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TenneT presents Hub and Spoke concept for large scale wind energy on the North Sea.

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By 2030, the originally planned capacity of 15 gigawatts of offshore wind energy will increase to 20 GW.

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Seetrassen2030

In the summer of 2020, the German government decided to push the expansion of offshore wind energy in order to achieve the goals of the 2030 climate protection program. At the same time, the federal government has also set higher targets: For example, the capacity originally planned for 2030 will increase from 15 gigawatts (GW) to 20 GW, with as much as 40 GW planned for 2040. Therefore, not only new offshore wind farms are needed, but also new power lines connecting them to the transmission grid.

Currently, the direct current connections of the offshore wind farms from the exclusive economic zone to Lower Saxony run via the border corridors N-I (Hamswehrum landfall, already fully exhausted) and N-II. The submarine cables via border corridor N-II run through the 12-nautical-mile zone to the Hilgenriedersiel landing point, crossing the island of Norderney in the process. However, due to the tight timing of construction work on the island and the large number of projects, additional route corridors are required. For this reason, Amprion and TenneT have launched the Seetrassen 2030 project in 2019 with foresight. The goal: Together, we want to develop new route corridors for offshore grid connection systems to be developed in the future in the territorial sea of Lower Saxony. Since the connection of these systems to the transmission grid will take place either in the control area of Amprion or TenneT, the companies jointly submitted an application for the implementation of a regional planning procedure (ROV) in December 2020. Within this ROV, the transmission system operators (TSOs) Amprion and TenneT are working together to secure areas suitable for laying offshore grid connection systems. The ROV is not about approving a specific grid connection system.

Spatial planning proceedings

What is a spatial planning procedure?

In a ROV (spatial planning procedure), the responsible state authority examines the spatial compatibility of spatially significant plans and measures from a supra-local perspective. This assessment also includes the identification, description and evaluation of probable environmental impacts of a project. Spatially significant planning with supra-local importance include the construction of high-voltage overhead power lines, the construction of a federal freeway or the expansion of federal waterways. The spatial planning ordinance specifies which plans and measures are to be examined in a ROV. The implementation of a ROV is not mandatory for underground cable planning in Lower Saxony. However, the responsible state planning authority can also initiate a ROV for other spatially significant plans of supra-local importance. This is the case in the ROV "Seetrassen 2030".

In addition to the participation of public agencies (municipalities, specialised authorities, associations, etc.), the procedure also serves as an early hearing and information of the public. After initiation of the ROV by the responsible state planning authority, there is an opportunity to inspect the documents and subsequently comment on the planning. This is followed by the so-called public hearing, in which the previously evaluated comments of all affected parties are discussed together with the planning authority, state planning authority, public interest groups and nature conservation associations. 

What is the result of a spatial planning procedure?

The ROV ends with a so-called spatial planning decision on the spatial compatibility of the planning which is to be taken into account in subsequent approval procedures and serves as an expert opinion on spatial compatibility. In the case of the planned offshore grid connection lines, a planning approval procedure is planned in the area of the territorial sea of Lower Saxony, in which a decision will finally be made on the permissibility under licensing law and the specific route of the lines will be defined. The state planning determination and the route corridor determined to be spatially compatible must be taken into account when weighing up all public and private interests.

What does the spatial planning procedure "Sea routes 2030" cover?

Subject of the ROV Seetrassen 2030 is the identification of further route corridors for crossing the territorial sea of Lower Saxony for future offshore grid connection systems. They enter the territorial sea - coming from the Exclusive Economic Zone - and extend to the landfall point on the coast. The corridors under consideration run from the 12 nautical mile line (border corridor N-III) via the islands of Baltrum and Langeoog to the respective landfall area near Dornumersiel or between Ostbense and Neuharlingersiel. The Department for Regional Development Weser-Ems is responsible for the implementation of the ROV "Seetrassen 2030".

 

 

Why do cable routes have to pass through Baltrum and/or Langeoog in the future?

