National Grid is Building a Giant Undersea Power Cable to Norway: Here's What That Means

By Tom Pritchard on at

When you think about undersea cables, most people will probably think of the ones that carry data. It's no secret that the world is connected by giant undersea fibre optics that let us all communicate via this lovely medium we call the internet. But there's a lot more being laid under the sea bed, including giant power cables that connect us to the various countries that lie on the other side of British water. Interconnectors, as they're called, have existed for quite some time, but right now the National Grid is working on another - connecting Tyneside to Norway.

It's quite a big deal, and the North Sea Link is a project that's been in various stages of planning since 2003 - with construction finally kicking off in 2015. In very simple terms it's a giant cable between Blyth and Kvilldal in Norway, connecting the two countries' electricity grids and allowing them to draw power from each other. But there's a lot more to it than that, and it's especially prudent given Theresa May's plan for the UK to reach emission net zero by 2050.

Image: The Crown Estate

Up there is a map of all the interconnectors the UK has, in various stages of development. So there are a lot of them already, mostly connecting us with France and Ireland. But there are a lot of other countries around the UK, so there's no need to stop there for the sake of geographical closeness. There are a lot of advantages to connecting ourselves up to Norway, and that's mainly to do with the fact Norway generates so much hydroelectric energy. And not just because it means we can pinch any surplus electricity they may have lying around. Here's an official video, in case you were confused:

What is the North Sea Link?

The North Sea Link is currently under construction, and is set to come online by 2021. It'll join the three existing interconnectors jointly operated by the National Grid, and by 2030 there will be six of them connecting our power grid to another point in Europe. The North Sea Link will be slightly special, however, since its 720km length makes it the world's longest interconnector.

The link itself is actually two cables running parallel, forming a complete circuit, with a capacity of 1,400 MW. Naturally the cables are being buried under the seabed where it's out of the way of passing ships and sea life. The goal is to be able to leave the cable alone to do its thing, and only dig it back up when repairs and maintenance need to be made. But those situations apparently don't happen very often, and when decades-old interconnectors have been dug up the cables themselves still look basically new.

Electrical engineering nerds will also be interested to hear that it carries 515 kV, and runs a direct current that has about one per cent loss. Even though our own grid runs on alternating current, it's not possible to keep that going on an undersea cable like this. That means electricity has to be converted before it can travel across the sea, and again before it can enter the receiving country's electrical grid.

So there's a converter station at each end, plus a substation that ensures the electricity is the right voltage and won't be frying any important equipment.

It's no accident that the Norwegian end of the link lands in Kvilldal, though. There are areas of the country that are physically closer to the UK, but Kvilldal is already home to a key piece of Norway's renewable infrastructure - it's the country's largest hydro-electric power station, and one of the six stations that generates its power from the Blåsjø reservoir.

The name may not mean much to you, but Blåsjø is truly massive, and has been referred to as "Europe's battery". That's because it holds enough water to generate 8TWh of electricity, and typically the three stations connected to the reservoir provide around seven per cent of Norway's hydro-electric power. That's around 3.4 per cent of Norway's overall use. But there's enough water in there to meet around 10 per cent of Norway's demand.

It's a very complicated system of water, tunnels, and six plants generating power

If you want that in geographical terms, it takes up 80.53 km², has a catchment area of just over over 272 km², and stores around 3,105 million m³ of water. In other words this is a fuck-load of water. Enough for Kvilldal's hydro-generators to run non-stop for around five months without any extra rainfall to top up the water reserves.

So What the Heck Will This Achieve?

The fact Blåsjø is so big is important for many reasons. The first is that it takes around four minutes for the Kvilldal hydro-electric station to start up - compared to the many hours it would take for nuclear or fossil fuel-powered power stations. So when there's a surge in demand, the station can bring things up to speed in almost no time at all. That means there's a lot of flexibility involved in hydro-electric energy, which isn't the kind of thing you can say for solar or wind.

