If you wanted to build a giant new solar farm, you’d probably choose desert over Dartmoor.
Many have dreamed of harnessing the desert sun, but one of the challenges has always been how to export that electricity.
Xlinks, an energy start-up, claims to have the answer with the the longest submarine power cable in the world.
A total of four cables are expected to wind 3,800 km (2,360 miles) along the sea floor from a solar and wind farm in Morocco, via Portugal, Spain and France, before landing in the village of Alverdiscott in Devon.
“It is absolutely doable,” insists CEO Simon Morrish. His company hopes to complete the project by the end of the decade.
If all goes according to plan, Xlinks’ cable will provide 3.6 gigawatts of electricity, enough to power seven million homes, for 20 or more hours a day. It will join several similar, albeit shorter, lines connecting the UK’s power grid to neighboring countries.
Energy companies plan to install even more submarine power cables here and elsewhere in the world in the coming years. But what do you need to install them?
And with a connection between France and the UK recently taken out of action due to a fire, will these cables really provide reliable power sources in the future?
“There is so much capacity coming off the grid in the next 5-10 years, we desperately need to be able to increase that capacity,” says Morrish, referring to the UK.
Sometimes a surplus of electricity from renewable resources is available in one country, while a neighboring country experiences a shortage of supply. It is relatively difficult to store energy, especially in the long term, so transferring it via a wire to the neighbor is in principle a good way to make sure it doesn’t go to waste.
But no one has yet built a submarine cable infrastructure on the scale proposed by Xlinks. Generally a small trench is prepared in the seabed to house cables of this type, which are sometimes subsequently buried under concrete or rock mattresses.
The cable will follow a path that reaches 700m below sea level at its deepest point, reducing the risk of damage from anchors and fishing gear. “It is not the shortest route to the UK, but it has the lowest technical difficulties. It will remain buried under the surface all the time,” adds Morrish.
There will be some energy loss along the cable – 13% – but Xlinks says the generation costs in Morocco will be low enough to ensure the viability of the project.
The technology needed to install cables of this length is already available, says Behzad Kazemtabrizi of Durham University, some of whose work is sponsored by the government’s Offshore Renewable Energy Catapult.
He says he is unaware of any other project planned on this scale: “It certainly is very ambitious.”
However, the hardest part may come in connecting the cable to the resources at both ends. Dr. Kazemtabrizi explains that Xlinks will have to carefully choose the right equipment to manage its high voltage direct current cables, to avoid unwanted efficiency losses.
A very, very detailed “resource study” to ensure a reliable supply of sunlight at the Moroccan site is also crucial. Xlinks says it has already carried out an assessment based on satellite data and that a more detailed study will soon take place using on-site wind trees and weather stations.
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These power lines are not only important for countries looking to connect their grids together – offshore wind farms, which are increasingly popular, also require submarine cables.
The recently completed North Sea Link, a 1.4 gigawatt link between the UK and Norway, currently holds the title of the longest submarine power cable in the world. At 720km, that’s less than a fifth the length of the cables required by Xlinks. However, North Sea Link had particularly challenging obstacles on its way to the Norwegian end, including a landlocked lake, a mountain, and steep fjords.
“It’s so, so steep,” says Caroline Opiyo-Mullings, project control manager at National Grid, referring to the seabed that plunges to depths of up to 600 meters off the Norwegian coast. “There are steeper parts of a ski jump.”
Installing any subsea power line requires care, he explains, because cables can only bend so much before they get damaged. Therefore, they need to be gently lowered into place in favorable weather conditions.
In addition, there are many other cables and pipelines on the sea floor. You can’t just dump new power lines onto it without permission. Sometimes special structures have to be made to allow, for example, one cable to cross another. North Sea Link has had to negotiate nearly 100 crossings between Norway and the UK, says Ms Opiyo-Mullings.
The next submarine cable, Viking Link, will connect the UK to the Danish network. At 760km, it will be longer in terms of total length than the North Sea Link, although a significantly larger portion, around 140km, will pass over land in the UK or Denmark. This also requires careful planning, so it is possible to dig small tunnels under roads and other infrastructure, for example.
We should be cautious about the proliferation of submarine power cables, says Prof Flynn. For one thing, there may be negative environmental consequences of increased activity on the sea floor.
A study recently found that brown crabs were mesmerized by submarine power cables off the coast of Scotland, which could adversely affect their mating and foraging.
Also, what if more cables are damaged by anchors or debris rolling on the sea floor? Or worse, does an opponent decide to sabotage them?
“This is something I have discussed with both the UK Department of Defense and other agencies involved in our critical infrastructure,” says Prof Flynn.
A spokesperson for National Grid says, “We consider the risks, including safety, and implement measures from the design and construction of the asset. We will not disclose the details of those measures.”
Xlinks says the recent interconnector fire reveals how important it is for the UK to diversify its sources of supply.
The company says that, like all power generation projects, its project will never be 100% risk-free, “but by using the latest, proven and tested technology we can minimize the risks to reliably deliver a complementary energy source for the British energy grid at the end of the decade ”.
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