The future of renewable energies greatly depends on the offshore wind energy generated in the North Sea. The Global Tech I wind farm is controlled from Hamburg.
Located in the middle of the North Sea, the Global Tech I wind turbine went into full-scale operation in July 2015. Comprising 80 wind turbines in the 5-megawatt class, and thus an installed output of 400 megawatts, the wind farm is one of the first and biggest projects constructed under the German government’s offshore strategy. The strategy calls for establishing 15,000 megawatts of wind-generated power in Germany’s North Sea and Baltic Sea by 2030. These efforts are based on the fact that offshore wind energy is an important strategic element in energy and climate policies to phase out the use of nuclear power and reduce the emissions of climate-damaging greenhouse gases. By 2030, half of the gross electricity consumption is to be supplied from renewable energies. The North Sea is particularly well-suited as the location for these new power plants as planners predict average wind speeds of almost 10 metres per second or 36 kilometres per hour. Based on these figures, the energy yield per unit would be between 4,000 and 4,500 full operating hours per year, and thus twice as high as achieved with wind farms on land.
But the North Sea’s rough environmental conditions with strong winds and metre-high waves also pose a tremendous challenge to the construction and operation of these high seas power plants. Foundations, substations, turbines and rotor components had to be constructed over 100 kilometres from the mainland and underwater cables had to be laid at a depth of 40 metres. In this, the safety of everyone working on the offshore wind farms had top priority. The individual steps in the construction process were planned meticulously and only implemented in accordance with strict specifications. Work was interrupted when the weather conditions worsen and was not resumed until it was safe to do so. This dependency on the forces of nature requires the use of suitable ships and construction equipment and the appropriate installation methods. Particularly the laying of the foundations and constructing the farm’s substations was pioneering.
Giant 900-tonne, three-legged steel tripods were used as foundations, each anchored in the sea floor by three piles. A new crane-equipped installation ship was used to transport them. This was a major advantage as the ship could carry and install three tripods and their piles. Construction work could be carried out up to a wave height of five metres as the ship can raise itself and its working platform high above sea level with its steel feet. A three-phase sound protection concept was used during the anchoring of the piles in the sea floor to protect noise-sensitive porpoises. These measures also included using a special ship to surround the construction site with a perforated nozzle pipe into which compressed air was pumped. The rising air bubbles immediately created a bubble curtain and thus a physical-acoustic insulating barrier which reduced the intensity of the sound waves. Corresponding examinations also showed that no porpoises were in the immediate vicinity during the installation work.
The eco-friendly suction bell installation method, commonly used in the oil and gas sector, was applied for the first time during the installation of substations in a wind farm in Germany’s North Sea. At the heart of the innovative platform concept is a closed body for all technical equipment to which the support structure is permanently attached. This allowed towing the platform to the wind farm on water. The support structure with the so-called suction bells at its feet could then be lowered so that it sank into the sea floor thanks to the 9,000-ton weight of the substation. Vacuum pumps then suctioned off the sea water from the steel cylinders from above, creating a vacuum which resulted in the sea floor flooding into the support structure from below, thus causing the structure to bury itself into the sea floor. After this the platform was raised 20 metres above sea level.
The substation is the centrepiece of the wind farm. This is where the electricity from 80 turbines is collected and transformed from 33 to 155 kilovolts and where the transmission grid operator, who is responsible for the mains connection, taps the 3-phase current via two export cables in order to then convert it to direct current for the low-loss transport to land. The platform is also a logistical base. Up to 38 people work offshore in two-week shifts so that they can perform service and maintenance assignments on the units without having to travel great distances. It is therefore designed as a “self-sufficient small town” with hotel operations, a hospital with telemedicine, helicopter landing site, seawater desalination plant and sewage treatment plant.
The offshore team works together closely with the operations control centre in Hamburg’s HafenCity. The operations control centre is not only responsible for the general operations monitoring and grid management, it also handles sea and weather surveillance, communication with the direct marketers and the grid operator. Thousands of data points from the turbines and the wind farm are collected and evaluated daily via an IT system in order to monitor the wind farm’ status and ensure a fault-free operation. The grid control operations monitor the wind farm’s cable network. Because the units are switched as loops, electricity can be diverted between two units in the reverse direction in case of damage to the cables. Switching operations for cable connections and large transformers are executed via computer mouse-click.
The 400-megawatt Global Tech I wind farm delivers, minus deductions for example for transmission losses, approximately 1.4 billion kilowatt hours of eco-friendly electricity annually, thus supplying 445,000 households with an average consumption of 3,310 kilowatt hours. This saves, when compared to conventional coal-fired power plants, more than one million tonnes of climate-harming carbon dioxide. These are goals that the three company shareholders, Stadtwerke München, ENTEGA in Darmstadt and the Swiss company Axpo, have dedicated themselves to.
The certified auditor and tax consultant Hendrik Steindam (born in 1973) has held management positions at renowned auditing companies and the GL Group, for example at Germanischer Lloyd as Post Integration Finance Manager. Hendrik Steindam is Commercial Director of the Global Tech I Offshore Wind GmbH.