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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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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TenneT records 21% increase in offshore transmission

28.07.2020

In the first half of 2020, the wind energy transmitted from the North Sea ashore by the Dutch-German transmission system operator (TSO) TenneT rose to 11.51TWh. This represents an increase of 21.1% compared with the 9.51TWh in the first half of 2019, bringing the North Sea’s share of total wind power generation in Germany to 15.6%. The maximum feed-in volume from offshore wind farms in the German North Sea was 6,035MW on 2 January 2020. By 30 June, the generation capacity of the German North Sea wind farms reached 6,679MW, a volume which is exceeded by TenneT’s offshore transmission capacity of 7,132MW. This amount, which is higher than the German government’s 2020 target (6.5GW for the North and Baltic Seas combined), is currently being achieved with twelve German offshore grid connections.

Tim Meyerjürgens, COO of the TSCNET shareholder, comments on the impressive figures: „The expansion and integration of offshore wind energy is of central importance for the European energy transition.” And offshore development is also keeping pace in the Dutch market: “With Borssele alpha and – from mid-August – Borssele beta, we have now also successfully completed the first two offshore connections in the Dutch North Sea.” TenneT promotes capacity expansion with technical innovations and, according to Meyerjürgens, wants to remain a driving force in the offshore sector: “Ever since TenneT set the standard for plastic-insulated DC cables at 320kV in the offshore sector around ten years ago, we have been defining a new global benchmark for the future with our 525kV DC subsea cable system and its transmission capacity of two GW.”

The 525kV development programme should lead to a standardised cable system that the TSO can employ by 2030 for the three German North Sea projects BalWin1, BalWin2, BalWin3 and the two Dutch projects IJmuiden Ver alpha and beta as well as in potential further projects of equal power and voltage. TenneT is expecting lower costs, greater security of supply and less impact on the environment. These efforts require considerable investment: “We have an investment programme of around €20bn earmarked for connecting offshore wind energy in the Netherlands and Germany by 2030,” explains Meyerjürgens. Important in this context are also hydrogen and hybrid initiatives. The North Sea Wind Power Hubs proposed by TenneT explicitly include power to gas concepts. Furthermore, in June, TenneT proposed to the EU and the Dutch and German governments an integrated energy system approach for the international offshore development.

TenneT increased its transmission of offshore wind energy by 21% in the first half of 2020 (picture: TenneT)

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Foundation laid for DolWin6 converter

28.05.2020

With a dozen operating offshore connection systems for wind farms in the German North Sea totalling a transmission capacity of 7.132GW, the Dutch-German transmission system operator (TSO) TenneT has already in 2019 exceeded the German government’s expansion target for offshore wind energy capacity for 2020 by more than half a million GW. A further 900MW will be provided by DolWin6, like the predecessor projects DolWin3 and BorWin3 a high-voltage direct current (HVDC) connection. The DolWin kappa offshore platform in the Wadden Sea near the island of Norderney will convert the three-phase wind current into DC for transmission via a 45 kilometre submarine cable to the East Frisian mainland and from the landing point via an underground cable, also around 45 kilometres long, to the TenneT site in Emden/East.

Here, the TSCNET shareholder is constructing the DolWin6 onshore converter station and a substation on 23,500m² to reconvert the DC into three-phase current for feeding into the onshore extra-high voltage grid. A significant milestone for DolWin6 was reached on 27 May: The laying of the foundation at the converter construction site was celebrated in Emden/East by embedding a time capsule with coins, a regional daily newspaper, and construction plans into the foundation stone. Due to the Covid-19 pandemic, the event was only celebrated with the most important project managers from TenneT and the plant constructor Siemens.

Concrete preparations for DolWin6 began in the summer of 2017 and 2018 with horizontal drilling on Norderney. In September 2019, the foundation work commenced in Emden/East. Work on the DolWin kappa offshore platform at a dockyard in Cádiz/Andalusia also started in mid-2019 and the DolWin6 cable laying will follow from summer this year. The completion of the HVDC offshore connection is scheduled for 2023.

