Improving biodiversity for submarine cabling

15.10.2020

Looking at the big picture – the energy transition and the achievement of the European climate targets – there is no alternative to expanding offshore capacity for the generation and transmission of North Sea wind power. For that reason, both the Dutch and German governments have set ambitious targets for offshore expansion, which the Dutch-German transmission system operator (TSO) TenneT is gradually implementing and has even exceeded for its German North Sea control area. In the individual case, however, each offshore construction and operational measure obviously has an impact on the valuable North Sea and Wadden Sea ecosystems. As TenneT strives to apply and monitor nature-friendly solutions in all of its offshore grid projects, the TSO is now conducting pilot tests with stone coverings of submarine cable intersections.

When the TSCNET shareholder lays submarine cables, e.g. currently for the high-voltage connection of the Hollandse Kust (zuid) wind region, the cables sometimes cross with existing oil and gas pipelines. In such cases, the cables protrude above the seabed and are usually covered with a layer of granite to protect them. To replace granite with alternative solutions that promote biodiversity, TenneT has launched a pilot project in collaboration with the offshore specialist company Van Oord. In this project, different types of stones are deposited at cable crossings to investigate which of these stimulates biodiversity best. In total, the pilot involves twelve locations in the North Sea. In the case of the first six, recently laid submarine cables already cross existing oil and gas pipelines. Another six intersections will follow during the construction of the Hollandse Kust (Zuid) connection in 2021.

On 14 October, the different stones were loaded onto Van Oord’s special vessel to be placed at the cable intersections in the coming weeks. Among them are small calciferous stones from a marble quarry, which are placed at three of the six cable intersections. Comparison with the other three intersections without calciferous stones will allow to assess the difference in the type of marine life developing at these intersections. “Our expectation is that the calciferous stones will ensure that various benthic species will find it easier to nest here and that a different habitat will emerge at these sites. Over the years, ‛artificial reefs’ can emerge at these sites in the North Sea, where plants and small creatures can settle,” explains Saskia Jaarsma, Head Offshore Developments and Large Projects Offshore at TenneT.

TenneT has launched a pilot project to promote biodiversity at submarine cable intersections (picture: Van Oord)

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> See TenneT press release (html)

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German field report on underground cabling

07.10.2020

The use of underground cables for power transmission in the extra-high voltage three-phase current range is partly still uncharted technical territory for the four German TSCNET shareholders 50Hertz, Amprion, TenneT, and TransnetBW. As most projects are in the planning, approval, or construction phase, no partial earth cabling project is yet in full system operation, let alone a project with exclusive cabling. However, Tennet has commissioned the Wilhelmshaven-Conneforde line as recently as last week: It is the first 380kV line with underground cable sections in three-phase technology connected to the meshed power grid by the Dutch-German transmission system operator (TSO).

To inform politics and public about the current status of underground cabling in the national transmission system, the four German TSOs have, at the request of the German Federal Ministry for Economic Affairs and Energy, jointly prepared a field report on the use of underground cables in the extra high-voltage three-phase current range. The 65-page report examines seven different key issues in respective main chapters, covering technical, administrative, economic, environmental, and social aspects: dialogue and acceptance, approval procedures and the environment, design and construction, operation and operational safety, underground cable technology, systems engineering, and finally economic efficiency. Key findings of 50Hertz, Amprion, TenneT, and TransnetBW can be summarised as follows:

  • Partial underground cabling does not per se lead to a greater acceptance of line construction projects – compared to the construction of overhead power lines, the concern merely shifts from the residents mainly to landowners and farmers.
  • As far as planning, approval, and construction times are concerned, current experience shows that partial underground cabling requires at least one to two years more than overhead lines. More extensive implementation planning, intensive soil investigations, and negotiations with the owners consumed a great deal of time in the pilot projects. The construction itself is also more complex due to the necessary crossing of infrastructures, 40 to 60-metre-wide aisles, and major interventions in the soil ecosystem.
  • Regarding operational and system safety, underground cable installations have a lower availability rate than overhead lines, as repair times are significantly longer in case of damage. Moreover, with an increasing share of partial underground cabling, the complexity of grid operation and thus the risk to system stability also rises.
  • In terms of economic efficiency, the costs of partial underground cabling are significantly higher than those of overhead lines, and this applies to planning, construction, and operation. Depending on the project-related terrain and soil conditions, the investment costs are usually six times higher.

