The proposed MarramWind Offshore Wind Farm would power more than 3.5 million homes. (Credit: ScottishPower)
The wind farm will be located offshore Scotland. (Credit: ScottishPower)
Shell and ScottishPower won bid to develop the MarramWind Offshore Wind Farm. (Credit: ScottishPower)

MarramWind is a proposed floating offshore wind farm in the North Sea, Scotland, the UK.

Once fully commissioned, the project will be capable of delivering up to 3GW of clean renewable energy. This will be enough to power 3.5 million homes.

The development of the wind farm will also support the Government of Scotland to reach the net-zero emissions target by 2045.

The wind farm will be developed by MarramWind Limited, a 50/50 joint venture company between ScottishPower Renewables (UK) and Shell New Energies Holding.

The two companies secured the rights to develop the floating offshore wind farm, as a part of Crown Estate Scotland’s ScotWind Leasing Round in January 2022.

MarramWind submitted the Environmental Impact Assessment- Scoping Report to Marine Scotland and Aberdeenshire Council, the respective planning authorities for the offshore and onshore elements of the proposed project, in January 2023.

According to the report, the construction of the project’s offshore infrastructure will take up to eight years. The onshore construction is expected to be completed in two to three years within the overall duration period.

The timeline is subject to final grid connection date, supply chain discussions and additional site surveys.

Location details

The MarramWind Offshore Wind Farm will be situated in water depths averaging 100m within northeast 7 (NE7) Plan Option, located off the northeast coast of Scotland.

The NE7 Option Agreement Area lies offshore between 75-110km of the northeast coast of Aberdeenshire. The agreement area is around 684km2 in size.

MarramWind Offshore Infrastructure

MarramWind ‘s offshore infrastructure will include Wind Turbine Generators (WTGs), including floating units (platforms and station keeping system), array cables, and accommodation platform(s) (if required).

The offshore components will also include offshore substation(s), reactive compensation platform(s) (if required), and offshore export cables.

The project is expected to have 126 to 225 WTGs. The final figure and the capacities of the turbines will be finalised following assessment of the optimum wind resource, prevailing site conditions, and environmental and engineering surveys.

According to the scoping report submitted, each WTG will have power generating capacity of up to 25MW with a maximum rotor diameter of up to 326m.

The WTGs will be installed on floating units consisting of a floating platform stabilised to the seabed by a station keeping system.

The project will use a single 3-core AC cable as array cable with additional mechanical protection.

Presently, 66kV is set as the standard offshore array cables voltage. However, higher voltage up to 145kV can also be used. The cables will be buried to a depth of 1-2m, subject to Cable Burial Risk Assessment (CBRA) and seabed mobility.

The WTGs will be connected to substation platform (s) located within the Option Agreement Area (OAA). The number of substations will be determined after the finalisation of selected technology and site layout.

The substations will contain the main electrical equipment, auxiliary, controls and operational systems and may also feature a helideck.

The MarramWind project may also use a permanent accommodation platform within the OAA to facilitate operations and maintenance of the WTGs and substations.

MarramWind Onshore Infrastructure

The onshore infrastructure of the project will include landfall infrastructure, onshore export cables, onshore substation (s), grid connection cables, and grid connection point.

The final landfall location(s) has/have not been finalised. However, multiple indicative options have been identified along the Aberdeenshire coastline through the optioneering process.

Up to 24 underground export cables will be used to connect the landfall transition bays to the onshore substation. The onshore export cable route corridor will be finalised during the detailed design and the EIA process.

The project may have up to two onshore substations housing necessary electrical components to ensure the offshore wind farm exports power complying with the UK Grid Code.

A section of onshore export cable route will run from the onshore substation site (s) to the grid connection point.

Power Transmission

The electricity produced by the wind farm will be transmitted to the onshore grid either via High Voltage Alternating Current (HVAC) approach or via High Voltage Direct Current (HVDC).

An HVDC transmission would require an additional offshore converter within OAA, while HVAC transmission would likely involve reactive compensation technology at a location midway between the OAA and the landfall(s).

The offshore export cables will export power to the transition joint bays onshore at the landfall(s) from the offshore substation. Up to eight cables will be used along an export route of up to 120km to transfer the power.

Before the ScotWind Leasing process, MarramWind secured a connection to the National Electricity Transmission System (NETS).

Initially, National Grid Electricity System Operator (NGESO) stated that New Deer will be the grid connection point for 3GW wind farm.

After the publication of NGESO‘s Holistic Network Design (HND) report in July 2022, the plan was changed. It confirmed that 1.5GW would be connected in the vicinity of Peterhead, while the remaining will be confirmed as part of the HND Follow Up Exercise (HND FUE).

According to the EIA Scoping Report, MarramWind is working with NGESO and Scottish and Southern Electricity Networks (SSEN) on the remaining capacity and the findings of HND FUE.

Grid connection dates are expected to be provided between 2030 and 2035, subject to NGESO and SSEN confirmation.

Contractors involved

WSP Environment & Infrastructure Solutions UK led the preparation of the EIA for the MarramWind offshore wind farm project.

Several consultancies also offered expert advice on the EIA aspect assessments. This includes ABP Marine Environmental Research, Subacoustech Environmental, Poseidon Aquatic Resource Management, Anatec and Coastal and Offshore Archaeological Research Services.