Ostwind 3

The line runs south from the offshore substation at the Windanker wind farm to the Vierow port area in the municipality of Brünzow, where the landing point is located. There, the line is connected to an underground cable of approximately four and a half kilometres up to the yet to be constructed Stilow substation. You can learn more about the 50Hertz offshore substation here.

Offshore route

In order to minimise the impact on the environment, it is important to keep the length of the cable as short as possible and, if possible, bundle it with existing cables. That is why 50Hertz has layed about two thirds of the submarine cable system in parallel with the lines of projects Ostwind 1 and 2. The 220-kV submarine cable transports the electricity generated in the wind farm from the Exclusive Economic Zone (EEZ) through the coastal waters and the Bay of Greifswald to the so-called landing point in the Vierow port area. The port area of Vierow is located in the municipality of Brünzow in the Vorpommern-Greifswald district of the state of Mecklenburg-Western Pomerania. The landing point is where the submarine cable reaches the shore.

Onshore route

From the landing point in the port area of Vierow, the electricity generated at sea is transported further via land cable to the onshore substation. The land cable of approximately four and a half kilometres in length is laid as an underground cable. The underground cable route should run as straight as possible but is nevertheless subject to a number of spatial planning criteria. Intersections with other lines, buildings, residential areas, streets and gas mains shall for instance be avoided as much as possible. Nature conservation areas and forests shall also be circumvented.

Onshore substation

50Hertz builds a new substation near Stilow, where the current will be transformed from 220 kilovolts (kV) to 380 kV. In the substation, the electricity generated at sea is injected into the German extra high voltage transmission grid.

For the onshore grid connection, the survey area in the municipalities Lubmin/Brünzow/Wuhsterhusen and Kemnitz was specified in the Grid Development Plan 2030 (2019). Within this area, an extensive and careful examination of many different criteria was performed to decide on the final location. The site should, for instance, be located outside of nature conservation areas and drinking water protection zones insofar as possible. The distance to residential and settlement areas also needed to be taken into account. The traffic connection of the substation shall also be possible via suitable streets and rails. Moreover, the existing 50Hertz extra high-voltage grid, in this case a 380-kV overhead line, shall also be nearby, so that the substation can be connected to the 50Hertz grid.

The substation will cover an area of approx. 10.5 hectares. An expansion area is added for future expansion stages. In total, 16 hectares are available at the site. More information on the substation can be found here.

The construction, expansion and conversion of electricity lines are infrastructural measures that affect many interested parties, like agriculture and nature conservation. That is why the legislator has clearly arranged the processes for the planning and approval, for example in the German Energy Industry Act (Energiewirtschaftsgesetz). The Ostwind 3 grid connection project was first confirmed in the draft area development plan 2019 (Flächenentwicklungsplan, FDP) according to the stipulations of the German offshore wind energy act (Windenergie-auf-See-Gesetz, WindSeeG) and in the grid development plan for electricity 2030 (GDP 2019-2030) as well as several times since then. Ostwind 3 is divided into three approval sections, which all went through the planning approval procedure. The planning approval procedure is a detailed permit review in which the building permit for the project is issued as well. Simply put, the planning approval procedure primarily deals with the “how” of the construction project (specification of the location, structures, technical implementation).

Permits for offshore route and offshore substation

For the section in the Exclusive Economic Zone (EEZ), the competent permitting authority, the Federal Maritime and Hydrographic Agency (BSH), made the planning approval decision. This concerns the cable route from the offshore substation and inside the German EEZ with a length of approximately 24 km in total as well as the construction of the offshore substation itself. The EEZ is the area beyond the coastal waters (12 nautical mile zone) up to a distance of 200 nautical miles.

The Ministry for Economics, Infrastructure, Tourism and Labour of Mecklenburg-Western Pomerania (WM M-V) made the planning approval decision for the cable route in coastal waters. This section covers the distance from the EEZ to the connecting element between the submarine and onshore cable near the port of Vierow and has a length of 77.5 km.

