Designing a ship that harvests energy at sea
Offshore wind, tidal power and wave energy are familiar parts of the renewable-energy landscape. Now a new concept has emerged – autonomous energy-harvesting ships, designed to sail into the open ocean, harvest energy from the wind and return carrying green fuel.
At first glance, DRIFT Energy’s vessels resemble catamarans fitted with modern fixed-wing sails. A closer look reveals the equipment that makes them something quite different.
“Fundamentally, it’s a sailing or wind-powered ship, but it’s got far more sails than you would normally need on a vessel of its size,” says Mike Mackay, Head of Vessel Design at DRIFT Energy, a UK-based marine tech start-up. “It’s like a Mini Cooper with a V8 engine on board.”
That extra sail power allows the vessel to accelerate and build kinetic energy as it follows favourable winds across the deep ocean. Once it is moving at speed, turbines beneath the hull begin generating electricity.
The turbines are essentially propellers working in reverse. “They open up, they feather out, they start dragging through the water. and generate electrical energy, very much like how a tidal turbine works,” Mackay explains.
At sea, the electricity must be converted into a storable form. Seawater is desalinated before an onboard electrolyser converts it into hydrogen, which is then compressed into cylinders and carried back to shore. There, says Mackay, “it’s a simple low-level cranage offload onto the quayside and then straight onto a lorry or connected directly to the end user.”
“It’s a very large integration challenge,” says Mackay. “We’re bringing in lots of technologies and putting them together on a relatively small platform.” Rather than redesigning every element, much of the vessel relies on “off-the-shelf, proven componentry, just working in a novel way.”
DRIFT’s Goldilocks routing algorithm also plays a role in bringing those elements together. “The routing algorithm allows the vessel to sit in the Goldilocks zone of weather – not too high, not too low,” says Mackay. “That allows it to spend the perfect amount of time in the perfect weather.”
The algorithm also times the vessel’s return so that it reaches port as its fuel tank becomes full. Otherwise, Mackay explains, it could be “sat in the middle of the ocean with a full tank of fuel”.
Creating a new class of ship
Creating any new vessel brings design challenges, but DRIFT faced a unique challenge: fitting an energy-harvesting ship into existing classifications.
“Ship types cover cargo vessels, fuel tankers and fishing boats. Our vessel didn’t fit into any of those,” says Mackay. “It does carry cargo, but it makes its own fuel. So, a whole new ship type means a whole new frontier.”
DRIFT recently received approval in principle from classification society RINA.
“There are no rules that cover energy harvesting vessels specifically, so we have to make our own way through this,” says MacKay. “RINA has really shown themselves to be leaning in and helping us get through this work whilst keeping us in line and making sure we produce something that is safe and ultimately will work.”
Built to adapt and scale
Although the first vessel is being designed to produce gaseous hydrogen, DRIFT sees it as a modular energy platform. Future versions could produce ammonia or methanol, or store energy in batteries. Vessel size could also be adapted to balance generating capacity and efficiency.
The way energy is delivered ashore could evolve too. The first vessel will offload hydrogen in standard tube-trailer containers, but future versions could connect directly to dedicated bunkering infrastructure as alternative-fuel systems become more widespread.
“It’s about making more energy, making it greener, and making it cost competitive,” explains Mackay. “If we always maintain the energy-harvesting ship to slot into known shipbuilding technologies and known fabrication facilities, we have an ability to scale like never before.”
The company recently entered into an exclusive strategic framework with Commenda Capital Partners to support the commercial deployment of at least 50 DRIFT vessels, targeting more than US$500 million of investment.
Image credit: Drift Energy
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