Dutch connection

As the nights draw in and the economic crisis bites, some in the UK energy industry are suggesting our collective misery may soon be compounded by the lights going out.

The National Grid has taken issue with reports suggesting surplus capacity is now so low that we are only one power station failure away from blackouts. However, many agree that while we may not be plunged into darkness this winter, sooner rather than later demand will outstrip supply.

One of the UK’s most influential energy experts, Prof Ian Fells, warned in a report published last month of the risk of blackouts within five years as the UK loses almost a third of its generating capacity.

Fortunately there is a solution, and it doesn’t involve sitting around with a candle patiently waiting for the next generation of power stations to be built.

Providing about the same capacity as a nuclear power station, but built at a fraction of the cost and in less than half the time, the BritNed Interconnector is a 260km long, 1,000MW sub-sea cable that will link the UK and Dutch national grids.

The aim of the €600m (around £470m) project — a joint initiative between National Grid and its Dutch equivalent Tennet — is to install a two-way high-voltage direct current (HVDC) sub-sea electricity cable between the Isle of Grain in Kent and Maasvlakte, near Rotterdam in the Netherlands. The cable will be connected into the AC grids of the two countries through two giant converter stations being developed by Siemens.

Work has just begun on the civil structures at these converter sites and, if all goes to plan, the cable should be in operation by the beginning of 2011.

Although the UK already has one 2,000MW link to France and another connector linking Scotland and Ireland, BritNed will be the first big UK interconnector for two decades.

The project has been on and off the drawing board for the past 20 years or so, but its National Grid programme manager Martin Croucher said growing concern about the UK energy gap has given it a renewed sense of urgency.

‘We’re seeing a situation in the UK where large amounts of the older coal and oil generation plants will be closed over the next 10 to 15 years. We’ve got the likelihood of more gas generation over the next five to 15 years and the possibility that we’ll see some of the older nuclear plants close down. Interconnection from other parts of Europe will enable us to use power when the networks require it.’

Fells, who touched on BritNed in his report, agreed that interconnectors are a prudent short-term measure that can take some of the strain while the rest of the energy infrastructure catches up. ‘It’s something that can be done very quickly, within two or three years, whereas anything else, with the exception of building more gas-fired power stations — which is exactly what we don’t want to do — takes rather longer,’ he said. ‘So this is buying time, making us more secure, more quickly than we might otherwise be able to do it.’

Coming hot on the heels of NorNed, a recently-completed 580km link between Norway and the Netherlands, BritNed also ties in with an EU-driven desire for an integrated pan-European electricity infrastructure, said Croucher. ‘From a security perspective, the better either of our systems are interconnected the more robust they are in terms of their ability to withstand problems on the network or our ability to meet demand at times when we can get support from other parts of Europe,’ he said.

The need for a harmonised system is, according to Fells, more pressing than many may think. ‘Europe imports 60 per cent of its energy — it’s enormously dependent on imports, so it needs a really good integrated system to provide security and supply all round.’

Designed to work both ways, the Dutch will, in theory, reap the same benefits as the UK. ‘It’ll be market driven whether it flows from UK to Holland or the other way,’ said Croucher.

Fells, however, questioned whether this will be the case in practice. ‘The French project was supposed to be exporting both ways. In theory we should have been able to help each other out at times of peak demand, but in effect all we’ve ever really done is import cheap nuclear electricity from France — cheaper than we can generate it ourselves,’ he said.

As Croucher said, the market will decide.

But before any of this can happen, the interconnector must be built, and although the technology and science of laying sub-sea cables is well understood, the scale of the engineering and the logistical demands posed by one of the busiest shipping lanes in the world present some big challenges.

Arne Abrahamsson is the BritNed project manager with ABB, which is not only manufacturing and supplying the cable but is also responsible for contracting out the various other elements of the project, from the initial marine surveys to the installation by highly specialised cable-laying vessels.

While work has already begun at the converter site, Abrahamsson said laying the two land-based sections of cable — about 10km at each end — will begin later this year.

But the biggest challenge lies in the sea and, following a range of sub-sea surveys that will carried out by geotechnical specialist Fugro, the marine cable installation is expected to begin next April.

The project uses a large number of highly-specialised devices and techniques. The sea cables will be installed from cable-laying vessels operated by Norwegian contractor Oceanteam Power & Umbilical in what Abrahamsson refers to as four ‘campaigns’. Part of the reason for this is the fact that the 119mm diameter cable weighs about 44kg/m.

The two inshore sections will be installed next summer and the remaining two in the middle of the channel in the summer of 2010. Each campaign will consist of about two 65km lengths of cable that will be laid in parallel from a giant horizontal reel onboard the laying vessel.

‘The two cables will be bundled together when leaving the barge,’ said Abrahamsson. ‘The reason for this is twofold; first, to keep the magnetic flux to a minimum and second to enable both cables to be buried with only one burial operation.’

Two different vessels will be used to lay the cable. For the inshore sections, a barge, the AMT Explorer, will be used. This will tow a plough along the seabed to simultaneously carve a furrow and bury the cable. These ploughs, exceptionally expensive pieces of machinery, are typically equipped with a variety of sensors and control mechanisms that enable engineers aboard the ship above to check the cable is being correctly laid, and, if necessary, to adjust the angle of the plough.

The sections of cable in the middle of the channel, where the water will be up to 60m deeper, will be laid by the North Ocean103, which is now being built in Vigo, Spain. This is expected to use a plough equipped with high-velocity water jetting apparatus that will blast out a trench in the seabed.

ABB must now get on with making about 500km of its HVDC cable, and it is a big job. ‘We started manufacturing it last August and will complete the two cables in April 2010,’ said Abrahamsson. ‘It’s a continuous manufacturing process.’

He added that while the company has more than 50 years’ experience of manufacturing HVDC cable, sub-sea systems are always more onerous. For instance, as well as requiring the additional production of a watertight continuous lead sheath, the cables on the BritNed project are also protected by a layer of armour; a mesh of galvanised steel wires that enable the heavy cable to cope with the considerable forces it will encounter while it is being transferred from a turntable to the bottom of the sea.

It is a complex expensive operation but it should be worth it. There seems little doubt the BritNed will be making an important contribution to UK energy security within the next few years.

But Fells believes we should not stop at BritNed. ‘I think we should also be hooked up to Norway or Sweden and Germany and have another connector to France — then we would become integrated into the European electricity market and that would provide additional security, which it looks as though we’re going to need,’ he said.

‘We lose 12GW of coal power generation by 2015, which is an horrendous prospect. interconnector to France is 2,000MW, the equivalent of two power stations. If you have another two to France, the Dutch one, and suppose we had one to Norway for 1GW, it could make a huge contribution. BritNed is a good thing but we need more of them.’