United Kingdom - London Array
With a peak rated power of 630 megawatts, London Array is the largest wind farm in Europe by capacity, and also the largest offshore plant in the world. It is named after London because its power goes to the London grid, and it is expected to reduce annual carbon dioxide emissions by 900,000 tons.
Built 20 kilometres off the Kent coast in the outer Thames estuary, London Array was a major challenge to construct because of high winds and unpredictable sea conditions.
The site required 5.5 million man hours to build, and at the peak of construction over 1,000 people and sixty vessels were working on the project.
In March 2011, the first monopiles were sunk into place. A whole year was required to install all of them. Throughout the following year the 175 turbines were assembled, and the wind farm was completed by mid-2013.
Denmark - Middelgrunden
When it was set up back in 2000, Middelgrunden was the world’s largest offshore wind farm. The plant is approximately four kilometres off Copenhagen, where the depth of the water is between 3 and 5 meters. The 20 turbines (of 2 megawatts each) give the plant a nameplate capacity of 40 megawatts, thus enabling the farm to deliver about 4% of Copenhagen’s power requirements.
The project was initiated in 1996 by the Copenhagen Environment and Energy Office (CEEO), and concrete gravity base foundations were chosen as the cheapest option to hold the turbines. Ownership of the wind farm is split between the 10,000 investors in the Middelgrunden Wind Turbine Cooperative on the one hand, and the municipal utility company on the other.
LM Wind Power, a pioneer in offshore wind, delivered the blades for the wind turbines. The company is partner of WINDTRUST , a European project that aims to reduce the cost of wind energy generation by further enhancing the design of three key-components: the rotor blades, the power electronics and the wind turbine controller.
Middelgrunden can be easily seen from Denmark’s capital. Its presence bears testimony of how important wind power is in the country that broke the world record for wind energy in 2016, for the second year in a row.
Denmark - Anholt
Denmark's largest offshore wind farm is the third largest in the world and has an installed capacity of 400 megawatts, equivalent to 4% of the total Danish power consumption. The array is situated a minimum 15 km out at sea between Djursland and the island of Anholt in the Kattegat, in waters 15 to 19 meters deep.
The distance between each of the 111 wind turbines is half a kilometre, making the array 20 km long in total. Each monopile is painted yellow to ensure safe navigation.
Construction began in January 2012 and was completed in September 2013, but still the Anholt wind farm employs around fifty people to monitor and maintain it.
Even if the turbines are usually placed in a grid pattern of lines and rows, at the Anholt array they have an unusual layout: most of them are located along the edges of a grid pattern, where the airflow from prevailing west-southwest winds is undisturbed. This increases the energy production by 1.5%.
Germany - Bard Offshore 1
Located about 130 kilometres off the German coast in the North Sea, BARD Offshore 1 is the world’s remotest offshore wind farm.
The development consists of 80 wind turbines rated at 5 megawatts each, and the total maximum power of 400 megawatts makes it the largest offshore wind plant to supply power to the German grid. The construction of the farm began in March 2010 and was finished in July 2013, with the official inauguration taking place in August of the same year. Unfortunately, a series of setbacks - including a fire at a transmission station in 2014 - delayed the commissioning of the farm.
The wind turbines were installed in a depth of 40 meters, and on the sea bed each foundation weighs 470 tons. The 200 kilometre cable connection is the longest of its kind in the world. The cables used are lightweight and made of eco-friendly polymers, and were also laid underwater and underground in order to minimise environmental impact.
Belgium - Thorntonbank
The Thorntonbank wind farm is located 30 kilometres off the Belgian coast, where the water depth ranges from 12 to 27 meters. Electricity production started in 2009 with a capacity of 30 megawatts, but the peak power of the plant has gradually increased to the current 325 megawatts of nameplate capacity, making it the most powerful offshore wind plant in Belgium.
The first phase wind turbines were built on gravity-based foundations, concrete cylindrical or conical structures used as stands and held in place by their own gravity. The successive turbines, instead, were built on jacket foundations, steel structures with four legs connected to each other with braces. The latter choice allows easier logistics and serial production in different manufacturing yards throughout Europe.
All turbines can be switched on or off individually, and on the whole they are sufficient to meet the requirements of more than half a million Belgian households. Despite the concerns about the array’s impact on fishing, the wind farm saves roughly 450,000 tons in carbon dioxide emissions each year, and is located far from the busiest shipping routes.
Netherlands - Gemini
In the Dutch part of the North Sea, about 85 kilometres off the coast of Groningen, the 600 megawatt Gemini wind farm is now under construction. After the beginning of the works last year, the project is expected to be completed and fully operational by the summer of 2017.
The development will be used by approximately 785,000 households and is expected to offset 1.25 million tons of carbon dioxide emissions every year. The wind farm is currently employing about 500 people for the construction, and some 100 jobs linked to maintenance will be kept once the project becomes operational.
The wind farm is being built at two locations, with 75 turbines in each: the first is situated north of Ameland, while the second is 55 kilometres north of Schiermonnikoog. In the two areas the water depth ranges from 28 to 36 meters, while the monopiles that hold the turbines have a total length of 65 meters, since almost half of their length is driven into the seabed. The aluminium-core cables that connect the wind farm to the shore are also buried at a depth of twelve meters beneath the sea floor.