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Subsea links on a roll

February 15 - Cheaper, easier to plan, quicker to construct than overhead land lines - high voltage subsea power interconnections are on a roll as Europe strives to harness the renewables boom.

In recent months Power in Europe has reported on contract wins relating to links between Denmark-Norway, Finland-Estonia, Malta-Sicily and Sweden-Lithuania.

Meanwhile construction continues on links between UK-Netherlands, Ireland-Wales and Spain-Balearics, while development is active on Norway-Germany.

Now January 2011 has seen a number of new developments in the direct current cable sector, with the focus on the UK as a hub for green power imports, exports and transits.

First, a big internal transit scheme. In late January, National Grid and ScottishPower Transmission revealed plans for a 400-km high voltage direct current subsea link connecting the Scottish and English/Welsh power markets, bypassing the UK's north-south transmission bottleneck.

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"It's very early days, but we are proposing an HVDC cable with a 4-km section onshore in Scotland, connecting a new converter station at Hunterston [Ayrshire, southwest Scotland] to the foreshore, then a 370-km subsea section to the Wirral [Merseyside], from where a 40-km section of buried cable will run to another new converter station at Connah's Quay on Deeside [North Wales]," National Grid spokeswoman Jeanette Unsworth told Platts January 28.

"The new circuit will enable the transfer of large volumes of energy from Scotland directly to England and Wales through subsea cables, by-passing the constraints on the existing transmission system," National Grid and SP Transmission said. "Scotland traditionally generates more electricity than it consumes and as new renewable energy projects continue to come on-line, it is anticipated that exports will increase."

New converters at Hunterston and Connah's Quay will connect the cable into the national grid electricity transmission system. National Grid and SP Transmission would be holding local consultations at Connah's Quay (February 7), Neston (February 8), Moreton (February 9) and Seamill (February 11).

"To develop their plans, National Grid and SP Transmission are working closely with the local councils and nature conservation agencies, as well as local environmental groups and landowners to develop an effective proposal which minimised the impact on the environmental and local communities," they said.

As such, a route taking the cable up the River Dee has been ruled out, the proponents said. "The Dee Estuary is protected by a number of International and European environmental designations, and home to a number of unique features including salt marshes, cockle beds and large populations of birds. The silt levels of the Dee can fluctuate greatly in places, making the route technically unacceptable," they said.

National Grid and SP Transmission will need permanent rights to install and maintain the cable where it crosses private land, they said. They would seek to reach voluntary agreements with affected landowners wherever possible.

Laying of the cable from its coastal landfall to the proposed converter station would take approximately two years from start to finish, they said.

A definitive start date is not yet known but work could start in 2013. A joint venture company, NGET/SPT Upgrades Limited, has been set up to manage the project.

New UK-Norway proposal

Scotland has huge potential as a source for carbon-free power. The Nordic market meanwhile is pretty much the fully-realized deal, and competition is building to land its cheap, predictable and low-carbon power on UK shores.

In October 2009, National Grid and Norwegian TSO Statnett agreed to reassess the potential for an HVDC cable linking Norway and Great Britain. (See related table: Europe’s major subsea interconnection projects in development).

Now Vattenfall has signed an agreement with Agder Energi, E-CO, Lyse and Scottish and Southern Energy to plan and build their own interconnector between the UK and Norway.

The partners have established development company NorthConnect and will over the next three to four years examine the technical and economic viability of developing, building and operating a 1,200-to-2,000 MW HVDC interconnector.

The ambition is to have NorthConnect in operation before 2020, Vattenfall said on February 1.

"NorthConnect will make an important contribution towards developing the European market for electricity with increased competition in regional markets, a secure supply of electricity and more stable energy prices for consumers," said Vattenfall's Harald von Heyden.

The interconnector would be a direct link between Vattenfall's core market Sweden and the UK, where it is investing in on and offshore wind.

"By interlinking flexible hydro power with intermittent energy sources such as wind power, NorthConnect may contribute to reduce the need for fossil fuelled electricity generation," Vattenfall said.

Meanwhile National Grid said its plans with Statnett "are still under consideration," spokeswoman Isobel Rowley said on February 1. "A feasibility study was carried out last year and that is still being worked on, with technical and regulatory aspects under investigation."

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