The European power sector faces a transformational challenge. By 2050 a total installed generating capacity of 200GW of offshore wind might be installed in the European Northern seas in order to meet the obligations of the Paris climate agreement.
In addition, by 2030, the European Commission suggested that EU member states should have realised the equivalent of 15% of their total installed generation fleet as interconnection capacity to other member states. This enables them to trade energy and optimally exploit geographically spread renewable energy resources.
To achieve those two goals, an entirely new high voltage transmission system must be installed in the North Sea. This undertaking is equivalent to rebuilding the current conventional fossil and nuclear onshore generating capacities of Germany, the Netherlands and Belgium combined. Only this time it will have to be done offshore, using relatively new technology and with an unprecedented degree of coordination and collaboration between neighbouring countries.
Thus far, interconnectors and some wind export links have been realised as point-to-point HVDC connections. However, as the installed offshore wind generation and interconnection capacity increases, these functions can be combined in an HVDC transmission network in which there is always more than one connection between any two nodes.
Such an interconnected, or meshed, offshore HVDC network improves both the reliability of the power supply and utilisation of the assets, unlocking a socio-economic welfare benefit of up to €7.8bn ($9.2bn) per year, according to various studies.
The PROMOTioN project aims to develop and demonstrate key technologies such as HVDC network control & protection, HVDC circuit breakers and HVDC gas insulated switchgear in full-scale industrial environments, and to provide insight into the factors underpinning the technical and non-technical choices. Complementary to this, a regulatory and financial framework will be developed for the coordinated planning, construction and operation of integrated offshore infrastructures, including an offshore network deployment plan (roadmap) for the future offshore network system in Europe.
The four-year project is carried out by a consortium of 33 partners from TSOs, OEMs, academia and consultancies from 11 countries, and is halfway through. Intermediary results and insights are shared at the midterm conference held on 6 June in Amsterdam.
Need for proven and tested HVDC technology
Future offshore wind resources in the Northern Seas are often located far from or between shores (>100 km) and have a large power capacity (>500 MW). Similarly, interconnectors can stretch over hundreds of kilometres and have capacities of more than a gigawatt. Beyond a certain distance from shore or power capacity, conventional 50Hz AC submarine cable technology is no longer a viable option, and High Voltage Direct Current (HVDC) must be used. Building a meshed HVDC network is unprecedented and poses several technical challenges.
Firstly, the operation of the converter stations which are needed to convert the power between the incumbent AC network and the HVDC network must be carefully controlled. There is currently no standardised method accepted by both TSOs and converter OEMs to do so.
Secondly, to achieve improved reliability, a protection system is required which can consistently detect and identify failures, and take appropriate action to remove the smallest possible part of the network which contains the failure. Several so-called fault clearing strategies have been proposed by industry and academia, but it is unclear which strategy offers the highest techno-economic benefit.
Thirdly, although several types of high voltage switches such as circuit breakers and compact gas insulated switchgear have recently been developed, none are in commercial operation in Europe today and operational experience is limited.
Verifying the performance of control, protection and switching technologies requires novel testing techniques and has not yet been done in independent accredited laboratories. Although the technologies are ready for deployment, work remains to be done on its standardisation, qualification and acceptance.
European OEMs have traditionally pioneered the development of HVDC technology, however, recent developments have seen Asian companies contest this industrial leadership.
Need for international regulatory coordination
Building a cross-border offshore transmission network in the EU has also never been done before and poses many legal, regulatory, economic and financial questions and challenges.
The investment required to realise the network is likely to exceed the financing capability of Europe’s transmission system operators. Public and private investment is likely to be required, potentially placing different requirements on the earning models used to recoup the investment and generate profits, but also on the technical requirements on the infrastructure.
These issues and differences are not insurmountable and solutions exist.
And even though zero-subsidy offshore wind farms are already on the horizon, a solution is likely to be needed for dealing with differences in renewable support schemes in different countries connected to the same transnational network.
These issues and differences are not insurmountable and solutions exist. However, work remains to be done on providing insight and a rationale for choosing a particular one.
Today, interconnectors and wind export links are being realised with national or bilateral coordination, leading to dependence on suboptimal routes, technology choices and investment from a European vantage point.
Cooperation and coordination at a European level is necessary to achieve lower energy costs, improved competitiveness of European OEMs, job opportunities – and a fairer Europe.
Cornelis Plet of the DNV GL Transmission & Distribution Technology team is technical coordinator of PROMOTioN
PROMOTioN will stage its mid-term project conference during the EU Sustainable Energy Week, on 6 June 2018 in Amsterdam