The existing 132kV high voltage transmission system has served Dumfries & Galloway well for many years and provides the region with a reliable source of electricity to the point where, within the south of Scotland, SPEN have sufficient confidence in their ability to maintain the system they have agreed a target with Ofgem of 224MWh of ‘energy not supplied’(ii) each year up until 2021 . Therefore, just because a transmission system is old does not necessarily mean it needs to be replaced, as the National Grid (2014) make clear:
“Transmission assets tend to have very long operational lifetimes, many in excess of 50 years. Although much of the equipment is obsolete, it is in good condition with many years of service left …” National Grid Electricity Ten Year Statement (2014, p.169).
Putting to one side the fact that the existing network is old and will eventually need to be replaced at some future time with more modern technology, the single most important factor driving the upgrade is the growth in on-shore wind where in 2015 there is approximately 380MW of capacity  connected to a network that is rated at 105MW (iii). Fortunately there is a degree of mitigation that reduces the risk of overload and this arises from the intermittent and variable nature of wind power which tends to reduce the load factor (iv) in the summer months. Notwithstanding this point, it is likely there will be times when network constraints restrict the amount of connected renewable generation resulting in turbines being shut down thereby triggering constraint payments.
A recent announcement (v) by The Secretary of State for Energy and Climate Change, the Rt Hon Amber Rudd, MP, proposes to end the public subsidy for on-shore wind in favour of encouraging other renewable technologies. Consequently, any wind farm not consented by the 18 June 2015 and having in place the necessary connection agreement as well as land rights will not be eligible for public subsidy. This announcement will limit on-shore wind turbines within Dumfries &
Galloway to around 1000MW ; still enough to supply the annual needs of nine times the number of homes in the region  but still less than half of what might have been had the announcement not occurred when it did.
Even with this restricted level of renewable generation, however, the existing network will be significantly overloaded and SPEN estimate that constraint payments of up to £16bn could be triggered throughout the south of Scotland by 2030 without the proposed upgrade. In addition to accommodating the indigenous renewable generation this project proposal will also help unblock the 500MW Maybole Interconnector where there is currently a constraint due to the amount of renewable
generation feeding into the network around the Kilmarnock area.
In summary, therefore, SPENs proposal seeks to overcome current and future restrictions in transferring renewable energy to England and Wales thereby off-setting constraint payments that would otherwise be incurred. Additionally it enables the Maybole Interconnector to operate at full capacity and it overcomes the problems associated with obsolescence. It can, therefore, be considered a strategic reinforcement project.