Offshore brochure I September 2024
Offshore wind solutions
Engineering that excites
Table of content
5 Combining past and present worlds 7 The design and engineering of offshore substations
Safety in design
Offshore substations 12 Pilot for offshore hydrogen production
Floating offshore substation
16 Sofia HVDC offshore converter platform
18 Neart na Gaoithe HVAC offshore substations
20 2 GW Programme IJmuiden Ver 22 Borssele Alpha & Beta HVAC offshore substations
24 Princess Elisabeth Island
26 HelWin Beta offshore converter platform
28 Thor HVAC offshore substation
30 DolWin Alpha HVDC offshore converter platform 32 Ostwind 3 and Gennaker East & West
32 HVAC offshore substations 34 Horns Rev HVAC offshore substation
2
Combining past and present worlds
Roots and renewables
Although most of our work today is in offshore renewables, our roots are in the oil & gas industry. This experience has provided a solid foundation for developing offshore wind substations, both HVAC and HVDC and, more recently, hydrogen energy solutions such as offshore hydrogen production. As a result, we have developed additional knowledge and skills to meet the challenges of these new projects: adapting to the evolving offshore wind market, meeting new operator requirements, engaging with new stakeholders, incorporating innovative technologies, and handling a broader engineering scope.
Iv is proud to be one of the first to operate in the offshore wind sector, paticularly in the field of offshore substations. We are proud to have developed and engineered the first HVAC substation Horns Rev. A, as well as the first HVDC offshore converter platform BorWin Alpha. Not only were we among the first in substations, we were also at the forefront of the step up to > 1,000 MW HVAC and to 1,300 MW HVDC. Our dedication to innovation did not stop there. A key milestone was the progression to 2GW-525 kV bi-pole HVDC, which is now being brought to life as 2 GW Standard Design for TenneT for application in the Dutch and German North Sea, highlighting our role in pushing the boundaries of offshore wind energy.
We constantly seek the optimum balance between flexibility, efficiency, sustainability and cost, while never compromising on quality and safety in our designs.
The design and engineering of offshore substations
Smart solutions, powerfull results
At the moment, onshore wind energy is the most economical way to produce sustainable energy. However, in the long term, the use of offshore wind farms offers significant benefits.
An offshore location provides ample space for the facility, higher wind speeds than on land and unobstructed areas. The energy generated by wind farm turbines is collected at an offshore substation, where it is transformed to a higher voltage for transportation to shore via large export cables.
Iv has gained a lot of experience in the design and engineering of HVDC offshore converter platforms and HVAC offshore substations over the last couple of years, excecuting many wind energy projects in close cooperation with our partners.
Safety in design
Our core principle
Our overall HSE project design objectives are to engineer a safe, reliable and operable facility for the entire service life of the installations. Throughout the design, we constantly ask ourselves and each other, “Can we make our design safer?” We view this as a responsibility towards our clients, stakeholders and their personnel.
Our ‘safety in design’ principle is always developed to at least comply with the applicable legislative codes and standards as a minimum. We are committed to going above and beyond the requirements. We actively encourage every member of our team to critically assess and challenge our chosen solutions to ensure we are adopting the safest practices possible.
