There is an increasing need to connect renewable developments with increasing electrical capacity and geographic density. Existing lowprofile, overhead lines (OHL) lack sufficient capacity to accommodate large individual or aggregated electrical capacity. The only current alternatives carry a stepwise increase in construction costs due to their complexity and need for engineered access during construction. The proposed 220kV low-profile designs will provide a lower-cost solution that will assist the energy system transition by reducing the costs of large or aggregated renewable energy connection.

Benefits

The cost benefit analysis is conducted in order to assess the feasibility of implementing 220kV low-profile poles for transmission network, as opposed to the conventional use of steel towers and wood poles.

There is a 60% saving in construction cost per km of 220kV low profile poles compared to the conventional steel lattice towers.

Although the construction cost per km of 220kV low profile poles compared to the single circuit wood poles would be 33% higher, in the eligible individual projects two parallel single wood pole lines would be required to accommodate the increase in capacity. This means costs will be doubled giving an increase of 50% when compared to 220kV low profile poles.

The construction cost per km is as follows:
• Double circuit 220 kV low profile pole line: £0.8 million per km
• Double circuit steel lattice tower line: £1.98 million per km
• Two parallel single wood pole lines: £1.2 million per km
• Approximately 86km in total from three identified projects and one cluster were analysed. There are three scenarios developed to study the cost variances between 220 kV low-profile poles (Scenario 3) with different combination of steel lattice towers and wood poles (Scenario 1 and 2). The results showed the below range of lifetime cost savings.
• Replacing wood poles with 220kV low-profile poles would lead to a lifetime saving of £17 million at 2018 real values. 
• Replacing significant portions of double circuit steel lattice tower with the low-profile poles is expected to result approximately to a lifetime saving of £72.4 million at 2018 real values.

The cost benefits at the end of the RIIO T3 regulatory period are estimated between £2.5 and £9.5 million for all identified lines.

These projects will be carried out through the asset life of the power lines (45 years). The capital budgeting method of Net Present Value (NPV) is used to account for the time value of money and expressed in 2018 real values based on Ofgem’s CBA template.

The budget of the 220kV low profile Innovation project to develop the final design is £1.4 million funded by NIA with 10% contribution from SSEN Transmission. This is not deducted from the final cost savings as it is one-off expense and does not represent the cost of the design during the BAU deployment. However, if the cost benefit of the innovation project  including Innovation project development cost is required, the £1.4 million (£1.17 million in 2018 real values) should be subtracted from the above reported cost benefits, so the net lifetime benefit value would be from £16.2 million to £71.2 million. This if risk-adjusted would range between £12.7 million and £56.3 million. Benefit values are risk-adjusted considering a 21% risk factor to reflect any changes in timelines, technical constraints, and market price fluctuations.

The cost saving kick starts from the first year of construction of the first eligible line which is 2027. If the innovation development cost is considered as part of the BAU budget, then the breakeven year will be delayed by a year only in Scenario 1. All estimated cost savings represent a direct SSEN Transmission benefit on CAPEX reducing construction costs 
associated with wood pole and steel lattice towers.