An Initial Needs Case (INC) has been submitted on a proposal to replace the existing Fort Augustus to Skye electricity transmission line by SSEN Transmission to Ofgem.

The INC, which is part of Ofgem's new Large Onshore Transmission Investment (LOTI) Uncertainty Mechanism for the RIIO-T2 price control period, is the first stage of the regulatory funding approvals process.

At an estimated cost of around £400m, the Skye reinforcement project would be one of the most significant energy investments in the West Highlands since power was first brought to the area in the 1950's.

The existing Fort-Augustus to Skye line, which was constructed in three distinct sections between 1956 and 1989, consists of a combination of steel lattice towers from Fort Augustus to Broadford, then overhead wooden poles from Broadford to Edinbane. The line is fast reaching the end of its operational life and is in urgent need of intervention. Its planned replacement is therefore essential to maintain network reliability and security of supply to homes and businesses along its route, as well as to the Western Isles which is primarily supplied by two electricity distribution subsea cables from Ardmore point.

To enable the connection of new renewable electricity looking to connect to the transmission network along its route, SSEN Transmission is also proposing to increase the capacity of the replacement line, supporting the UK and Scottish Governments transition to net zero emissions. The existing line has already exceeded its capacity limit, preventing the connection of new renewable electricity in the area.

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Rob McDonald, Managing Director of SSEN Transmission, said: "Submission of our Initial Needs Case marks a major milestone in unlocking the significant investment required for the Skye reinforcement project. The project is essential to maintain and improve network reliability and security of supply, whilst also supporting local and national efforts to tackle the climate emergency and deliver a pathway to net zero emissions.

"We now look forward to working constructively with Ofgem and our stakeholders to make the investment required in a timely manner, delivering on Ofgem's commitment to an agile and flexible regulatory framework and in doing so, create hundreds of skilled jobs throughout the supply chain to support a green recovery from the coronavirus pandemic."

Given the scale of the project, stakeholders have made it clear the replacement line should anticipate future electricity generation looking to connect in the years ahead, avoiding an iterative approach to network development and associated local impacts and disruption this would cause. This 'do it once do it right' approach, which the Electricity System Operator's own independent Cost Benefit Analysis (CBA) supports, will greatly reduce the need for additional major works in the future, responding positively to stakeholders asks.

To meet the required increased capacity of the replacement line, steel structures will be required from Fort Augustus to Edinbane; with wooden pole remaining from Edinbane to Ardmore.  Upgrades to the existing substations at Broadford and Edinbane will also be required as part of the Skye reinforcement.

SSEN Transmission continues to progress the detailed design for the replacement line and expects to consult on its preferred route and technology later in the autumn. As part of this and in response to stakeholder feedback, SSEN Transmission is actively exploring potential mitigations. This includes assessing the potential for undergrounding as the line passes the Cuillin Hills and where it connects to Fort Augustus substation; and alternative routes as it passes Kylerhea.

Separately, work to progress a 600MW HVDC connection to the Western Isles continues with SSEN Transmission committed to continuing to work constructively with Ofgem, Government, Western Isles generators and wider stakeholders to overcome barriers to unlock the islands vast renewables potential.