Why pylons are needed for an affordable net-zero future
Listen to this blog read by Holly Thomas, Policy Manager for Grid and Networks at Scottish Renewables, here.
With the UK government’s target of Clean Power by 2030 (CP30) and Scotland’s own target of net-zero by 2045, we need to roll out new grid infrastructure at scale, and fast. While the preferred type of network infrastructure to meet these needs is a hot topic, it is important to understand the full range of regulatory, engineering and economic factors behind such decisions.
The National Energy System Operator (NESO) considers four separate design objectives when deciding upon network infrastructure: cost, deliverability, environmental impact and impact on local communities.
As the communication of factors informing network decisions can often be quietened by opponents of pylons, this blog aims to reveal the misconceptions around different network infrastructure in clear, digestible terms to help foster a greater understanding of the electricity network beyond its various facades.
Let’s start with ‘why can’t we put it all offshore?’
The UK is already positioning huge amounts of renewable energy generation at sea, which is helping to reduce the amount of infrastructure needed onshore.
As outlined in the NESO’s recent recommendations for the electricity network, over three times as much new transmission infrastructure is set to be built offshore compared to onshore. However, not all new grid infrastructure and reinforcements can be placed offshore.
It is perhaps unsurprising that offshore subsea cabling costs significantly more than pylons and ungrounding cables onshore. Pylons are on average five times cheaper than underground cables and can be over eight times cheaper than offshore subsea cables*, with the final cost ultimately being recovered through consumer bills.
Furthermore, each repair of failed offshore cabling costs on average £12.5 million and, as the cable routes are complex and hard to access, issues that arise can take months to resolve and fixing underground cables can take several days.
Meanwhile, pylons can be repaired in several hours and as climate change and extreme weather events continue to affect the UK, particularly in Scotland, the questions of system resilience and security of supply are being more highly prioritised in network decisions.
So why can’t we put it all underground?
The undergrounding of onshore cables, is only viable for routes under 20km due to ground conditions, including river crossings, steep bends around mountains and the complex challenge of routing high voltage cables across longer stretches of the electricity network.
Undergrounding is also much more expensive than pylons due to the more invasive process required to lay the cables, which also carries a host of environmental challenges. Ground conditions including hydrology, woodland and peat among others all have to be evaluated to assess whether a site is suitable. Once approved, the construction and maintenance phases can be highly disruptive to the natural environment.
The scale of laying an underground cable can be compared to constructing an underground motorway.
For 400kV projects, developers need to dig a cable corridor stretching 40m wide, the width of a motorway, with a depth of one to seven metres. For maintenance works, the entire area has to be dug up, which not only leaves a considerable eye-sore but can also disturb any nature that may have taken root. While underground cables are technically invisible, their construction and continued maintenance can pose significant disruption to surrounding areas.
What about putting it all onto offshore hubs, like in other European countries?
Countries such as Denmark are developing ‘energy islands’ where multiple wind farms connect to an offshore energy base, which then feeds energy to shore via a direct cable route.
Although this is an intriguing development, the technologies required to support this type of infrastructure have not yet been developed at scale and may not be available in time to deliver on the UK’s net-zero targets. Other uncertainties for offshore energy hubs include investment, commercial viability and necessary market arrangements - in other words: who’s going to pay for it and is it affordable? Energy hubs are an unknown, capital-intensive infrastructure that would not support the UK’s immediate climate ambitions.
The benefit of overhead pylons
Even if there were no drawbacks to offshore infrastructure, there simply are not enough factories in the world producing the types of cable needed to put our entire electricity transmission needs under the sea whereas pylons are not hindered by a constrained supply chain.
As the transmission network evolves for future demand, its components should be able to withstand the test of time. As demand and generation continue to grow, our electricity network needs to have a level of flexibility if capacity requirements change over time. With 125GW of offshore wind potentially needed by mid-century, the network needs to be redesigned to accommodate increased demand. Pylons are the easiest way to divert, reroute and adapt the electricity network so projects can connect in the future.
The visual and community impact of transmission infrastructure is always considered in network planning decisions and for this reason, all technology types are being used where appropriate. However, considering all the onshore options, pylons offer the most benefits for protecting consumer bills, the environment, securing our energy supply and reaching our climate targets on time.
Notes
- *when considering lifetime costs for a 75km, 6000MW transmission route.
- For more information on the decisions behind electricity transmission lines, see SSEN’s recent webinar with industry experts from the UK and Europe.
- See also BiGGAR Economics’ report evidencing the lack of adverse impact from transmission lines on house prices in Scotland.
- A report from Scottish Renewables ‘Why investing in electricity transmission infrastructure is a priority for Scotland’ is available, here.
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