Offshore substations
UNITED STATES CANADA
EMPIRE WIND
800 + 1,200 MW
VINEYARD WIND
800 MW
SEAGREEN 1,500 MW
BERWICK BANK 1,150 MW
NEART NA GAOITHE 2 X 225 MW
SOFIA 1,320 MW
SOUTH COAST 1,300 MW
MARWIN 420 MW
ATLANTIC OCEAN
IRELAND
Engineering that excites
UNITED KINGDOM
IJMUIDEN VER BÉTA 2,000 MW
POSHYDON 1,250 MW
NSE HYDROGEN 500 MW
GREATER GABBARD 2 X 252 MW
PRINCESS ELISABETH ISLAND 3,400 MW
HORNS REV B
NORTH SEA
DENMARK
HORNS REV A
MW
BORKUM RIFFGRUND 2
MW
BORWIN ALPHA
IJMUIDEN VER GAMMA
MW
DOLWIN ALPHA
NETHERLANDS
BORSSELE ALPHA + BETA
2 X 700 MW
THORNTON BANK 325 MW
BELGIUM
OSTWIND 3 300 MW
GERMANY
GENNAKER EAST + WEST 460 MW
HVAC
• THOR
• GENNAKER EAST + WEST
• OSTWIND 3
• NEART NA GAOITHE
• PRINCESS ELISABETH ISLAND
• BORSSELE ALPHA + BETA
• BORKUM RIFFGRUND 2
• GREATER GABBARD
• THORNTON BANK
• HORNS REV A
• HORNS REV B
HVAC STUDY
• BERWICK BANK
• EMPIRE WIND
• MARWIN
• SEAGREEN
• VINEYARD WIND
HVDC
• SOFIA
• DOLWIN ALPHA
• HELWIN BETA
• BORWIN ALPHA
• IJMUIDEN VER BÉTA
• IJMUIDEN VER GAMMA
HVDC STUDY
• IJMUIDEN VER
• SOUTH COAST
HYDROGEN
• POSHYDON (PILOT)
• NSE HYDROGEN (PILOT)
Client Rijksdienst voor Ondernemend Nederland (RVO)
Platform operator Neptune Energy
Facts
Type: PEM electrolyser
Nr. of cell stacks: 1
Input power: 1 MW
Water consumption: 300 l/h
Hydrogen flow: 246 Nm3/hr
Hydrogen purity: 99.998%
Outlet pressure: 30 barg
Footprint: 2 x 40 ft stacked containers
Lifting weight: <20 tonnes ( 2 x 20 ft cont)
Cable: 9 MVA, 25 kV
Production: 400 kg/day
Pilot for offshore hydrogen production
The Q13a-A hydrogen pilot project aims to demonstrate green hydrogen production offshore, on a live oil and gas production platform. The lessons learned will help enable large-scale green hydrogen production in the North Sea.
Off the coast of Scheveningen (The Hague), the first pilot project for the integration of three working offshore energy systems will take place on the Q13 working platform, which is already electrified with renewable energy via a cable to the shore. Energy from wind and demineralised seawater will be converted into green hydrogen offshore, according to the wind profile of Eneco’s Luchterduinen wind farm. The green hydrogen will be blended with natural gas and transported via existing pipelines, allowing the existing infrastructure to be shared. The platform is expected to be in production by the end of 2024.
Iv is working with several partners in the PosHYdon consortium to create a safe environment for handling hydrogen (and oxygen) on a live oil and associated gas platform.
Technical limitations of co-production of hydrogen and North Sea gas, seawater desalination, power fluctuations and electrolyser performance will be addressed. The other partners in the consortium are responsible for identifying and addressing the requirements related to permitting, certification, and entry specifications.
A logistics, training, and skills gap analysis will also be carried out, and economic calculations will be made to determine how the value of hydrogen can be maintained when blended with natural gas. The economics of large-scale offshore hydrogen production will also be considered.
Iv is responsible for the basic and detailed engineering of the necessary adaptions to the platform to accommodate the electrolyser system, Iv is involved in the risk assessment and mitigation, and provides offshore expertise. Iv also provided the list of offshore requirements for the containers containing the electrolyser, the seawater desalination system and the power conversion system.
For the hydrogen production system to be tested on land, only a few adaptations are needed: power supply, sufficient space for the system, supply of (sea)water, disposal of brine, hydrogen use/release, oxygen release, permits to test, and permits to construct. Iv prepared a conceptual design document describing the system interfaces and further requirements for adaptations and modifications to be carried out onshore.
