It is necessary to distinguish between direct current (DC) and alternating current (AC) powerlines.
When it amended the Federal Requirements Plan Act at the end of 2015, the legislature introduced a priority for underground cables. Since then, priority has been given to building the new DC transmission lines as underground rather than overhead powerlines. Prior to this, overhead powerlines were given priority, underground cables were the exception. Now, consideration is only given to overhead lines in exceptional cases, such as for reasons of nature conservation, the use of existing routes, or at the request of affected municipalities, except where overhead lines are generally prohibited because they would be too close to settlements. And when existing routes are to be used, overhead lines will only be considered if no additional serious environmental impacts are to be expected. DC Project 2 (Ultranet) is excluded from the rules giving priority to underground DC cables.
In the case of AC cables, the Act provides for a moderate extension of the existing possibilities for partial underground cabling. For technical reasons, priority will continue to be given to overhead AC lines. At the same time, additional pilot projects using underground cables are to be carried out in order to gather experience with underground cabling, and its technological development is to be advanced. Alongside the pilot projects already envisaged, partial underground cabling will be deployed in further pilot projects, and the use of such cables will be considered not only where they are close to settlements, but also for nature conservation reasons and for the crossing of major federal waterways like the rivers Rhine and Elbe.
The costs of underground cabling vary widely. They depend on the technology used, the voltage level, the nature of the soil, and other individual parameters. Underground cables tend to be more expensive than overhead powerlines. These additional costs are borne by the users of the grid – i.e. by businesses and households – via the grid charges.
Where major electricity highways are concerned (= new ultra-high voltage DC transmission lines), the Act will give priority to underground cables as a principle in federal planning. Ultra-high voltage overhead cables will only be used exceptionally in certain cases, e.g. in order to protect the natural environment. To put it simply, this means that there will be an absolute ban on ultra-high voltage overhead cables being used wherever people live. So overhead cables can only be used in very strict exceptions.
There will be only manageable delays caused by the change to underground cables. The largest grid development projects, such as SuedLink and SuedOstLink, were at an early stage of the planning when the changes were made. So the decision came at the right time.
In view of the fact that the new priority for underground cables has meant that the entire planning for ultra-high voltage DC transmission system has to be changed, the Bundesnetzagentur has developed a position paper outlining the roles the transmission line operators must abide by when conducting this planning work. Public consultations were held in connection with this paper. Comments were made by authorities, associations, universities, companies and citizens' initiatives, and fed into the final version of the paper. The Bundesnetzagentur published the in April 2016.
It is hard to predict this, because it will depend on tests in the later planning stages, i.e. particularly on environmental aspects. But it is clear that the vast majority of the cabling is to be placed underground. At the same time, it is very difficult to put a precise figure on it.
According to the plans of the project managers, DC Project 2 (Ultranet) can to a large extent use overhead powerlines that are already in place, have been licensed, or are well advanced in terms of planning approval. It is therefore likely that very little construction work will be needed for the project. In the case of Ultranet, existing routes offer great potential to combine the project with existing infrastructure, whereas the other DC projects contained in the Federal Requirements Plan Act are connections which have to be planned from scratch. For this reason, the legislature decided not to list the Ultranet DC project as an underground cabling project.
Further to this, it is also to be possible to operate the powerlines with AC should DC operations not be available (e.g. if a converter fails). This would not be possible if underground cables are used, or it would involve a lot more expense and effort, since the underground cable systems cannot be used for both DC and AC. In this case, separate underground cables would have to be installed for both DC and AC.
Must a powerline which is subject to the priority for underground cabling be routed as the crow flies?
The main electricity lines should be routed along straight lines as far as possible, i.e. they should be routed “as the crow flies”. In this way, the new powerline can be kept as short as possible, avoiding higher costs for a longer powerline. Also, if the route is as straight as possible, this can mean that fewer land-owners are affected and that the impact on nature and the landscape is reduced. The requirement that routes follow a straight line plays a particularly important role in the weighing up of the respective interests. However, there can also be important arguments against a straight-line route, e.g. where settlements would be crossed.
It is true that the use of underground cables will result in higher costs. But it is also clear that, in macroeconomic terms, even if the grid is expanded using underground cables, this is still the cheapest route to a successful energy transition.
In macroeconomic terms, grid expansion which meets with local acceptance and is actually built will reduce the costs of the energy transition. At present, congestion management is causing high costs (combined costs for redispatch, feed-in management, reserve power stations). These annual costs exceeded €1 billion in 2015. Unless there is significant progress on grid expansion, these costs will continue to rise in the coming years.