Additional offshore grid connection systems are required in order to achieve the legally prescribed expansion targets for offshore wind energy of 40 GW by 2040. From a planning and technical point of view, it is possible to implement a total of twelve systems via Norderney. Currently, this area is already occupied or planned with ten systems. The realisation of two additional systems by 2030 will lead to spatial and technical bottlenecks due to the necessary project sequences on Norderney and at the landfall in Hilgenriedersiel. These will therefore only be realised after 2030. In order to avoid the bottlenecks and to enable long-term planning, new corridors for the landings and in the 12 nautical mile zone of the German North Sea are necessary. The studies carried out by TenneT and Amprion in advance show that the route corridors via Langeoog and Baltrum have the least conflict spatial resistances compared to other corridors.

Why are Amprion and TenneT responsible for connecting offshore wind farms in the North Sea?

Transmission system operators in whose control area the grid connection of offshore wind turbines is to take place based on Article 17d (1)  of the Energy Industry Act are obliged to "construct and operate offshore connection lines in accordance with the requirements [...] of the Wind Energy at Sea Act." The location of the onshore grid connection points is listed in the grid development plan in accordance with Section 12b (1) No. 7 EnWG, which results in the allocation for the respective transmission system operator. Depending on the location of the individual grid connection point, either Amprion or TenneT is then responsible for connecting the wind farms. The grid development plan is drawn up jointly by the transmission system operators and confirmed by the responsible regulatory authority in every odd calendar year (Article 12c (4) EnWG).

Why does the ROV only cover the area of the territorial sea?

The routing of the cable through the coastal sea of Lower Saxony, and in particular through the "Lower Saxony Wadden Sea" National Park, is associated with intensive planning conflicts, so that only a few areas can be considered for cable laying in principle. Planning conflicts are also to be expected on the mainland, but experience has shown that these can generally be minimised to a large extent through small-scale route variants and adapted construction. Therefore, we first consider the cable routing in the coastal sea. Starting from a landfall area on the coast, route corridors are to be developed at a later stage that allow the cable connection to be continued on land.
For the land route, only a study area with a radius of five kilometers around the potential landfall area is to be considered within the ROV in order to exclude landfall in very sensitive areas. This radius will be examined for spatial planning and environmental planning obstacles and taken into account in the ROV. The continuation to the grid connection points will then be planned in further procedures.

What has happened so far? What is the current status of the proceedings?

The process was kicked off by the application conference in November 2019, in the run-up to which Amprion and TenneT prepared a detailed desktop study. For this purpose, numerous route corridors were developed throughout the German bight and examined with regard to the aspects of spatial and environmental compatibility, technology and economic efficiency. The corridors were discussed at the application conference with the affected municipalities, authorities and other public interest groups. As a result, an investigation framework was created that specifies which variants are to be investigated and what information the application documents for the ROV must contain. A total of four corridor variants proved to be preferable and are now being considered in greater depth in the ROV: two lead via the island of Langeoog, two via the neighboring island of Baltrum. The landing areas are located in the municipalities of Neuharlingersiel and Dornum.

The Department for Regional Development Weser-Ems initiated the ROV on 11.01.2021. The application documents could be inspected from 28.01.2021 to 01.03.2021 inclusive. The purpose of the ROV is to involve public bodies, including municipalities, specialist authorities and associations, and to inform and consult the public at an early stage. Up to and including 01.04.2021, comments on the present planning could be submitted in writing, as a transcript or in electronic form, to the Department for Regional Development Weser-Ems. Subsequently, the comments are assessed and discussed with the planning authority, the planning authorities, the public interest groups and nature conservation associations at the following discussion meeting.

The ROV ends with the state planning determination on the spatial compatibility of the planning. This must be taken into account in approvals, plan approvals and other official decisions on the permissibility of projects. For each planned offshore grid connection system, a planning approval procedure must then be carried out at the Lower Saxony State Authority for Road Construction and Transport.

The ROV documents can be viewed on the following website (German version only):

https://www.arl-we.niedersachsen.de/Seetrassen-2030/seetrassen-2030-181711.html  

To what extent has the landward course already been considered?