Client Internal R&D project
Technical data
Dimensions: 85 x 85 x 30 m
Weigth
Topside: approx.11,000 mT
Floater: 10,000 mT
Floating offshore substation
Worldwide, the best wind conditions for generating wind energy are often found at sea in areas with deeper water. The question is: how can this be achieved as effciently, reliably, and cost-effectively as possible?
At water depths beyond 150 metres, the costs of the renowned ‘bottom-founded’ offshore structures (such as transformer and converter platforms and wind turbines that are anchored to the seabed via a structure) increase exponentially, making floating solutions an interesting alternative. Iv and Nevesbu jointly developed a concept for an offshore substation. A concept with potential!
Water depth Over 150 m
Iv and Nevesbu are consistently carrying out innovative studies. In light of the forthcoming energy transition, Nevesbu began investigating which unique floating applications could be devised to provide a solution. Many concepts for floating turbines already exist, but not for a floating substation. We formed a joint initiative because Iv has already designed many offshore wind substations, and Nevesbu has unique expertise in floating structures. The challenges presented with this type of floating solution include the lifespan of the dynamic power cables and the allowable motions of the transformers, rectifiers, and associated systems. Floating an offshore substation weighing roughly 10,000 tonnes with minimal motions is a complex challenge, but our studies show that it is possible.
In Europe, the Mediterranean, North Sea, Bay of Biscay, and the Aegean Sea, in particular, are deepwater areas that are very suitable for generating wind energy. Especially in the area above Scotland and the United Kingdom towards Norway and Denmark, there are almost continuous strong winds. The concept that Iv and Nevesbu have developed is therefore designed for the harsh weather conditions that are characteristic of these areas. The concept also minimises the impact on marine life.
Some essential principles for the design of the floating offshore substation are: the concept must conform to the set requirements for wind energy at sea, it must not be too heavy in steel weight and must not be complex in terms of fabrication. Safety and reliability must also be guaranteed. It must be possible to guarantee a very high availability, and the platform must have a lifespan of at least 30 years. In addition, the social costs of supplying sustainable electricity must remain affordable, and the solution itself should therefore not be too expensive in terms of costs.
The main challenge is the transition from a static bottom-founded substation to a dynamic, floating substation. Wind turbines must be capable of operating in conditions up to Beaufort 8, which means that the floating substation must continue to function when contending with waves of 8 to 12 metres. Existing high voltage (HV) equipment, however, is not suitable for high accelerations. To guarantee motions are kept to a minimum, motion analyses were carried out to calculate how different models behave at sea in strong winds with high waves. These analyses are based on the roughest seas in the world, such as the North Atlantic Gulf Region, the Bay of Biscay and the sea near Santa Barbara, California. If the concept is suitable for these waters, it can certainly also be applied in calmer waters.
The floating offshore substation concept is designed to operate in water depths in excess of 150 metres and with minimal vertical motions in sea conditions. The deck area is 85 by 85 metres and is positioned approximately 20 metres above the water’s surface. When the substation is installed at sea, it will be held in position with the help of so-called ‘tendons’ that are vertically anchored to the seabed. The floating structure is designed to minimise the vertical motions, which also reduces the loads on the export cables suspended below the platform. Tuning the motion behaviour of the platform for different water depths and wave conditions is also relatively simple.
Client Seatrium. (formerly Sembcorp Marine Offshore Platforms)
Technical data
Dimensions
Topside: 80 x 43 x 45 m (excl. helideck) (lxwxh)
Jacket: 58 x 39 x 44 m (lxwxh)
Weight
Topside: 11,000 mT
Jacket: 4,350 mT
Water depth
28,5 metres below sea-level
Field power capacity: 1.4 GW
No of offshore substations: 1
No of WTG’s: 100
Sofia HVDC offshore converter platform
One of the largest wind farms in Europe, the Sofia Offshore Wind Farm, will be realised 195 km off the coast of North East England, in the area known as Doggersbank. With 100 wind turbines covering a total area of 593 km2, totaling a capacity of 1.4 GW and an innovative high voltage direct current (HVDC) converter platform, this wind farm will supply approximately 1.2 million British homes with sustainable energy in the future.
