MINIMISING THE VISUAL IMPACT OF new TRANSMISSION LINES
In the TRANS-CSP report, it is proposed that, in the period up to 2050, a large-scale grid of HVDC transmission lines should be constructed to facilitate the transmission of renewable electricity around EUMENA, including the import of CSP electricity into Europe from the Middle East and North Africa. For this EUMENA-wide 'supergrid', a total of 20 lines are proposed, each one of 5 GW capacity. Three examples are analysed in the report and shown on a map which is reproduced here:
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But laying overhead HVDC power lines throughout EUMENA would be visually intrusive and there may be objections to them for that reason. The next three sections describe ways in which the visual impact of transmission lines may be reduced or eliminated.
Use existing transmission grids and upgrade them
There appears to be considerable scope for minimising (new) problems of visual intrusion by making better use of existing transmission grids:
- Although HVAC transmission lines are relatively inefficient over long distances, it is possible to use an existing HVAC transmission network to achieve the effect of long distance transmission without the corresponding inefficiencies. This is explained in a separate page about the cascading principle. This principle should make it possible for countries throughout Europe to begin to benefit from CSP imports on relatively short timescales, although it is likely that, with increasing quantities of electricity to be transmitted, upgrading would be required as described next.
- There appears to be quite a lot of scope for improving the efficiency and transmission capacity of an HVAC transmission grid by removing bottlenecks, by the introduction of FACTS technologies, by the conversion of HVAC lines into HVDC lines and by the addition of new HVDC lines. This kind of upgrade, which ultimately has the effect of converting an HVAC transmission grid into a hybrid HVAC/HVDC transmission grid, is described on the page about How to increase the capacity of an HVAC transmission grid. With the possible exception of the building of new HVDC transmission lines, most of this upgrading will have little or no visual impact.
Minimising the impact of overhead lines
If it proves necessary to lay new overhead lines, it is very likely that these would be HVDC lines rather than HVAC lines. In terms of visual intrusion, HVDC overhead lines are better than HVAC lines because pylons do not need to be so high and insulators can be smaller (because peak voltages are lower), and because only two cables are needed for each line instead of three.
The visual impact of HVDC overhead transmission lines may, in principle, be minimised by some combination of the following measures:
- Screening the lines with trees.
- Building them alongside existing infrastructure such as existing transmission lines, railways or main roads.
- Integrating them into existing infrastructure.
Regarding the second point, it may be possible to use the central reservation of motorways for HVDC transmission lines.
Regarding the last point, it might, for example, prove possible to add new lines to existing pylons. Because the pylons for HVAC lines are relatively tall, there may be scope for adding new HVDC lines at lower levels, especially if the existing cables were being converted to HVDC. Where railways are electrified using overhead power lines, it may be possible to add HVDC power lines above the power lines that supply the trains.
Under water and under ground
Any problems of visual intrusion would largely disappear if it proved possible to lay new HVDC transmission lines underground or under the sea.
With HVAC transmission lines, it costs about five times as much to put them underground (or under water) as to mount them on pylons. But ABB says that, with its HVDC Light technology and for distances greater than about 500 km, underground (and submarine) cables are only about 10% to 20% more expensive than overhead lines. A chart from ABB that shows these relationships is reproduced here:
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The relative affordability of this technology is part of the justification for Airtricity's proposal for a European supergrid composed entirely of submarine cables as sketched here:
It is not hard to imagine how such a grid may be extended to accommodate imports of CSP electricity from North Africa. Indeed, the map shows a link southward from Spain that could well connect with North Africa.
EU energy commissioner Andris Piebalgs has endorsed this concept (see EU's Piebalgs says grid infrastructure needed quickly for offshore wind energy, 2008-03-31).
Recent developments show that this vision is already beginning to take shape.
Last updated: 2009-08-20