To bring renewable energies to the people, Amprion is busy connecting wind farms in the North Sea to the power grid on land. If we are to transmit electricity over long distances, we need to install the necessary electrical and ancillary equipment on platforms located on the high seas. And they need to be able to withstand more than just storms.
The North Sea in the German Bight: on normal days, the waves are five to ten metres high. “Once-in-a century waves” – breakers that statistically occur once every 100 years – reach heights of up to 19 metres. “We're preparing for once-in-a-millennium waves up to 20 metres high,” says Fred Wegener. The 54-year-old mechanical engineer is responsible for the engineering side of one of two projects that feed wind power from the North Sea into the power grid on land. Experts call them “grid connection systems”.
Hundreds of kilometres of power cable will have to be laid – on the bed of the North Sea as well. These cables can only be used to transport electricity as direct current – but the wind farms generate alternating current. Special facilities therefore convert this AC current to DC current while still out at sea. These “converters”, which are built in a steel enclosure (known as the “topside”) for protection, stand on gigantic foundations positioned immediately next to the offshore wind farms – and they, too, need to be able to withstand once-in-a-millennium waves.
“Every cubic metre of extra space not only adds weight, it adds cost, too.”
Fred Wegener
Overall Project Manager Engineering for DolWin4
The planning team at Amprion consequently has its hands full. “The difficult conditions out on the high seas make planning much more challenging than it is for onshore installations,” Wegener explains. More than 60 men and women at Amprion’s Dortmund and Hamburg sites are working to ensure that Amprion's first converter platforms will go into service in 2028 and 2029 – as part of the grid connection systems DolWin4 and BorWin4. They are playing their part in making Germany's energy supply more climate-friendly. Together, these two systems will be able to transmit a capacity of 1,800 megawatts. This corresponds to the needs of a major city such as Hamburg. Completing these systems on time is priority no. 1 for our planners. The energy generated by the wind farms is to be fed into the grid as agreed.
Technical and logistical challenges have to be overcome when planning the converter platforms. As demanding as the planning tasks are, Fred Wegener takes these challenges with typical northern German calmness. Colleagues say there's not a lot that could ruffle his feathers. Presumably partly because he knows a lot about converter platforms: before joining Amprion, Fred had already planned, built and supervised the installation of platforms while working for a shipyard. “At Amprion, I can use my experience to advance the offshore sector,” he says. “DolWin4 and BorWin4 will not be Amprion's last grid connection systems.”
GIGANTIC DIMENSIONS
The converter platforms for DolWin4 and BorWin4 are being erected around 60 and 125 kilometres from the mainland, respectively, out on the high seas. They are up to 70 metres long, 35 metres wide and 35 metres high. Their footprint is equivalent to the area of ten tennis courts. The substructure of the platform alone – what's called the “jacket” – weighs 5,000 tonnes. That's half what the Eiffel Tower in Paris weighs. The steel piles of the platforms are anchored 60 metres into the seabed. Where exactly this is done depends on the conditions of the seabed on-site. “For example, when we're driving the piles, we want to avoid coming across things like boulders,” explains Wegener. To make sure we do, geologists will examine the subsoil by drilling boreholes.
GIGANTIC DIMENSIONS
The converter platforms for DolWin4 and BorWin4 are being erected around 60 and 125 kilometres from the mainland, respectively, out on the high seas. They are up to 70 metres long, 35 metres wide and 35 metres high. Their footprint is equivalent to the area of ten tennis courts. The substructure of the platform alone – what's called the “jacket” – weighs 5,000 tonnes. That's half what the Eiffel Tower in Paris weighs. The steel piles of the platforms are anchored 60 metres into the seabed. Where exactly this is done depends on the conditions of the seabed on-site. “For example, when we're driving the piles, we want to avoid coming across things like boulders,” explains Wegener. To make sure we do, geologists will examine the subsoil by drilling boreholes.
The converter platforms are located 60 and 125 kilometres from the mainland. Each transport run must be planned meticulously.
