A somewhat conflicting fact for the clean energy produced by offshore wind farms is that they do have a carbon cost through the operation of commissioning service and operation vessels (CSOVs).

As it currently stands, these ships are not wildly dissimilar from the oil and gas offshore support vessels (OSVs) from which their design is derived and require various fossil-fuelled generators to generate electrical power to support their daily activities.

This represents an industry misalignment. Much of the work that these CSOVs undertake involves ferrying crews between shore – where, in many places, there is grid power available – and turbines, which generate enough energy to power a ship with practically every spin.

Extraordinary efficiency gains have been seen on deck, where equipment has switched from hydraulic to electric, allowing energy to be reconstituted and reclaimed, with motorised winches using electrical power when pulling and regenerating it when slackening. This has been responsible for a vast improvement in the efficiency of workboats, some of which now burn 3tonnes of fuel per day where their antecedents burned 20tonnes.

But even so, compared with the potential to hook up and charge from a turbine, using marine diesel to generate electricity for this purpose is a woefully inefficient use of resources.

Something has to give, and now offshore vessel operators are exploring ways to reduce their fossil fuel reliance and transfer to battery power. This is easier said than done. Even with the aforementioned electrification upgrades, CSOVs and other offshore vessels use enormous power in a day.

In conversation with Ulstein, one systems integrator told The Naval Architect that ship Masters tend to spin up four diesel generator-sets as a matter of course during gangway and crane operations, to prevent a power spike causing a blackout on the vessel. So pervasive was the practice, the engineer said, that on vessels using Ulstein’s X-Connect, ship Masters had to be coached not to do this.

In January 2025, Bibby Marine charged Spanish shipyard Armon with the construction of a world-first, a fully electric Commissioning Service Operation Vessel (‘eCSOV’). Not merely to be retrofitted with containerised batteries positioned on-deck, this vessel would be equipped with Corvus Blue Whale lithium-ion-phosphate (LFP) batteries amounting to 25MWh, deemed to be the amount of electrical energy required to power a vessel of its type during a typical 24-hour work period. (New 15MWh turbines currently being installed in the North Sea can generate this in just under two hours.)

These are lithium-iron-phosphate (LiFePO₄), which is more thermally stable than previous generations of lithium-ion battery. In the case of the Corvus Blue Whale, the cells are physically isolated from its neighbours, in accordance with DNV standard Pt6 Ch2 Option 1. This means that physical thermal barriers between cells, often composed of high-tech heat-resistant aerogels and heat-expanding sealant, prevent transmission of heat between cells, while a gas venting system exhausts hot gases out and away from the assembly.

Meanwhile, the vessel will feature a full DC grid throughout. Batteries are natively DC, while diesel generators always produce AC –  meaning conversion hardware and associated 2-5% conversion losses are unavoidable on a traditional AC grid ship. An all-DC grid eliminates these conversions, reducing losses and simplifying integration of inherently DC power sources such as batteries, solar panels, and regenerative systems like electric cranes, which can return power directly to the grid when lowering a load.

As well as retractable and tunnel thrusters, the vessel will be fitted with a Kongsberg rim-drive azimuthing propulsion, which confers a significant reduction in noise. Its rotor is driven by stator windings at the rim, with a hub in the middle. This means that its blades, functionally, have no tips, eliminating the turbulent vortices widely understood to be the main cause of cavitation and noise.

The vessel is set to deliver next year. “At Armon, we have been deeply focused on developing solutions that significantly reduce emissions, and this vessel allows us to further demonstrate the expertise we have built in this critical area,” said Armon shipyard CEO Laudelino Alperi, at the time of the announcement. “While ambitious, we feel confident that our vast experience, coupled with our advanced facilities and skilled team, will enable us to deliver a vessel that sets new benchmarks for efficiency, sustainability, and innovation in the offshore wind industry.”