Tips for transporting electricity to the shore

Nicola Brittain

A review of additional equipment required for long-distance electricity transportation.

As the global demand for electricity increases, the need to scale up renewable energy generation is more important than ever. The International Energy Agency (IEA) estimates that renewable energy will contribute 70% of the global energy mix by 2050 under a net-zero scenario. 

With regards to windpower, the total installed capacity of electricity was approximately 906 gigawatts (GW), accounting for almost 11% of global power generation capacity by the end of 2022. The International Energy Agency (IEA) predicts that this capacity will reach 7,795 GW by 2050, accounting for 23% of the worldwide energy mix.

Wind power may be generated both onshore and offshore. Offshore wind power is generated by wind turbines installed close to the beach or further out to sea.

Europe currently has around 30 GW of installed offshore wind capacity, and this is predicted to grow to about 200 GW by 2030.  Most of the expansion is likely to come from the North Sea, which, as a shared resource, will help all of Europe meet energy-dependability targets.

Electrification of energy systems is an important part of the move towards achieving net-zero.

Offshore HVDC challenges

Offshore wind farms in the North Sea are being built further from the shore (100-150 km) and long-distance transportation of wind turbine-generated power is a challenge.

When a wind farm is within 80km of the shore, electricity may be transported in alternating current (AC) type. However, for wind farms located more than 80 km from the shore, additional equipment is required to avoid considerable power losses during transmission.

An offshore HVDC converter station, a high-voltage cable system, and an onshore HVAC converter station are among the additional pieces of equipment required.

Offshore HVDC converter stations convert the AC power provided by wind turbines into DC electricity. DC power has fewer transmission losses than AC electricity, making it more efficient for long-distance transmission. When the power reaches the onshore HVDC converter plant, it is converted back to AC and sent into the grid.

The size of a converter station is determined by the number of wind turbines linked to it for power conversion and stations can vary in size from 520 MW to 2GW. Heat is produced as a byproduct of electricity conversion and the heat-emitting equipment, known as thyristors/rectifiers, must be constantly cooled to keep the system working.

The most effective method for cooling large HVDC converter stations is to utilise deionised water in a closed system. The deionised water is cooled using saltwater pushed through a heat exchanger that absorbs heat from the deionised water. Some systems blend chemicals like glycol to keep the water from freezing.

Offshore wind energy will play a critical role in developing a sustainable and renewable power-generating model. As offshore wind generation extends further from shore, converter platforms and large cable networks are required to reduce transmission losses before the electricity reaches the onshore power system. These converter platforms convert low-voltage energy generated by turbines into high-voltage electricity needed for transmission, providing efficient power delivery over great distances.

For more information visit Rotork