FAR OUT AT SEA
The location on the high seas presents a genuine logistical challenge for the planners. This is because the platforms are manufactured onshore and only then shipped to their installation location. The smaller and lighter they are, the easier they are to transport. “Every cubic metre of extra space not only adds weight, it adds cost,” explains Wegener. Individual components must not exceed a certain size and weight, otherwise ships and cranes will not be able to transport them. “If we forget to pack a certain tool and it's missing during erection of the platform, that's a real problem,” says the Overall Project Manager Engineering, because it has to be brought in by helicopter or – if weather conditions are too poor to fly – by ship. “That's why we have to plan installation meticulously.” To avoid long turnaround times, the fitters stay in rooms provided on accommodation platforms – known as “jack-up barges” – out on the North Sea.
The converter platforms are located 60 and 125 kilometres from the mainland. Each transport run must be planned meticulously.
MATERIALS UNDER CONSTANT STRESS
The conditions on the high seas subject the materials of the platform to constant stress. The strength of the waves varies greatly, as do the direction of the waves and current. The Amprion team is also expecting extreme winds of up to 180 kilometres per hour that will put pressure on the materials. And then there's the sea salt, which attacks the steel of the platforms. In order for them to last 32 years, which is the service life the planners are counting on, a sophisticated coating system is needed. Because unlike ships, platforms cannot be brought into port for a “respray”. “Unfortunately, we don't have much empirical evidence to work with in terms of corrosion protection for such a long period out at sea,” says Fred Wegener. “That's why we avoid large surface areas when planning and keep the number of attachment parts as low as possible. It's also important that the platform is not damaged during construction or maintenance work.”
PROTECTING NATURE
In addition to the technical and logistical challenges involved, the planners must also take into account the fact that the converter platforms are located in the middle of a unique natural habitat. Amprion believes in the fundamental necessity of sustainability. Protecting mankind and nature is a top priority for our employees. “This is why we always adhere to the environmental regulations and in some cases even go above and beyond,” says Wegener. For example, common porpoises that live in the North Sea must be protected from excessive noise levels owing to their very acute hearing. We do this by taking special measures when driving the platform piles.
The North Sea is a unique natural habitat. Amprion also pays special consideration to the common porpoises that live there.
PROTECTING NATURE
In addition to the technical and logistical challenges involved, the planners must also take into account the fact that the converter platforms are located in the middle of a unique natural habitat. Amprion believes in the fundamental necessity of sustainability. Protecting mankind and nature is a top priority for our employees. “This is why we always adhere to the environmental regulations and in some cases even go above and beyond,” says Wegener. For example, common porpoises that live in the North Sea must be protected from excessive noise levels owing to their very acute hearing. We do this by taking special measures when driving the platform piles.
SENSITIVE ELECTRONICS
Each converter is made up thousands of transistors, diodes, capacitors and reactors. “The electronics are very sensitive,” says project manager Wegener. The equipment must be installed so high up that even once-in-a-millennium waves cannot touch them. Special ventilation systems run day and night to dehumidify, purify and desalinate the sea air.
But even the most resilient of components will break down at some point and have to be replaced. Other components need to be regularly serviced. This can only be done on-site. This is something the Amprion team must take into account when designing the platforms. The weight of potential components must also be taken into account: “It’s like playing Tetris,” Wegener says. “We go through a thousand replacement variations and constantly face the challenge of keeping the centre of gravity of the platform centred. Only then will the platform be stable.”
“We're constantly faced with the challenge of keeping the platform's centre of gravity centred.”
Fred Wegener
“We're constantly faced with the challenge of keeping the platform's centre of gravity centred.”
Fred Wegener
What do Converters do?
Converters are the key elements of an offshore grid connection system. The wind turbines of an offshore wind farm generate alternating current, which is then converted to direct current on-site by converters. The technology of high-voltage direct-current transmission (HVDC) enables us to transmit large amounts of energy by cable and over long distances with very low losses. This allows the electricity to make the long journey to the mainland. At the point where the grid connection system is connected to the mainland grid, a further converter is required that converts the direct current (DC) back to alternating current (AC). This is because the German power grid operates predominantly with alternating current technology.