The Sofia HVDC converter platform, to be installed at the heart of the wind farm, will be one of the largest and most powerful offshore HVDC converter platforms currently in existence or under construction.
A 25-metre-high telecom mast will be placed on the top deck of the topside. This telecom mast will provide a direct connection to the satellite dish on land. However, the challenge here is that when the platform was ready, it was transported by ship around the Cape of Good Hope in Africa. The platform will convert electricity from 66 kV alternating current (AC) to 320 kV direct current (DC). Two export cables of approximately 220 km in length, which together form a single high voltage direct current circuit, will transport the power from the wind farm to the onshore substation in Lackenby.
When converting alternating current to direct current, heat is produced, which must be cooled. The HVAC system (i.e. heating, ventilation, and air conditioning), that is required for cooling the HV system demands a lot of space. Iv has therefore applied a new cooling concept for the Sofia HVDC converter platform. Conventionally, the cooling system is subcontracted to an HVAC contractor to design the system and supply the components.
For this project, Iv is responsible for the HVAC system, including designing it, purchasing the necessary components, and the integrating it with the process systems.
For the Sofia HVDC converter platform, an HVAC system has been chosen that uses cold water to cool the condenser rather than air. Cooling with cold water has the advantage that the highest design temperature of the seawater used is lower than the temperature of the outside air. Furthermore, the heat transfer of water is better than that of air, allowing the system to be more compact.
The water-cooling system allows lower temperatures to be achieved in the air conditioning system, and smaller ducts to be designed, which in turn require less space.
The cutting of the first steel for the fabrication of the platform took place in August 2021.
The construction of the wind farm began in early 2021, with the construction of the onshore substation in Lackenby. The offshore installation has already taken place, and the platform is expected to be operational by 2026.
Client EDF Energy Renewables (EDF-ER)
Technical data
Dimensions
OSS Topside (lxwxh): 36 x 26 x 20 m
Jacket: height 41 m + height of the buckets 12 m
Weight
OSS Topside: 1200 mT Jacket: 1261 mT
Water depth
Variation between (-)28.6 m and (-)29.8 m
Field power capacity: 450 MW
No of offshore substations: 2
No of WTG’s: 54 x 8.4 MW
Accommodation: 12 POB
Neart na Gaoithe HVAC offshore substations
Iv was awarded the contract to provide the detailed engineering and procurement services for the two Neart na Gaoithe (NnG) alternating current (AC) offshore substations. NnG is a 50:50 JV owned by EDF Renewables UK and ESB. As a subcontractor of HSM, Iv provided the detailed design and procurement of all piping, auxiliary and HVAC equipment, as well as the integration of the high voltage equipment.
Structural workshop drawings for both platforms were also produced by Iv. HSM has joined forces with General Electric Grid System (GEGS) for the engineering, fabrication, load-out and commissioning of this wind park development in the North Sea near the Scottish coast.
The Neart na Gaoithe (‘strength of the wind’ in Gaelic) offshore wind farm consists of a total of 54 Wind Turbine Generators (WTGs), located approximately 15.5 km from Fife Ness and 29 km from the East Lothian coastline. It covers an area of 105 km2. Each WTG has a capacity of 8.4 MW, resulting in a total capacity of 450 MW being fed back to the two HVAC offshore substations by inter-array sea cables.
The two offshore substations are connected via an interconnector. Each one is connected to the onshore support station via an export cable, which then connects to the onshore station to the Scottish grid system. The project will supply renewable energy to around 375,000 Scottish homes and will offset over 400,000 tonnes of CO2 emissions each year.
The offshore substation configuration consists of a receiving end connected to the 66 kV GIS. The main transformer (MT) transfers the power to the export cable at 220 kV.