Approval of onshore route and substation

The point where the submarine cable reaches land is called the landing point. From the landing point, the electricity generated at sea is transported to the onshore substation by means of an underground cable running along the onshore route. The submarine cable of 220 kilovolt (kV) alternating current is connected to the German extra-high-voltage transmission grid by means of a substation. The necessary transformation of the voltage level from 220 to 380 kV takes place in this substation.

In order to connect it to the existing overhead line, a so-called double tap point is necessary that forms the connection between the existing overhead line grid and the substation. The tap point is installed as an overhead line.

The planning approval decision for the 4.5-km onshore route as well as the 10.5-hectare substation in the municipality of Brünzow, including the double tap point, was made by the Ministry for Economics, Infrastructure, Tourism and Labour of Mecklenburg-Western Pomerania.

During the permit procedure, the public was formally involved in accordance with the legal requirements. 50Hertz supported this with informal public participation, also known as citizen dialogue. Citizen dialogue builds on 50Hertz's own experiences, not on legal stipulations. This difference is important as the citizen dialogue ends where the formal public participation laid down by law begins (see also Transparency and public participation).

The construction of Ostwind 3 started with the approval of the off- and onshore route as well as the on- and offshore substations.

Preliminary measures at sea

Ships and fleets were repeatedly deployed along the marine route on behalf of 50Hertz to prepare the route on the seabed. For this purpose, several thousand rocks were moved a few meters to the side. Afterwards, a tugboat dragged a grapnel across the seabed along the planned route. The grapnel run removed such things as oil sails, chains and nets from the seabed. During the so-called pre-lay run, the actual cable laying was tested. For the transition from sea to land, the so-called landing point, horizontal directional drilling (HDD) was carried out to pass under the beach, minimising the impact on the landscape. A cable conduit was then pulled into the borehole which will later accommodate the cable.

Offshore cable laying

Especially the water depth and the composition of the soil determine which laying technique is used. The bottom of the Baltic Sea has glacial characteristics and its composition varies from region to region. It consists of soft materials such as silt, sand and peat, but also of hard materials such as clay, marl and rocky soils. In case of soft soil conditions, the submarine cable was flushed or ploughed into the seabed. These methods are particularly considerate of nature and environment. If the seabed is extremely hard, rocky or very peaty, other laying tools were used, such as cutters or excavators. After laying, the cable was covered with seabed material. A cable system of around 100 km cannot be laid as a single piece, but consists of several cable sections. The individual sections were connected to each other with so-called joints (connectors).

Preliminary onshore construction measures

To prepare the onshore construction sites, various works were carried out. Environmental protection measures are implemented, such as installing amphibian or reptile fences, putting up tree protection or removing woody plants outside of the bird breeding season. Furthermore, archaeological surveys were carried out. Furthermore, storage areas for construction materials and the construction sites themselves had been set up.

Onshore cable laying

From the area of the landing point in Vierow, the cable route continues another four and a half kilometres over land, up to the new Stilow substation in the municipality of Brünzow. When railway lines, streets, water bodies or biotopes were crossed, 50Hertz passed underneath them using closed construction wherever possible. For this purpose, horizontal directional drilling (HDD) and microtunnels were used. Just like for submarine cables, the length of the onshore cables is limited. Underground cables cannot be produced as a single piece. The route is therefore divided into several cable sections. All sections were connected by means of joints.

Onshore cable route for three systems

Along the onshore route, cable conduits for the Ostwind 4 and Bornholm Energy Island systems were installed together with the conduits for the Ostwind 3 cable system. Combined laying has the following benefits: simultaneous construction of three cable conduit systems took around nine months and made it unnecessary to repeat the work over the course of several years. As the construction of the cable conduits takes place in one go, the surface could still be used for agriculture after the work has ended (with the exception of the cable pits for later cable pulling).