The four German TSOs have published their joint “Field report on the use of underground cables in the extra-high voltage three-phase current range” (picture: TenneT)

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> See TransnetBW news release, in German (html)
> Open Field Report, in German (pdf, 2.9MB)

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Wilhelmshaven-Conneforde line put in operation

05.10.2020

With the Wilhelmshaven-Conneforde line, the Dutch-German transmission system operator (TSO) TenneT has commissioned an important grid expansion project for the German and European energy transition. The 380kV line from the new substation Fedderwarden near Wilhelmshaven on the German North Sea coast to the Conneforde substation in Ammerland, both in the federal state of Lower Saxony, is not only crucial for the transmission of mainly wind power and electricity from regional generators, but also for strengthening security of supply in northern Lower Saxony. Furthermore, it represents a novelty for the TSCNET shareholder in terms of technical implementation: “With this new line, we have put into operation the first pilot project with two underground cable sections in three-phase technology and connected it to the meshed power grid in Germany,” explained Tim Meyerjürgens, COO of TenneT.

The commissioning ceremony on 2 October 2020 in Fedderwarden was attended by representatives from politics, including Andreas Feicht, State Secretary at the German Federal Ministry for Economic Affairs, and Energy and Olaf Lies, Minister for the Environment, Energy, Construction, and Climate Protection of Lower Saxony. The new line is only about 30 kilometres long, but – together with the new construction of the Fedderwarden substation – “of great importance for the entire European electricity trade”, commented Olaf Lies. The Minister was impressed by TenneT’s latest milestone in the energy transition. State Secretary Feicht referred to the newly gained potential for integrating large amounts of wind power into the German electricity market and the technical relevance of the pilot project: “Knowledge obtained in such pilot projects about the construction and operation of the technology will be of great benefit for further power grid expansion in the future.”

The line project was successfully completed after less than two years of construction. Almost 5 kilometres of the line were implemented as underground cables. However, even if TenneT can be satisfied with what has been accomplished so far and is strongly committed to expanding the transmission of green electricity throughout its entire grid area, Meyerjürgens sees a need for further action, especially in view of the increasing offshore wind volumes: “Still, we already see today a further demand for expansion in the Wilhelmshaven and Friesland region.”

TenneT commissioned the new Wilhelmshaven-Conneforde line (picture: TenneT)

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> See TenneT press release, in German (html)

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TenneT commissions North German grid node

02.10.2020

The town of Wilster is located about 10 kilometres north of the Elbe river in the German federal state of Schleswig-Holstein, which falls within the control area of the Dutch-German transmission system operator (TSO) Tennet. Schleswig-Holstein is of eminent importance for the generation of wind power. In Wilster, after a four-year construction period, the TSCNET shareholder commissioned the renewed Wilster/West substation on 1 October, a significant grid node for the energy transition in the north and beyond. This is because the so-called Westküstenleitung (West-Coast-Line), the NordLink interconnector, which directly links the electricity markets of Germany and Norway, are converging here – and later also the SuedLink “electricity highway” for the transmission of green electricity to the German consumption centres.

For the two high-voltage direct current (HVDC) transmission projects NordLink and SuedLink, the capacity of the former Wilster/West substation was no longer sufficient. An extension of the switchgear was necessary to exclude impermissible load flows and guarantee the short-circuit resistance required in future. Thus, a new 380kV switchgear was built on the ground of the former 380kV substation and the new construction now replaces the old substation on the same site. Furthermore, the connection facilities for the converter stations of SuedLink and NordLink had to be provided. And finally, a 110kV switchgear was installed, which enables the dismantling of the 220kV switchgear in the near substation Itzehoe-West.