Each offshore substation consists of two deck levels. The cellar deck houses the auxiliary systems for control,
platform power, communications, and platform operations, with a dedicated area (the cable deck, part of the substructure) for the pull-in of the inter-array sea cables and export cable. On the main deck, the MT is installed in the centre, with the GIS installed on either side. To improve the overall schedule and allow for the full completion, installation, and commissioning of the HV Equipment before lifting onto the main structure, the GIS modules are built separately from the main structure.
The offshore substations are normally unmanned. However, a shelter (12 POB) will be provided for emergencies. Furthermore, the substations are equipped with lifting trunnions, a pedestal crane, laydown areas, W2W platforms, a heli-lift area, and other facilities to accommodate the installation work and future maintenance services.
The engineering phase started in June 2019. On 15 January 2020, the first steel was cut. The loading of the offshore substations took place in the summer of 2022, and the substations were fully commissioned and handed over to EFD in Q1 of 2023.
Layout of the Neart na Gaoithe development.
2 GW Programme IJmuiden Ver
On 26 February 2020, Iv signed the contract with TenneT TSO b.v. to carry out the Front End Engineering and Design (FEED) for the world’s first 525 kV offshore grid connection. The FEED is part of the development of a new standard design for two network connections to the IJmuiden Ver wind farms, located in the North Sea.
The two high voltage direct current (HVDC) offshore platforms, Alpha and Beta, will have a capacity of two gigawatts (GW) and will be the world’s first HVDC platforms based on 525 kV. This voltage level is just one example of HV technologies that have never before been applied offshore.
With this innovatively high level of voltage, the platforms will be suitably equipped to supply green electricity to around four million households. This would be enough to supply around half of all private households in the Netherlands with sustainable electricity.
The technology required for this capacity has never been applied before, making this project unique. Throughout the entire design process, trade-offs will be made with regard to the lowest ‘Levelised Costs of Energy (LCOE)’ and the enhancement of nature. It is Iv’s and TenneT’s intention that nature should benefit from this project. Therefore, environmental measures have been integrated as fundamental conditions into the design criteria of the HVDC platforms.
Client
TenneT TSO b.v.
Technical data
Borssele Alpha
Dimensions
Topside (lxwxh): 58 x 32 x 25 m
Jacket (lxwxh): 28 x 27 x 55 m
Weight
Topside: 3700 t
Jacket: 2900 t
Borssele Beta
Dimensions
Topside (lxwxh): 58 x 32 x 26 m
Jacket (lxwxh): 37 x 35 x 57,5 m
Weight
Topside: 3700 t
Jacket: 2950 t
Piles: 61 m each
Field power capacity: 2 x 700 MW each
Borssele Alpha & Beta HVAC offshore substations
The offshore high voltage substations Borssele Alpha and Beta are required to link the wind farms built offshore in the Dutch North Sea. The Borssele Alpha project, followed by the Borssele Beta project, are the first large-scale grid connections to be constructed under the National Energy Agreement for offshore wind farms in the Netherlands.
HSM Offshore has taken on the engineering, procurement, construction, transport, installation, connection, and testing of the offshore substation under an EPCI contract. Iv is the subcontractor for this project and is responsible for the design, engineering, and procurement support, including the integration of the TenneT-supplied high voltage components and the balance of plant materials.
The detailed design and engineering includes both the steel jackets with skirt pile foundations and the liftinstalled topsides.
Iv is responsible for the procurement of all necessary services, materials, and equipment, as well as the onshore and offshore commissioning of all systems for the jackets and topsides, including the TenneT-supplied HV equipment. Iv also manages the interfaces with the other parts of the network connection, such as the 66 kV wind farm and 220 kV export cable connections.
The Borssele Alpha offshore substation was delivered during the summer of 2019. The Borssele Beta offshore substation, which is almost identical to the Alpha platform, was delivered in July 2020.
