Electricity flows – but how? This question is crucial to the energy transition. After all, it is not just the production of electricity that must be sustainable, but also its transmission. As the national grid company, Swissgrid faces the challenge of expanding the extra-high-voltage grid while at the same time reconciling ecological, technical and economic aspects. A life cycle assessment study has shown that overhead lines are much more environmentally friendly than underground cables. This is a surprising finding that prompts a rethink.
A life cycle assessment over the entire service life
At first glance, underground cables are a big plus for the landscape. When underground cables are used, a large part of the line infrastructure is buried – invisibly – in the ground. However, underground cables also leave traces in the landscape, for instance in the form of aisles in forests, access roads, compensation systems to reduce the voltage and transitional structures that connect overhead lines to the underground cables.
On closer inspection, both overhead lines and underground cables have specific advantages and disadvantages in terms of project planning, construction, operation and maintenance. Swissgrid examines the overhead line and underground cable options for every grid project – and analyses their environmental impact over the entire life cycle. In this context, Swissgrid commissioned a life cycle assessment study from Umtec Technologie AG that was conducted in accordance with the methodological recommendations for life cycle assessments issued by the Federal Office for the Environment (FOEN) and reviewed by an external expert on life cycle assessments. The study compares the environmental impact of overhead lines and underground cables at the extra-high-voltage levels of 380 kV and 220 kV. The methodology is based on recognised standards and takes Environmental Impact Points (EIP), greenhouse gas emissions (CO2eq) and cumulative energy consumption as assessment parameters. The study examines the transmission of 1 GWh of electrical energy at the 380 kV or 220 kV extra-high-voltage level over a line length of 1 km – in the period under consideration from raw material extraction to dismantling (around 80 years).
The results of the life cycle assessment are clear: underground cables are up to three times less environmentally friendly than overhead lines. The main reason for this is that underground cables require much more material, and their production uses significant amounts of energy. In addition, there are high transmission and compensation losses, and costly replacement is necessary after around 40 years – while overhead lines last twice as long.
Sensitivity analysis: the service life, electricity mix and choice of materials all count
The life cycle assessment study clearly indicates that certain parameters have a significant influence on the environmental impact of transmission technologies. The sensitivity analysis examines how changes in these parameters – in particular the service life, electricity mix and choice of materials – affect the environmental balance of the infrastructure.
- The longer a cable system remains in use, the greater the reduction in the environmental impact of its manufacture and construction over its entire service life. In the 220 kV grid, savings of up to 13.5% can be achieved by extending the service life.
- The life cycle assessment shows that transmission and compensation losses account for a high proportion of the environmental impact. The electricity mix plays a key role. Assuming that the electricity transported in Switzerland consists of a renewable mix, the environmental impact of transmission losses is reduced by over 60%. Nevertheless, the main finding remains that overhead lines are environmentally friendlier, especially at the 380 kV level.
- Overall, the materials used in the manufacturing and construction phase dominate the life cycle assessment. As far as underground cables are concerned, the materials are responsible for up to 80% of the environmental impact, depending on the construction method. Components with a high metal content such as copper cables, concrete or steel cable conduits – have a particularly high environmental impact. There is potential for optimising this impact by using recycled or alternative materials.
Whether electricity pylons are 400 or 600 metres apart makes virtually no difference to the environment. Less spacing between pylons means less material per pylon, but more pylons in total. The effects balance each other out. From an ecological point of view, the pylon span hardly matters; technical and regional planning aspects are more important when choosing a location.
Digital line planning: integrated sustainability
Swissgrid uses the Gilytics software for route planning. This innovative tool allows Swissgrid to identify the best corridors and routes for transmission line projects on the basis of facts. It takes into account technical, legal, economic and regional planning criteria – and in the future, it will also consider ecological aspects such as the CO2 footprint and environmental impact. The integration of life cycle assessment data into digital planning is an important step towards systematically considering sustainability criteria. This will make it possible to identify variants with a lower environmental impact in the early planning phase and incorporate them into the decision-making process.
In conclusion, sustainability is not always invisible
Overhead lines are visible – but they also make ecological sense. The life cycle assessment study shows that overhead lines at the extra-high-voltage level have a consistently lower environmental impact than underground cabling construction methods. The results remain stable, even if individual parameters are changed.
Grid expansion must not only be technically and economically well thought out, but should also pay attention to ecological aspects. Swissgrid is committed to ensuring that sustainability is taken into account from the outset – digitally, transparently and based on facts.
The principle is that underground cables should only be used to a limited extent in the Swiss extra-high-voltage grid. Their physical properties make stable grid operation and troubleshooting more difficult. An excessive proportion of underground cabling can jeopardise security of supply. For future grid projects, the possibility of installing an underground cable should therefore be considered from an overall perspective. More information in the following video.
Swissgrid: a climate strategy that considers the entire value chain
As part of its sustainability strategy, Swissgrid is pursuing the goal of reducing its direct and indirect Scope 1 and Scope 2 emissions to net zero by 2040. A key element in the design of the climate strategy is the use of life cycle assessment data (LCAs). This data serves as the basis for identifying the most important emission drivers along Swissgrid’s entire grid infrastructure and value chain. In line with the results of the life cycle assessments for transmission technologies, an important focus is placed on reducing and decarbonising transmission losses, which currently account for around 95% of the company’s direct and indirect emissions. Swissgrid is also working on systematically recording the indirect emissions (Scope 3) of the materials used in the manufacturing and construction phase and reducing them in the long term. Initial pilot projects as part of the sustainable procurement strategy show that many suppliers can already provide relevant data. This is an important basis for climate-friendly infrastructure development along Swissgrid’s entire value chain.
Author
