11-10-2021 | By Sam Brown
A new solar and wind farm will be built in Morocco to provide to the UK, and the two will be connected via an undersea cable. What challenges does laying cables in the sea present, why is Morocco chosen as a UK power plant site, and how do undersea cables meet these challenges?
Recently, Xlinks, which specialise in renewable energies, announced that they will be setting up a solar and wind farm in Morocco to provide power for the UK. Furthermore, getting power from the site to the UK will be done using undersea cables, and it is estimated that the site will provide up to 10.5GW of power.
The project has an expected completion date of 2030 and will provide enough power for 7 million homes. The project will also integrate battery storage technology to help store power during peak production and feed the electrical grid during low production. Four undersea cables will be installed between Morocco and Devon that will each be 3,800km in length carrying HVDC.
The reason why Xlink has selected Morocco as their power production site comes from multiple factors. The first and most apparent is that Morocco is in Africa and closer to the equator means that it receives more usable daylight hours than the UK (the sun is more intense and experiences less cloud cover). However, another reason for choosing Morocco is that prevailing southern winds help produce a constant flow of wind that wind farms can exploit.
Undersea cables are found in telecommunications and power industries and are ideal for connecting to places separated by the sea. In fact, most internet communication is done using transoceanic cables that help connect major continents together, including the US, UK, Europe, and Australia.
However, undersea environments are far from pleasant or stable, and cables that are not designed correctly can fail. To make matters more complex, a cable that fails can be extremely challenging to repair, with both sides of the cable needing to be identified, resurfaced, repaired, and then reburied (some cables at the ocean floor are buried).
The first significant challenge is that a cable must be waterproof, and standard plastic sheaths cannot achieve this. Cables at the bottom of the ocean are subject to saltwater under tremendous amounts of pressure, which can easily weaken even the most robust plastic materials.
The second challenge faced by undersea cables is the wildlife. There have been instances of marine life taking an interest in cables and sometimes will attack the cables (often through biting). As such, any cable used in the ocean needs to be able to resist such an attack. Cables can also find themselves victim to anchors of ships that drag along the seafloor.
The third challenge is that cables also face sabotage from rouge and/or hostile nations. This is commonly a worry for internet service providers with undersea cables between countries, as cutting such a cable is trivial compared to the cost of repair and the economic damage it would cause.
Mitigating against damage is mainly done using different sheaths and armour. Depending on the number of cores used in the cable, a steel wire wrapping is usually used on the outside to provide a basic level of protection. This steel wire is coating in bitumen to protect it from corrosion from the seawater.
However, water often penetrates this layer and can adversely affect the inner conductors used to carry power (which are made from copper). To date, only one material is suitable for preventing water intrusion into the inner conductors; lead. Lead can be easily formed and extruded at low temperatures, and this allows for cable lengths as long as 50km to be sheathed in lead armour.
Another interesting factor that undersea cables need to consider is whether they carry AC or DC current. AC current has the advantage that it can be easily stepped up and down using transformers. In contrast, DC has the advantage of not suffering from capacitive issues caused by the close proximity of different phases. Generally speaking, longer lengths of cables that use an armour sheath and high voltages will opt for DC as the capacitive effect can result in a current flow comparable to the load current if AC was used.
Overall, undersea cables are an amazing feat of engineering, and their use may become more important as the world tries to move towards net-zero carbon. Solar panels in the UK don’t make much sense, and countries near the equator have vast amounts of unused desert that could easily generate power for the world.