“This substation is a central hub for electricity transmission from north to south,” explains TenneT’s COO Tim Meyerjürgens. “Here, electricity from renewable sources is fed into the grid and distributed to regions with high consumption. The Wilster area is of outstanding importance for the energy transition. Because in the grid area between Wilster, Brokdorf, Itzehoe, and Brunsbüttel, three new extra-high voltage lines from TenneT converge: the Westküstenleitung, NordLink, and later also SuedLink.”

TenneT has put into operation the new substation Wilster/West (picture: TenneT)

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> See TenneT press release, in German (html)
> Watch video on the construction and commissioning of Wilster/West, in German (YouTube)

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Network Agency decides on southern routing of SuedLink

25.09.2020

700 kilometres of underground cable to be laid and an investment volume of around €10bn – this makes the 525kV line SuedLink the largest and probably most important individual project of the energy transition in Germany. The exclusive use of underground cables in the project is politically specified to increase the acceptance of the project by the population: For only if one succeeds in effectively connecting the windy regions of northern Germany with the centres of consumption in the industrially highly developed south and west via such “electricity highways” as SuedLink, the German – and European – climate targets can be achieved.

SuedLink is jointly implemented by the two TSCNET shareholders TenneT, the Dutch-German transmission system operator (TSO), and TransnetBW, the TSO from southwest Germany. The project is making step-by-step progress in the regulatory, planning, and implementation areas. This year, for example, regional planning offices have already been set up and the contracts for the cables awarded. Now the competent government authority, the Federal Network Agency (Bundesnetzagentur), has decided on the southern section between the Lower Franconian Arnstein near Schweinfurt and the Großgartach substation in the Stuttgart Metropolitan Region (SuedLink section E). This 137 kilometre long section runs through the control areas of both TSOs involved.

The Bundesnetzagentur’s decision largely follows the proposal by TenneT and TransnetBW, according to which the Würzburg metropolitan area is largely bypassed in the west. The proposal of the two TSOs had already incorporated the results of the application conferences and requirements of the Bundesnetzagentur. The last 16 kilometres to the Großgartach substation are a special construction feature. Here an existing salt mine is to be used for an underground course of the cable project. This increases construction costs, but these are outweighed by other benefits, in particular the reduced impact on the environment and residential areas. After the completion of the federal sectoral planning for the SuedLink section E, planning approval procedures are to follow which will determine the exact route of the line within the corridor and the technical implementation.

The German Federal Network Agency has decided on the southern section of the SuedLink power line, a joint project of TenneT and TransnetBW (picture: TenneT)

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> See press release by Bundesnetzagentur, in German (html)

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Deep Dig-It starts work for Hollandse Kust (zuid) grid

24.09.2020

Hollandse Kust (zuid), an offshore wind area in the Dutch North Sea, is located a good 20 kilometres off the coast of the Dutch province of Zuid-Holland. The Dutch-German transmission system operator (TSO) TenneT is installing the related offshore grid to connect the new offshore wind farms in the area via two offshore platforms and submarine cables to the onshore high-voltage substation that is being built in the Maasvlakte industrial and port area. The jacket for the first of these two offshore platforms has recently been installed and the offshore connection project is now making further progress with the start of the laying of the submarine cables on 22 September.

Four 220kV AC cables with a total length of 42 kilometres each are to be installed in the seabed, of which the first two to the Alpha platform will be laid this year. The other two to the Beta platform will follow in 2021. First, the two cables were brought ashore to the planned Maasvlakte substation via direct drilling. Thereupon the TSCNET shareholder started the marine installation, with the first ten kilometres of the route from the coast at Maasvlakte being extremely challenging. Over this distance, the cables cross the entrance to the port of Rotterdam – Europe’s busiest cargo port – and thus need to be buried more than 5.5 metres deep. For this purpose, the contracted specialist company Van Oord uses its Deep Dig-It trencher, an enormous remote-controlled trencher.

