Switch to the Axpo Group website.

Go to Axpo Group website.

17.05.2022 | In the canton of Glarus, hydropower reveals its potential

Unassuming but essential

Almost unnoticed by the outside world, both the oldest and the youngest hydropower plants in the canton of Glarus are busy producing electricity. Each plays an important, albeit different, part in securing Switzerland’s electricity supply. Despite its role as a key resource, however, hydropower is at risk of being taken for granted. After all, things that have always been there, and that the human eye does not see, tend to lose their significance. 

Below ground and inconspicuous, the turbines of the oldest hydropower plant in Glarus are in action on the outskirts of Netstal. Especially at the end of the working day, during mealtimes and on TV nights, the generators of the power plant on the river Löntsch are constantly humming away. The plant produces what is known as ‘peak energy’ to cover consumption peaks. 

The power station on the river Löntsch was built 114 years ago. Together with the Beznau run-of-river power plant in the canton of Aargau, it formed the first electricity network for the then newly founded Nordostschweizerische Kraftwerke NOK (now Axpo). These two plants, both of which are over a hundred years old, can therefore be considered as the foundations of Axpo.

4 horses for 1 water tube: Heavy transport 1918-style

They came about as a result of pioneering work. ‘What our ancestors built here in the Glarus mountains by hand, with horse-drawn carts and a great deal of dynamite in just three years, deserves the utmost respect,’ says Deputy Operations Manager Jürg Meili. Meili, who has 40 years of service at the Löntsch plant, emphasises: ‘The builders were true visionaries. There’s not much we’d do differently if we were to build the plant today.’ Over a hundred years on, a large part of the tunnel built at that time and the dam are still in use.

Klöntalersee lake – a natural ‘bath plug’ idyll

The water used comes from the Klöntalersee lake. Just an hour’s drive from Zurich, this recreational area at the foot of the Pragel Pass is very popular with visitors. Evidence of the lake’s use in electricity production is not easy to find – the 220-metre-long earth dam at the beginning of the lake, for example, also serves as a road. Only the striking spillway near the dam, reminiscent of an oversized bath plug, contrasts with the idyllic setting. This spillway prevents the lake from overflowing during periods of heavy rain and/or melt water, and is connected to the Löntschbach stream via a tunnel.

Natural idyll of Lake Klöntal: Somewhat less idyllic, the spillway of the lake.

A four-kilometre-long pressure tunnel leads from the water intake at the bottom of the lake right through the mountain to the surge tank above Netstal. The water plunges 365 metres down the pressure line and drives the turbines in the valley. As the old pressure tunnel limits the amount of water to 20 cubic metres per second, the maximum power plant capacity is 60 megawatts (MW). This would be enough to operate 60,000 vacuum cleaners simultaneously.

Moving inside the mountain

Today, most of the electricity production takes place below ground. During the first major overhaul (1971–1975), the pressure line that ran along the outside of the rock was moved inside the mountain, and all visible pipes were dismantled. For many years now, the hydropower plant has been controlled directly from the control centre in Baden, in the canton of Aargau. ‘When our machines start up, we can feel it in our offices above the machine room,’ says Jürg Meili. In addition, an emergency control centre for the Löntsch plant has been in operation in the control room of the Linth-Limmern power plants since the beginning of 2014. This enables the oldest Axpo power plant in Glarus to benefit from a direct connection to the young, ultra-modern powerhouse at the back of the valley. 

Powerful understatement

The pure understatement of cutting-edge technology is located 30 minutes southwards by road at the furthest end of the Linthal. Only a cable car, an operations building, a small hotel and two moderate equalisation reservoirs can be seen. Converted into a pumped storage plant between 2009 and 2015 without a single objection, inside the mountain one of Europe’s most powerful plants makes sure the lights never go out in Switzerland.

An agile pulse with a 15-minute rhythm

In the control room of the operations building, those aspects that are not visible become clear. Whether the level of the lake, water speed or revolutions – all of the data from the mighty Limmern pumped storage plant are projected onto a large screen in real time. Around 15 computer monitors provide further measurement data. The Linth-Limmern power plants (KLL) as a whole can be mobilised to produce electricity with a capacity of 1,520 MW for short periods of time. This is more than the output of Switzerland’s largest nuclear power plant, and is equivalent to 1.5 million vacuum cleaners running simultaneously. ‘Our strength is not in marathon performance, but in agility,’ explains Martin Steiner, Deputy Operations Manager at KLL.

