The wind farm will comprise a number of key components that will all work together to generate, transmit and convert green energy to be fed into the National Grid. It requires state-of-the-art technology and innovative engineering and each component has to work seamlessly with the others, each playing a pivotal role in the success of the project.
Wind turbine generators
Sofia will use Siemens Gamesa Renewable Energy's SG 14-222 DD - a 14 MW platform featuring 108 metre carbon and fibreglass blades cast in a single mould and a 222 metre-diameter rotor sweeping an area of 39,000 m2. Each turbine will stand at 252 metres - that's just 60 metres less than the UK's tallest building, The Shard - the nacelle is a lightweight of 500 tonnes. Being a brand new machine, the prototype is planned for 2021 and commercial deployment is set for 2024. More on the technical specifications can be found in this fact sheet.
High voltage direct current transmission system
A consortium of GE Renewable Energy’s Grid Solutions and Sembcorp Marine will supply Sofia's high voltage direct current transmission system. The system will include two HVDC converter stations - one offshore and one onshore - with innovative converter modules and a new high-tech control system deployed. The offshore converter station will be the most powerful ever fabricated, and the farthest from shore.
The system will utilise GE Grid's second-generation voltage source convertor valve and feature the first application of its state-of-the-art eLumina™ HVDC Control System. eLumina is the industry’s first HVDC solution to use a digital measurement system fully based on International Electrotechnical Commission (IEC) 61850, an important international standard defining communication protocols for intelligent electronic devices at electrical substations.
The offshore converter platform will be the heart of the wind farm and will comprise a 10,000 tonne topside attached to a 7,000 tonne jacket foundation piled into the seabed. The onshore converter station will convert the electricity generated by the wind farm to 400 kV, before it enters the national grid.
Submarine and land export cables
Prysmian Group will provide a turn-key high voltage submarine and land export cable connection, including use of brand-new cable installation vessel Leonardo da Vinci for Sofia. The company will carry out the design, supply, offshore route preparation, installation, commissioning and protection of the 320 kilovolt (kV) high voltage direct current (HVDC) cable system that will carry power from Sofia’s offshore converter station 227 kilometres to the project’s onshore converter station in Teesside.
Foundations
Sofia will use steel monopile foundations without a transition piece. The foundations will be between 80 and 90 metres in length and weigh between 1200 to 1400 tonnes each. Their diameters will be between 7.5 to 8.4m at the mudline. They will be installed by Van Oord's jack-up vessel Aeolus. Four giant legs, each measuring 85 metres, allow Aeolus to be jacked up and work in waters up to 45 metres deep.
Array cables
There will be 109 individual array cables, totalling approximately 360 kilometres, installed in 18 strings feeding into the offshore converter station. Pairs of strings will be configured into nine loops, each with a total of 10 to 12 turbines. Each loop will employ interlink cables to ensure maximum flexibility for the wind farm's network. Power generated by the turbines will be able to be transmitted to the converter station in either direction around the loop. Van Oord's cable installation vessel Nexus is due to install the cables.
