Wave heights pose risks for floating firms

Floating offshore wind has reached an inflection point in its global growth. Just look at the 15GW of floating projects in last week’s ScotWind tender.

With a global development pipeline of floating wind projects now approaching 54GW, according to RenewableUK, it is clear the wind sector wants to access the stronger and more consistent winds that are outside of the reach of fixed-bottom structures.

But as developers move closer to deployment, research firm Aegir Insights has warned the industry that the ‘metocean’ conditions – the combination of wind, waves, and climate – could critically impact project installation and operation. Bigger waves in some parts of the world could pose challenges for projects and hurt profitability.

This is the subject of Aegir research project ‘Big Float’, which benchmarks the 40 most cost-competitive sites for floating offshore wind over a six-month period based on wave heights and wind speeds.

It aims to help developers and investors to better understand the technical and commercial pressures that they will face as they seek to take advantage of floating wind technology in future projects.

A Word About Wind spoke to Scott Urquhart, CEO of Aegir Insights, to find out how wave conditions could affect installations of floating offshore wind farms, and the steps that developers could take to mitigate this risk.

Prominent regions

Aegir data shows there is a general correlation between wind and wave conditions (see graph below). This is to be expected given that stronger winds tend to correlate with bigger waves. Windier sites may be more attractive but also more challenging.

Several key floating markets, such as Scotland, Ireland, and the west coast of the US, have very high wind speeds, which are great for generating power, but also severe wave conditions that can make installation and operations difficult.

In much the same way as offshore wind companies have had to deal with ‘weather windows’ to dictate when they can install, they will also need to understand ‘wave windows’. These are the periods where waves are smaller and installation is easier.

In addition, the graph reveals regions off the coast of China, as well as parts of the North Sea and Celtic Sea, that have very strong winds and benign waves. This makes them amongst the most competitive locations for floating wind globally. This is one reason floating projects did so well in ScotWind.

Furthermore, breaking down the monthly wave height variability of different regions suggests some will face major installation challenges.

The Humboldt area off the US west coast sees waves higher than two metres for 11 out of 12 months annually. Installing is significantly more challenging in waves of two metres or higher, because this makes it more difficult to install using conventional anchor handle vessels.

Other areas including Morro Bay and Oregon, and some locations in Ireland and New Zealand, also have annual installation windows of just three months.

“The fundamental challenge when it comes to gigawatt-sized projects is whether we can do year-round installation, like we are able to do for fixed bottom. If we can only work in the three summer months, then the floating sector will not be competitive,” said Urquhart.

Potential solutions

Urquhart said this analysis should help prompt companies to think about potential installation issues when they are commercialising floating wind technology. He explained many firms do not feel these challenges are being addressed and regional adaption is going to be needed where site conditions differ from existing demonstration projects.

Given that some sites will have limited accessibility throughout the year, he suggests that the selection of construction and O&M ports could be key to achievable projects: “It’s about minimising the time you need to be out there,” he says.

This includes finding ways to make it faster for vessels to connect and disconnect at sea, and by using single-point anchored floating turbines rather than three-point anchored turbines. Floating dry docks are an option too.

Based on today’s standard capabilities, the floating offshore wind industry must develop logistics solutions capable of operating in harsher metocean conditions if ambitious targets are to be achieved. That could be bigger vessels or other innovative solutions to speed up deployments. At this crucial point in floating wind’s growth, all sensible options must be considered.