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Grid connection sol'n to slash offshore wind power cost

Posted: 21 Oct 2015     Print Version  Bookmark and Share

Keywords:Siemens  wind power  grid  diode rectifier 

Siemens has unveiled an innovative solution for connecting offshore wind turbines to the grid. According to the company, the direct-current technology allows a cost-efficient and simplified connection of offshore wind power plants far from the coast.

The platform housing the transmission technology is much smaller and more compact than before. Until now, these plants have been connected to the grid via large central converter platforms. Siemens is further developing the transmission technology, enabling a large number of much smaller platforms to be built. With the solution, a direct-current cable can connect several of these platforms sequentially in a wind farm and then route them to an onshore transformer substation. Overall, this solution costs less and is also more efficient than the approach used with conventional platforms.

New grid connection

The picture shows the model of the new grid connection: Thanks to the application of the new diode rectifier unit, the volume of the platform topside is reduced by four-fifths, and the weight is cut by two-thirds.

The compact design permits encapsulated high-voltage electrical equipment to be used, especially diode rectifier units (DRUs), which are installed instead of the usual air-insulated transistor modules. The system is also modular and flexible when it comes to installation. The volume of the platform structures is reduced by four-fifths, and the weight is cut by two-thirds. As a result, costs are reduced by more than 30 per cent. At the same time, the new solution enables transmission capacity to be increased by one-third, while transmission losses fall by one-fifth. This is a significant step towards significantly reducing the cost of offshore wind power and making it competitive compared with conventionally generated electricity.

Connection of offshore wind power plants

Siemens offers the complete portfolio for the connection of offshore wind power plants and develops these solutions continuously: For the connection of near-shore wind power plants in AC-technology Siemens has launched the offshore transformer module (OTM) in the beginning of 2015, which is one third smaller in size and weight compared to a conventional AC platform. High-voltage direct-current transmission is the more efficient technology to connect wind power plants far off-shore. Siemens has reduced the size of the transmission technology, enabling much smaller platforms to be built. The volume of the platform structures is reduced by four-fifths, and the weight is cut by two-thirds. At the same time, the new solution enables transmission capacity to be increased by one-third, while transmission losses fall by one-fifth.

"As the only provider on the market, we have already successfully commissioned four offshore direct-current connection projects. Now we are applying our experience directly to the next generation of direct-current grid connections. Our new solution will play a major role in decreasing the cost of offshore wind power below ten cents per kilowatt hour by 2020. This is how we plan to make the direct-current technology used in Germany more interesting to other markets, too," said Jan Mrosik, CEO of the energy management division at Siemens.

A diode rectifier unit has a transmission capacity of 200MW. Typically, two DRUs are installed on one platform. Up to three of these platforms can be connected to each other to create an offshore grid node that replaces collection platforms in the wind farms. This link enables a connection to the mainland of multiple offshore wind farms with a total capacity of up to 1,200MW. The electricity is transported to a grid infeed point on land via cables. A converter station converts the direct current back into alternating current for subsequent transmission and distribution. The land station will also be built by Siemens using a proven design.

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