Replacing overhead lines with underground cables in Finland

Elenia, Finland's second-largest electricity distribution operator, has been investing in underground cabling since 2009 to meet the outage requirements of Finland's Electricity Market Act and to protect the grid from climate-linked hazards such as storms, heavy snow loads and falling trees, whose risk is expected to rise as warming extends the leaf-bearing season of deciduous trees.

Elenia's target is to bring 75% of its network underground by 2028, up from 41% at the time of reporting, in order to improve security of supply and reduce weather-related outages and repair costs.

Cabling is buried in trenches roughly 0.45-1 metre deep. Where possible, Elenia coordinates 'co-construction' excavation with telecommunications companies laying fibre-optic cable, to share costs and minimise disruption. Recent innovations include digitisation and GIS mapping of underground cable routes to warn other excavators and reduce accidental damage.

Elenia's planned investment for 2018 was EUR 140 million, with installation and excavation the largest cost components. Finland's 7th National Communication to the UNFCCC estimated total distribution-network investment needed nationally to secure supply, including underground cabling, at EUR 2,800 million. Benefits such as improved supply security and local employment were, at the time of reporting, not quantified, and a study of the social costs and benefits of underground cabling was still under review.

Availability of appropriate technology for installation, monitoring and management is identified as the key success factor, alongside collaboration with telecommunications companies to share excavation costs and minimise disturbance. Underground cabling introduces new, so far largely hypothetical, exposure to flooding and landslide-related soil movement, and remains vulnerable to accidental damage from unrelated excavation work.