The pulse of the hidden plant beats every quarter of an hour. This is the rhythm of the electricity trading business. Martin Steiner: ‘Trading determines whether we draw an oversupply of electricity from the grid using pump operation to regulate the grid, or produce electricity via the turbines and feed it into the grid as quickly as possible.’ The four state-of-the-art machines can be controlled individually and are capable of running completely in the opposite direction within just six minutes. ‘This is all dictated by developments with Axpo Trading in the short-term energy market.’ In addition, the Linth-Limmern power plants regularly provide grid-stabilising system services for the operator of the Swiss extra-high voltage grid Swissgrid. Anyone who, like Axpo, has such a flexible plant in their portfolio, is an important player in the European electricity grid. 

"Our strength lies not in marathon operations, but in agility"
Martin Steiner, Deputy Operations Manager KLL

Depending on the weather conditions in countries with a lot of solar and wind power, pump operation often starts before noon. But in the late afternoon, the direction changes. The same water that was previously pumped up is then used to produce electricity. Martin Steiner: ‘For us, rush hour comes after sunset.’ From 6 pm onwards, the Linth-Limmern power plants are easily a match for the Löntsch power plant downstream, producing electricity at full capacity. Only after midnight, when people, traffic and a lot of industry are at rest, does the Limmern PSPP revert to pump operation. 

Out of sight, out of mind?

The fact that both electricity production and pump operation take place within the mountain itself makes it difficult for outsiders to grasp the magnitude of the complex plant. Not even the two impressive dam walls can be seen from the operations building. While the Limmernsee dam, built in the 1960s, is hidden in a side valley, the new Muttsee dam, over 1,000 metres in length, is located in high alpine terrain at over 2,400 metres above sea level with no access for vehicles.

Oh, a dam! Imposing view on the air side of the Limmern dam

The contrasts between the oldest and the youngest plants in the canton of Glarus could not be greater. But what both have in common is that employees take numerous groups of visitors on tours of each site every year. The tour guides take this opportunity to show visitors why Switzerland would soon run out of electricity without hydropower – the backbone of Switzerland’s electricity supply.

Guided tours at the Löntsch power plant:

  • Groups can visit the Löntsch power plant and the technical museum as part of an informative guided tour. Booking: +41 (0) 55 285 27 11.

Guided tours at the Linth-Limmern power plants:

Technical data on the Löntsch hydropower plant

Turbines:   two vertical Francis turbines of 40.5 MW each, one horizontal Pelton turbine of 8.1 MW

Max. capacity: 60 MW (limited by pressure tunnel cross-section)


  • Dam: wall 220 m long, 21 m high
  • Net volume: 39.8 million m3

Technical data on the Linth-Limmern PSP

Max. capacity: 1,520 MW (Limmern PSPP: 1,000 MW/other Linth-Limmern power plants: 520 MW)

Max. pump capacity: 1,174 MW (Limmern PSPP: 1,000 MW/PSPP Tierfehd/Hintersand: 174 MW) 


  • Dam: arch dam 370 m long, 146 m high
  • Net volume 92 million m3


  • Dam: gravity dam 1,054 m long, max. 36 m high
  • Net volume 23 million m3

More articles for you

Show all


Hydrone propels pilot expertise sky-high

Aerial efficiency: monitoring power plants and the grid using drones

Read more

Energy market

Weather and politics strong drivers of energy markets

European Energy Markets Monthly, July 2024

Read more


Pigniu reservoir: the first-ever removal of deposited sediments via flushing

The Pigniu reservoir of Kraftwerke Ilanz AG was temporarily completely emptied

Read more

Energy regulations

Additional regulation for electricity companies with ‘systemic importance’?

In the wake of the energy crisis, the Federal Council has presented a draft for the regulation of electricity companies with ‘systemic importance.’

Read more