TenneT celebrated the laying of the foundation stone for the DolWin6 converter in Emden/East (picture: TenneT)

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TenneT develops 525kV HVDC offshore cable system

20.04.2020

In just 10 years, 40% of the Dutch electricity demand will be covered by offshore wind power. Furthermore, the Dutch-German transmission system operator (TSO) TenneT will increase the German offshore grid connection capacity to 17GW by 2030. To meet these high ambitions, the TSCNET shareholder expands its current connection plans and additionally intends to implement a total of five 2GW offshore connections in the Dutch IJmuiden Ver wind energy area and in the German LanWin and BalWin areas. However, since such 2GW offshore grid connections do not yet exist, innovative project development is necessary.

The integration of 2GW offshore grid connections into the onshore grid requires a suitable certified cable system that operates at a voltage level of 525kV DC using extruded insulation types. TenneT has contracted a total of eight cable suppliers to develop these “next-level” submarine cables for the intended high-performance offshore connections. An extruded 525kV high voltage direct current (HVDC) cable system with a 2GW output is currently not implemented in any project worldwide and would thus set a new standard for the connection of offshore wind farms.

The new cable system is expected to reduce manufacturing and installation costs for the entire connection concept, including the HVDC offshore and onshore transformer stations. A reduction in dredging costs is also anticipated, as all cables can be laid in a single trench. Moreover, fewer offshore platforms and shore stations are required, resulting in lower emissions and environmental impact. The adoption of a 525kV 2GW grid concept is a logical step for TenneT after the installation of eight standard AC connections in the Netherlands. The TSO can already draw on extensive experience with DC projects in Germany.

TenneT has contracted eight cable suppliers to develop a 525kV HVDC offshore cable system with a 2GW capacity (exemplary picture of Riffgat cables: TenneT)

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Deep Dig-It trencher at work for TenneT

09.03.2020

The Hollandse Kust (South) offshore wind area in the Dutch North Sea is located 22 kilometres off the coast of the Dutch province of Zuid-Holland. TSCNET shareholder TenneT is responsible for connecting the wind farms under construction there via two corresponding offshore platforms to the onshore high-voltage substation in the industry and port area of Maasvlakte, from where the green electricity is transmitted further to the Randstad 380kV South Ring power line in the Dutch Randstad region, the most densely populated area in Europe, and further.

But there is a major challenge to be met by the Dutch-German transmission system operator (TSO): On the first ten kilometres of the offshore route, the four submarine cables to be laid are crossing the entrance to Europe’s busiest cargo port, the port of Rotterdam. To pass through the busy Rotterdam-Maasmond shipping lane, the cables here must be buried more than 5 metres deep into the seabed. For this specific job, the Dutch maritime contracting company Van Oord designed and built the Deep Dig-It trencher, a gigantic remote-controlled trencher.

Last Friday, final tests were carried out in the Aleksiahaven of Maasvlakte in preparation for the actual laying of the submarine cables in July. The innovative device is a so-called Tracked Remotely Operated Vehicle, which drives unmanned over the seabed, creates a deep trench for the cables, inserts the cables and closes the trench again. The Deep Dig-It is the largest and most powerful machine in its class. The trencher weighs 125 tonnes, is more than 17 metres long, well over 8 metres high and 11 metres wide. This makes it possible to bury cables in very hard ground, while the burial depth that can be achieved with the Deep Dig-It is well over 5 metres.

TenneT employs the powerful Deep Dig-It trencher to connect the Hollandse Kust (South) wind farms to the onshore grid (picture: Van Oord nv)

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COBRAcable proves to be a great success

06.03.2020

It is now half a year since TSCNET customer Energinet, the transmission system operator (TSO) from Denmark, and TSCNET shareholder TenneT, the Dutch-German TSO, made COBRAcable available to the market. The high-voltage DC cable with a length of about 325km and a capacity of 700MW is the first direct connection between the electricity markets of Denmark and the Netherlands. The basic idea behind COBRAcable is to compensate for the volatility of wind power. Consequently, the Netherlands imports electricity via the cable on days with large Danish wind power generation, while on days with little wind in Denmark the electricity is transported in the opposite direction.

