The 120 MW Q7 windfarm was built by Econcern and opened in 2008 when it was renamed Princess Amalia in honour of the five year old daughter of the heir to the Dutch throne. But in 2009 Econcern was declared bankrupt, putting in jeopardy the development of Amalia’s sister project Bligh Bank. In the event Dutch utility Eneco bought some Econcern divisions (but not Bligh Bank which was ring-fenced by the administator) and secured the backing of the Danish credit agency EKF, and with it new financing for the €610 million facility which is now being built. Danish wind turbine manufacturer Vestas is initially supplying 165 MW of turbines for Belwind NV, a company formed initially by Econcern’s development arm Evelop and now owned by a consortium of Belgian and Dutch investors, specifically to develop Bligh Bank, which is located 46 km off the coast of Belgium near Zeebrugge. The two phases of the 330 MW project will each use 110x3MW Vestas V90 turbines. The contract for shore connection has gone to Nexans who will supply and install 52 km of 170 kV cable with an optical fibre insert.

Vestas’ contract covers design, delivery, installation, testing and commissioning of the 55 Phase 1 V90s as well as a five-year service and availability agreement. Delivery and installation of the turbines is scheduled to take place during 2010 with final completion expected in early 2011. By September 2009 construction had started, two of the monopiles having been put in place: now, in June 2010, all the foundatins and in-field cabling have been completed and half of the turbines have been installed. Vestas Offshore and marine contractor Van Oord are building the facility and Vestas will operate it under a medium term operations and maintenance contract.

The construction of two similar windfarms presented a unique opportunity for the developers of Belwind to gather and record useful information on a daily basis during the construction of Amalia that would help them optimise the design, construction and commissioning process, in particular the logistics, to help prevent future mistakes and potentially save a great deal of money.

But it dos not follow automatically that experience constructing one windfarm can be used in developing the next. First it is necessary to know to what extend the characteristics of the wind farms are comparable. Second, it was necessary for Evelop to ensure an optimal knowledge transfer from project to project.

Register of lessons

The Belwind team includes many individuals and project partners who had also worked on Princess Amalia – financiers, contractors, suppliers, insurers and consultants. This gave the project a flying start, based on mutual trust, and because each participant knew the company culture of the others.

To ensure that this pooled knowledge could be passed on, a detailed ‘Lessons Learned’ register was set up and continuously updated during construction. The maintenance of this register has become an integral part of the development and construction process for these projects. At the start of the Bligh Bank enterprise, the register was consulted and measures taken to help prevent the repetition of mistakes. It contains lessons learned in the fields of design, contracting, financing and planning. This know-how is kept up to date and is to be transferred to future projects.

The following are some examples of practices that resulted from that register.

• Health, safety and environmental considerations were integrated in the early design process, to ensure adequate measures are taken where necessary.

• The design was based on the O&M strategy for the windfarm (for example, the siting and type of access systems)

• Wind farm layout planning should include both optimisation for production (eg wake studies) and construction (eg material cost and installation process). For example – it turns out that the shortest cable layout is by no means the best if it has crossover points and unpredictable angles (Figure 3).

• The location of vulnerable HV components was transferred to the substation onshore.

• The insurance partner is in-house and part of the design team, making it possible to calculate different scenarios very quickly. For example – when dealing with the potential need for jack-up vessels to make urgent repairs, should one just wait and search the market for favourable terms at the point of need, or close a contract for standby jack-up? And how do these two approaches affect the business interruption premium?

The method in practice

To ensure that lessons are learned and passed on it is helpful to have a degree of continuity in the project team, and essential to keep and refer to the ‘lessons learned’ register.

Figures 3 to 9 show several examples of the successes of this working technique, in secondary steel design, tower construction, progress monitoring, cable pull-in methods and welding of access rails on the monopiles. But things don’t always go to plan. Figure 9 illustrates a case where the methodology allowed a problem to be identified but not solved. For these two wind farms a monopile foundation was selected. A steel monopile weighs 300 tonnes, has a diameter of about

5 m and a length of up to 50 m. Each monopile is driven 30 metres into the seabed. A J-tube is then fitted around the monopile. The last section of the foundation is the transition piece joining the monopile to the tower.

The studs to take the J-tubes, along with the rails to aid access, are welded to the side of the monopiles. Finite Element analysis showed that stress points were created by these studs, and that they were in the most vulnerable part of the monopile, just above the mudline. Unfortunately it was not possible in the time available to come up with a better solution.

A more typical example is illustrated by the process of deciding the cable layout among wind turbines. Cable and cable laying are expensive and for Amalia the shortest route had been calculated, as shown on the left in Figure 3, in order to achieve the minimum cable length. However, for Belwind a minimal risk option was chosen, in effect a route with the minimum of cable cross-overs, for ease of installation, to minimise the risk of cable damage, to optimise access to the boatlandings and to ease any future jacking operations in the field. This resulted in a quite different layout, as shown on the right of Figure 3, while the photo illustrates a practical consequence of the confusion and expense that can occur with poor cable layout. It occurred during a cable pull in. According to the design drawings, the cable with tag ‘A’ should have emerged from J-tube ‘A’ (a J-tube is a curved tube that leads the cables smoothly from the wind turbine to the sea-bed), but it came out of J-tube ‘B’. So now the question was: were only the tags erroneously swapped, or were the cables pulled in the wrong J-tubes? To find out, it was necessary to send down a diver.