Floating vertical axis wind turbines (VAWTs) – designed with blades that are set at angles to the tower rather than upright as on the vast majority of industrial models turning today – have long been heralded by many in the offshore engineering community as key to harnessing the vast, high-velocity wind resource streaming over the world’s deep waters in the years ahead.
Despite clear design advantages over conventional three-bladed versions, including having no gearing or cooling systems and mass-manufacturability, lower-cost and more durable rotors, and generators built in at water-level instead of high above in the nacelle to add stability and make for easy maintenance and repair access during operation, VAWTs have so far failed to crack the market, with only a few models in active development today (see panel below).
Norwegian technology developer World Wide Wind (WWW) thinks it has solved the commercial impasse with one word: contra-rotation. The Oslo-based start-up says its eye-catching design, which features two omnidirectional rotors spaced apart on a tower-spar structure all anchored with a novel turret-shaped mooring system to the seafloor, could be a game-changer for the sector, deflecting away “destructive levels of torque and vibration” – and slashing floating wind’s levellised cost of energy (LCOE) to €50/MWh ($49.85) from current levels over 2.5-times higher.
Stian Valentin Knutsen, the founder of WWW, who along with chief technology officer Hans Bernhoff devised the innovative contra-rotating vertical turbine (CVRT) design, enthuses to Recharge: “We believe this could be floating wind’s ‘Tesla moment’.”
“There has been a lot of head-scratching over the last ten years on floating wind but no solution [to commercialising it] today,” he tells Recharge, “and we think the current path will not solve it either, that is, to get the technology to a LCOE that will be competitive [on future power markets].”
WWW’s contra-rotating design, which it reckons could be scaled up to a giant 40MW nameplate model, is engineered to neutralise torque on the tower – a well-recognised show-stopper for VAWTs – and because both the concept’s stator and rotors turn at once, it has made it possible to use a “simpler, lighter, and less expensive generator” while “getting two turbine’s output merged into one”.
“Representing a design without a legacy, a more integrated design can also be made from the start, specifically for floating, to further improve costs,” Knutsen adds, pointing to the collaborative environment among partners including Norwegian R&D outfits Sintef and North Wind, Uppsala University and classification body DNV that has informed the project so far.
CEO Trond Lutdal states: “The battle [of industrialising wind] is offshore, in 60 metres [of water] and deeper, so you need floating structures. [Our concept] moves away from the complexity of three-bladed technology which was designed for land or at best fixed [offshore] foundations – I mean, no one was thinking floating when they designed the first windmill-type turbines – and resolves many of the issues around scaling, which is key to cutting cost.”
The slender-profiled CRVT, which tilts in the water with the wind, “part vertical and horizontal axis”, he notes, also has “much lower” wake effect [the turbulence created as wind moves through a rotor-star] than three-bladers, meaning a developer could “halve the distance between turbines on a wind farm, which is super-important for efficiency in capturing wind in a project site area”.
“Four times as many turbines of our design [than conventional models] could be installed on an area – Utsira Nord [one of two zones being opened to offshore wind development by the Norwegian government], for example, could be 6GW not 1.5GW [the current capacity cap].”
Lutdal adds: “People talk about the profitability of floating wind and it soon becoming competitive [with bottom-fixed offshore]… but there is a step-change needed in the technology to really answer the ‘how’.”
A very big part of the ‘how’ in fact has nothing directly to do with the turbine concept, but instead the birthplace of WWW’s design – and the Nordic nation’s maritime industrial heritage.
“Norway has a fantastic point of departure [into the floating wind sector] given our maritime and oil & gas history, our technologically advanced industrial culture, a strong tradition of public-private partnership – and, of course, our great offshore wind resources,” says Lutdal.
Despite these native advantages – and numerous market reports highlighting the industrial transformation potential – the offshore wind sector off Norway still consists of only two units: the Hywind Demo deployed by Equinor in 2009 and since remodelled as an R&D centre called Zephyros, and the Stiesdal TetraFloat now in sea-trials backed by Shell, RWE and Tepco, both off which are installed of the West Coast at the Met-Centre testing site.
Research analysts Menon Economics calculated recently that a domestic floating wind market would create 50,000 jobs and over $10bn in annual turnover but continued to be delayed by lack of clarity of “concrete ambitions” from government.
Norway has since set its first long-term offshore wind target with an ambition to unlock acreage for 30GW of capacity by 2040, to build on the 4.5GW of fixed and floating demonstration projects that are expected to be developed as part of its flagship auction round.
“Looking today at floating wind from a historical vantage point, we could say [in Norway], “We’ve done it before, from the 1970s in offshore oil & gas, but for many, many years before than in maritime. And I think people in our country are beginning to see the dignity of the potential of floating wind. That’s the macro,” says Lutdal.
“From the market standpoint, we have the offshore technology development knowledge, the people and the skillsets to solve complex industrial problems. And the political climate is changing [in favour of offshore wind].
“I can’t speak for [Norway’s] government but I believe we are finally ready to make serious effort to [accelerate the sector’s development].”
Next-gen innovation in sustainability
Next-generation innovation runs in the veins of the WWW concept, with lower-cost materials for the tower and foundation – aluminium over steel – and recycled fiberglass over new-use fiberglass and carbon for the blades – “factored in” to coming designs.
“There are on first inspection five or six areas where we can see real opportunities for greater sustainability in the CRVT than with horizontal axis turbines,” says Lutdal.
Moving forward WWW aims to accelerate development of the technology with “rapid prototyping” to get up to a 3MW model by 2026 of the CRVT and then make the leap to the giant 40MW design by 2029, “spinning off designs for a range of offshore applications along the way”, including deepwater charging stations, renewables-powered aquaculture and green hydrogen generation.
“The time is right for this technology to be tested out,” says Lutdal. “Five years ago, I don’t think it would have flown. But with the energy crisis in Europe, the energy transition globally, the absence – to our minds – of a solution for floating that will really make a fundamental difference to its economics, we are at the pivot point.”
Vertical axis wind turbine (VAWT) designs have long been seen to hold untapped promise, with experimental models having undergone development and trials in onshore settings, and several high profile pilot units, including French contractor Technip’s Vertiwind, WPL’s Aerogenerator, and a concept collaboration between EDF and Nenuphar, but none reaching commercialisation.
The US government, through its Atlantis technology development programme is underwriting an up-to-15MW concept hatched at the University of Texas at Dallas, but Sweden’s SeaTwirl stands alone currently among commercial-scale VAWT designs heading for the water.
A study published by Oxford Brookes University in the UK last year concluded VAWTs would “outcompete” the mainstream models now being built in their thousands for projects around the world.
The research, based on more than 11,500 hours of computer simulation, found that VAWTs – which fly angled, upright blades around a rotor shaft turning a direct-drive transmission – would be “far more efficient” than traditional turbines for industrial-scale wind farms, and when installed “in pairs” would up each other’s performance “by up to 15%” more.