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Since 1 October 2022, Alpiq Hydro Aare AG has reduced the residual water volume at the Gösgen hydropower plant to the regulatory minimum in order to increase electricity production. This autumn, in order to prevent a potential energy shortage, the Federal Council obligated the operators of run-of-river power plants with residual flow sections to temporarily reduce the residual flow volumes. Thanks to this measure, the Gösgen hydropower plant will be able to generate an additional 4 GWh of electricity in the period between October 2022 and April 2023. This equates to slightly more than 1% of the power plant’s annual production.
Since October 2022, the water volume in the Old Aare downstream of the Winznau weir has been 10 cubic metres per second. Normally, 15 m3/s would be discharged over the weir in the winter months. The residual flow volumes are graduated seasonally and, in the absence of temporary measures, range between 15 and 25 m3 per second. Since the reduction is limited to seven months, the Federal Council views the impact on the environment to be acceptable.
A second temporary measure will enable Alpiq to increase electricity production at the Ruppoldingen run-of-river power plant this winter. This measure relates to the reservoir water level. Between December 2022 and April 2023, Alpiq will operate the power plant on the Aare at a constant reservoir water level of 398.4 metres above sea level. Typically, a variable reservoir regime is applied in the winter half-year in order to simulate the river’s dynamics and thus provide ecological benefits. On the initiative of the Federal Council, this reservoir regime will be suspended until the end of April 2023. The two cantons of Solothurn and Aargau have approved the measure. As a result, the gradient at the low water mark is increased by several decimetres compared to a normal winter, which in turn results in higher electricity production. In total, this will yield an additional production of around 4 GWh of electricity by the end of April 2023. This corresponds to approximately 3.5% of the Ruppoldingen power plant’s annual production.
Combined, the two measures will enable Alpiq to generate an additional 8 GWh of electricity this winter. This corresponds to the average annual electricity consumption of almost 2000 households. The measures at the two hydropower plants on the Aare are elements of a broader effort to strengthen the security of supply in Switzerland.