When it comes to the expansion of the transmission grid, people often wonder: why not just put new lines under the ground? Well, it’s... let’s say... «complicated». At first glance, underground cables (lines buried under the ground) appear to be an elegant and sensible solution. But they also cause problems, especially for the extra-high-voltage grid. Here are the five most important reasons why extra-high-voltage lines (in the AC grid) should generally be installed as overhead lines.
1. Speed instead of bureaucracy
Today, we also have to examine underground cable variants (i.e. lines under the ground) for every grid project. Regardless of whether they make sense or not. This means longer procedures and higher planning costs. By focussing on overhead lines, grid expansion could be implemented much more rapidly and in a more streamlined manner. Underground cables would remain an exception. And security of supply would be strengthened more quickly. Anyone who says yes to the energy future must also say yes to the associated infrastructure.
2. The bill, please!
You can do the sums as often as you like: underground cables are expensive – they cost up to ten times as much as overhead lines. Partly because their service life is only half as long. These additional costs do not disappear into the system, but ultimately have to be borne by all electricity consumers. So anyone who argues in favour of more underground cabling must also explain why we should all pay more for electricity.
3. Peace and quiet for twice as long
Overhead lines are robust: they last around 80 years and can often be repaired in just a few hours or days in the event of a disturbance. Underground cables, on the other hand, have to be replaced after about 40 years. And if they stop working, things get really complicated. This is because these are custom-built. Outages can last weeks or even months.
4. Security of supply comes first
If we looked exclusively at the issue of security of supply, we would install virtually nothing but overhead lines. If too many sections of the transmission system are laid as underground cables, grid stability suffers (voltage stability, resonant frequencies). In the worst-case scenario, an excessive proportion of underground cables can even make restoration more difficult after a major disturbance – this is also shown by the Swiss cable study.
5. What you can’t see isn’t necessarily green
Cables in the ground = better for the environment? Unfortunately not! They may be easier on the eye, but the ecological balance shows a very different picture: underground cables require much more material, their production uses more energy, and compensation losses are higher. The bottom line is that overhead lines are much more environmentally friendly.
Conclusion
We all need electricity. Overhead lines are required in the transmission system to ensure a secure, affordable and ecological supply of electricity and the rapid modernisation of infrastructure. Underground cables can be useful in clearly defined, exceptional cases. However, if there are too many of them, they jeopardise security of supply.
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