Offshore wind transmission - this is how wind energy is transported

Underwater cables are thus the backbone of an offshore wind farm; without them, the energy would be literally stuck at sea.

Transporting energy to shore starts with converting wind energy into mechanical energy, and then into electrical energy. The generated electricity is sent to a substation through underwater cables. Export cables, such as HVDC cables, transport and convert the energy. The underwater cables then transmit the electricity to an onshore substation. Finally, the electricity is fed into the electrical grid, which brings the electricity to our homes and businesses.

These underwater cables feature advanced technology and several types of cables are used in a single offshore wind farm.

Subsea umbilical cables are important for transporting electricity to shore. The term “umbilical” is used because, like a human umbilical cord, these cables deliver vital resources for the offshore wind substation to function properly.

Unlike a regular power cord, a subsea umbilical cable combines multiple types of cables within a single sheath. The subsea umbilical cable can contain electrical wires, data lines and tubes for fluids, all housed securely to protect them from the harsh subsea environment. They are essential for offshore operations, providing reliable data transmission, power, and fluid supply to ensure safe and efficient underwater activities.

A HVDC cable is a cable used for high-voltage direct current (DC). These cable systems enable efficient long-distance transmission at high power levels. Using DC to transport power significantly reduces energy losses, especially over long distances. This makes HVDC lines ideal for connecting remote power sources, such as offshore wind farms, to the onshore grid. Moreover, the voltage level in DC is steady and doesn’t fluctuate over time, making it a good option for equipment that needs a stable power supply.

An HVDC converter station links the direct current (DC) and alternate current (AC) together. Its primary function is to convert power from DC to AC or vice versa to deliver electricity to local grids. With AC, the electricity voltage varies and the electric charge changes direction periodically. AC can easily adapt to different voltage levels and is more suitable for general power distribution than DC, which provides efficient long-distance transmission of electricity with minimal energy loss.

Inter array cables are a network of cables that connect the individual wind turbines in a wind farm together and to a central collection point, or substation, located either offshore or onshore. The cables transmit the electricity generated by the turbines to the substation, where it is then converted for transmission to the grid.

The installation process for underwater cables is complex and an integral step in installing an offshore wind farm. The planning phase is extremely important, as seabed surveys can reveal potential obstacles and provide valuable insight into the terrain that will be selected for the cable routes. Proper planning facilitates a safe and efficient installation process.

After the survey has been completed, the cables are custom-made to fit the lengths between the turbines and the substation. This phase also includes rigorous testing to ensure that the cables can withstand the harsh environmental conditions. Once this phase is completed, specialised cable-laying vessels install the cables, usually below the seabed as this is often the safest option both for the cables and for the marine environment.

Once the cables are laid, the ends are connected to each wind turbine and the offshore substation. When the installation is complete, tests are run to make sure the cable connections are running smoothly.

In addition to transporting power, underwater cables can be used to connect entire wind farms together, enabling them to share infrastructure and optimise power transmission. Underwater cables also allow for scalability of offshore wind farms, as it is possible to extend an existing cable network to new wind farms.

Underwater cables also play an important role in wind farm monitoring, transmitting critical data on turbine status and performance as well as maintenance needs.