The offshore wind farm already has its own Wikipedia page. ‘Neart Na Gaoithe’ (meaning ‘strength of the wind’ in Gaelic) has an area of 105 square metres, is thirty kilometres off the coast and fifty metres deep, located just north of the Scottish city of Torness. An additional challenge is that the wind farm must be built on a partly rocky and partly muddy seabed which is not a particularly easy location for constructing a wind farm. But that’s how it works nowadays; there was still some space there. Because of the busy marine traffic, a large wind farm cannot simply be installed just anywhere in the North Sea. Furthermore, pipelines and electricity and internet cables have been run almost everywhere over the seabed.

In 2009, the initial idea for the wind farm was: 125 units of the 3.6 MW wind turbine or 75 units of the 6 MW wind turbine, which would collectively generate 420 to 450 megawatts of electricity. Enough to simultaneously supply half a million households with electricity. Eventually, the French EDF Group obtained the permit for the wind farm and issued a concept study for other parties, ultimately won by Iv-Offshore & Energy together with General Electric (GE).

“We first took a fresh look at the original design”, says Fedor. “A consideration was whether we should opt for one or two transformer platforms. Two is more expensive, but on the other hand...if it’s decided to build only one substation, for example, longer cables will be needed to connect all the wind turbines to the central platform. And those cables aren’t exactly cheap either. For several reasons, EDF preferred the option of two smaller platforms with the lightest and simplest possible design”, says Fedor. “After all, the lighter the platform, the cheaper and the easier it is to install. To put the platforms and wind turbines in place, a crane vessel must be reserved during the study phase, two years in advance. With the chosen concept, the turbine foundations and the platforms can be installed using the same ship, considerably limiting the contractual risk for the customer.” 

In the United Kingdom, it is the general rule of thumb that substations must be as simple as possible. They are purchased by the wind farm developer, who has the legal obligation to resell the substations to the Offshore Transmission Owner (OFTO), the party responsible for the transportation of the electricity. “This works differently in our country”, says Norman. “Here, the net operator usually buys the platform, and then determines the operational and maintenance requirements.” The difference can be seen in the design.

Iv-Offshore & Energy’s design for the ‘Neart Na Gaoithe’ wind farm ultimately consists of 54 wind turbines, each generating 8 megawatts of electricity; quite different from the original idea. Wind turbines are becoming increasingly powerful. Electricity generated by the turbines is carried via sixteen subsea cables and will arrive at the two identical substations with a voltage of 66 kilovolts. Here, the electricity is ‘collected’ and converted to a voltage of 220 kilovolts to minimise transportation losses. This power is then transported to the onshore station via two (export) subsea cables. Extensive coordination is needed with the various involved parties (among which wind farm owner EDF and cabling contractors) for the installation of the necessary technical facilities at the substations, such as the laying and connecting of the subsea cables. A substation looks very much like a labyrinth of pipes and tubes. There are kilometres of electricity cables and electrical boxes full of wires and software that keep the primary process and all auxiliary systems (area heating and emergency power supplies) in the air. 

The flexible plug & play concept that we are applying to the ‘Neart Na Gaoithe’ wind farm is particularly suitable for HVAC platforms. HVAC platforms are usually placed close to the coast due to high power losses when alternating current is transported offshore over a long distance. Since areas near the coast are gradually filling up, the need for High Voltage Direct Current (HVDC) stations at sea continues to grow. There is still space available for wind farms there, but this requires larger and more expensive installations, both at sea and ashore. However, from approximately eighty kilometres off the coast, HVDC is the most economical solution. 

Larger wind farms, with even larger and heavier wind turbines for generating more power, in ever deeper water. That’s the trend. There are now eight offshore HVDC stations in use worldwide. Iv-Offshore & Energy was involved in the design of three of these substations: BorWin alpha, DolWin alpha and HelWin beta. “We’re good at designing such complex platforms. This is partly due to our knowledge of offshore constructions and the multidisciplinary engineering experience we have accumulated in the oil and gas market”, says Fedor. 

Construction of the ‘Neart Na Gaoithe’ platforms will start at the end of 2019. This is when the first shipment of steel will arrive at HSM Offshore in Schiedam. Completion is scheduled to take place in 2021. An average of forty employees will be working on the design for more than a year and a number of 
Iv-Offshore & Energy employees will also be continuously present on site.