Thanks to a clever participation model, the project enterprise behind the new Stanzer Valley power plant in the Tyrolean Oberland region is very diversified.
The owners are all of the local communities in the Stanzer Valley, three Tyrolean utility companies and the project development company INFRA. This factor gave the power plant project a great deal of prestige in the region. What is more, it is regarded as a real showpiece power plant which sets standards both in organisational and technical terms and not least also from an ecological perspective. The project partners have invested around 58 million euros in the plant, which each year will generate around 52.2 GWh of eco-friendly electricity and due to its storage tunnel will be capable of supplying peak current when it is needed. The Stanzer Valley is the extension of the Inn Valley in a straight line in a westerly direction. The valley is drained by the River Rosanna, which ultimately flows as the River Sanna into the River Inn. The corresponding catchment covers an area of 205 km2. The new plant is specifically a run-of-river plant with a storage tunnel. The water catchment of the power plant is situated in the community of Flirsch. From here, the water is channelled via a headrace, which is 5.4 km long in total and includes the 4.8 km long inflow and storage tunnel, to the machine house in the community of Strengen. There it encounters three 6-nozzle Pelton turbines which together have an installed capacity of 13.5 MW. The generated power is fed from the powerhouse via 25 kV cables into the public grid. Trial operation of the first machine began at the end of October of last year.
Communities become operators
The project developer INFRA had developed a participation model for the power plant project which was to prove to be pioneering. The crucial aspect was that the intention was to incorporate not just utility companies but also the local communities in the participation model. In contrast to the majority of normal power plant projects, the communities were not compensated but instead became joint owners of the power plant. This meant that it was possible to win over all four of the communities in the Stanzer Valley, as well as the community of Zams. Today the four local communities of Flirsch, Pettneu, St. Anton and Strengen each have a 6.25 per cent stake in the operating company; 5 per cent was assigned to the community of Zams. The biggest shareholder is EW Reutte with a stake of 34 per cent, a further 11 per cent stake is held by EWA St. Anton, STW Imst have secured 15 per cent and another 10 per cent stake is currently held by the project developer INFRA. INFRA will be provided with its shares following the commissioning of the project. In 2011, the plans for the project had already progressed to such an extent that it was possible to submit the project in the autumn of the same year. The official procedures were worked through in 2012. After all of the approvals and notifications from the authorities had been put on the table back in 2012, it was possible for the ground-breaking ceremony to take place in February 2013.
TBM eats its way through the mountain
The construction of the tunnel was considered to be the really big challenge of the construction project. The headrace tunnel was created using a tunnel boring machine (TBM) which weighed 380 tonnes and was designed to eat its way through the ground over a length of 4 kilometres. And this proceeded essentially without any major complications. There were just a couple of geological fault zones accounting for around 380 m over a total length of 4 km that slightly slowed down the rapid speed of progress of the machine. The 120 m high vertical well including a surge chamber with a diameter of 3 to 4 m was produced using what is known as the Alimak method, an "overhead breakout" which has proven its worth in underground mining for more than half a century. The bottom of the headrace tunnel was lined with tubbing segments. The total length of the discharge channel up to the powerhouse is 500 m. DN 2200 steel pipes were used as plating for the pressure shaft.
Machines made in Austria
As part of the bidding process to provide the electromechanical equipment, the Tyrolean hydro power specialist offered the most persuasive choice and was commissioned to construct and deliver three vertical-axis 6-nozzle Pelton turbines of identical construction. This option represented the ideal machine solution for the general prevailing conditions. The turbines reach their optimum efficiency with a nozzle opening of 75 per cent and each produce 4.5 MW of power. Conversely, they can also be operated with a minimal flow rate of 200 l/s. Coupled directly onto the Pelton turbines, three powerful synchronous generators from ELIN Motoren GmbH were installed. These are water-cooled machines with a brushless exciter and a rated output of 6000 kVA. Each of the generators weighs 50 tonnes and the bridge leading to the location of the powerhouse had to be specially reinforced so that they could be delivered.
Tunnel management requires finesse from the e-technology specialists
Together with Geppert and ELIN Motoren, Schubert Elektroanlagen, the specialist in electrical technology and control technology from the Austrian state of Lower Austria, formed the triumvirate that was responsible for providing all of the electromechanical equipment for the entire plant. It was in August 2013 that the team from Schubert led by the responsible project engineer Mario Manseder embarked on the power plant project, which for Schubert was to be the biggest and most complex that had so far been undertaken in the company's long history. "From the generator terminal, the main responsibility for all of the measurement and control technology rested with Schubert. This ranges from establishing a connection with the public mains power grid, installing emergency power generators and a safety power supply across the entire electrical installation, fitting a fire alarm system, the safety lighting right through to the building systems, measurement technology and network technology and incorporating the new process control technology into the existing control room technology at the master control room," explains Mario Manseder. In addition, the team from Schubert was also responsible in the area of the powerhouse for another package of measures and services – starting with the medium-voltage switchgear with cabling and distribution, the machine transformers and auxiliary power transformers, and the medium-voltage switch cabinets through to the machine control, the process control technology and the associated visualisation. The most demanding challenges included programming the storage tunnel management system. Manseder: "For us the objective was to adapt the control and regulation of the power plant to reflect the fluctuations in the electricity market prices. This enables the operator to generate the maximum return from the production of electricity." In the end, the total amount of time spent working by the team from Schubert Elektroanlagen was 23,000 hours.
Water Framework Directive implemented
A significant aspect is controlling the residual water and fish ladder doping, which was configured entirely independently of the operation of the power plant. This is necessary in order to ensure reliable doping in this area even if the power plant is shut down. Ecological considerations and measures generally played an important role: "The residual water specification is stipulated with different levels in different months, but at least 1.2 m3/s must remain in the River Rosanna. This means that the Stanzer Valley power plant is one of the first hydroelectric power plants in Austria to implement the latest specifications of the Water Framework Directive in full." Electricity has been generated at the new Stanzer Valley power plant since the end of October 2014. Following the successful commissioning of machine I, machine II began operating just one month later (in November), and machine III finally followed in December. In spite of the operation on a trial basis, the operators are delighted that it proved possible to achieve the half-year quantity for winter. It is pointed out that even in its first few weeks and months of operation the power plant generated power strictly in accordance with the fluctuations in the curve of the stock market prices. An essential requirement for this is the storage tunnel, which is generally emptied during the day and then refilled overnight. The storage capacity of the entire tunnel is around 50,000 m3. The machine control is designed in such a way that the tunnel can be run almost completely empty before the machines then automatically run down.
A project for 100 years
Against the background of tough economic conditions for hydro power in Central Europe, the project in the Tyrolean Oberland region is viewed in an extremely positive light. "The electricity price traded on the exchange has fallen by 40% from the decision to go ahead with construction to the present day. This is critical for the financing, but it must not be forgotten that hydro power is a long-term enterprise. This project is designed for 100 years. And ultimately I know of no major hydro power project in the past which did not face the situation where the electricity price went up and down," says the project coordinator Jakob Klimmer in summary. The Stanzer Valley power plant became a very special project thanks to the successful participation model. Klimmer says: "If the region and the local communities are involved, there are far fewer problems. Many different forces all pull together – and as a consequence the level of cooperation with the authorities was also exemplary. This was the only way that we were able to implement the project in such a short space of time." In total, the partners in the power plant project have invested 58 million euros in the power plant project. This means that the project management team have managed to deliver the project for around 1 million euros less than the costs which were originally envisaged. There are still a few remaining tasks, landscaping and recultivation works as well as approvals to be carried out over the new few months. The official handover can only be commenced when the full design discharge capacity has been reached.