Underground laying costs 11 to 40 times more than overhead lines
An expected motion The project for a 380 kV power supply line between Chamoson and Chippis has for some years now been the subject of heated discussions amongst the local population, in the media and amongst political authorities at municipal, cantonal and federal levels. The project deals with the construction of an overhead transmission line. The motion tabled by Jean-René Fournier in April 2008 demands a feasibility study by independent and neutral experts for the underground laying of the high voltage power supply line planned for the Rhone valley.
Three independent companies check out two alternatives In the summer of 2008 Alpiq, or rather EOS, commissioned three independent companies with the elaboration of methods for the underground laying of the power supply line Chamoson-Chippis and the calculation of the costs. An initial study by the consulting engineering company NivAlp SA from the municipality of Grimisuat permitted the definition of a potential route for a corridor for the power supply line cabling. Subsequently two offers for the cabling were obtained from the engineering company ABB, one for alternating current and one for direct current. The company Montani-Schopp in the town of Sierre prepared an estimate for the clearing and excavation work necessary for the construction of the two trenches and the pipes in which the cables would be laid. For the cabling with a transmission capacity of 4000 MW and an operating reliability equivalent to that of an overhead transmission line, two separate pipes are necessary.
The corridor for the underground laying of the power supply cable is a huge challenge The corridor along the slopes of the valley planned for the overhead transmission line cannot be used for the underground cabling primarily for technical reasons. For the construction of the concrete pipes therefore, a new 23 m wide corridor was sought in the Rhone valley. It proved to be extremely difficult in the immediate vicinity of the town of Sitten to find a route that was outside of nature reserve areas and residential districts. The river Rhone had to be crossed three times; in Aproz, St. Leonhard and Granges. For the excavation work alone costs of CHF 420 million will be incurred. The work with several consecutive building sites would take between 3 and 4 years. An overhead transmission line, on the other hand, could be completed in around 18 months.
Cabling variant with alternating current (AC): 11 times more expensive than an overhead transmission line The costs for the underground laying of the alternating current (AC) cable between Chamoson und Chippis with a capacity of 4000 MW are estimated to be CHF 799 million. A comparable overhead line would cost CH 70 million. The main reason for the large price difference is the civil engineering work, which means the excavation of the trenches and the construction of the two pipes. For this work alone, costs of CHF 420 million will be incurred.
Cabling variant with direct current (HDVC Light): 40 times more expensive than an overhead transmission line The costs for a cable variant with direct current exceed CHF 3 billion. The complete laying of the direct current transmission would thus cost 40 times more than a comparable overhead line. In addition to the civil engineering work, for this solution substations must also be built for the conversion from direct current to alternating current. This leads to high additional costs. Along the relevant cable section, 11 of these substations each with a capacity of 1000 MW would have to be constructed: 5 in Chamoson, 5 in Chippis and 1 next to the Chandoline power station. The price of these installations lies at CHF 2.3 billion. Each of these substations will require a building area of 80 x 150 m. In Chamoson and Chippis the switching stations would cover a total area equivalent to the size of 8 football fields.
Risks for the electricity supply security In addition to the costs, the technical and operating reliability aspects must be taken into account. These include, for example, the adverse effects on the environment resulting from the civil engineering work necessary for underground laying or the longer construction time and the shorter life expectancy of the systems. And last but not least, the maintenance of the cabling in a closed shaft is not only more expensive but it also involves greater risks for the security of the electricity supply.
Confirmation of two offers from an independent engineering expert At the end of October 2008 Alpiq presented the two estimates for the underground laying of the power supply cable from Chamoson to Chippis to the Swiss Federal Office for Energy (SFOE) (Bundesamt für Energie). The SFOE submitted them for independent checking to Professor Hans-Jürgen Haubrich at the University of Aachen in Germany. He confirmed the technical and financial validity of the offers.
Chamoson-Chippis: The basis for a decision is available The power supply line from Chamoson to Chippis is absolutely essential for the supply security in the western Switzerland extra-high voltage supply grid. It joins the national grid from the north to the south between Chippis and Bickigen (in the region of the town of Burgdorf). In view of the planned commissioning of the Cleuson-Dixence storage power station at the beginning of 2010 and the implementation of the hydroelectric projects in Emosson and on the Simplon, an increase in the transmission capacity in the Valais is urgent. With the ABB offers for the underground cabling of the power supply lines, all the necessary elements required to permit a decision to be made are now available. Alpiq is convinced in the case in hand that both from an ecological as well as from a technical and financial point of view, the overhead power supply line represents the optimal solution. Since the coming into force of the Federal Electricity Supply Act (StromVG) on 1 January 2009, the network costs are billed to the customers as a separate item. Against the background of the current economic crisis, an increase in the price for a kilowatt-hour of electricity for households and industry would be anything but welcome.
380 kV power supply line from Chamoson to Chippis The construction of the 380 kV power supply line between Chamoson and Chippis permits the grouping of a number of existing supply lines on common pylons:
- 2 extra-high voltage lines (2 x 380 kV = new transmission lines)
- 1 high voltage line (1 x 220 kV = existing line)
- 1 high voltage line (1 x 65 kV as far as Aproz = existing line)
- 2 SBB power lines (2 x 132 kV as far as St. Leonhard = existing lines)
The new power supply line covers a distance of 28 km and has 72 pylons. The costs are estimated at CHF 70 million. With the implementation of this project, it would be possible to dismantle and remove the existing 60 km section of the supply grid with 190 pylons in the Rhone valley. The total capacity of the power supply line is 4000 MW.