Complete upgrade of Mühleberg hydropower plant
Provider
BKW is investing around CHF 120 million in the complete upgrade. The aim is to increase efficiency, raise environmental standards and ensure reliability of supply in the long term.
The complete upgrade includes replacement of all electromechanical equipment – including turbines, generators, auxiliary systems, control systems and automation – as well as the renovation of the machine hall and building shell in line with heritage requirements. The six turbines will be replaced by four modern Kaplan turbines. The screen cleaning system is also being modernised and will be operated automatically in the future. The investment will increase average annual production from 157 gigawatt hours to around 163 gigawatt hours – enough to power an additional 1,350 four-person households. At the same time, BKW is implementing important environmental measures. New intake screens with tighter rod spacing will prevent fish from entering the turbines, and a new bypass solution allows them to descend to the Aare without injury. These measures are financed under the FOEN’s programme to improve free movement for fish. A fish lift installed in 2021 ensures safe ascent.
To minimise outages, the upgrade will be carried out in two construction stages – under current plans, the first two new turbines will be commissioned in 2030 and the second two in 2033. Electricity production will be largely maintained during construction.
«Hydropower is a key pillar of Switzerland’s electricity supply. That’s why we’re investing in the future today. Not just anywhere, but right here – in our own region, with our experience, for our shared goals.»
Fish bypass and fish lift
The complete upgrade of the Mühleberg hydropower plant includes refurbishment of the fish bypass. The fish lift installed in 2021 allows fish to migrate upstream – and now their downstream route is set for improvement. Plans include larger, narrower screens in front of the turbines, a more fish-friendly Kaplan turbine, and a new bypass that will safely lead fish from Lake Wohlen to the Aare. These measures are being implemented in close collaboration with the Canton of Bern and the Federal Office for the Environment.
The fish lift
In 2021, fish migration upstream of the power plant was modernised. Here the fish have to overcome a height difference of around 20 metres. A fish lift (see graphic) lifts the fish about 20 metres in a tray before they reach Lake Wohlen via a chute. Researchers are still investigating viable solutions for downstream migration. BKW is contributing its many years of experience to a number of different research projects.
The power plant in figures
For over 100 years, multiple generations have dedicated their heart and soul to the Mühleberg hydropower plant. It is thanks to the dedication of all these people, and regular maintenance and modernisation, that BKW has been able to operate the plant without interruption. Since the 1970s, when the plant increased its capacity, it has been producing almost 160 gigawatt hours (GWh) of clean electricity per year. That’s enough to supply the cities of Bern and Thun with electricity. Now with this complete upgrade, BKW is investing in the next generation: state-of-the-art technology, greater efficiency and higher environmental standards are making Mühleberg fit for the future.
| The plant today | Complete upgrade project | |
|---|---|---|
| Commissioning | 1920 | 2028 (start of construction) 2030 (commissioning of 1st stage and fish bypass) 2033 (commissioning of 2nd stage) |
| 1st concession | until 2017 | |
| 2nd concession | until 2097 | |
| Installed capacity | 45 MW | approx. 36 MW |
| Average annual output | 157 GWh enough for approx. 35,700 four-person households (CH) | approx. 163 GWh (+4%) enough for approx. 1,350 additional four-person households (CH) |
| Bodies of water | Aare/Lake Wohlen | |
| Machine/turbine type | 6x Francis, 1x Kaplan | 4 x Kaplan |
| Gradient | 17 - 19 m | |
| Maximum usable water volume | 291 m3/s | 212 m3/s |
| Investment costs | - | CHF 110–130 million |
Lake Wohlen
| Length | 12 km |
| Greatest width | 650 m |
| Area | 3.2 km2 |
| Depth | 18 m |
| Length of shoreline | 29.3 km |
| Surrounding municipalities | Wohlen, Bern, Frauenkappelen, Mühleberg, Kirchlindach |
In 1952, the Schutzverband Wohlensee (Lake Wohlen Protection Association) was founded on behalf of the five municipalities that surround the lake. The association assumes responsibility for the natural surrounds, the landscape and the environment along the shoreline and in waterways under uniform criteria and with cooperation between the municipalities.
History of the power plant
Who better to describe the history of the hydropower plant’s origins and the spirit of the time than Hans Markus Tschirren, author of the book “Wohlensee”. In it, he writes: “While Europe bled out during the First World War and death and destruction dominated people’s thinking, something new was emerging west of Bern: the Mühleberg power plant. Electricity meant the beginning of a new era. It wasn’t just excitement about the new technological possibilities; it had also become apparent that the First World War had greatly reduced coal and oil reserves.
The River Aare and the development of electricity as an alternative energy source proved ideal. When the Aare was dammed in Mühleberg with a wall 35 metres high, it resulted in a lake 15 kilometres in length. It was able to generate an endless amount of electricity. (...) On this basis, Bernische Kraftwerke took on the project under the leadership of its director, National Councillor and Colonel Eduard Will. (...)
In autumn 1920, Mühleberg power plant began producing electricity for the first time, initially with two turbines. A further four were added the following year. The water now flooded the Aare Valley and mourning for the sunken landscape mingled with the joy that came with the new lake.”