Part of the desktop study for Seetrassen 2030 is also a consideration of possible corridor routes within a five-kilometer radius of the landfall areas. This is to prevent the emergence of a so-called planning torso (also immediately beyond the five-kilometer limit). I.e. it should be ensured that a further course towards the south is possible. The planning of the further corridor course towards the south is not part of the Seetrassen 2030, but will be considered in further procedures. The course depends, on the one hand, on the result of the seaward ROV and, on the other hand, on which grid connection points for the optimal integration of offshore generated electricity into the onshore transmission grid are confirmed in future grid development plans. In these project-specific procedures, any existing obstacles will then also be recorded and can be taken into account depending on their impact. Preliminary planning is currently underway for the three offshore projects with grid connection points Wilhelmshaven 2 (one project) and Unterweser (two projects) that have already been confirmed in the grid development plan. This procedure is being prepared a ROV Landtrassen (land routes) 2030.

What are the future plans?

Comments on the ROV were be submitted by April 1, 2021. These will then be evaluated by the project developers. The results of the assessments will be explained in detail at a public hearing which is expected to take place in the summer of this year. At the end of the process the spatial planning decision will be made.

Planning approval procedures for the individual offshore grid connection systems will then follow for the respective sea and land routes.

The commissioning of the first projects to be implemented via one of the islands is scheduled for 2029, so construction activity on or around one of the islands would be scheduled for around 2024/2025. In their application documents, Amprion and TenneT propose to develop the corridors from west to east, starting in the Baltrum area.

Island crossing using the horizontal drilling method

The plans for further offshore grid connection systems in the German North Sea within the scope of the ROV Seetrassen 2030 provide for the island crossing with the so-called horizontal drilling method. This concerns the two East Frisian islands of Baltrum and Langeoog. In the case of the lines implemented to date via the island of Norderney, the island crossing was also carried out by means of horizontal drilling using the so-called HDD method. This method is state of the art and has significant advantages in terms of minimising the required intervention. On the island of Norderney, seven grid connection systems have been implemented in this way in recent years or are currently being implemented.

The crossing of the island of Baltrum would be from the Baltrum island tidal flat to the northern beach of Baltrum, i.e. the island would be crossed with a water/land borehole, starting from the tidal flat area and ending at the northern beach. Accordingly, the site would be supplied from the seaward side.

The island of Langeoog would be crossed from the Langeoog island tidal flat by means of horizontal drilling to the north beach of the island. This means that Langeoog would be crossed by means of a water/land borehole, starting from the tidal flats and extending to the northern beach. The supply of the construction site would accordingly also take place from the seaward side.

What is the horizontal drilling method?

Horizontal Directional Drilling (HDD) is a directional drilling technique for horizontal drilling. A directional drilling technique is a method that allows the direction of drilling to be influenced. This makes it possible to cross special protection areas such as dikes, dunes and seagrass meadows in a closed construction method, i.e. without having to dig up the ground for cable laying.

In the offshore grid connection systems implemented to date via Norderney, the island crossing was already carried out by means of horizontal drilling using the HDD method. This method is state of the art and has significant advantages in terms of minimising the required intervention. On the island of Norderney, seven grid connection systems have been implemented in recent years or are currently being implemented. The most recent of these were DolWin6 and BorWin5. 

How does horizontal drilling work?

Essentially, a horizontal drill works like this: Special equipment is used to drill an underground channel into which an empty cable protection tube is inserted. A power cable can then later be pulled into this cable protection tube. 

The process consists of three steps. In the first step, a pilot hole is drilled with a relatively thin rod. In the second step, a reamer is mounted on the drill pipe at the exit point and pulled in the direction of the drill entry point. This brings the drill channel to the required width. In the third step, the cable protection pipe is then pulled into the drill channel. Flowing waters, roads or rails can also be crossed underneath using this method. The boreholes can be over a thousand meters long and, thanks to innovative technology, very precisely controlled. The horizontal drilling method is used for all offshore grid connections, in addition to the island crossing, for example, also for crossing the dike to land the grid connections to the mainland.

