Reducing fuel consumption and emissions makes offshore charging an attractive option for offshore wind vessels. A number of potential solutions are under development and due to begin testing
A recent report published by the Offshore Renewable Energy Catapult and Workboat Association suggests that, before long, it is ‘highly likely’ offshore charging of crew transfer vessels (CTVs) and service operation vessels (SOVs) will be needed to meet their requirements.
Maersk Supply Service and Ørsted have already joined forces to test a prototype buoy that will act as a safe mooring point and a charging station for vessels, but there are other options under development.
Offshore charging is an attractive concept for many reasons, not least that it can displace a significant amount of marine fuel use with green electricity, reducing emissions in the process. If offshore charging were implemented at scale, it would create greater investment confidence in battery-powered vessels and increase their operating window, which would reduce O&M costs.
While initially aimed at CTVs in offshore wind, the technology could be developed and utilised by fishing and leisure vessels with the buoy being powered from shore and located in geographically protected areas such as estuaries and sea lochs.
However, as the report makes clear, before systems can be made commercially available, several key challenges need to be solved. One is that electrical design capabilities to charge CTV and SOV batteries are still being developed. It has been estimated that 2 MW and 20 MW are required for CTV and SOV vessels, respectively, to fast charge in the field with the current connector rating limiting this.
From a market operating perspective, to ensure interoperability, it is also important to agree and standardise connection interfaces between receiving vessels and charging systems and the frequency of the phase supply (50 Hz vs 60 Hz) so the design can be universal and not specific to an operator or a vessel designer.
Depending on the power requirements, significant modifications, including some large components, may need to be made to wind turbines and/or vessels. In the case of the latter, this could have a knock-on effect on the available space and payload capacity of a CTV. There is also the challenge of designing an electrical charging system that can recharge CTV batteries in just 1-1.5 hours, which is the expected downtime of a vessel in the field while maintenance activities are underway. Challenges also remain with regard to regulation and metering. None is insurmountable, but as the Workboat Association and ORE Catapult point out, it is important to consider the barriers to adopting this enabling technology.
In 2020, Ørsted and Maersk Supply joined forces to test a prototype buoy that will act as both a safe mooring point and a charging station for vessels. The solution, developed by Maersk Supply Service, will be tested on one of Ørsted’s offshore windfarms in 2021.
The buoy can be used to charge smaller battery- or hybrid-electrical vessels and to supply power to larger vessels, enabling them to turn off their engines when idle. Ørsted is responsible for the buoy’s integration with the electrical grid at the offshore windfarm. The charging buoy will be tested in the second half of 2021, where it will supply overnight power to one of Ørsted’s service vessels.
“Charging buoys have significant potential, in the short to medium term,” says Maersk Supply Service. “They can contribute to reducing emissions for the maritime industry. This will happen by displacing tens of thousands of tonnes of fuel consumed every year, enabling vessels to turn their engines off and replace energy consumption and charge batteries with renewable electricity.”
Ørsted intends to make any intellectual property generated in integrating the buoy into an offshore windfarm publicly available, to maximise uptake. The companies believe that, apart from offshore windfarms, the buoy has potential applications in ports and at other offshore installations. It could, they believe, help to reduce air pollution in and around ports.
For the demonstration phase of the project, Maersk Supply Service has received one of the largest Energy Technology Development and Demonstration Programme grants to be awarded in 2020 and will receive Dkr22M (US$3.5M) for engineering and demonstrating the buoy. The Danish Maritime Fund provided initial co-financing for the project.
Another solution being developed is based on the successful Mara Buoy, a four-point mooring and dynamic cable buoy system. It is designed to charge battery-powered CTVs in the field. Developed by Oasis Marine Power, the Oasis Power Buoy harnesses power directly from a wind turbine, providing a zero-emissions energy source, acting as an offshore mooring and charging point. At the time of writing, the design and build phase for the system was nearing completion. The concept was awarded a grant for technology and innovation from Maritime Research and Innovation UK. Oasis Marine Power director George Smith says the key feature of the concept lies in its simplicity of use and maintenance.
Oasis Marine Power envisages two to three buoys placed within a windfarm, each supplied with power from a wind turbine. A CTV would connect to the buoy via a dedicated boat hook system. Once connected, a telemetry signal will be set to the wind turbine which will electrify the buoy and start charging the CTV. The buoy system is currently being designed to operate in a 2-m significant wave height to match standard maximum CTV operating conditions.
The report says the prototype of Oasis Power Buoy was priced to be fabricated using the UK supply chain with the aim of having a working prototype in the water in 2021, with release of a commercially available product planned for early 2022. The prototype is nearing completion.
MJR Power and Automation is also developing offshore charging systems together with several industrial partners. The system would allow CTVs and SOVs to dock and recharge from batteries which draw down excess power from an offshore windfarm’s electrical infrastructure.
There are several advantages to ‘in water’ offshore charging systems, not least that they are manoeuvrable and can be accessed from all sides allowing for different swell direction and would be easier to maintain than a seabed connector. MJR has proposed two solutions, the first being a feeder buoy, fed with electricity to charge vessel batteries with a cable run from a wind turbine. The cable would feed out of the foundation of a turbine, run along the seabed and through a mid-water arch with buoyancy and bend restriction. Cable would be stored within the buoy.
It has also proposed an ‘in air’ solution accommodated on the platform of a turbine’s transition piece. The cable reel would be located on the platform. A connector deployment system would deploy the connector to the deck of a vessel. This could, the Workboat Association/ORE Catapult report suggests, offer a lower cost alternative, avoiding any requirement for subsea mooring or cable installation and offering access for all maintenance works without the need for subsea inspection, maintenance or repair.