If you’ve ever plugged an EV into a highway fast charger, you already know the routine. You park, you wrestle a heavy cable into a port that isn’t going anywhere, and you go buy a coffee you didn’t really want. Nobody expects the car to drift sideways halfway through the session.<\/p>\n
Now try doing that with a ship. In open water. Next to a wind turbine.<\/p>\n
That’s the problem a Danish company called Stillstrom has been chewing on since 2019, and on November 3 it said it had finished building and testing the piece that goes on the ship. Stillstrom calls it the Vessel Container Unit, or VCU. It’s basically a high-voltage socket for boats, and it lives in its own container so it can be bolted onto a vessel instead of being built into the hull.<\/p>\n
DNV was there to witness the testing. If that name means nothing to you, DNV is a classification society, which is a private inspector that writes a lot of the safety rules ships are built to and then checks whether the builder actually followed them. Having one watch your test doesn’t mean the product is certified for work at sea. It does mean someone other than the company was standing there with a clipboard.<\/p>\n
The boats Stillstrom has in mind are service operation vessels, or SOVs. Think of them as floating hotels for wind turbine technicians. They stay out at an offshore wind farm for long stretches, get those crews onto the turbines and back again. Traditionally, they’ve run on marine gas oil, which is essentially diesel.<\/p>\n
That’s a slightly awkward look for an industry that sells clean electricity. Stillstrom points to a joint study with ScottishPower Renewables that puts SOV operations at somewhere around 15 to 20% of the greenhouse gas emissions over an offshore wind farm’s whole life. So the obvious fix is to give these ships big batteries and top them up from the turbines they’re already parked next to. Obvious on paper, anyway.<\/p>\n
Stillstrom is a Maersk company. It started in 2019 as an innovation project inside the shipping giant, became its own business in 2022, and now has more than 30 people split between Copenhagen and Aberdeen, Scotland, working mostly on the UK and European wind markets. Those waters are getting busy, too. (Here’s what happened when hundreds of Dutch offshore turbines were slowed down for birds<\/a>.)<\/p>\n According to Stillstrom’s announcement<\/a>, the VCU reels in a high-voltage cable that drops down from the turbine, then clamps it into an 11,000-volt connector package. A funnel built into the unit guides the cable in. That funnel is what lets the ship point whichever way suits the weather while it charges, instead of being forced to hold one exact position relative to the turbine.<\/p>\n The person in charge of all this is the dynamic positioning operator. Dynamic positioning, or DP, is how a ship stays parked in open water without dropping an anchor. A computer fires the thrusters over and over to cancel out wind, waves and current, so the ship holds roughly the same spot. Roughly is doing a lot of work in that sentence, though. A ship on DP is always shuffling around a little, which means the cable has to cope with a socket that never quite sits still.<\/p>\n Stillstrom says the DP operator is the one running both the hookup and the disconnect. The unit also has a control system and what the company calls integrated safety interlocks. An interlock is just a rule baked into the hardware: one thing can’t happen until another thing has been confirmed. Your microwave won’t run with the door open for the same reason. Given what 11,000 volts can do to a deckhand, I’d frankly rank the interlocks as the most important thing in the box.<\/p>\n The cable side got its own workout in August. Stillstrom ran a trial at a Semco Maritime yard in the Danish port of Esbjerg, with the vessel operator ESVAGT and a ship holding position on DP. A connector dropped from about 51 feet up, roughly the height it’d hang from a turbine or substation, and a reel on a tower held about 410 feet of cable. As the ship backed off, the system paid out more cable on its own. As it came back, it reeled the slack in. DNV witnessed that test too.<\/p>\n Fair question. Stillstrom hasn’t said.<\/p>\n And this is where it’s easy to get fooled by a big number. Voltage is basically electrical pressure. Power, measured in kilowatts or megawatts, is how much electricity actually flows through the wire, and power is what decides how quickly a battery fills up. Your house runs on 120 and 240 volts, and that tells you nothing about how long your EV takes to charge in the garage.