A 20 mile tunnel almost as big as a tube tunnel is to be dug under South London, linking Wimbledon to Crayford near Dartford, via New Cross.
This long tunnel will be carrying not humans, but electrons — it’s part of the London Power Tunnels project to upgrade capacity in London for its ongoing electricity demands.
The new tunnel will replace a maze of cables running under London’s streets which are wearing out and need replacing, but rather than digging up loads of roads, the National Grid has opted for a deep tunnel instead.
The £400 million construction contract has just been awarded to a consortium of Hochtief and J Murphy and Sons. The tunnel will then be dug in three sections, all starting in March 2020, and completing in late 2024-2026.
Once completed, they will carry up to 400kV of electricity. The project follows on from a similar tunnel construction across north London.
A number of shafts are also needed to be dug down, for access to the electricity tunnels, but mainly for ventilation to keep the cables cool. Most of the headhouses on the surface will be on existing UK Power Networks sites, but one, at Eltham is currently occupied by the Welling and District Model Engineering Society, who will need to find a new home for their miniature railway and meetings.
There is also a suggestion that the ventilation shafts could find a use in the heat they extract, to heat homes or offices. A typical length of electricity tunnel between ventilation shafts produces around 400 kilowatts of heat, enough to heat 100 homes or a small commercial office.
If implemented, then not only could the new tunnels carry electricity to heat homes, they will do so while actually heating homes indirectly as well.