Clustering a large proportion of Europe's offshore wind projects in hubs could save EUR14 billion up to 2030 compared with connecting wind farms individually to shore, according to the long-awaited OffshoreGrid report released on 5 October. Further cost savings could derive from more advanced grid designs, it argues.
Windpower Monthly received an advance copy of the draft of the techno-economic study, co-ordinated by UK engineering consultancy 3E and funded by the European Union's Intelligent Energy Europe programme. It pulled together experts from the European Wind Energy Association, the German Energy Agency, wind-energy research centre ForWind, Poland's Institute for Renewable Energy, Athens University's renewable-energy sources unit Renes, energy solutions specialist Senergy and Norwegian research institute Sintef to produce an in-depth analysis of how to build a cost-efficient transmission grid in the North and Baltic Seas.
The project's remit was to develop a scientific view on the need for an offshore electricity grid in northern Europe and to develop a blueprint that would allow policymakers, developers and transmission-grid operators to plan and design a meshed offshore grid.
It takes as its starting point the challenges and opportunities offered by offshore wind power. European capacity is expected to reach 150GW in 2030, but the high cost of grid connection and limited grid availability act as constraints on development in deeper or more distant waters.
The report looks at how a grid - or series of grids - could transmit electricity from offshore wind farms to load centres while facilitating trade and competition between European countries. The study seeks to establish whether and how a grid approach can best deliver the three strategic energy-policy aspirations of security of supply, competition and markets, and integration of renewables in Europe.
OffshoreGrid assesses the connectivity to shore of 321 offshore wind-farm projects in the North, Irish and Baltic Seas and recommends clustering 114 of these in hubs. Doing so would save EUR14 billion up to 2030, the study finds. Having made the case for hub connections costing EUR69 billion instead of EUR83 billion, the study then takes a further step to draw up two advanced grid designs - the direct design and the split design.
In the direct design, interconnectors are built to promote unconstrained trade between countries and electricity markets. This model builds on high-capacity direct interconnectors, which allows it to profit from significant price differences, after which meshed links are built.
The split design is essentially an offshore grid built around planned offshore wind farms. It starts by building less expensive interconnectors by splitting wind-farm connections so that they are linked to two shores, then integrating them and building out meshed links.
Costs for both models are similar, in the region of EUR86 billion for the direct design and EUR84 billion for the split design. Overall circuit length for both grid designs would be around 30,000 kilometres - 10,000 kilometres of alternating-current cables and 20,000 kilometres of direct-current cables.
The cost of either model would represent about a fifth of the value of the 13,300TWh that would be generated offshore - at a market value of EUR421 billion, based on an average spot-market price of EUR50/MW - over 25 years.
Financially, the benefits of both models are considerable, according to the report. Additional interconnection would only account for EUR7.4 billion for the direct design and EUR5.4 billion for the split design. This represents only about EUR0.1 for every kilowatt hour of electricity consumed in the EU over the project life time, the study finds. These additional investments would generate system benefits of about three times the investment over 25 years.
The report goes on to ask whether the overall benefits would warrant this level of investment. It also looks at the practical implications of cable laying at sea on such a massive scale.
From a security of supply perspective, either model would reduce dependency on gas and oil from unstable regions by transmitting indigenous offshore renewable energy to where it could be used onshore - and also bypass onshore electricity transmission bottlenecks.
In terms of competition and market development, interconnectors between countries would enhance trade and increase possibilities for arbitrage, limiting electricity price spikes as a result.
As for the third objective, integration of renewable energy, both models would facilitate large-scale offshore renewable projects and crucially reduce variability by linking together projects that are located far away from each other. Connection to large hydropower capacity in Scandinavia would also introduce flexibility into the power system to compensate for variability from wind and other renewable-energy sources.
Alongside the benefits it would bring to security and stability, connecting up offshore wind farms in an integrated manner would reduce the investment costs of offshore renewables and require less cabling. The maritime space would also benefit thanks to the lower environmental impact deriving from shorter and more concentrated construction times.
A properly planned North Sea electricity grid, concludes the report, would create a more orderly, rational and cost-effective electricity transmission system with myriad benefits.
Finally, the study examines the issue of who should pay for it. It argues that grid development should be a joint or co-ordinated activity between the developers of wind farms, their hub connections and transmission system operators. To make this happen, warns OffshoreGrid, North and Baltic Sea countries need to adapt their regulatory frameworks to foster such an approach. Joined-up thinking on grids will, as ever, require joined-up regulation.