This works perfectly, as the interconnector’s transmission data from the first six-month period prove: In total, Denmark has imported almost 700GWh via the COBRAcable and the Netherlands almost 1,400GWh. On average, COBRAcable was operated at full capacity 79% of the time during the last half year. The impressive traffic on this binational connection proves its adequacy through its operation. The new interconnector therefore substantially contributes to the energy transition by exchanging volatile renewable energy across borders and additionally creates a trading profit on the spot market for electricity – a multiple benefit for nature, society and the companies involved.

The transmission data from the COBRAcable of Energinet and TenneT confirm a high level of traffic on the line (picture: screenshot taken from Energinet-video “Constructing the green COBRAcable”, Vimeo)

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Ostwind 1 in regular operation

14.02.2020

In April 2019, the Arkona wind farm in the “Westlich Adlergrund” cluster in the Baltic Sea near the German island of Rügen was commisioned, giving the go-ahead for full operation of the Ostwind 1 grid connection of TSCNET shareholder 50Hertz, the transmission system operator (TSO) from northeast Germany. Ostwind 1 is the first grid connection in the Baltic Sea with 220kV three-phase current technology, which enables a higher transmission capacity.

Now Ostwind 1 has gone into regular operation and the two connected wind farms, besides Arkona also the Viking wind farm, have been successfully connected to the onshore grid on schedule. But 50Hertz considers this success no cause to rest on its laurels, for the expansion of offshore wind energy must continue if the energy transition is to succeed. This is why the TSO has already made good progress with the follow-up project Ostwind 2.

For instance, 50Hertz has long since begun preparations for the construction of three submarine cable systems for the Ostwind 2 project. For the land section, the 12 nautical mile zone of Mecklenburg-Western Pomerania and an approximately 5km-long section in the exclusive economic zone, the building permits have already been issued. 50Hertz has set up a new website for the Ostwind 2 project, where further information can be found.

Ostwind 1 grid connection of 50Hertz in the Baltic Sea has gone into regular operation (picture of Arkona wind farm: Ein Dahmer / CC BY-SA 4.0)

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Borssele Alpha ready to operate

05.09.2019

Just one month ago, TSCNET shareholder TenneT fully implemented BorWin3 in the German Bight, the twelfth offshore grid connection project of the Dutch-German transmission system operator (TSO). Now there is once again good news for the energy transition, this time from the Dutch North Sea: Borssele Alpha, TenneT’s first and largest connection system for wind farms in Dutch territorial waters, is ready for operation – right on schedule and within budget. From 2020 on, Borssele Alpha will supply the green electricity from the offshore wind farms Borssele I and II ashore.

The two Borssele wind farms will have a capacity of around 700MW. The Borssele Alpha grid connection will transmit the electricity to the substation near the town of Borssele in the Dutch province of Zeeland, where TenneT has built a new transformer station next to the existing station. The Borssele grid connection is TenneT’s first Dutch major project under the National Energy Agreement for offshore wind farms and fully complies with the conditions set out in the Dutch government’s Offshore Wind Energy Development Framework.

According to the Energy Agreement, TenneT will have installed 3,500MW of grid connections for offshore wind farms by the end of 2023. The next project is Borssele Beta, followed by Hollandse Kust (zuid) Alpha and Beta and Hollandse Kust (noord). TenneT’s standardised procedure for offshore connections will make it possible to complete these projects more efficiently, quickly and economically. In line with the Dutch Follow-up Roadmap for Offshore Wind Energy, a further 6,100MW of offshore wind energy will be realised between 2024 and 2030.

The Borssele Alpha offshore grid connection of TenneT is operational (picture: Screenshot taken from the Borssele video)

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