Dutch transmission systems operator TenneT has proposed a new concept for a future European electricity system in the North Sea based on a ‘hub and spoke’ principle and an artificial island to accommodate it.
Central to the vision is the construction of an island in the middle of the North Sea to which numerous offshore windfarms could be connected; from which electricity will be distributed and transmitted using direct current cables to North Sea countries; with the same direct current cables serving as ‘interconnections’ between energy markets in the countries, distributing electricity generated by wind and acting as ‘international electricity highways’.
TenneT’s thinking is based on an island with a modular structure, with each module covering approximately 6km². This is big enough to provide space to connect around 30 gigawatts of offshore wind capacity. The island would be expandable by adding one or two modules of 6 km² each.
TenneT’s chief executive Mel Kroon, said: “In Germany and more recently in The Netherlands, TenneT has the role of developer and operator of the offshore grid. 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 co-ordinated joint effort in Europe. Co-operation 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 co-operation in the North Sea.”
The need for co-operation
TenneT notes that such a vision is not achievable by individual European member states, so there is a need for co-operation, and highlighted the European political declaration of 6 June 2016 on energy co-operation between North Sea countries as 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 company said. “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.”
“It will be important for the six European North Sea countries to be willing 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,” Mr Kroon said. “The areas relatively close to the shore, which are the first that must be utilised for offshore windfarms, 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 windfarms are higher and these must be connected via many relatively expensive, single direct current connections. Alternating current technology cannot be used far out at sea because of unacceptably high losses during transmission to the onshore grid. By building an island surrounded by windfarms, 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 connections. Further considerable cost benefits can be derived from an island, as it offers a permanent place for people and resources.” These include a joint permanent base for builders of windfarms and infrastructure; joint storage of components such as turbines, rotor blades, pylons, HV equipment; a significant reduction in transport costs, which could be achieved by using a landing strip for aircraft. Other benefits include joint maintenance facilities and joint port facilities.
“Energy generated from offshore wind has to be transmitted to the consumer as efficiently as possible,” said TenneT. “Alternating current generated by the windfarms will be changed by converter stations on the island to direct current for transmission to the mainland of one of the North Sea countries. Another great advantage would be that it is no longer necessary to build converter stations on platforms offshore. This would provide substantial cost advantages.”
TenneT notes that currently utilisation of a connection between an offshore windfarm and the mainland is around 40 per cent. This is because there is not always enough wind or because turbines have to undergo maintenance or repair. “Capacity utilisation can and must be greatly increased by giving the direct current connection the role of an interconnector,” said TenneT. “The transmission capacity of a direct current connection will then be used not only for the outward movement of wind energy, but also for electricity trading between countries, creating a ‘Wind Connector.’ In effect, the island will act as a ‘spider’ in a North Sea web of offshore windfarms and international connections. This will increase the utilisation of a connection between a windfarm and the mainland from around 40 per cent to more like 100 per cent.”
TenneT says an island at a location such as Dogger Bank has many other potential advantages. 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 windfarms and the island. Another very important point is that winds are usually strong and reliable in that part of the North Sea. This produces high yields.
Were such a concept to become reality, the company claims, “far-shore will become near-shore, which means lower costs.” Direct current connections will double as interconnectors and the efficiency of the connections will increase dramatically.
The company says the next logical steps in the plan would be to examine the possibility of collaboration between the UK and The Netherlands. It notes that the Borssele, Hollandse Kust (zuid) and Hollandse Kust (noord) projects are already under development and are due to have entered service in 2023. Another project, the IJmuiden Ver (5-6GW) and other wind energy areas that have already been designated may be developed, and the possibility therefore exists of international co-operation between IJmuiden Ver and a UK wind energy area, such as East Anglia. “This might also be feasible in combination with an interconnector to the UK and an island. This might be from 2025-2030,” said TenneT. “The island could perhaps be built on the Dogger Bank, between 2030 and 2050.”
TenneT says it plans to enter into talks with the EU and the member states to see whether the required European co-operation can be established. Factors that play an important role include legislation, regulation, targets and financing. TenneT will also make a start on studying IJmuiden Ver in terms of engineering, interconnection, conversion, shore feed-in and integration with existing infrastructure, and examine, together with UK stakeholders, the potential for connecting IJmuiden Ver to a UK wind energy area such as East Anglia.