An idea that's worth floating

Across the North Sea from Scotland to Norway, clusters of giant wind turbines generate abundant clean power for northwest Europe. Worldwide, however, offshore wind is rare because most oceans are too deep for turbines to be drilled into the sea floor. If the industry is to go global turbines must float on the sea surface instead. Fifteen years after such a wind farm was first trialled off the coast of Italy, investment from energy companies finally appears set to take the technology mainstream.

Since Denmark built the first offshore wind farm in 1991 this corner of the renewables industry has developed with the shallow depth of the North Sea in mind. Turbines are constructed onshore and then towed into place where supports, up to 60m in length, are drilled into the seabed.

Most oceans and seas, however, are far deeper than 60m, meaning 80 per cent of offshore wind energy resources simply cannot be tapped by these so-called fixed-bottom turbines, according to Wind Europe.¹ Offshore turbines have barely spread beyond Europe and at the end of 2017 countries bordering the North Sea were still responsible for 82 per cent of global offshore wind capacity.²

Even in the European core of the industry, offshore wind is expensive. Each fixed-bottom turbine must be constructed to match the needs of the specific seabed on which it will sit. Detailed and costly surveys are required to develop bespoke specifications, while the complex installation process requires vessels that cost between GBP350,000 and GBP500,000 to hire out per day.

“If you get out there and suddenly have three days of bad weather, that's a million pounds down,” notes Steven Jermy, the CEO of Celtic Sea Power, an offshore wind energy company.

The combination of a small local market, high costs and bespoke products that cannot be mass produced have all limited the attraction of offshore wind.

A floating future

At current rates of installation, the Global Wind Energy Council (GWEC) forecasts that by 2030 the world will have less than two-thirds of the wind energy capacity required to prevent temperatures rising beyond 1.5°C of pre-industrial levels, a key target for the Intergovernmental Panel on Climate Change.³ That makes installing additional capacity essential.

Currently just 7 per cent of global wind energy capacity is offshore, according to GWEC, reflecting the comparative ease of securing onshore wind turbines on land. Installing floating turbines in the world’s seas has the potential to significantly grow global wind capacity.

The world's first floating wind turbine was installed off the coast of Italy in 2007.  Rather than drilling a base into the floor, it was kept in place by anchors. This takes the nature of the seabed out of the equation, meaning it should be possible to manufacture floating turbines in bulk.

“The surface of any sea is always the same,” notes Jermy from Celtic Sea Power, which is seeking to develop floating turbines. “That means if your turbine has a floating foundation, you can mass produce it because it’s always the same.”

The potential repeatability of floating turbine manufacture has made them theoretically attractive since the 1970s, when the technology was first theorised at the University of Massachusetts, Amherst.  However progress was painstakingly slow because researchers needed to show that floating turbines could withstand heavy waves for many years, allowing investment to be recouped over a long period.

The first turbines off Italy were designed only as a six month proof of concept before being decommissioned, but that was enough for Equinor, Norway’s state-owned oil company, to gamble on developing Hywind, the world’s first commercial floating wind farm in the North Sea in 2009.  Equinor operated the facility for 10 years proving floating turbines could be durable and when it sold the facility in 2019, investors also saw an exit was possible.

Since then several floating turbine projects have received private investment in Europe, including one off the coast of Portugal moving the industry beyond the North Sea for the first time.  Global manufacturing and energy companies have begun to invest in the technology, fuelling further innovation. Last year Bechtel, the largest construction company in the US, launched an offshore wind pilot project in the UK, while General Motors led the Series A funding round for Wind Catching Systems, a Norwegian start-up.

Wind Catching Systems’ innovation has been to stack large numbers of smaller turbines on top of each other, rather than having a single giant turbine. The design means that a single floating platform can sweep twice the area of a traditional turbine while the high number of rotors further multiplies the power generated. The small rotors can also be repaired by maintenance teams in situ, rather than being towed back to shore, reducing costs.

The renewables arms of utility companies and oil majors are also entering the fray. In the UK the recent ScotWind auction saw BP and Royal Dutch Shell win the right to develop wind farms off the coast of Scotland. “We’re beginning to see companies that have both the balance sheets and the technology enter the industry and that is very encouraging,” says Ole Heggheim, Wind Catching Systems CEO.

New markets

While commercial floating wind farms only exist in Europe so far, the big prize is to export the technology to other markets. In 2013 the US Department of Energy funded the first trial of floating turbines outside Europe off the coast of Maine, Equinor is exploring a floating farm off the coast of South Korea, and Celtic Sea Energy say deep waters off the US West Coast and around Japan are now viable for floating turbines.

Wind Catching Systems is also interested in markets outside Europe. “If you've got a floating foundation, then it's much simpler to build new projects, because you can put turbines in whatever depth of water you want,” says Heggheim from Wind Catching Systems.

In a sign of how quickly the offshore wind industry can grow as large power markets are opened, China was responsible for 80 per cent of capacity added globally in 2021, according to GWEC⁴ and now leads the world for offshore wind capacity, according to the World Offshore Wind Forum.⁵ So far it has only built fixed-bottom turbines in the shallow waters off its east coast, but floating turbines would open up much more of its coastline.

Challenges to expansion remain. As they can be positioned further into the ocean, floating turbines may disrupt previously unspoilt ocean habitat, for example trapping fish or large ocean mammals in their cables. Deep-ocean-based maintenance also poses safety risks and could prove costly if vessels are repeatedly called out. Installing and maintaining floating turbines far offshore may also become harder as extreme weather events increase in frequency and intensity thanks to climate change. An offshore wind installation vessel recently sank off the coast of China’s Guangdong Province during a typhoon, for example.

Nevertheless with investment flowing into R&D to overcome these hurdles, an industry that for decades has been a European affair may finally be going global with huge benefits for renewable energy generation.

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