Client Elia
Location
45 KM off the Begium Coast
Technical data
Dimensions 6 hectares
Weight
9,000 metric tonnes
(all modules combined)
Special features
2 x 1,050 MW AC Modules
2 x 700 MW AC Modules
Facility Module
Garage
2x Diesel Generator skids
General island electrical infrastructure
All modules will be placed on an artificial island
Field power capacity: 3,400 MW
Princess Elisabeth Island
The HSI Joint Venture, consisting of HSM Offshore Energy, Smulders, and Iv, has been awarded the contract for the development of Princess Elisabeth Island—the world’s first artificial energy island off the Belgian coast, commissioned by transmission system operator Elia.
Iv is responsible for designing four high-voltage substations for Princess Elisabeth Island: two with a capacity of 1,050 megawatts each and two with a capacity of 700 megawatts. The total capacity amounts to approximately 3.5GW, sufficient to meet the annual energy needs of more than three million households.
In addition to designing the four high-voltage substations, Iv is also responsible for the facilities module and garage design. The design, which includes the development of the layout and 3D model of all transmission assets on the energy island, will be carried out from Iv’s office in Papendrecht. For prefabrication, Smulders will use its Belgian facilities, while HSM will use its facilities in Schiedam. Final assembly of the modules will take place at the HSM Offshore Energy yard in Schiedam and at the Smulders yard in Vlissingen.
The project includes 330 km of 220-kV HVAC cables, divided into two contracts of 165 km each. Additionally, the island will feature five HVAC substations equipped with transformers and gas-insulated switchgear (GIS). A unique aspect of this project is that the island will combine high-voltage direct current (HVDC) and alternating current (HVAC) for the first time. Princess Elisabeth Island will also serve as a hub for future hybrid interconnectors, efficiently combining offshore wind energy transmission with cross-border electricity exchange.
The high-voltage electrical equipment market is currently under pressure due to high demand and rising material costs, which has influenced the tender process. Despite these challenges, the contracts were awarded on competitive terms, aligning with current market conditions.
Client TenneT TSO b.v./Siemens
Dimensions
Topsides (lxwxh): 100 x 43 x 75 m
Jacket (lxwxh): 63 x 42 x 48 m
Weight
Topsides: 10,4000 T
Jacket: 4,700 T
HelWin Beta offshore converter platform
HelWin Beta is an offshore high voltage direct current converter platform. This means the incoming alternating current from the wind farms is converted into direct current by the converter platform. The converted current is then transported via inter-array sea cables and land cables to a converter station onshore, where it is changed back into alternating current. This conversion process minimises energy losses during the transport of energy from offshore wind farms to shore. The HelWin Beta platform has been installed in the German part of the North Sea in a water depth of 23 metres, and 55 kilometres off the coast of Germany.
TenneT Offshore, the operator of the project, has selected Siemens as the main contractor for the entire offshore link. Siemens granted Heerema Fabrication Group (HFG) the contract for the construction of the platform, with Iv responsible for the engineering and design of the topsides. The jacket has been engineered and designed by HFG Engineering. As engineer, Iv is also responsible for the procurement of the non-high-voltage equipment.
Iv’s Consult division will provide the workshop drawings for HFG. HelWin Beta is designed as an unmanned platform, normally operated remotely when there are no personnel on board. The HelWin Beta platform will be operated from the control centre of the electricity network in Lehrte or from the land station in Büttel.
The wind turbines in the connected farms will provide power as 33 kV AC. The turbines are connected to socalled HVAC transformer platform in the middle of the wind farm, which transform the energy to 155 kV AC. From there, the energy will be delivered to the HelWin Beta transformer platform. The energy is then first converted to 320 kV HVAC and thereafter to 320 kV DC.
During the process of energy conversion, a significant amount of heat is released in the transformers and converters. To cool down this equipment, the platform has a large water cooling system and an HVAC system, connected to the water cooling system.