What are the advantages of the horizontal drilling method?

The HDD method has significant advantages in terms of minimising the required intervention. It is a trenchless and at the same time extremely environmentally friendly and gentle installation technique, as earthworks can be kept to a minimum. In addition, dike safety is not compromised by this method.

Further information and film material on the subject of the horizontal drilling method can be found under the following link: Horizontal drilling method TenneT

How long will the construction take?

The planned route corridors for future offshore grid connection systems run through the Wadden Sea National Park. In order to protect flora and fauna there, we adhere to specified, annually recurring construction time windows that result not only from nature conservation restrictions but also from dike law restrictions. Construction work on the island and dike crossing is therefore essentially limited to a few months in the summer. In this way, the impact on the animal and plant world is to be kept to a minimum.

Why are the cables not routed around the islands?

The strong currents caused by the ebb and flow of the tide have such a strong effect on the seabed that safe cable laying and operation between the islands is technically not feasible. In addition, only a single system could be laid per sea lane (current channel between the islands) due to the limited space and the required distances between the grid connection systems.

What does the drilling fluid consist of?

The drilling fluid mainly consists of fresh water and bentonite, a natural clay mineral. Additives required in small quantities to regulate its flow properties are substances that are also used in food production. Both bentonite and the additives are also used in drilling for the development of drinking water wells.

What happens to the drilling fluid and cuttings after drilling?

The drilling fluid and cuttings are separated after drilling. As with all other horizontal drilling operations, the materials are disposed in accordance with legal regulations.

How will impacts to the tidelands be avoided?

In principle, the so-called zero discharge principle applies in the national park which is ensured by various measures. All machines, equipment and materials are tested for environmental compatibility, for example, and must comply with this principle. Proof of this must be provided by TenneT and Amprion before the relevant measure is started. In addition, on Norderney, a nature conservation construction monitoring is specified for the measures, which is also to be expected for Baltrum and Langeoog.

Freshwater lentils beneath the East Frisian islands

A local characteristic of the East Frisian Islands is the occurrence of freshwater lenses. Within the ROV Seetrassen 2030, this concerns the islands of Baltrum and Langeoog. The latter uses one of its three freshwater lenses for the island's drinking water supply. The other two serve as reserves for the population of Langeoog and are currently not used for drinking water production. The island of Baltrum, on the other hand, is connected to the mainland via a drinking water pipeline and keeps its freshwater lens as a reserve.

What is a freshwater lens?

Essentially, a freshwater lens, also called a Ghyben-Herzberg lens, is a watchglass-shaped body of freshwater that floats on saline groundwater. Similar to a fat eye, this property of freshwater is due to its lower density. The freshwater lens is formed by the percolation of precipitation, that is, the cavities of the sandy soil absorb the freshwater. Salt water and fresh water are further separated by a so-called brackish water zone. In this area, a mixture of both types of water takes place. Due to the nature of freshwater lenses, they cannot be clearly delineated. They change depending on the water withdrawal as well as precipitation and spread accordingly also differently. Information on the topic of freshwater lens can also be found, for example, on the pages of the University of Oldenburg or the Federal Institute for Geosciences and Natural Resources.

If drilling were to occur through a freshwater lens, would drinking water supplies be in jeopardy?

The exact location and design of the boreholes will only be decided in the planning approval procedure. One thing is certain, however: no adverse effects on the protected groundwater are to be expected. Amprion and TenneT will ensure this through intensive testing, appropriate precautions and strict compliance with the official requirements.

During drilling, an exchange between the freshwater lens and the saltwater is prevented by the sealing effect of the drilling fluid. The use of the drilling fluid will not adversely affect the chemical nature of the freshwater lenses or drinking water resources on the islands.

After completion of the drilling, the resulting annular space between the pulled-in empty pipe and the drilling channel is dammed up and seals it against the formation of seepage lines and thus the penetration of salt water.