A new independent report has been published through the Institution for Engineering and Technology (IET) that compares a large number of electricity transmission network technologies across a range of factors including cost, visual and environmental impacts, adaptability, technology readiness and resilience. In this blog, Keith Bell, leader of the UKERC research theme on infrastructure, reflects on the report and the challenge of transmission network development.
Governments all over the world agree that the protection of lives and livelihoods from the massive impacts of climate change demands reduction of greenhouse gas emissions. For that to happen, energy systems must be transformed over time to eliminate the unabated use of fossil fuels. Although that is extremely challenging, the means to do it are available, primarily through wind and solar energy.
In Britain, we’re lucky to have fantastic wind resources and an industry that has proven its ability to deliver wind farm projects with a lower average cost of energy production than new gas-fired electricity generation, certainly at current gas prices. Moreover, making more use of low carbon energy reduces our reliance on an uncertain fossil fuel market – one that has cost the UK taxpayer tens of billions of pounds in recent years to protect energy users from the worst impacts. However, only in certain locations do the availability of space and good wind speeds add up to it being possible to build wind farms. And these are not the places that the existing electricity network was built for, most particularly in the 1960s.
If we’re going to make use of cheap energy from wind farms and make sure electricity bills are as low as possible, we’re going to need the network to be developed to access it. (That’s not the only thing we’re going to need to do, though the rest of it is a discussion for another day).
The IET’s new report on electricity transmission, produced by the consultants Mott Madconald, highlights lots of different technologies that could be used, many of them already in use somewhere in Britain’s network. The National Energy System Operator (NESO) responsible for strategic network planning and network owners responsible for detailed design and delivery must evaluate all options. The “right answer” depends on future power needs, current capacity, and local conditions like terrain, land use and natural resources. These factors, along with electrical engineering basics like managing voltages on long AC cables, determine the viability of different solutions.
The first thing the network owners need to do is consider ways of getting the most out of existing network infrastructure. The report outlines options such as using existing overhead line towers – “pylons” – but with different conductors that can carry more current than the existing ones without risk of breaching limits for the space that needs to be kept clear underneath the line. It also needs to be checked that these conductors won’t exceed the mechanical loading that the towers can handle. Another option, first used more than 30 years ago, is technology that can modify the share of power carried on several parallel routes in order to make full use of the capacity of each individual line.
The amount of additional network capacity that these options can unlock is quite limited and, eventually, it becomes necessary to rebuild the infrastructure in an existing network corridor or make use of a new one. That’s when things can become contentious. Although many opponents of overhead lines argue that lines should be undergrounded, this is not only technically challenging but has its own environmental impacts and, indeed, is not viable in some terrains. It is also, as the new report shows, much more expensive, which energy users would have to bear the brunt of, making the goals of affordable energy, tackling fuel poverty and boosting British industry’s competitiveness more difficult to achieve.
Something else the network owners have been doing in the last few years is building new long-distance capacity offshore. This reduces the need for onshore network capacity but doesn’t eliminate it as it’s still needed to reach the places where energy is used. It’s also expensive.
The decision-making on quite which network option is the right one for any given set of circumstances isn’t easy with lots of dimensions to consider.
The IET’s report shows a summary finding that, on average, it costs 4 and a half times more to move each MW of power over each km of distance using AC underground cables than overhead lines, 5 times more to do so using high voltage direct current (HVDC) subsea cables between two locations in the onshore transmission network, and more than 10 times more using an offshore HVDC network that connects multiple locations. However, the actual ratio depends on the context and the relative impacts of fixed costs to connect new infrastructure into the existing network, the costs that vary with the length of a new or rebuilt route and whether an alternative technology is being used for part of a route, e.g. partial undergrounding. The report provides a large set of examples of such effects with different technologies, capacity additions and distances.
There is pressure to get on with the necessary investment in the electricity system: the sooner we can get access to cheap, low carbon energy, the more benefit we can gain from it. However, the infrastructure development decisions that are taken need to have legitimacy: all stakeholders – people living and working near a development, and those who need to pay for it – need to be confident that their views are being heard and all options evaluated correctly. The new report – the product of lengthy, independent research – is intended to give everyone access to information they can trust. It won’t tell you ‘the right answer’ in any given circumstance and it needs to be used in the right way, but it will tell you a lot of the things that need to be taken into consideration.
A version of this blog first appeared in Engineering and Technology magazine and is reproduced by kind permission of The IET.
Keith Bell holds the Scottish Power Chair in Future Power Systems at the University of Strathclyde and leads the UKRTC research theme on Delivering Energy Infrastructure.
Read the IET report on “A comparison of electricity transmission technologies: Costs and characteristics”.