Offshore wind energy

Offshore wind farmStrong winds in the shelve zones of continents and islands may be used to produce highly efficient clean energy. Offshore wind farms are among the most promising segments of renewable energy and have already drawn billions of investments primarily in Europe in countries like Great Britain (which reportedly possesses around 30% of EU‘s wind resources), Denmark, Belgium, Germany.

History of offshore wind energy

The world’s first offshore wind power plant named Vindeby was built in Denmark in 1991 as a cooperation project of Danish energy giant DONG (now DONG Energy) and German Siemens.

Offshore wind farm construction

Installing monopiles for wind turbines in sea bed

Monopiles for offshore wind farmAn offshore wind turbine needs to be installed in a foundation which is securely driven into the sea bed. Hallow ready-made foundation piles which are called monopiles are usually used for this purpose. These up to 72 meters (79 yds) long tubes having a diameter of about 5 meters (5.5 yds) and a weight of about 300-550 tons (660-1230 thou lbs) are so giant that it’s too hard to transport them by ship, thus they are just floated to the construction site with both openings sealed airtight.

Each of the tubes is then unsealed and forced 35 meters (38 yds) in the sea bed by the special huge floating crane, which takes around 3 hours. A special sound signal is used before the work starts to scare away marine animals. After the installation is completed there are tops of the foundation piles sticking out of the water.

Installing turbine base

A transition piece is installed on the top of each foundation pile, with a mooring area, a 25 meters (27 yds) high ladder, a platform, an entrance door and inner pipes to protect energy cables from water. The transition pieces are transported from the land and installed by the special lifting platform which then corrects the vertical axis of the piece to place it perfectly.

Assembling and installing wind turbine

Offshore high voltage stationEach wind turbine is mostly assembled onshore as it is difficult to perform such activities in the water. Two pieces of the tower, the nacelle and the rotor head are put together and the installation is electrically tested. After that the floating platform transports it and the blades to the site where the wind turbine is installed into the transition piece of the foundation. In favorable weather conditions this stage takes about six hours to accomplish.

Connection cables, onshore and offshore high voltage stations

The turbines are connected to each other and to the offshore high voltage station by high voltage cables which are then buried into the sea bed for protection. The station converts the voltage to 150 KV to reduce long-distance transmission losses. The offshore station or a number of stations are located in the middle of the power plant and connected using a very thick single-piece multikilometer cable to the onshore station which finally feeds the power into the general transmission grid.

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