Insight into an offshore wind farm II: The journey of electricity from offshore to onshore.

An offshore wind farm consists of wind turbines, array cables (undersea cables), an offshore substation, export cables, and an onshore substation. The wind turbines catch wind at sea and convert its movement into electricity. This electricity is carried through array cables to the offshore substation where it is maximized the voltage and transmitted through export cables and onshore cables to the onshore substation. The onshore substation converts the incoming electricity to be fed into the power grid for distribution to factories and households. All this equipment is essential for electricity to complete its "journey.”

 


Electricity generated from an offshore wind farm has to go through subsea cables, an offshore substation and an onshore substation before reaching household users. (Source: EnBW)

 

The "indispensable teammates" of offshore wind turbines
Wind turbines are often regarded as the most critical components in an offshore wind farm (extended reading: Insight into an offshore wind farm: Turbines – powering offshore wind farms.) However, according to the research conducted by Ship and Ocean Industries R&D Center in 2016, wind turbines only accounted for 41% of the total cost of an offshore wind farm [Note 1], compared to 80% of an onshore wind farm. The study shows that components other than wind turbines also play a significant role in an offshore wind farm. Let’s take a closer look at the "teammates" that support offshore wind turbines!

 


Cost analysis for offshore and onshore wind farms in Europe. (Information Source: Ministry of Economic Affairs)

 

Offshore substation
The offshore substation is mainly responsible for consolidating electricity generated from offshore wind turbines and converting it to the appropriate voltage, so that electricity can be transmitted through export cables and into the power grid with minimal potential electrical losses. An offshore substation is typically equipped with a step-up converter, data gathering and monitoring system, diesel generator, alarm system, and marine communication system. To withstand the strong winds, water currents, high salt content and corrosive environment at sea, an offshore substation has to be built within an enclosed steel structure, and all metallic components must be treated to resist corrosion. This requirement makes construction and maintenance of offshore substations much more difficult compared to their onshore counterparts.

 


EnBW's offshore substation at Baltic 2. (Source: EnBW)

 

Subsea cables and onshore cables
Subsea cables are the artery that connect an offshore wind farm to the power grid on shore. Subsea cables laid between wind turbines are called "array cables," and they connect wind turbines in a series array. Subsea cables used for transmitting electricity from an offshore wind farm to shore are called "export cables"; they connect to onshore cables, which then take over power transmission on land. Compared to onshore wind power, offshore wind power is presented with more uncertain sea conditions and weather, and a greater number of variables including water depth, geological conditions, seabed changes and sea currents need to be taken into account. These technical difficulties are reflected in the higher development costs. Taiwan’s Ship and Ocean Industries R&D Center also reports that installation of subsea cables alone accounts for 13% of the total cost of an offshore wind farm [Note 2], which is even higher than the cost of a substation (5%). This cost breakdown shows just how critical subsea cables are to an offshore wind farm.

 


EnBW laying array cables in its offshore wind farm. (Source: EnBW)

 

Onshore substation
The onshore substation is the part of an offshore wind farm responsible for distributing electricity into the power system on land. Its main task is to adjust electricity to the appropriate voltage before joining the power grid to meet the needs of different users. In Taiwan, for example, electricity generated from offshore wind farms is stepped down to 22-11 kV at a primary substation to supply small and medium industrial users, or it is stepped down at a distribution substation or secondary substation for domestic use [Note 3].

 


Electricity generated from an offshore wind farm, once stepped down, can be connected to the power grid and distributed to users. (Source: EnBW)

 

New opportunities from an emerging industry
Every equipment used in offshore wind power involves intricate technologies and requires the support of a strong supply chain. To succeed, the industry requires talents from a wide variety of disciplines, including marine engineering, electrical engineering, project management, and offshore wind farm operations & maintenance.

Scheduled for completion in the end of 2019, EnBW's Hohe See and Albatros projects (currently the largest offshore wind farm project in Germany) provide the best examples of how talents are coordinated to achieve remarkable feats. Since construction activities began in 2017, more than 600 employees have worked on the two wind farms at sea, and more experts from other fields are gathered at EnBW's offshore wind power headquarters in Hamburg, Germany, to provide support for offshore construction.

In fact, according to the survey conducted by the Ministry of Economic Affairs Industrial Development Bureau, Taiwan's offshore wind power industry is expected to have additional demands for 2,010 to 2,700 talents by 2020 [Note 4]. As localized production becomes a reality in 2020, a local offshore wind power supply chain will start to take shape, offering more job opportunities and making Taiwan a competitive player for the emerging industry!

 


More than 600 employees have worked on EnBW's Hohe See and Albatros projects located in the North Sea. (Source: EnBW)

 

Sources

Sources of quoted data:
[Note 1][Note 2] Page 3 of 2016 Energy Technology Project Report (by MOEA) - OFFSHORE WIND FARM Operational Safety Evaluation Technology Development Program
[Note 3] Taiwan Power Company - 
Introduction to the power supply system
[Note 4] iTalent - Estimated Talent Demand for Offshore Wind Power Industry 2018-2020

For reference:
2016 Energy Technology Project Report (by MOEA) - OFFSHORE WIND FARM Operational Safety Evaluation Technology Development Program
CSBC Corporation - 
Introduction to Offshore Substation
Taiwan Power Company - Introduction to the power supply system
iTalent - Estimated Talent Demand for Offshore Wind Power Industry 2018-2020 
EnBW, 
“Milestone in North Sea”

 

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