Keeping Overheads so far Down, They’re Underground

We automatically think, in this country, that if power needs to be sent from generating station A to a town rejoicing under the name of B, then some line joining the two points must be sown with large metal skeletons keeping high-voltage wires safely above our heads.

It ain’t necessarily so.  Thomas Blakeslee of Clearlight Foundation, writing in RenewableEnergyWorld.com, makes the case that using high-voltage DC instead of AC and burying the cables underground can cost the same or less than stringing them through the sky, for four reasons:

1. The electronic voltage converters required by HVDC grids (which are the kind we will need for the national backbone described in the above article) are no longer cost-prohibitive, thanks to falling semiconductor prices.

2. Costs for AC transformers, land and steel are rising dramatically.

3. DC transmission requires two cables, AC three.

4. Planning to bury cables along existing rights of way instead of proposing to mar landscapes with towers will likely avoid years of expensive legal battles with environmental and local citizens’ groups.

Images courtesy of ABB

That last reason may sound conjectural, but no-one who has been involved in the permitting process for an energy project of any size can doubt its basic verisimilitude.  It’s not hard to imagine that legal fees and cost overruns induced by delays in permitting could easily exceed the disparity between above-ground and below-ground construction costs.  And if the project in question happens to be the supergrid described in the previous article, using what appears to be the more expensive (underground) route to connect CSP output to load centers half-way across the country could well turn out to be the fastest, cheapest option.

You can read Blakeslee’s full article here.

Distance also plays a role in this cost analysis.  ABB, the huge Swiss-based power and automation technology group, estimates that for distances greater than about 500 kms, the use of underground (and submarine) cables for its HVDC Light technology would only cost about 10% to 20% more than overhead lines—even without accounting for permitting/legal delays.   It’s an option that’s evidently being seriously considered overseas, and should be here.

Graphic courtesy of ABB