered vessels, which can contribute 10- 20% of the project life cycle carbon emissions [2].
For closer to shore projects, which make up the majority of installed capacity in the UK, Crew Transfer Vessels (CTVs) support turbine through-life operations and maintenance activities, with an estimated 4000 hours of CTV time producing 2000 Tonnes of CO2e per year for a single 180MW wind farm [3].
A candidate to reduce the carbon footprint of offshore wind maintenance activities is to use electric Crew Transfer Vessels (eCTVs). However, the limited energy density of battery storage severely reduces the operating capability and range of eCTVs, which limits the adoption of such vessels.
Having a method to charge batteries in the field – ideally during offshore downtime – would be a key enabler for the large-scale deployment of eCTVs to unlock carbon emission reductions.
There are multiple viable options available for transferring power from offshore turbines to a CTV, most of which have a well proven pedigree in the oil and gas industry [4]. Of all the available approaches, three feasible options were shortlisted for the project, with a high-level assessment of the relative advantages and disadvantages