The water cooling system sends fresh cooling water through circulation pumps to the equipment, maintaining a controlled temperature of 18 to 25°C. The heated water returning from the equipment is cooled by seawater heat exchangers. In order to do this, seawater is pumped up, passed through the heat exchangers, and then discharged back overboard.
The maximum capacity of HelWin Beta is 680 megawatts, enough to supply over 500,000 households with energy. The HelWin Beta platform is designed as a ‘daughter’ platform of the ‘mother’ platform HelWin Alpha.
Client RWE Thor Wind Farm
Technical data
Dimensions
Topside (lxwxh): 41 x 32 x 25 m
Jacket (lxwxh): 35 X 35 x 50 m
Weight
Topside: max. 2,900 T
Water depth
28 m
Field power capacity: 1,050 MW
Thor HVAC offshore substation
Situated in the Danish North Sea, near Thorsminde, Thor is set to become Denmark’s largest wind farm, with a capacity of approximately 1,000 MW. This project is the first of three initiatives envisioned under the country’s 2018 Energy Agreement, aiming to supply sustainable energy to over 1.5 million households. Iv, in partnership with HSM Offshore Energy, is entrusted with the role of designing and integrating the offshore substation.
This offshore substation is essential for the efficient transmission of electricity generated by the farm’s 72 wind turbines to the mainland, thereby solidifying Thor’s role in Denmark’s renewable energy strategy.
Central to this initiative is the implementation of two main 66/275 kV HVAC transformers and associated equipment, engineered to revolutionise the efficiency and environmental impact of offshore wind farms. The Thor offshore substation, one of the most powerful HVAC substations under construction, will transform 66 kV AC generated by the wind turbines into 275 kV AC and weighs less than 3,000 mT.
Upon completion, the Thor offshore wind farm will mark Denmark’s shift towards a greener future, significantly reducing reliance on fossil fuels and and increasing the use of clean, renewable energy. Led by RWE, this project reflects the necessary investment and focus on developing green energy technologies.
Expected to be operational in 2027, Thor highlights Denmark’s commitment to sustainable energy. It also demonstrates the technical expertise and innovation needed to make renewable energy a key part of global energy systems.
Client
TenneT TSO b.v./ABB
Technical data
Dimensions
Topside (lxwxh): 62 x 43.3 x 40 m (excluding helideck)
Jacket (lxwxh): 45 x 42 x 44 m
Weight
Topside: 11,000 T
Jacket: 4,000 T
Water depth
27m
Accommodation
24 persons
Input
8 cables of 155 kV AC
Output
2 x 320 kV DC
Throughput
800 MW
Power generation
2 x 3050 kV A / 10 kV Diesel
DolWin Alpha HVDC offshore converter platform
TenneT Offshore GmbH is the electrical network operator of the HVDC platforms in the German sector of the North Sea and the client for the design, manufacturing and installation of the HVDC platforms.
ABB Offshore Wind Connections is the main contractor for the entire DolWin project, which consists of the DolWin Alpha offshore HVDC converter platform, an onshore transformer substation in Dörpen (Germany) for the connection to the German electricity grid, and all the interconnecting onshore and offshore cables. Heerema Fabrication Group in Zwijndrecht (the Netherlands) was contracted by ABB to design and construct the converter platform, including its support facilities, with Iv commissioned to provide the design.
The DolWin Alpha converter platform consists of a jacket with a large topside and is equipped with an auxiliary and emergency generator, helideck, and an accommodation quarters. The legs are supported by six foundation piles driven approximately 55 metres into the seabed.
The DolWin Alpha converter platform houses an 800 megawatt HVDC converter substation. The key components of the HVDC substation comprise a 155 kilovolt Gas Insulated Switchgear (GIS) for connecting the AC cables to the wind farm, main transformers of 155 kilovolts/320 kilovolts, and a 400 kilovolt rated GIS for linking and protecting the main step-up transformers.
