New connections bring North Sea renewable energy onshore

Major grid connection projects have got underway in the North Sea. They will bring electricity from renewable tidal and wind energy ashore and feed it into Europe’s distribution grids. Sean Ottewell reports

Power and automation specialist ABB has been awarded a contract by Atlantis Resources to provide the onshore grid connection for phase one of the MeyGen tidal stream project in Scotland’s Pentland Firth.

According to ABB, this project is at the forefront of world marine energy development and will harvest the tidal resources of one of the most energetic maritime sites in Europe - the strait connecting the Atlantic Ocean to the North Sea between the Orkney Islands and the Scottish mainland.

The first 6MW demonstration phase of the UK’s first large-scale tidal array scheme will see four submerged turbines installed in the Inner Pentland Firth just north of Caithness, with first power expected to be delivered by 2016.

ABB is responsible for the onshore power conversion and grid connection systems to feed the electricity safely and reliably into the local distribution grid. ABB’s project scope includes design, engineering, supply and commissioning of the power conversion, switchgear and transformer solution as well as associated civil engineering and cabling works. Major product supplies include transformers, medium voltage switchgear and power converters.

“We are pleased to facilitate this innovative project and tap the potential of marine energy,” said Claudio Facchin, head of ABB’s Power Systems division. “It reaffirms the faith our customers have in ABB’s technology and proven capability to deliver safe, reliable and efficient grid connections which play a key role in integrating renewables that are making an increasing contribution to the energy mix.”

Studies including those by engineers from the University of Edinburgh and University of Oxford indicate that the Pentland Firth’s tidal stream has vast energy potential, with ocean currents estimated at five metres per second, among the fastest in the British Isles.

“Forming partnerships with the leading players in the energy sector is key to delivering commercial-scale tidal power projects that allow us to harness the untapped potential of global tidal resources. ABB has clearly demonstrated exceptional expertise in this area and we are confident they will deliver the highest quality results. We look forward to working with the team at ABB to ensure the success of the MeyGen project,” said Tim Cornelius, ceo of Atlantis Resources.

The initial phase of the MeyGen development has the potential to generate up to 86MW of electricity, enough power for around 42,000 homes, potentially catering to the needs of almost 40% of households in the Scottish Highlands. Within ten years the company hopes to see this figure rise to 398 MW.

In another North Sea development, Siemens has completed installation of the offshore platform for the direct-current connection HelWin2.

Working under contract from the German-Dutch grid operator TenneT, Siemens says it has achieved a decisive milestone in German grid connection projects.

“We have now installed three high-tech platforms for TenneT in the North Sea. The HelWin2 project is now in the homestretch to begin operation in the coming year," said Jan Mrosik, ceo of the company’s Power Transmission and Smart Grid divisions. “We have achieved one more major interim milestone, and are step by step accomplishing the German government’s offshore expansion goals,” added Lex Hartman, member of TenneT's executive board.

The newly installed HelWin2 platform lies 35 km north of the island after which it was named, Heligoland, directly adjacent to the HelWin1 platform Siemens successfully erected in August 2013.

In April this year Siemens completed the BorWin2 platform off the coast of Borkum. All told, Siemens is building five North Sea grid connections for TenneT.

The first four are to begin commercial operation successively over the rest of 2014 and the first half of 2015, and in sum total provide transmission capacity of over 2.9 GW. The fifth connection recently ordered this year, BorWin3, is to be ready for operation in 2019.

Using the Siemens technology installed on the platforms, the alternating current power generated by the wind turbines is transformed into direct current for efficient transmission to the mainland. At the associated land-based stations, the electricity generated by the connected wind farms is converted back into the alternating current power required for feeding into the transmission grid. Thanks to Siemens' low-loss high-voltage direct current (HVDC) technology, transmission losses are less than 4%.

The platforms are designed to operate for decades in the rough North Sea conditions, and are fully automated. The HelWin2 platform was constructed and installed by Heerema. The marine and land-based cabling were supplied and laid by the cable specialist Prysmian Group.

Meanwhile TenneT has has installed its sixth HVDC offshore platform in theGerman part of the North Sea. The SylWin alpha converter platform is located approximately 70km to the west of the island of Sylt (after which the platform is named) and has a capacity of 864MW for bringing offshore wind energy onshore. At present, the platform is the most powerful installation in the North Sea for converting alternating current into direct current.

“In the past weeks, we have erected two platforms in quick succession that will provide approx. 1.5GW of additional capacity for feeding offshore wind energy into the onshore transmission grid,” said Wilfried Breuer, offshore director at TenneT Germany. The five converter platforms erected by TenneT in the North Sea since the autumn of 2013 will be ready to transport approximately 3.7GW of offshore wind energy to the onshore grid, starting in the first quarter of 2015. The other offshore grid connections already constructed by TenneT add a further 0.6 GW of transmission capacity.

“The German government has decided to increase the transmission capacity for offshore wind energy by 6.5 GW in the period until 2020. In 2015, two-thirds of that target will already be achieved,” Breuer emphasised.

Prysmian lands Greek interconnector role

Prysmian Group has won a €95 million (£76 million) order for an interconnector to link the island of Sryos and the mainland power transmission system in Lavrion, Greece. The contract was awarded by IPTO, the transmission system operator of the Greek electricity network.

The project involves the design, supply and installation of a turn-key high voltage alternating current (HVAC) cable system designed to transmit a power of 200MVA and consisting of 150kV cables and associated fibre optic cable system along a total route of more than 110km. 108km of this will be underwater, the remaining 2km on land. The system is being designed in such a way as to allow other nearby islands such as Paros, Mykonos and Tinos eventually to join the same network.

The cables will be manufactured at the Arco Felice plant in Naples, Italy, in 2015. Installation is expected to be complete in 2016.

“The Cyclades project further highlights Prysmian's strategic role in supporting the realisation of the important development plans in the field of power grid interconnections,” said Massimo Battaini, Prysmian Powerlink ceo.

Prysmian has a long-standing track record in the development of submarine interconnection milestone projects in the entire Mediterranean region, such as Italy-Greece, Sardinia-Italian Peninsula, two interconnections between Spain and Morocco, two projects in the Balearic islands (Spanish Mainland to Majorca and Ibiza to Majorca) and the Dardanelles in Turkey.

The Group is also a founding member of the industrial partnership Medgrid, launched to study the feasibility of a high-voltage direct current interconnection project to transmit electricity from solar or wind power plants to load centres on either rim of the Mediterranean.