Hydropower gets fit for the future

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Hydropower Ernesto Casartelli
Hydropower Ernesto Casartelli

In 1886, the first hydropower plant went into operation in Littau, Lucerne, to supply the Swiss AC grid. Today, hydropower is the main pillar of the nationwide electricity supply. To keep it that way, this form of energy generation must be continuously modernized. A stocktaking with the expert.

Ernesto Casartelli, Switzerland is the water castle of Europe. Are hydroelectric power plants a Swiss invention?

Not at all. The use of water power is an ancient cultural technique. Just think of the use of water wheels in ancient times. However, Switzerland has played a significant role in the development of the machines that can be used to generate electricity from water power. Companies such as Escher-Wyss, Sulzer and Brown-Boveri/ABB were leading manufacturers of turbines and generators.

What role does hydropower play in our electricity supply?

As in Norway or Austria, hydropower is very important in Switzerland. It currently covers around three-fifths of Switzerland’s electricity consumption. That’s still a lot, even if the percentage is lower than 50 years ago. At that time, there were no nuclear power plants, and hydropower supplied practically as much electricity as the entire country consumed. Since then, Switzerland’s electricity consumption has doubled. However, the production of electricity from hydropower has increased only slightly. Instead, nuclear power plants have been built. These currently cover about a third of the country’s electricity needs. Today, nuclear power is viewed critically, but hydropower remains a largely undisputed pillar of Switzerland’s electricity supply.

So Switzerland can continue to rely on hydropower?

Hydropower remains important, but the Energy Perspectives 2050+ of the Swiss Federal Office of Energy show that the potential of hydropower in this country is pretty much exhausted. According to official expectations, hydropower production can still be increased somewhat by 2050. This is to be achieved by renovating existing small hydropower plants and building new ones. Another important factor is the increased use of pumped storage. The main increases in production will not come from hydropower, but from solar and wind power. This trend can also be observed worldwide: According to estimates by the International Energy Agency, energy production from wind and solar power will soon exceed that from hydropower.

If solar power expands so much, will hydropower eventually become obsolete?

Not at all - for two reasons: First, the yields from solar power in our country are too low, even in the long term, to replace hydropower. Second, with the expansion of solar energy and wind power, hydropower is taking on an important new role: it must supply electricity when there is too little available from solar and wind power plants. It must absorb these weather-related fluctuations in production and thus ensure the stability of the power supply. Pumped storage power plants are also likely to become more important again: They can use surplus solar and wind power to pump water back into the reservoirs and thus store the energy that would otherwise be lost.

You are working on pump turbines at the HSLU. What do we have to imagine by that?
It’s a machine that can be used with a turbine to generate electricity, but also to pump the water back into the reservoir. Experience shows that pump turbines do not always run stably, which can lead to problems during operation. We have looked for causes and improvements in our laboratory, using flow simulations as well. To do this, for example, we simulated the water flows in the turbine on the computer and investigated them experimentally in the laboratory.

Most hydropower plants are now well over half a century old. Are signs of age showing?

It goes without saying that the machinery of the hydropower plants has to be kept fit all the time. Turbines, generators and other components have to be overhauled or replaced. How often such so-called retrofit measures are necessary also depends on the region: In plants with small storage basins, the water contains a lot of sediment, and the wear of the turbine blades is therefore greater than in plants with larger storage volumes, for example. Locally evaporating water, as sometimes observed in water streams, also stresses the turbines.
It is important for power plant operators to know what damage sediments do to turbines, partly because it reduces turbine efficiency. The Lucerne University of Applied Sciences and Arts, together with the Swiss Federal Institute of Technology in Zurich and the Goms power plants, has investigated this in field tests over many years. In order to estimate the losses due to worn turbines even better, we have reproduced worn turbines in the laboratory on a small scale and then used them for measurements.

What needs to be done to modernize hydropower?

One approach is to further improve the efficiency of the power plants during renewal measures. This can be achieved, for example, by building turbines with the latest blade design. Another challenge stems from the fact that hydropower plants are operated more flexibly today than in the past because they are used more frequently to keep the power grid in balance, i.e. to match power production to power consumption. This causes turbines to stop and restart frequently, for example. Or it means that hydropower plants more often deliver only part of the technically possible output. This was the case in the past, but not in such a wide range between full operation and very low output. Research is working, for example, to ensure that turbines also operate at high efficiency at partial load. Digitalization is also making an important contribution to operational optimization and monitoring.

In the past, hydropower occasionally struggled with image problems. Can this form of energy re-establish itself in the public consciousness as a genuine ’green’ energy?

They are probably alluding to the situation when pumped storage power plants use nuclear power to fill reservoirs. This practice put large-scale hydropower in an unfavorable light in the past. However, if solar power production capacities are greatly expanded and the temporary surpluses are temporarily stored in reservoirs, it is a win-win situation. That’s why I see hydropower playing a central role in a carbon-neutral energy supply.
Like all energy production, the generation of electricity from hydropower also leads to an intervention in the ecosystem. This is a sensitive issue, as the discussion about residual water volumes shows, for example. There is great sensitivity to these issues when it comes to the expansion or even new construction of power plants. Improvements have also been made for fish migration. I remember a nice example in Fribourg. There, at Lac de Pérolles, there is a fish lift that allows thousands of trout and other fish to migrate across the dam in both directions every year. Such examples also improve the image of hydropower.

Even dams need care

The more than 200 dams in Switzerland are also getting older. "Normally, their lifespan is designed for up to 100 years," says Dieter Müller, HSLU expert in hydraulic engineering. A large proportion of the dams in Switzerland were built between 1950 and 1970 ¬ so they are now 50 to 70 years old. Maintenance costs increase with age. It is therefore inevitable that by the year 2050 we will be faced with large expenditures for the maintenance and new construction of dams. That’s exactly what’s happening right now at the Grimsel Pass, where a new wall is being built directly in front of the existing 90-year-old Spitallamm wall. "As far as the costs are concerned, we are talking about 2 to 3-digit million sums, depending on the size of the facility," Müller knows.

Safety has top priority
Climate change poses new challenges for hydropower: One relates in part to the spillways of dams, which must be expanded due to changes in precipitation events. In addition, Müller points out that landslides from moraines and avalanches that fall in a reservoir can trigger small tsunamis there.

And finally, a pitfall that was not known when the oldest dams were built is revealed: concrete swelling. This is a chemical reaction that special concrete aggregates exhibit in conjunction with water. It necessitated the premature rehabilitation of some walls. "For new walls, we therefore make sure that the concrete mix has a specific composition in which this can be avoided," Müller emphasizes.

Permanent monitoring of such critical facilities is standard. "The owners of the plants carry out continuous checks themselves. Every five years, there is an additional external inspection by the Swiss Federal Office of Energy (SFOE)," says Müller. The safety of the plants in Switzerland is therefore in good order, he says. "However - there is always a small risk. That’s why a good emergency concept is needed in any case."

Interview: Benedikt Vogel
Pictures: Contribution picture: Priska Ketterer, Spitallamm new building: Dieter Müller