DONG Energy subsidiary won the concession to construct the Borssele 1 and 2 offshore windfarms. Credit: Dong Energy.
TenneT TSO engaged HSM Offshore for the construction of the offshore transformer station for the Borssele Alpha platform. Image: courtesy of TenneT TSO BV.
Construction of the Borssele Alpha offshore transformer station was started in April 2017. Credit: TenneT TSO BV.
The offshore transformer station will be connected to the onshore substation at Borssele by 60km of subsea cables. Credit: TenneT TSO BV.

The Borssele 1 and 2 windfarms will be located 22km off the coast of Zeeland province, the Netherlands. The two offshore windfarms, which will have a combined capacity of 752MW, are part of the Borssele windfarm zone, which comprises the development of five projects.

DONG Energy Borssele 1, a subsidiary of DONG Energy, won the concession for the 1 and 2 offshore windfarms in a public tender conducted by the Netherlands Ministry of Economic Affairs. The tenders were issued under the subsidy programme, Stimulation of Sustainable Energy Production (SDE+ or Stimulering Duurzame Energieproductie).

Dong Energy will receive the SDE+ grant, which is a financial compensation (subsidy) for a period of 15 years. The compensation was capped at €124/MWh for the Borssele windfarm sites 1 and 2 tender, while DONG Energy bid the lowest amount of €72.7/MWh, excluding transmission costs.

Expected to be completed in mid-2020, the two windfarms are anticipated to generate renewable electricity equivalent to the annual power consumption of one million households.

Borssele 1 and 2 windfarms make-up

Extending over 128.3km², the Borssele 1 and 2 windfarms will be located in water depths ranging between 14m and 38m. The annual average wind speed in the region is estimated to be 9.5m/s.

The windfarms will be equipped with Siemens Gamesa 8MW turbines, which are based on Siemens’ offshore direct drive platform. The energy generated by each of the turbines is sufficient to supply for roughly 8,000 European households.

The direct drive wind turbine has a rotor diameter of 154m and a swept area of 18,600m². Siemens Gamesa plans to assemble the turbine nacelles at its Cuxhaven factory in Germany and the blades in Hull, England.

Details of the Borssele windfarm zone (BWFZ)

The Government of Netherlands initiated an Energy Agreement for Sustainable Growth in 2013 with an aim to develop 3,500MW offshore wind projects. It also set the target of meeting 16% of the nation’s electricity needs through renewable sources by 2023.

A total of 40 organisations agreed to develop the projects as a result of which three offshore windfarm zones are proposed to be built, namely Borssele (1,400MW), South Holland coast (1,400MW), and North Holland coast (700MW). TenneT was selected to develop and operate an offshore grid in March 2016.

The BWFZ will extend over approximately 344km² and is further divided into five sites, numbered 1-5. Sites 1, 2, 3 and 4 are being developed through two separate tenders, while the fifth 20MW site will be developed separately as an innovation site.

Grid connection for Borssele 1 and 2

The power generated by Borssele 1 and 2 will be collected by TenneT’s Alpha offshore transformer station (platform), which will be operational from 2019. The 66kV power will be transformed to 220kV and transported to an onshore substation, which will be connected to the national extra-high-voltage (EHV) grid by means of two 220kV export cables.

A steel-cutting ceremony for the Borssele Alpha platform was conducted at the HSM shipyard in Schiedam on 9 April 2017.

Subsea cables of 60km in length will connect the offshore platform to the onshore substation. The cables will be buried at a depth of 1m in the North Sea, while the depth through the Western Scheldt estuary will be 3m.

TenneT will install another offshore platform named Beta for the Borssele 3 and 4 windfarms.

Contractors involved with Borssele 1 and 2

DONG Energy awarded a contract to Siemens Gamesa in July 2017 for the supply of 94 turbines with a rated power of 8MW each for the Borssele 1 and 2 offshore windfarms.

Zeeland Seaports will install an operation and maintenance base in Vlissingen Buitenhaven for the windfarms. A letter of intent for the same was signed between the two companies in August 2017.

In late-2016, TenneT was contracted for the construction and installation of the Borssele Alpha and Beta platforms, as well as the export cable to be used for the 1 and 2 windfarms.

“The energy generated by each of the turbines is sufficient to supply for roughly 8,000 European households.”

TenneT and DONG Energy entered a grid connection agreement with regards to the construction, operation and ownership of the substations of the Borssele windfarms in July 2017.

Fugro and Boskalis were employed to identify unexploded ordnance (UXO) at the windfarm zone along the cable routes for the grid connection between the two offshore platforms and the onshore substation.

Contractors involved with Borssele Alpha

TenneT contracted HSM Offshore (Schiedam, the Netherlands) for the construction of offshore transformer platforms in October 2017. HSM subcontracted Joulz Energy Solutions for the systems integration of all high-voltage (HV) components on the Borssele Alpha platform.

Under a contract awarded by HSM, Iv-Oil and Gas will design the platform, handle all procurements, and integrate the HV components supplied by TenneT and the balance-of-plant materials.

TenneT contracted the consortium of VBMS and NKT Cables for the delivery and installation of subsea and land cables for the Borssele Alpha platform.

CG Power Systems Belgium and Alstom Grid Netherlands will supply power transformers and gas-insulated switchgear (GIS) respectively for the offshore power grid being developed by TenneT, under framework agreements signed in March 2015. The initial supplies will be for the Borssele 1 and 2 windfarms.