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

TenneT has developed a vision for building a large European electricity system in the North Sea, based on a 'hub and spoke' principle. The TenneT vision seeks to make CO2 reduction targets feasible and affordable. Central to the vision is the building of an island (1) in the middle of the North Sea:

• to which numerous wind farms can be connected;
• from where the generated wind electricity will be distributed and transmitted over direct current cables to the North Sea countries, i.e. the Netherlands, the United Kingdom, Belgium, Norway, Germany and Denmark;
• with the same direct current cables serving as interconnections between the energy markets of the aforementioned countries, so besides distributing electricity generated by wind they will also be international electricity highways for international power trade: the Wind-connector.
• in a location with relatively high and stable wind speed.

(1) TenneT’s thinking is based on an island with a modular structure, with each module covering approximately 6 km². This is big enough to provide space for connecting roughly 30 GW of offshore wind capacity. The island will be expandable by adding one or two modules of 6 km² each.

TenneT CEO Mel Kroon commented: ‘In Germany and more recently in the Netherlands, TenneT has the role of developer and operator of the offshore grid. From this responsibility we have taken the initiative to establish a realistic and achievable plan for further development of the North Sea.The success of the energy transition depends largely on the extent to which we mount a coordinated joint effort in Europe. Cooperation between national governments, regulators, the offshore wind industry, national grid administrators and nature and environmental organisations is a precondition for achieving Europe’s environmental targets. The vision we have presented shows the relevance of cooperation in the North Sea.'

North Sea Infrastructure: the vision

Solar and wind energy will be necessary on a large scale because attainment of Europe’s targets for reducing CO2 emissions depends largely on the production of renewable electricity. Moreover, wind and solar energy are complementary: from spring to autumn there is more sun, while the colder months of the year bring more wind. So a sustainable and stable energy system for the future will need both sun and wind, both on a big scale (2). High volumes like these are unattainable by individual Member States, so there is a need for optimum cooperation. The European political declaration of 6 June 2016 on energy cooperation between the North Sea countries was an important step in this direction. TenneT’s vision creates a basis, or point of departure, for a joint European approach up to 2050 and focuses specifically on developing the North Sea as a source and distribution hub for Europe’s energy transition. The location for the island must satisfy a number of suitability requirements. There must be a lot of wind, it must be centrally located and it must be in relatively shallow water. These criteria qualify the Dogger Bank as a location for the central hub.

(2) Approximately 2000 GW of photovoltaics (according to the Delft University of Technology) and approximately 600 GW of wind energy (according to the European Wind Energy Association EWEA).

Mel Kroon: ‘It will be very important for the six European North Sea countries to be willing, in due course, to make their targets independent of national borders, which means agreeing that the electrons generated offshore must not necessarily be transmitted to their own country.’

Far out at sea, but still cheaper

The areas relatively close to the shore, which are the first that must be utilised for offshore wind farms, will provide insufficient possibilities over the long haul to develop the required volumes of offshore wind energy. This makes it necessary to look for possibilities far out at sea. The disadvantage here is that the costs will be significantly higher. The construction and maintenance of the wind farms are higher and these must be connected via many relatively expensive, single direct current (DC) connections. Alternating current technology cannot be used for connecting offshore wind farms far out at sea because of an unacceptably high loss of electricity during transmission to the onshore grid. By building in the years ahead an island surrounded by wind farms (at a relatively short distance), wind energy obtained way out at sea will assume the cost benefits of near-shore wind – thanks to the island. The smaller distance will allow use of the far cheaper alternating current (AC) connections. Further considerable (cost) benefits can be derived from an island, as it offers a permanent place for people and resources:

• A joint permanent basis for builders of wind farms and infrastructure
• Joint storage of components (e.g. turbines, rotor blades, pylons, HV equipment)
• Strong reduction in transport costs: landing strip for airplanes and permanent residency opportunities for staff
• Joint maintenance facilities
• Joint port facilities

