StormGeo Assists Construction and Maintenance of Offshore Wind Farms

Building and maintaining an offshore wind farm requires extremely accurate predictions of the weather windows available for each operation.

Navigating a specially built vessel with a wind-sensitive load of turbine parts on its deck, jagging up the vessel to prepare for turbine installation, positioning and fastening turbine foundations, towers and rotors, and accessing turbines from helicopters or small crew boats are all operations that rmake great demands on weather, waves and currents – and therefore on the weather forecasts.

Offshore Wind Farm Nordsee Ost

Morten Milthers of Wind and Water Maritime Consultants puts it like this:

“Based on 10 years” experience with more than 15 offshore wind farms, I can only emphasize the importance of getting the best possible weather forecasts and the best possible wind & wave data. Forecasts and recorded data are essential tools for optimizing construction, avoiding costly delays and ensuring the safety of personnel working on vessels and turbines.”

Milthers is heading the marine co-ordination team at Nordsee Ost, an offshore wind project owned and managed by German energy giant RWE. Based on the weather forecasts provided by StormGeo and the support delivered by StormGeo”s forecasters over the phone, Milthers and his people guide the vessels and working teams, so that the weather windows for the construction work can be utilized in the most efficient way, without putting people or equipment at risk.

 Further and further Offshore

The Nordsee Ost wind farm site is located in open waters in the German Bight, more than 110 km, or 60 nautical miles, away from the base port of Bremerhaven. The long distance from the port to the site means that an installation cycle can easily take more than a week to complete, depending on the weather conditions. This makes good long-term predictions of the weather windows very important. As Milthers says,

”With the next generation of wind farms being built further and further offshore, route planning and forecasts for critical installation weather windows as well as for everyday work are crucial.”

Offshore weather and wave forecasting is of course nothing new to StormGeo. From the very first day, more than 15 years ago, StormGeo has been delivering daily metocean forecasts and warnings to offshore oil and gas operators in the North Sea, and today StormGeo provides these services for clients all around the globe, from the Greenland Sea to the waters of Indonesia.

What is different in offshore wind, however, are the tolerances. Typical oil and gas installations and vessels are built to withstand much higher winds and waves than those that limit the sensitive operations involved in constructing and maintaining wind farms offshore.

 Offshore Wind Farm Gwynt y Môr

Although a large distance to shore is a challenge, for most offshore wind farms built so far it is actually the other way round – it is the closeness to shore that presents the greatest challenges for weather forecasters and marine workers. A second RWE site, the Gwynt y Môr, can serve as an example:

Gwynt y Môr is located in the Liverpool Bay, only about 15 km (8 nautical miles) from shore and a few hours” sailing trip from the port of discharge, Birkenhead near Liverpool. This is an area where several offshore wind farms are already in operation, including RWE”s own wind farms North Hoyle and Rhyl Flats.

Although weather conditions are generally not as rough here as further offshore, complex local wind and wave patterns can develop along the coast, making forecasting difficult. The North coast of Wales and the island of Anglesey have a pretty steep coastline, and it can make all the difference for the wind and waves whether or not the site is in lee of the coast. As long as the wind is southerly or southwesterly, the site is in the lee and no high waves will develop. However, if the wind turns slightly towards the west, the wind will pick up, while at the same time the distance that the wind travels over water before reaching the site, known as the “fetch”, will become much larger, meaning that higher waves will develop.

On other sites, particularly those that are located in river mouths or areas with high tidal variations, it is the current that – in combination with the waves – poses the greatest forecasting challenges. An example of this is the London Array wind farm, where rapidly changing sea-bed conditions due to moving sandbanks are an additional, complicating factor.

 Forecasting in British, German, and Norwegian waters

At StormGeo, all forcasting for offshore wind farms is handled by our metocean forecasting team in Aberdeen. At present, this means forecasting for 10 offshore wind farm sites in British, German, and Norwegian waters, four times a day. The forecasters have built up considerable experience in how to meet the special requirements of offshore wind, and forecasting tools and services are constantly developing in response to the needs of the offshore wind industry.

One service that has been developed especially to help marine co-ordinators like Milthers, as well as construction managers and captains working in offshore wind, is the short routing service, which was developed and put into operation last Autumn for the Nordsee Ost and Gwynt y Môr projects. With this new, on-line interactive tool, the user can enter the expected start time and vessel speed for a given sailing route, and the tool will then return a forecast of the conditions along the route, displayed in a table or graph. Compared to before, where users had to compare several different forecasts for locations and waypoints, and from those deduce the conditions along the route, this new tool makes route planning much more efficient and less prone to errors.

 StormGeo is playing a small yet essential part in offshore wind

Although good weather and wave models, robust IT systems, and reliable communication links are indispensable for delivering a good forecasting service, no computer can replace an experienced and knowledgeable forecaster when it comes to providing the necessary support for offshore wind operations. Milthers describes the needs of good advisory personnel like this:

”An experienced forecaster must be available 24/7 to assist Marine Coordinators and construction managers with evaluating the credibility of forecasts, and the site office must have experienced marine coordinators to ensure that relevant weather data is assessed, handled professionally and communicated to vessels offshore.”

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Offshore Nieuws  Staff, March 30, 2012; Image:  StormGeo