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Dag Christensen was the first with the idea of a floating wind turbine. Knut Solberg was in the right place at the right time — and turned his idea into reality. Hywind is the result.

The best ideas often happen when you least expect them—and when you’re not at the office.

Read the full story on how Hywind was born below.

The brainwave that became the Hywind floating turbine

Two becalmed sailors started to doodle on the back of a napkin – and had a brainwave. Today, nearly 20 years later, those strokes of genius have been transformed into a technology that is virtually synonymous with floating wind turbines: Hywind.

We went sailing with the inventors behind Hywind to discover how they came up with the concept — a design that is at the heart of the recently opened wind farm, Hywind Tampen, the largest floating wind farm in the world.

“There’s always a calm in the middle of the night of the Færder race,” says Dag Christensen from the cockpit of his sailing boat. He has often participated in this famous Norwegian regatta, held in the Oslo fjord every year in June, and infamous for its light airs and challenging conditions.

And on this occasion, over two decades ago, he had brought friend, colleague and equally keen sailor Knut Solberg along on the voyage for company.

“Was it one of those occasions when the secret to winning was to drop anchor to avoid drifting backwards out of the fjord?” we teased him.

“Well, there’s no guarantee that you’ll win, but at least you don’t come last,” laughs Solberg.

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I was looking at a floating marker buoy on the water, and I thought—if we could make one of those 100 metres high instead of four metres, we’d have a tower for a wind turbine.

Dag ChristensenSenior engineer, retired
Hywind grunder Dag Christensen

Now retired, both these former senior engineers had competed many times in the regatta, usually in separate boats. But on this occasion, for once sailing together, the calm night gave Dag room for new thoughts.

“I had started working on Hydro’s wind power projects. And I was sitting looking at a floating marker buoy on the water, and thought to myself—if we just made one of those 100 metres high instead of four metres, we’d have a tower for a wind turbine,” he says.

Back in the canteen in Oslo, Dag and Knut started talking. The year was 2001.

“If you get an idea that’s vaguely in the direction of what you work on, it’s only natural to share it with somebody. It’s not any more mysterious than that,” says Dag modestly.

If you installed one wind turbine per square kilometre in an area of 70 km x 70 km, you could double Norway’s power production.

Knut Solberg Senior engineer, retired
Knut Solberg

“But if Knut hadn’t been there, nothing would have come of it. There are people who have ideas, and there are doers. Knut was the implementer. He’s a bit of a Heath Robinson.”

“We sketched it on a serviette, right there and then,” says Knut. “I drew a couple of solutions with a tension leg floater. Then I got hold of the wind data for the Frigg field, and it suddenly struck me that Norway really was a superpower in terms of wind.”

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“To put it in context, if you put one wind turbine per square kilometre in an area 70 km x 70 km, you could double Norway’s power production,” he says.

They applied for—and were granted—NOK 300,000 which they spent on a study by Aker Solutions. And the answer that came back was positive—this was worth considering. In the next budget year, they applied for NOK 3 million—and got it.

So, someone was willing to invest money in this?
“That’s one of the advantages of companies like Hydro and Equinor; there’s freedom with responsibility. People appreciate initiative. That opens doors,” says Dag, who is grateful to his managers at the time for recognising the project’s potential and championing their cause internally.

The project entered a new phase. Through a technology forum, the R&D centre in Bergen—now part of Equinor, after the merger—took over the reins. Could they carry out a feasibility study on wind turbines at sea?

Senior researchers Finn Gunnar Nielsen (right) and Tor David Hanson.
Researchers Finn Gunnar Nielsen (right) and Tor David Hanson had to solve challenging mathematical modelling tasks for Hywind.
Photo: Colin Dobinson

Senior researchers Finn Gunnar Nielsen, Tor David Hanson and Dagfinn Sveen brought Hywind to the prototype stage. Finn Gunnar Nielsen explains:

“We brainstormed together about how such a construction would look, and how it would behave dynamically, how the interaction between a wind turbine under load from the wind would behave in conjunction with a floating structure under load from waves and currents. It was very challenging. Tor worked the whole time on the computations, while Dagfinn worked on the design and details. Combining analyses and design we came up with Hywind as it appears today. It all looks terribly simple, but it’s a simple structure with complicated dynamics.”

But doesn’t Equinor have extensive experience with floating offshore constructions?
“Yes, there’s a lot from the offshore industry that technically speaking could have been used, but the problem was to make the whole thing pay based on the price of electricity alone. You can forget all about expensive solutions, you have to make it simple.”

So, this was pioneering work. No one had previously attempted to model the kinds of dynamics you get with a slender cylinder with a wind turbine atop. It all culminated in a series of successful experiments in a test tank in Trondheim in November 2005. That paved the way for the full-scale prototype built in Finland — and towed to Karmøy for trials offshore in 2009.

“Technically speaking the biggest challenge was to get this construction to last for 20 years, since fatigue is the big problem here,” says Tor David Hanson. The stresses on the vast construction are enormous; the rotors alone are 82 metres long.

The Hywind Demo project completed eight years of flawless operation off Karmøy in 2017, proving that the design concept performed satisfactorily in all wind and wave conditions. Hywind Scotland is the first full-scale commercial wind farm built on Hywind technology, and opened in October 2017.

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