Weather forecast in the North Sea to support offshore wind farms

“The North Sea will be the biggest green energy hub in the world.” Declared the Prime Minister of Belgium, Alexander De Croo, during the summit in Ostend, on April 24 of this year.

At that event, nine European countries pledged to multiply the capacity of offshore wind farms in the North Sea by eight times current levels by 2050 - which means reaching a production of 300 GW!

The challenge is enormous, but this region has vast potential in energy generation. Currently, it is already the world's leading offshore wind power generator, with Europe accounting for 80% of global production, primarily in the North Sea, with around 2630 turbines already in place.

Sea and weather conditions such as wind and waves have a direct impact on these sites, from construction, power generation to maintenance of the entire infrastructure. Every company managing offshore wind operations needs to plan and execute frequent visits and maintenance on each turbine.

This is where sea and weather intelligence comes in to support planning and increase the safety and efficiency of operations.

With high accuracy hyperlocal forecasts on an intelligent platform it is possible:

1. Avoid cancelling vessel trips mid-journey,

2. Identify which turbines have safe conditions for maintenance work,

3. Facilitate daily decision-making.

Keep reading to learn more about wave conditions in the North Sea and their impact on operations at Vattenfall's DanTysk offshore wind farm. In addition, discover how the use of highly accurate wave forecasts can enhance capacity and bring significant benefits to this expanding sector.

From fossil fuel to Wind Energy

Vattenfall is one of the leading companies in the production of renewable energy and is present in most of northern Europe, with headquarters in Solna, Sweden.

Founded in 1909, the Swedish company has been treading a path of energy transition with a clear objective and in line with the commitments of the Paris Agreement: to allow a life free of fossil fuel within a generation.

Vattenfall currently operates more than 1,200 wind turbines with a total installed capacity of approximately 4.4 GW in five European countries.

The Dan Tysk offshore wind farm, located 70 km west of the island of Sylt and close to the Danish border, is one of the first large offshore wind farms built in the German North Sea. And the first to carry out a benefit study with the i4cast® sea and weather intelligence platform.

Impact of sea and weather conditions on offshore wind farms

There are two main operational challenges with respect to weather conditions in the management of offshore wind farms.

1. Navigation to the park. Which can be tens of kilometers from the coast.

2. Turbine maintenance. The distance between them varies around 1000 meters.

These operations involve a high cost with equipment, inputs and specialized labor, in addition to the safety of assets and, mainly, of the people involved.

In the case of the Dan Tysk offshore wind farm, waves with a height of more than 1.5 m make the transfer of technicians for turbine maintenance operations unsafe using a CTV (crew transfer vessel). Larger SOV (Service Operation Vessels) could be used in waves of up to 2.5m.

Wave conditions on the North Sea

Between December 17, 2022 and February 7, 2023, sensors installed in DanTysk recorded 639 occurrences of waves with a height greater than 1.5 meters and 331 occurrences of waves greater than 2.5 meters.

This finding demonstrates that operations were restricted for 76% of the time, and in 39% of the analyzed time, environmental conditions rendered operations risky.

These waves greater than 2.5 meters occurred distributed in 16 continuous events with waves higher than 2.5 meters, with a maximum duration of 87 hours (3.6 days) and a minimum of 3 hours.

In addition to the high frequency of high waves, an extreme event with waves up to 7 meters high was also recorded by the sensor in mid-January 2023.

Wave forecasting in the North Sea

During this period, i4cast® predicted 314 of the 331 occurrences of waves higher than 2.5 m recorded by the sensor, 6 hours in advance. The accuracy rate for waves exceeding 2.5 meters stood at 87% for a 6-hour forecast and consistently remained above 81% for a 24-hour forecast.

This value is 15% better than the accuracy achieved by the alternative globalforecast.

In terms of continuous events, i4cast® predicted 14 of the 16 actual events - 3 more than the global prediction, 6 hours ahead. Which means an improvement of almost 30% in comparison.

In practice, this means that i4cast® was able to predict a greater number of events and with more precision, as exemplified in the clipping below.

Comparable advantages were also attained for the Port of Açu, Santos Brasil, and the Rhine River.

Advantages of climate intelligence for offshore wind farm management.

Offshore wind farms in the North Sea demand a frequent flow of vessels in a region with intense environmental conditions and, therefore, a constant need for decision-making with a great impact on the safety of people and the use of resources.

High-resolution weather forecasts on an intuitive and personalized platform for daily decision-making yield time and resource savings, while boosting safety and operational efficiency. In the words of Simon Jury, marine forecasting specialist at Vattenfall:

‘Due to model resolution, ‘traditional’ lower resolution weather forecasts will never be able to fully describe the wave height variations across an offshore wind farm, due to changes in bathymetry, the effects of site infrastructure and complex surrounding coastlines. The use of a hyperlocal forecast model will account for this and allow us to predict conditions at each turbine location, showing us which areas of the site are suitable for operations and which aren’t. Also, when coupled with wave height observations from 2 or more sources, the model can provide a pseudo real-time wave height map of the site. This would be a step change in forecast performance, improving safety, limiting the need for multiple wave sensors across the site as well as reducing vessel operating costs.’ - Simon Jury, Marine Forecasting Specialist, Vattenfall.

This holds true for both the maintenance of Vattenfall's DanTysk wind farm and for the many others that are yet to come by 2050.