River under current

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The Sihlsee dam is part of the Etzelwerk pumped storage power plant.   (Photo: A

The Sihlsee dam is part of the Etzelwerk pumped storage power plant. (Photo: Alessandro Della Bella, Eawag)

Switzerland is proud of its strongly developed use of hydropower. This covers almost 60% of the country’s electricity needs. The production of around 36 terawatt hours (TWh) per year is now to be increased by a further 3 TWh by 2050 as part of the energy strategy. Eawag, the water research institute, is today presenting internal and external experts at the Swiss Museum of Transport in Lucerne on the challenges this poses for water bodies and the approaches society can take to meet these challenges. More information can be found in the conference proceedings.

Taking better account of the ecological impacts of small hydropower plants

70 percent of Swiss hydropower plants - around 1500 - are considered small. They have outputs of less than ten megawatts and can benefit in part from the cost-covering feed-in remuneration (KEV). However, their share of Switzerland’s total hydropower production is relatively low at around 10%. This is even more evident in the case of very small plants. All 300 KEV-supported micro plants (outputs below 100 kW) together produce 40 MWh/a. This corresponds to about one millionth of Swiss hydropower production. Researchers have now investigated the assumption that small power plants also have small effects. [1] T hey come to the conclusion that plans for the use of small hydropower often take too little account of the long-range ecological effects and the cumulative effects of several plants in the same catchment area. For example, the number of species of invertebrate organisms is halved on residual water stretches. This in turn affects species that live along the watercourse, for example because the spiders on the bank lack food.

Using lakes as batteries, taking climate change into account

Natural lakes are increasingly being included in pumped storage systems. Water is pumped up from Lake Zurich to Lake Sihl or from Lake Geneva to Lac de l’Hongrin to produce electricity when needed. One project has investigated how such shifts in entire water packages affect the physical, chemical and biological situation in the lakes: large fluctuations in lake levels, for example, can endanger near-natural shores, cloudy glacier water can inhibit the growth of plants in clear lakes, or water withdrawals and returns lead to temperature differences and changes in the seasonal stratification in the lake. The researchers’ conclusion: With appropriate measures, negative impacts of such changes can usually be mitigated. It is important, however, that the influence of climate change is also taken into account, as pumped storage plants have been in operation for many decades.

The same applies to the extraction of large quantities of water from lakes and rivers for heating or cooling purposes. A study by Eawag has identified enormous potential here. With clever planning of new plants, the use of heat or cold can even be used to compensate for the negative effects of climate change: Cooling water from great lake depths, for example, can help prevent rivers from becoming too warm in hot summers, even after it has been used.

Hydropower enjoys high acceptance

A social science study has investigated the acceptance of renewable energies. [2] According to the results, there is strong support for the expansion of large-scale hydropower, and the respondents are also prepared to pay for it - for example with higher electricity prices if the plants have to invest in ecological clean-up measures. As soon as the local population has a say in decision-making, projects are questioned more critically or, in some cases, even combated.