The past ten years has seen over 20 GW of offshore wind capacity connected to grids worldwide. In the next ten years, we will see around another 130 GW installed. The lessons learnt from past offshore wind projects – from standardized products to connection approaches – will help developers and investors address new challenges when moving further offshore and building truly transnational grids.
From AC to HVDC
A staged development emerged naturally in offshore wind, with phase 1 (nearshore: 30-40km) and phase 2 (far-shore: 50-70 km) both based on AC grid technology. However, longer distances and larger clusters of wind farms require HVDC connections, as in the German North Sea. The future phase 3 will feature a set of 10 to 15 GW North Sea hubs, combining different energy markets for a total of 150 GW. The first pre-feasibility studies have already been performed. And with projects and knowledge throughout the UK, Germany, Denmark and the Netherlands, Europe is clearly beyond the pilot stages of offshore wind development.
Significantly extending offshore generated power can impact transmission systems. Substantial power flows to load centres will require grid extensions and reinforcements for long-distance transport. Given a strong transmission connection point, distributed connections might be the most cost optimal solution. The further away load centres are, the greater the transmission of offshore generated power required.
Cooperative investments in transmission infrastructure
Europe has led offshore wind development since the technology’s inception. A key lesson is to involve all stakeholders to ensure successful grid planning. Europe has established the comprehensive Ten-Year Network Development Planning (TYNDP) concept by ENTSO-E and ACER, which ensures the future national/regional energy balance between supply and demand. With more fluctuating elements connected to the grid system, achieving and maintaining reliable operation under new conditions is paramount and combined offshore and onshore grid plans have been prepared to address this.
Standardization has enabled offshore substations to minimize costs as transmission system operators become responsible for establishing appropriate connection schemes. The first offshore wind farms had 33/66 kV innerpark cabling connected to a 150 kV offshore substation, delivering energy directly to a 150/400 kV onshore transformer station. Newer solutions are based on 66 kV innerpark cabling delivered to a standardized 700 MW AC offshore substation with a 220 kV AC export cable.
Clearly, additional countermeasures including flexibility options, such as sector coupling, demand-side management and electrification, are needed to avoid a negative socio-economic outcome. With offshore wind taking up to 20% of system peak load, the same capacity must be established as flexibility options (power-to-gas, PV battery storage, large-scale batteries, demand-side management). This can only be achieved in a cooperative approach, targeting optimized grid connections to smoothly integrate offshore wind.
Energy islands: the future of North Sea HVDC grid
Based on DNV’s projections about the energy transition to 2050, new utility business models are also required. For example, creating a North Sea HVDC grid to connect the more than 100 GW of offshore wind, and allowing energy to cross national borders and connect different power markets. But who absorbs the investment costs? What happens in failure and emergency situations? How are potential risks shared?
Through our participation in PROMOTioN, a European project that prepares future DC technology, it is becoming clear that a single market alone might not be able to establish the required innovation. These questions can only be answered by new European and national regulations.
In addition, technological challenges still exist for certain essential HVDC components. Only by creating a flexible and manageable offshore DC grid with large-scale consumption and generation capability can we ensure a reliable energy supply to regions with more than 100 million people across many neighbouring countries.