<\/p>\n The closest thing we’ve got is Stillstrom’s bigger plan. On October 27, it announced that the EU’s Innovation Fund had picked it to build and install its first commercial offshore charging station<\/a> for battery-powered SOVs, and the company describes that system as an 8-megawatt charger. That’s a rating for the whole charging system, though, not a figure Stillstrom has attached to the unit it just tested. The company hasn’t put a charging time on any of this, and I’m not going to invent one.<\/p>\n It also hasn’t published how big the VCU’s container is or how much it weighs. For something designed to be bolted onto a working ship, you’d think that’d be near the top of the spec sheet, so hopefully it shows up before anyone starts measuring their decks.<\/p>\n Stillstrom says the VCU can go up front at the bow, back at the stern, or below deck, and it can be fitted to new ships or added to existing ones. It can even be shifted between ships, as long as the second ship already has the right cabling on board. That condition is a big one. The box is the socket, not the battery, so you can’t just swap it onto any old diesel boat and call it electric.<\/p>\n Still, I think the retrofit angle is arguably the smartest thing about the design. Ships stick around for decades, and an operator that can add charging to a vessel it already owns is going to be a lot easier to sell than one that has to order a whole new ship. Stillstrom also says it’s already working on a Mark 2 version that takes today’s partly manual alignment and makes it fully automatic, which tells you the current version still leans on a human for part of the lineup.<\/p>\n A factory acceptance test is the manufacturer proving that a piece of equipment does what the spec says, on land, before it ships. It’s a real milestone. It’s also done on a floor that doesn’t roll.<\/p>\n The bigger catch is that the VCU is only half of the plug. The other half sits on the wind farm, and Stillstrom says work on that turbine-side interface is still in progress. Semco Maritime also has a letter of intent from Stillstrom, signed in September, to build a local equipment room, which is a container holding the transformer and medium-voltage switchgear that step the wind farm’s power down and route it to the ship. Offshore Wind reports<\/a> that the first unit is set to be built at Semco’s Esbjerg facility, with completion targeted for next spring.<\/p>\n Graeme Wood, managing director of Stillstrom UK, said in the company’s statement that for vessel operators, “charging at sea is no longer a concept.” I’d say that’s a pretty confident line for a system whose wind farm half isn’t finished yet. To be fair to Wood, the hardware on the ship side does exist now, and DNV watched the critical steps. But until a ship actually takes power from a turbine in real weather, I’d call it a well-tested socket waiting for its other half.<\/p>\n Then there’s the “world’s first” label, which Stillstrom put right in the headline of its press release. Stillstrom’s specific claim is about an 11,000-volt interface unit on the vessel, and it may well be first at that. But it isn’t the first company to chase offshore vessel charging. A couple of summers ago, the Belgian wind developer Parkwind and the British firm MJR Power & Automation said a system on a substation at the Nobelwind farm off Belgium had shown it could pass power from the turbines to ships, according to Marine Insight. Other players, including Norway’s Seaonics, are working on their own takes. So it’s a crowded race, and “first” depends a lot on how you word it.<\/p>\n People keep coming up with creative ways to power things offshore, from wind turbines to radioactive seabed batteries for underwater drones<\/a>. Stillstrom’s approach is a lot more down to earth by comparison. It’s a plug, a long cable and a ship that holds still-ish.<\/p>\n If everything stays on schedule, Stillstrom says the full charging system should be out at sea for longer offshore trials by next summer, and Wood expects the whole end-to-end setup to be ready for real work offshore by the middle of next year.<\/p>\n","protected":false},"excerpt":{"rendered":" If you’ve ever plugged an EV into a highway fast charger, you already know the routine. You park, you wrestle … <\/p>\nSo what does the box actually do?<\/h2>\n
11,000 volts sounds like a lot. How fast does it charge?<\/h2>\n
You can bolt it onto a ship that already exists<\/h2>\n
So is it ready to charge ships at sea?<\/h2>\n