The substation and all its supporting systems have a minimum service life of 30 years.
Ostwind 3 and Gennaker East & West
HVAC offshore substations
Client
50Hertz Transmission GmbH
Gennaker East
Technical data
Dimensions
Topside (lxwxh): 48 x 33 x 20 m
Jacket (lxwxh): 40 x 33 x 20 m
Piles: 104 inch, 75 inch
Weight
Topside 4,800 mT
Jacket: 3,100 mT
Water depth 17 m
Field power capacity
MW
Transmission
Client
50Hertz Transmission GmbH
Gennaker West
Technical data
Dimensions
Topside (lxwxh): 48 x 33 x 17 m
Jacket (lxwxh): 40 x 25 x 40 m Piles: 104 inch, 75 inch
Weight Topside: 4,800 mT Jacket: 3,100 mT
Client
50Hertz Transmission GmbH
Ostwind 3
Technical data
Dimensions
Topside (lxwxh): 48 x 33 x 20 m
Jacket (lxwxh): 60 x 43 x 65 m
Piles: 104 inch, 75 inch
Weight
Topside: 4,800 mT
Jacket: 4,500 mT
Water depth
Field power capacity
The Ostwind 3 and Gennaker East & West projects, with a combined generation capacity of 1.2 GW, have been designed to significantly boost green energy production in the German Baltic Sea region. These projects will be overseen by the HSI consortium, consisting of HSM Offshore Energy, Smulders, and Iv, responsible for the engineering, procurement, construction, transport and installation, and commissioning of the HVAC offshore substations and jackets in these 50Hertz Transmission GmbH projects.
Initially awarded the Ostwind 3 contract, the German network operator 50Hertz has expanded its collaboration with our HSI consortium by awarding the EPCI contract for two additional substations for the Gennaker wind farm - Gennaker East and Gennaker West. The Gennaker wind farm is the largest offshore wind farm in the Baltic Sea.
Ostwind 3 will have a capacity of around 300 MW, whereas both Gennaker projects will have a total capacity of approximately 900 MW, underlining our ongoing partnership to deliver green electricity to over one million households.
These projects not only signify a strategic move towards local manufacturing in the Netherlands, reducing dependencies and strengthening economic resilience, but they also represent engineering innovation that contributes to sustainable development in the local context.
Crucially, the substructures of these projects are designed for efficient transport and installation, using a vertical barge transport method and a crane lift system.
These tailored designs, which support the topsides with a six-leg jacket, are engineered to withstand the challenging conditions of the Baltic Sea and meet the environmental noise restrictions during installation. The engineering approach for each substructure is carefully tailored to the specific site conditions. For example, Ostwind 3 will be provided with a skirt pile jacket. The Gennaker locations require an innovative solution resulting in a jacket supported by suction buckets.
Ostwind 3 is scheduled for offshore completion in Q2 2026, followed by the Gennaker East & West projects in 2027, ready to efficiently transform wind energy from 66 kV AC to 220 kV AC. It is Iv’s goal to support 50Hertz in setting new benchmarks for the efficiency and reliability of offshore power transmission, marking a significant advancement in the transition to green energy.
Client
Technical
Weight
Dimensions
Location
Horns Rev A, Danish North Sea
Capacity 160 MW
Water depth
8 metres
Horns Rev HVAC offshore substation
Horns Rev A is the first offshore (transformer) substation ever built and was installed in the world’s first large-scale offshore wind farm ‘Horns Rev 1’, which is located in Danish waters in the North Sea. Horns Rev. HSM was awarded the EPC contract of the topside and jacket. Iv performed the design and engineering and the topside with a capacity of 150 MW and 3 support piles in a water depth of 8 metres. This Tripod was designed with 5 x 36 kV J-tubes and an independent boat landing structure.
Engineering that excites
