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| Fig. 1: Hydroelectric power plants across Switzerland. [6] (Courtesy of Sustainability under a CC attribution license.) |
Nuclear power has long been controversial on the global stage. In 2017, Switzerland joined the growing list of nations which have rejected nuclear power by voting to decommission their remaining nuclear plants in the coming years. [1] Though no deadline to reach the goal of a nuclear-free power grid was officially set, it is reasonable to ask how the country will transition away from a resource which provided 17% of the nation's energy in 2021. [2] Despite being a landlocked country, Switzerland has a significant number of lakes and rivers; more than 900 lakes and roughly 61,000 km of rivers run through the country. [3,4] Annual snowmelt from the Alps provides a strong flow which feeds these bodies, and the nation has capitalized upon this. In 2021, hydroelectric power contributed 32% of Switzerland's energy, twice the contribution of nuclear energy. [2] Given that hydroelectric power is more popular than nuclear power locally, one might reasonably ask whether hydroelectric power output could be increased in order to offset the electricity lost from soon to be decommissioned nuclear power plants? [5]
To begin, we consider how much nuclear-generated electricity is consumed by Switzerland. According to the bp Statistical Review of World Energy, the country used 0.17 Exajoules of nuclear power in 2021. [2] We therefore seek to determine how 0.17 Exajoules of hydroelectricity could be generated by hydroelectric sources. According to the same reference, the country also used 0.34 Exajoules hydroelectric power in 2021, indicating that the national hydroelectric power output must be increased by 50%. [2]
Hydroelectric power comes from using a turbine to capture the conversion of gravitational potential energy of a body of water into kinetic energy as it falls to a lower point. This can be achieved by releasing water stored in a dammed reservoir, or by installing a turbine which uses the flow of a river. In terms of the density of water, ρ, the acceleration due to gravity, g, the surface area of the body of water, A, and the height that the water falls, h, the amount of energy produced can be computed as:
| E | = | ρgAh2 4 |
Rearranging this equation and knowing that ρ = 103 kg m-3 and g = 9.8 m sec-2, we find that in order to store the 0.17 × 1018 Joules of energy needed to offset the decommissioned nuclear power plans, we would need some dam of height h and body of water of surface area A such that
In order to illustrate the size of this quantity, imagine converting the entire country into a reservoir. Given it's surface area, the country would have to be dammed by a 41 m structure in order to produce such a large amount of electricity. Clearly, we must look elsewhere to meet this excess demand.
Alongside reservoirs, run-of-river plants are another important source of hydropower. These plants install turbines to rivers to generate electricity without storing water, and they account for 48% of the power generated in the country, as shown in Fig. 1. [6] Though it is not possible to stimulate runoff from the Alps and increase the flow through these plants at will, climate change is already changing annual runoff patterns. Increased flow would increase the amount of power generated by these plants, and it could fill existing reservoirs faster, allowing them to be drained at an increased rate and generate more power. Storage plants account for another 48% of hydropower plants, so we seek to increase power output by 50% using 96% of power plants, or increase the output of each run-of-river and storage plant by 52%. [6]
Our equation above tells us that power output is linear with water flow rate, so in order to increase power output by 52% with existing run-of-river and storage plants, we seek to find a 52% increase in flow rate across these structures. Temperatures in Switzerland are expected to rise by 6.8℃ by the end of the 21st century, which will radically impact the country's snowmelt and runoff from glaciers. [7] Due to this warming, runoff in the winter months is predicted to increase by 48% by the end of the century, however it is also predicted to decrease by 35% in the summer months, leading to an overall annual decrease of 8% after also accounting for the spring and autumn months. [7] Not only will this radically change the availability of hydroelectric power throughout the year, it will not compensate for the dearth of electricity left by decommissioned nuclear power plants when averaged across all 12 months. Increased flow across existing plants is therefore also not likely to be a viable method for increasing hydroelectric power supply.
As Switzerland seeks to phase out nuclear power plants, hydroelectric power could be seen as a viable alternative. It is a well-regarded source of energy without reliance on fossil fuels, and the country has a large number of bodies of water and a significant annual watershed off of the Alps to serve as fuel. In order to match the demand left by decommissioned nuclear plants, however, outputs from this source of electricity would have to be radically increased. Without building new reservoirs, which is unlikely to be feasible at the scale necessary for providing enough extra power, the volume of water passing through existing plants would have to increase by 52%. Climate change is expected to radically change Switzerland's annual runoff patterns, however rates of watershed are predicted to become more erratic and overall decrease over the course of the year. It is therefore not likely that hydroelectric power could be ramped up at the necessary scale without a significant investment in infrastructure such as more run-over-river plants, which may not be feasible given the country's current saturation of plants, as shown in Fig. 1. It would therefore be advantageous for the country to look towards other sources of energy in order to match the demand left by its decommissioned nuclear power plants.
© Toby Satterthwaite. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] "Switzerland Votes to Phase Out Nuclear Power," BBC News, 21 May 17.
[2] "BP Statistical Review of World Energy," British Petroleum, June 2022.
[3] S. Rohde et al., "Room for Rivers: An Integrative Search Strategy for Floodplain Restoration," Landsc. Urban Plan. 78, 50 (2006).
[4] N. Mölg et al., "Inventory and Evolution of Glacial Lakes Since the Little Ice Age: Lessons From the Case of Switzerland," Earth Surf. Process. Landf. 46, 2551 (2021).
[5] A. Tabi and R. Wüstenhagen, "Keep It Local and Fish-Friendly: Social Acceptance of Hydropower Projects in Switzerland," Renew Sustain. Energy Rev. 68, 763 (2017).
[6] W. Hediger, "The Corporate Social Responsibility of Hydropower Companies in Alpine Region Theory and Policy Recommendations," Sustainability 10, 3594 (2018).
[7] R. Muelchi, "River Runoff in Switzerland in a Changing Climate Runoff Regime - Changes and Their Time of Emergence," Hydrol. Earth Syst. Sci. 25, 3077 (2021).