In the Tyrolean town of Kühtai, around 40 kilometers west of Innsbruck, a new pumped storage power plant and reservoir are being built, an extension of an existing facility belonging to the Tyrolean state energy supplier TIWAG, short for Tiroler Wasserkraft AG. The project at over 2,000 meters above sea level can confidently be described as enormous: the new reservoir will have a volume of 31 million cubic meters of water and a height of 113 meters (from the valley floor to the top of the dam).
The new Kühtai storage facility will be connected to the existing Finstertal storage facility, which is twice as large, via a tunnel with a diameter of 4.5 meters. The power plant itself is completely underground. Two turbines are designed to ensure that energy is not only generated, but can also be stored: for generation, water flows from the higher Finstertal reservoir in the direction of Kühtai, for storage the direction of rotation of the turbines is reversed and water is pumped up with excess energy, so that it can then be used for the power generation can be drained again.
The dimensions inside the mountain are also impressive: the cavern for the turbines and generators is to be around 45 meters high. The upper third of the cavern is currently being built and dug down. The basis of the natural rock fill dam is also in the works, the entire dam fill material is extracted on site, on the one hand from the tunnel construction, on the other hand from the excavation for the reservoir itself, says project manager Klaus Feistmantl. Some infrastructure such as a 220 kV line is already in place.
Hydropower is also possible on a small scale
The generation of energy in the municipality of Assling in East Tyrol is dimensioned completely differently. Five hydroelectric power plants the size of single-family houses and four photovoltaic systems supply electricity for around 1,750 people and around 800 customers in the community, which is spread over a wide area in terms of area, in the entire network of the Elektrowerk Assling cooperative (EWA). The cooperative has existed since 1927, and when required, energy production has been expanded again and again, says managing director Harald Stocker.
The hydroelectric power plants are located on two small streams, the youngest power plant from 2019 generates around 2.7 million kWh annually with an output of 495 kW, the largest with 2,550 kW 16.5 million kWh annually. There are also four large-scale PV systems, each with a peak output of 500 kW. For comparison: The Kühtai expansion project should enable a further 216 million kWh to the existing 531 million kWh, and an additional 15 million kWh are expected through an increase in efficiency.
The upper stage 2 in Assling, which was completed in 2019 at an altitude of around 1,500 meters, cost around four million euros, including the day storage facility further above with a capacity of around 5,300 cubic meters, Stocker continues. In contrast to previous buildings, the upper level 2 was clad in wood in order to blend in better with the overall picture. Nevertheless, 3,000 cubic meters of concrete had to be transported up narrow streets, and the truck drivers coordinated by radio so that they did not block the narrow path.
Assling is self-sufficient – in theory
With the current systems, Assling is energy self-sufficient – theoretically, says Stocker. In practice, the cooperative sells all of the electricity in order to then buy back the energy it needs. The electricity price is still unbeatably low, since EWA also gains from the sale. At TIWAG, too, the electricity price is relatively cheap – still, because according to TIWAG, a “painful” increase is also imminent. In principle, enough electricity would be produced in Tyrol for the state itself, but not all power plants belong to TIWAG, but rather to Verbund and ÖBB.
Energy self-sufficient municipality of Assling
The reason for selling the electricity generated in Assling is simple: there is a lack of suitable storage options. Stocker explains that hydropower has the advantage of being able to produce energy around the clock and in a CO2-neutral manner – but the demand for energy is not the same around the clock, but fluctuates and increases sharply from morning to evening with little demand.
This also applies to photovoltaics (PV), which delivers the most power at midday – if there is a surplus, energy then has to be dissipated. The day storage helps here, says Stocker, because it can be used to store energy that is currently not being used for other times of the day – like in Kühtai, albeit in completely different dimensions. All in all, hydropower supplies the most electricity, and does so continuously, but the expansion possibilities in the community are not endless, Stocker continues.
Production and consumption must balance each other out
Electricity is not a very simple energy product: Basically, the same amount has to be consumed or stored as is produced in order for the power grid to remain stable. The power grid must be kept at a uniform frequency (50 Hertz in Europe) – if too much power is fed into the grid, for example from PVs at noon, the frequency increases and the power has to be drawn from the grid and consumed or stored. Conversely, the frequency drops when there is not enough electricity in the grid.
Since the power grids in Europe are all connected to one another, they are also regularly monitored so that, in the event of deviations, rapid, stabilizing action can be taken. Both EWA and the Silz on-demand power plant near the Kühtai can intervene to regulate this. With its 500 megawatts, Silz, for example, can reach full load within 140 seconds, says Kühtai project manager Feistmantl. After commissioning in 2026, the Kühtai power plant should then be able to switch from generation to storage within 120 seconds.
Numerous compensatory measures are necessary
Apart from the sheer numbers and scaling, the challenges for the operators are quite comparable: compensatory measures were prescribed for both Kühtai and the upper level 2 in Assling. In Assling, for example, an amphibian lake was built next to the storage facility. The daily storage itself is invisible because it is underground, only a hut with a WLAN router can be seen on it – the operators can monitor the system via the Internet, the amount of honey is measured in the nearby beehives and the data is transmitted to the valley.
Construction work on the Kühtai dam
Biotopes for amphibians were also built in Kühtai, but the measures go much further there, also in terms of location: Among other things, in Kühtai itself, special plant communities in intermediate moors, small seggenriede, were transplanted square meter to the upper end of the reservoir, in the Ötztal the Ötztaler Ache was restructured and renatured and revitalized over three kilometers in the Inn valley. Six to seven percent of the total project volume are compensatory measures, says project manager Feistmantl. In the end, however, only the lake should be visible from the power plant.
Both operators explain that there are strict requirements, such as how much water may be taken from the streams at which time of the year: In the Kühtai, water from six water intakes in the Ötztal and Stubaital is diverted from a distance of up to 25 kilometers. Studies were carried out on both projects to determine the extent to which the intervention impacted nature. For the Kühtai project, the entire process up to the final approval lasted from 2006 to 2019. According to Stocker, the approval process is complex.
Tyrol is the leader in hydropower
Tyrol is the leader in hydropower, even if oil dominates the energy mix in Tyrol with 41 percent. Hydropower accounts for 22 percent, wood for 15 percent, six percent for other renewable energy and two percent for coal, according to a request from the Tyrolean state government. According to the plans, hydropower should account for 46 percent of the energy mix by 2050, followed by wood and PV with 19 percent each, when the state wants to cover its energy requirements 100 percent from domestic renewable energy sources – including wind power, so far not an issue in Tyrol , should have a part in it.
In addition to hydropower, PV in Tyrol is also to be greatly expanded. In 2021, more than 2,000 new systems were already connected to the grid, an increase of 22 percent, according to the state government. At the same time, energy requirements are to be reduced by 37 percent by 2050, for example through the renovation of buildings and new technologies. In the area of mobility, the savings potential is greatest at 65 percent.
Energy is already being saved in Assling, says Stocker, and because of the prices people are doing it themselves. However, the switch to heat pumps in new buildings and e-cars means that the demand for electricity will simply continue to increase for the time being – and with it the demand for power plants such as those in Assling and Kühtai. The alternative to this could only be doing without, say Stocker and Feistmantl in unison. But that is only conditionally capable of winning a majority.