They're both reliant on wind and light levels being high enough to generate enough power to meet demand, but the problem is that it's not always consistent. It doesn't matter how many advancements you make in the technology, if there's no wind or sun you can't produce any power. But at the same time if it's a particularly sunny or windy day, there may well be too much power and something needs to be done to stop it going to waste. Because why should you turn off the wind turbines simply because they're doing their job too well? An interconnector can help in these situations, and is part of a system that ensures better energy security for the countries involved.

 The top of one of the four turbines inside the Kvilldal power station.

In the case of the North Sea Link the UK grid will be connected to Norway's, meaning Norwegian hydro power can be used to top up the UK's power reserves when necessary. Likewise if the UK is producing too much energy it can transfer some to power Norway. Because the excess going to Norway means they can shut down their hydro-generation for a bit, it essentially works as an indirect form of energy storage. The battery analogy is designed to be quite literal, and the water that's not in use stays exactly where it is - preserving its potential to generate energy for another day. Plus, if deemed necessary, any excess power can be used to pump water back up the mountain for a more direct way of saving (some of) it for future use.

Admittedly at first the relationship will focus heavily on Norway exporting renewable electricity to the UK, but it will change. As the UK increases its renewable capacity there will be more opportunity to export our excess energy to the Norwegians - especially as we build more off shore wind turbines. Interestingly it was suggested than any North Sea wind turbines could connect directly to the local interconnector, meaning it could go straight to Norway without much faffing around. Assuming, of course, that they need the power more than we do at any given time.

 The converter station being built outside Kvilldal, which is due for completion sometime this summer. The cable will reach it around May next year

Put another way, it also means the UK can focus more on inflexible renewables like wind and solar without needing some sort of fossil fuel-powered energy generation to fall back on. Because we have that back up sitting around in the form of a giant lake on top of a mountain. And, in fact, around 63 per cent of the energy Britain has received this year via interconnector came from zero-carbon sources (yes, that includes nuclear), and by 2030 it's expected that the six interconnectors will bring in 90 per cent of its power from zero carbon production - reducing the emissions produced by Britain's energy requirements by 17 per cent.

Of course you can't stop energy produced from fossil fuels getting in via interconnector, because it's not like the energy is all separated when it's in the grid, but you see what they're getting at.

 The cable has already hit dry land in Blyth.

But it's not just about being able to pinch power from each other. As explained by Sveinung Rotevatn, State Secretary for Norway's Ministry of Climate and the Environment, interconnectors also expand the available electricity grid, and a larger grid means more consistency across the whole network. Apparently the lack of consistency is why a lot of developing countries have been opting to build coal-centric power stations. We can all agree that coal is bad, but there are still plenty of them in production and the lack of infrastructure sends countries with less-advanced grids into the arms of coal in order to maintain their own energy security.

But the interconnectors make it more beneficial to work with more variable methods of energy production like solar and wind, because the larger the area the less likely it is that the weather is universally the same. For instance if there's not enough power being produced by the wind in Wales, but there is in Ireland or Norway, the connection means energy can travel from one region to another and help balance out the load. And that's better for everyone, especially since being able to take advantage of large amounts of cheap energy will help keep our energy bills down. We can all agree that's a good thing, and it'll only get better as the cost of using carbon-intensive fuel goes up and the price of renewable technology goes down.

So What Else?

It's important to remember that interconnectors, as useful as they may be, are not a magic bullet. As was described to me by Nigel Williams, Construction Director on the North Sea Link, sustainable renewable energy relies on a lot of different pieces coming together like a giant jigsaw - each one offering something to complete the picture. Generating enough renewable energy is one part, and so is working on energy efficiency, energy storage, and of course the interconnectors themselves. All them coming together in tandem is the best way to ensure we can have a sustainable source of zero-carbon energy.

Each thing has its own respective positives and negatives, so on their own they're not going to work long term. After all, energy efficiency is all well and good, but you still need to generate the electricity from somewhere. Likewise there's no point generating as much renewable energy as we can if we're just going to burn through it all too quickly with inefficient power systems.

Every bit helps complete the picture, in other words, and by diversifying everything we have the added bonus of something to fall back on in case something does catastrophically wrong. Like a ship drops an anchor right into an interconnector line (it has happened).