The Wind Connector: a smart combination of wind farms with interconnectors

The generated wind energy has to be transported to the consumer as efficiently as possible. The alternating current generated by the wind farms will be changed by converter stations on the island to direct current for transmission to the mainland of one of the North Sea countries. Great additional advantage is that it is no longer necessary to build converter stations on platforms in the sea. This provides substantial cost advantages again.
The present utilisation of a connection between a wind farm and the mainland is around 40%. This is because there is not always wind (or not always equally strong) and the wind turbines also have to undergo maintenance or repairs. The capacity utilisation can and must be greatly increased by giving the direct current connection the role of interconnector. The transmission capacity of the direct current connection will then be used not only for the outward movement of wind energy, but also for electricity trading between the connected countries, creating a "Wind Connector." In effect, the island will act as the spider in a North Sea web of offshore wind farms and international connections. This will increase the present efficient utilisation of a connection between the wind farm and the mainland from roughly 40% towards 100%.

Advantages of an island in the middle of the North Sea

Besides the combination of wind farms and interconnectors and the achievable efficiencies of scale – because numerous wind farms with a total capacity of over 30 GW can be connected on an island of roughly 6 km² – an island at a location like the Dogger Bank offers even more advantages. The Dogger Bank is relatively shallow and is large with the space needed for large-scale wind energy. The shallower the water, the lower will be the cost of building the wind farms and the island. Another very important matter is that there is often a strong wind in that part of the North Sea. This produces a high yield of wind energy. In short, an island in the middle of the North Sea offers everything necessary to make offshore wind energy a success.

• Large wind farms way out at sea will connect to an island. Far-shore will become near-shore, which means lower costs.
• Direct current connections will double as interconnectors. The efficiency of these connections will increase from roughly 40% towards 100%.
• People, parts and assembly factories can be placed on the island, thus optimising logistics in Europe.
• The Dogger Bank has a lot of strong wind. This will optimise the yield.
• The area is relatively shallow. The shallower the water, the lower will be the cost of building the wind farms and the island.
• An island in an area with a lot of space will provide the scale necessary to reduce costs (through economies of scale).

In developing the Dogger Bank as a location for large scale offshore wind and an artificial island the impact on marine flora and fauna should be taken into account by the cooperating parties. TenneT has been in close contact with a number of environmental organizations. A first 'quick-scan' of the impact on flora and fauna on the Dogger Bank shows both opportunities as potential risks for animals and biodiversity.

Tjerk Wagenaar, director of leading Dutch environmental NGO Natuur & Milieu: "TenneT is a reliable state-owned partner that can help ensure a successful energy transition in the North Sea. They can do this cost-effectively, with a focus on sustainable and ecological values. It is precisely in large-scale projects of this kind that we have to take marine flora and fauna into consideration as much as possible."

Step-by-step development

In TenneT’s vision, the creation of an island is not the starting point of this development. Before that stage is reached, it will first be necessary to utilise other possibilities. In sequence these are onshore wind energy and near-shore wind energy. This development is necessary for the structural reduction of the costs of offshore wind energy.

The next, logical steps for the Netherlands are:

• The wind energy areas of Borssele, Hollandse Kust (zuid) and Hollandse Kust (noord) are already under development. According to planning, all will have entered service in 2023.
• The offshore areas of IJmuiden Ver (5-6 GW) and possibly other wind energy areas already designated will be developed.
• The possibility of international cooperation between IJmuiden Ver and a UK wind energy area, such as East Anglia, can be examined. This might also be feasible in combination with an interconnector to the United Kingdom and an island. This might be from 2025-2030.
• The island could perhaps be built on the Dogger Bank, between 2030 and 2050.

Next steps

TenneT will enter into talks with the EU and the Member States to see whether the required European cooperation can be set up. Factors that play an important role include legislation, regulation, targets and financing. TenneT will further make a start on studying IJmuiden Ver in terms of engineering, interconnection, conversion, shore feed-in and integration with existing infrastructure. Also, there will be an examination together with UK stakeholders of possibilities for connecting IJmuiden Ver to a UK wind energy area, possibly East Anglia.