The Deep Dig-It is one of the largest and most powerful devices in its class. The trencher weighs 125 tonnes, is more than 17 metres long, well over 8 metres high, and 11 metres wide. With its enormous power it can bury cables deeply even in very hard ground. The trencher is controlled from an offshore installation vessel equipped with a crane to lower and lift out the high-performance machine. The Deep Dig-It moves unmanned over the seabed and creates a deep trench for the cables by liquefying the seabed. Simultaneously, the Deep Dig-It inserts the cables into the trench and seals the seabed afterwards. With work progressing well, Tennet expects the 1,400MW Hollandse Kust (zuid) grid connection to be completed in 2022.

TenneT has started the laying of submarine cables for the Hollandse Kust (zuid) grid connection (picture: Van Oord)

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> See TenneT press release (html)
> Watch TenneT video of the Deep Dig-It at work (YouTube)

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Cooperation to link offshore wind farms

22.09.2020

Realising the full potential of offshore wind energy in the North Sea will be crucial for the decarbonisation of the European economy and society. The transmission system operators (TSOs), whose control areas border the North Sea, are aware of this, including the Dutch-German TSO TenneT and National Grid from the UK. Both the Netherlands and the UK have set ambitious targets for their respective development of wind capacity in the North Sea. However, to achieve large-scale growth in offshore wind energy, significant amounts of new infrastructure and close cooperation between the countries around the North Sea will be essential.

On 22 September, TenneT and National Grid announced a cooperation agreement to examine the feasibility of interconnecting Dutch and British wind farms to the energy systems of both countries via submarine cables. The announcement is following a recent decision by the Dutch government to secure the first 2GW offshore transmission grids for high-voltage direct current (HVDC) in the Netherlands for the IJmuiden Ver wind farm zone, located some 80km off the Dutch north-west coast. Under the cooperation agreement, TenneT and National Grid will explore the development of a multi-purpose interconnector (MPI) to simultaneously connect up to 4GW of Dutch and British offshore wind energy between the two national electricity systems, thereby creating an additional 2GW of interconnection capacity.

By connecting to both systems, the MPI will allow the use of free transmission capacity for electricity trade between the two countries, thus improving the utilisation of offshore infrastructure – and possibly decreasing the need for additional infrastructure. This will also reduce the environmental impact on coastal communities compared to the current approach of separately developing and connecting interconnectors and wind farms. The two TSOs intend to have defined a “pathfinder project” by the end of 2021 with the aim of creating an operational system by 2029.

Manon van Beek, CEO of TenneT, comments on the agreement: “TenneT has been at the forefront of developing multi-purpose interconnection to enable the large-scale growth of offshore wind in the North Sea. This agreement allows us to work with National Grid in the North Sea to develop innovative infrastructure that uses every spare electron of offshore wind generation to reach our decarbonisation targets.”

TenneT has concluded an agreement with National Grid to investigate the interconnection of UK and Dutch offshore wind farms (exemplary picture: TenneT)

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> See TenneT press release (html)

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Delay for Interim Coupling

11.09.2020

To introduce single day-ahead coupling in a total of 23 European countries, the so-called 4M Market Coupling Countries (4M MC) – Czech Republic, Hungary, Romania, and Slovakia – are to be connected to the Europe-wide Multi Regional Coupling (MRC) of the electricity market. The initiative to implement the MRC extension is the DE-AT-PL-4M project, also referred to as “Interim Coupling Project”. It aims to establish implicit capacity allocation based on Net Transfer Capacity (NTC) at six borders: PL-DE, PL-CZ, PL-SK, CZ-DE, CZ-AT, and HU-AT. The TSCNET shareholders 50Hertz, APG, ČEPS, MAVIR, PSE, SEPS, TenneT, and Transelectrica – transmission system operators (TSOs) from Austria, Czechia, Germany, Hungary, Poland, Romania, and Slovakia – participate in Interim Coupling.

