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Offshore Wind Journal

30-GW hub would connect thousands of offshore turbines

Fri 10 May 2019 by David Foxwell

30-GW hub would connect thousands of offshore turbines
A North Sea hub of the type envisaged in the Danish study would enable electricity from offshore wind to be distributed across borders

New grid connection concepts are being developed as part of European research projects, including an offshore island in the North Sea, for which Danish companies are examining the technology needed to make such a vision a reality

The Centre for Electric Power and Energy at the Technical University of Denmark (DTU) is leading a research project examining the feasibility of a wind power ‘hub’ in the North Sea that would handle power from multiple windfarms and distribute power to countries in the region.

Working closely with Energinet, Vestas, MHI Vestas, Siemens Gamesa, ABB, NKT, Siemens and Ørsted, the DTU is focusing on the technology required to make such a hub feasible.

The hub, should it be built, would be based on an artificial island or a large floating structure built in a suitable location to service offshore windfarms and provide power to the Netherlands, Germany, the UK and Denmark. Energy from offshore windfarms in the North Sea would be transmitted via the hub.

It may sound like a far-off vision, but Professor Jacob Østergaard from DTU Electrical Engineering believes it can become reality in the near future.

“With this concept, it will be possible to ensure green energy for most of northern Europe,” said Professor Østergaard. “At the same time, this could fuel a new North Sea industry that could eventually replace oil, so we need to quickly start mapping the technological challenges we need to overcome.”

Over the next 18 months, the project partners will bring together Danish companies and R&D organisations to determine what kind of research and technological development would be needed to realise the vision.

The Danish Energy Agency’s Energy Technology Development and Demonstration programme (EUDP) has provided €295,000 (US$330,000) for the project. EUDP chairman Thea Larsen said, “We are happy to support the North Sea Energy Hub because it helps look after long-term Danish commercial interests and the associated need for new technology. This is in line with the EUDP’s strategy.”

The hub would need capacity to receive energy from several thousand wind turbines and handle around 30 GW of offshore wind capacity. 

The project partners believe an energy island in the North Sea has a number of benefits. Rather than windfarms located far offshore in the North Sea having to transmit power over great distances to land, they could transmit the power they produce to the hub, which would reduce complexity and costs.

In addition, energy from the hub could be transferred from the offshore island to shore through powerful shared connections which, in addition to transferring energy to shore, could be used as international interconnectors that would enable countries to trade electricity.

The idea is that the structure would be built in modules, so that, over time, it would be possible to expand the hub with more islands or enlarge it so that up to 180 GW of offshore wind capacity could ultimately be handled. To get to that point, a lot of new technology would be required, both to transmit energy and to store it, hence the project.

Ørsted vice president Ulrik Stridbæk said, “offshore wind power has now become so cheap that it is one of the most competitive forms of energy in the green transition in Europe. According to the EU Commission, 400 GW of offshore wind capacity is to be built by 2050, and the North Sea is becoming a key part of Europe’s energy transition. The hub concept is a tremendous opportunity for Denmark, Danish consumers, and Danish industry, but it will require advances in technology and new solutions, particularly in terms of transmission. This project could be an important step on the way.”

Future grid connections could take a very different form to existing concepts, and make use of huge hubs that collect and distribute electricity from multiple windfarms

In the nearer term, more conventional technical advances are being made, among them a project by Dutch transmission system operator TenneT to build 2-GW convertor stations – which would be significantly larger than existing ones – and install cables with the same capacity in a bid to reduce their number and to reduce costs.

The company is currently in the planning stage for the grid connection for offshore windfarms due to be brought online between 2024 and 2030 and said it plans to use 2-GW connections for the IJmuiden Ver wind area.

In total, the transmission system operator (TSO) is to connect 6.1 GW of offshore wind to the Dutch high-voltage grid in that period. It wants to use technology that is as cost-efficient and as ‘future-proof’ as possible and to do so while protecting the environment during construction.

TenneT chief executive Manon van Beek said the plan would help accelerate the energy transition. “Based on our experience with innovative technology in Germany, we can achieve Dutch ambitions for the development of offshore wind with fewer cables and fewer platforms and less impact at sea and on land,” she said.

TenneT’s standardised concept based on 700-MW offshore transformer stations will be used in the Hollandse Kust (West) and North of the Wadden Islands areas to ‘bundle’ electricity from the windfarms there and transmit it ashore using 220-kV cables.

In the IJmuiden Ver wind energy area, which is further out at sea, two direct current connections consisting of cables and converter stations will be used that will have a capacity of 2 GW. The cables used here will be 525 kV.

By scaling up to 2 GW, only two cables instead of six will be required, reducing costs overall, and they will require less space. Fewer cable routes on land will also be required. The TSO said a connection from IJmuiden Ver to the UK has the potential to be used as an interconnector.

The Flemish Government and Belgian transmission system operator Elia have proposed plans for a new high-voltage grid connection for offshore wind that will connect to the Stevin line and potentially form the basis of an interconnector with the UK. They have launched a consultation on ‘Ventilus’, a high-voltage project in west Flanders. Flemish Environment Minister Koen Van den Heuvel said the project would be essential to enable Belgium to connect additional offshore wind power. The route for the connection will be determined once the general public and interest groups have had their say. Ventilus will also help Belgium to meet its climate targets, including a National Energy and Climate Plan that states that 18.3% of its energy consumption must come from renewable sources by 2030.

Wind energy is Belgium’s biggest source of renewable generation (8% of the total energy mix). This will grow as more offshore wind is built in the Belgian part of the North Sea. Ventilus will enable this additional electricity to be transmitted from the North Sea to consumers onshore. There will also be a link with the existing Stevin line, which became operational in 2017. Connecting the two projects with each other will make Belgium’s power grid more robust and more reliable. In the long term, Ventilus will also make it possible to build a second subsea connection with the UK, alongside the existing Nemo Link project that became operational at the start of this year. 

The government hopes to determine the final route for Ventilus in 2021. The next step will be to apply for an environmental permit. Work on building it is expected to begin in late 2022.

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