Greater use of underground cables will cost an additional €3 billion to €8 billion in investment costs (compared to the costs under the former legal situation). These are one-off investment costs which do not recur annually. These increased investment costs will be passed on in the form of grid charges.
Overall, it is very difficult to arrive at a precise cost estimate in this current stage of the planning. The extent to which costs will increase due to the use of underground cables in the ultra-high voltage transmission grid will very much depend on local conditions (actual route, soil conditions, transverse infrastructure, actual cost of components, etc.).
How does the determination of the route corridor for underground cables differ from the same process for overhead lines?
The methodology does not differ greatly. However, there are planning differences in terms of the technical requirements, the legal framework, and the assessment of the environmental impact on aspects like the ground. The ground is much more affected by underground cables than by overhead lines. In the case of underground cables, the straight-line requirement is of greater import. In the case of overhead lines, in contrast, the possibility to combine powerlines is of more importance than it is in the case of underground cables, since the combining of underground cables offers fewer advantages than the combining of overhead lines.
Is a project subject to the priority for underground cabling automatically built as an overhead line if it can be combined with another overhead line?
No. In the case of underground cable projects, overhead lines are only possible in a few exceptional cases stipulated by law. Such cases might be the combination with another, existing overhead line – but only in the few cases in which no substantial environmental impact is to be expected. A substantial environmental impact would exist if, for example, the height of the existing pylons needed to be increased.
Is there a threshold above which an overhead line should be given preference because it is more economical to construct it than an underground cable?
No. Economic reasons alone cannot justify the construction of an overhead line. Where a project is subject to the priority for underground cables, it is only possible to construct individual sections as overhead lines where the statutory exemptions pertain. But even if these exemptions do pertain, the powerline can only be realised as an overhead line in “technically and economically efficient” sections.
There are no specific rules on the distances from settlements to be maintained by underground cables. However, underground cables must always comply with the statutory limits for electrical and magnetic fields.
When ultra-high voltage cables are used, they generate heat. The degree to which the soil actually heats up, particularly at the surface, depends on various factors. In addition to the transmission technology, the insulation of the cables and the bedding material, key roles are also played by the ability of the soil to conduct heat and the degree to which the cable is being used. The soil ecologist Prof. Dr. Peter Trüby of Freiburg University has conducted various field tests on behalf of the transmission system operators to study the effect of heat emissions on soil. His conclusion is that the effects are of little relevance to the soil ecology. Trüby’s findings also suggest that fears of effects on crop yields are unfounded. At present, he is working on the first underground AC cable pilot project in Raesfelt, North Rhine-Westphalia. Following the laying of the underground cable, various crops are being cultivated there, and the findings are being evaluated. In comparison with underground DC cables, the operation of underground AC cables generates much less heat. The Bundesnetzagentur is continuing to monitor the research work being done in this regard.
Underground cabling technology is more complex where AC powerlines are concerned. So underground AC cables will only be used as part of pilot schemes.
As far as new ultra-high-voltage AC cables are concerned, the Act expands the criteria and the number of pilot projects for this type of underground cable to allow for experience to be gained more quickly. The number of pilot AC projects (allowing for partial underground cabling) has been increased from three to four and will ultimately rise to a total of eleven.
Will there be any changes to the starting/finishing points of the Süd-Ost or SuedOstLink DC passage?
Under the new legislation, the Requirements Plan has been brought into line with the Power Grid Expansion Act, and the Federal Requirements Plan with the Federal Requirements Plan Act. This was done on the basis of the Network Development Plan for 2024, which was approved by the Bundesnetzagentur in September 2015.
In this document, the Federal Network Agency confirmed which powerlines will be urgently needed in the coming ten years. According to this, a total of approx. 5,800 km of new powerlines will have to be built by 2024, of which optimisation and upgrading of existing routes account for approx. 3,050 km. New calculations have shown that a total of 6,100 km of new powerlines (of which optimisation and upgrading of existing routes account for 3,050 km) will be needed by 2025.
In one of the key expansion projects – the SuedOstLink, formerly known as the Süd-Ost DC passage – the starting and finishing points were altered as a result of the relevant consultations. This outcome of the consultations has now been anchored in statute, making Wolmirstedt the starting point of SuedOstLink and Isar the finishing point.
It is important to note that at the stage of grid development planning, only the starting and end points are defined. The exact geography of the lines, in between the starting and finishing points, will be further specified in the future. But the starting and finishing points of essential powerlines have been bindingly stipulated by the legislator in the Federal Requirements Plan.