After the project had completed the design phase and entered the implementation phase at the end of 2019, Interim Coupling was actually supposed to start in September 2020. The TSOs and Nominated Electricity Market Operators (NEMOs) involved have now announced that the kick-off must be postponed. This is due to several project parties experiencing local implementation bottlenecks in the first quarter of 2020 because of interrelations between ongoing parallel projects. This led to a delay of several months in the implementation activities for Interim Coupling. National regulatory authorities have asked the European Commission to provide guidance on how to proceed with this project. Market players will be informed as soon as possible about the next steps.

The start of the AT-PL-4M MC project has been postponed

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> See MAVIR press release, html
> See PSE press release, html
> See SEPS press release, html
> Open AT-PL-4M MC information paper provided by Transelectrica (pdf, 262.12kB)

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Jacket for Hollandse Kust (zuid) Alpha platform installed

08.09.2020

The offshore wind area Hollandse Kust (zuid) is located 22 kilometres off the coast of the Dutch province of Zuid-Holland. The Dutch-German transmission system operator (TSO) TenneT will connect the wind farms in this area to the onshore substation in the industrial and port area of Maasvlakte via two offshore platforms – Alpha and Beta – and submarine cables. The jacket for the Hollandse Kust (zuid) Alpha platform was transported to the operation site by a heavy-duty vessel on 5 September and successfully installed on the seabed. The Alpha jacket is 29 meters long, 20 meters wide, 46 meters high and weighs 3200 tonnes. It will be further installed in the coming days.

The two 220kv submarine cables will be connected to the jacket over the next few months. In 2021, the platform top side will be placed on the jacket. The Hollandse Kust (zuid) Alpha platform is expected to be operational by the end of 2021. The projects in this new wind area are part of the large-scale offshore expansion programme of TenneT. By the end of 2023, the TSCNET shareholder will have installed 3.5GW of offshore grid connections in the Netherlands, of which the first 1.4GW have already been achieved with Borssele Alpha and Beta. The connection to follow Hollandse Kust (south) will be Hollandse Kust (nord). For all the wind farms in these two areas, TenneT will deploy five identical 700MW transformer platforms and identical 220kV cable connections. “Such standardisation enables TenneT to complete these projects more efficiently, more quickly, and more economically,” explains TenneT COO Tim Meyerjürgens.

The Dutch national roadmap for offshore development provides for an additional 6.1GW of offshore wind farms in the wind energy areas Hollandse Kust (West), Ten Noorden van de Waddeneilanden, and IJmuiden Ver from 2024 to the end of 2030. For the first two areas, TenneT will again use standardised 700MW offshore platforms. The efficient connection of IJmuiden Ver, which is located further out in the North Sea, partly requires other technologies based on DC instead of AC. IJmuiden Ver will have two offshore transformer platforms with a capacity of 2GW each, which is unique in the offshore wind industry.

TenneT has installed the jacket for the Hollandse Kust (zuid) Alpha platform (picture: TenneT)

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TenneT commisions “green” substation

04.09.2020

In recent years, the seaport of Eemshaven in the province of Groningen in the north of the Netherlands has become more and more important for the Dutch energy transition. Eemshaven has taken on the role of an energy port: with power plants, sustainable generation, connections to offshore wind farms, and submarine cable interconnectors to Norway and Denmark. The Dutch-German transmission system operator (TSO) TenneT – together with regional distribution system operator (DSO) Enexis Netbeheer – now has commissioned the new high-voltage substation Eemshaven as the first substation entirely built for the suply of wind and solar energy.

The station was built as part of the grid reinforcement for the growing amount of sustainably generated energy in the north of the Netherlands which requires an increase in transmission capacity. Other measures of the TSCNET shareholder include a 380kV connection between the Eemshaven (Oudeschip) high-voltage substation and Vierverlaten near Groningen as well as the extension of the Vierverlaten substation. This new 380kV “power highway” will replace the existing 220kV line. Until it is put into operation – scheduled for 2023 – TenneT will commission a provisional 380kV substation in Eemshaven (Oostpolder) in October 2020.

TenneT has put into operation the new substation Eemshaven for the supply of green electricity (picture: TenneT)

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> See TenneT press release, in Dutch (html)

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