Stress tests for the Swiss power system

According to the Climate and Innovation Act, Switzerland is aiming for its energy supply to be CO₂-neutral by 2050. Rising electricity demand due to the electrification of transport and heating is primarily to be covered by hydropower, solar and wind energy as well as imports. By 2050, the existing nuclear power plants will no longer be in operation.

But how dependent should a stable energy system be on other countries? This question has been at the heart of Switzerland¡¯s energy policy discussions since the cut in Russian gas supplies. The last two winters especially have been overshadowed by fears of electricity and gas shortages.

Scientists at ETH Zurich and ZHAW Winterthur are now simulating in a new study various shock scenarios for the climate-neutral Swiss energy system in 2050. They aim to illustrate how it needs to be structured to offset drastic restrictions in cross-border electricity trading as cost-effectively, securely and sustainably as possible.

¡°The question of which technologies make economic sense depends on how sharp and frequent the decline in import options proves to be,¡± explains Ali Darudi, an energy researcher at ZHAW Winterthur and one of the study¡¯s authors. The scientists¡¯ model could contribute to an objective debate about Switzerland¡¯s supply security.

Simulating import shocks

The scientists have based their calculations for 2050 on the federal government¡¯s energy forecasts and anticipate an annual demand of 76 terawatt hours (TWh). They have defined as a starting point the most cost-effective energy system of the future without taking into account the politically defined expansion goals and excessive dependency on other countries. This model covers 45 percent of demand with cheap electricity from abroad and hydropower. The rest is accounted for primarily by photovoltaics and wind energy. ¡°

The scientists are exposing this energy system to various shocks: they are modelling scenarios in which electricity imports to Switzerland fall at varying degrees and frequencies for a full year, with gas imports being possible or impossible in the shock year. In order to offset these import shocks as cost-effectively as possible while ensuring that enough electricity is available at all times, the authors of the study are testing a mix of different technologies ¨C ranging from reserve power stations operated with gas or liquid fuels, additional photovoltaic systems and wind power plants to various storage technologies and new nuclear power plants.

The scientists are also taking into account the estimated investment and operating costs of these technologies. A further core aspect of the analysis is that, unlike in previous studies, the power plant portfolio is always planned for operation under both normal conditions and the shock scenario.

How robust is the energy system of the future?

The model calculations show that the system could withstand up to a 70 percent reduction in import capacity for one year without the necessity for additional measures. This would primarily be made possible by hydropower reserves: ¡°Switzerland¡¯s reservoirs can store almost nine terawatt hours of electricity. This together with the remaining import options would offset the availability shortage,¡± says Jonas Savelsberg from ETH Zurich¡¯s Energy Science Center.

Additional production capacities would only be required to cover demand in the case of more than a 70 percent reduction in the possibility of electricity trading. The question of which technologies would be inexpensive and efficient to offset import losses depends on the severity and frequency of a shock. According to ETH scientist Savelsberg, ¡°the less frequent we are confronted by drastic restrictions of 70 percent or more in electricity trading abroad, the more efficiently we can overcome them with technologies that have high operating costs but low investment costs¡±. Such technologies mainly include reserve power stations operated with gas or liquid fuels.

Liquid fuel power stations

In most scenarios in which no gas imports are available and electricity trading is restricted by 90 to 100 percent every 10 to 100 years, power plants operated with liquid fuels such as petrol, oil or synthetic fuels can be an economically viable option.

These plants are relatively inexpensive to build but expensive to operate. The reason for this is that the resulting CO₂ emissions have to be filtered from the air or the power plants have to be operated with expensive synthetic fuels. However, the high operating costs carry less weight over the entire service life of these power plants, as they are very infrequently used. Furthermore, Switzerland already has considerable capacities for the storage of liquid fuels that will not be fully utilised due to the decarbonisation of the energy system by 2050.

Technologies incurring high investment costs and low operating costs only make more sense if we assume that Switzerland has to manage entirely or practically entirely without electricity imports every two to five years. These technologies include photovoltaics, wind power and ¨C under very extreme shock scenarios ¨C nuclear power.

Gas-fired power stations

If, on the other hand, gas imports from abroad are possible in a shock year, the model relies primarily on reserve gas-fired power stations to offset the drop in electricity imports. Here too, filtering the resulting CO₂ emissions out of the air is expensive.

¡°Gas imports have a key role to play in the design of a robust Swiss energy system,¡± says Savelsberg. As soon as gas imports are available, nuclear power plants no longer offer an economically viable option for offsetting shocks. ¡°The availability of gas reduces the economic incentives for investing in new nuclear power plants,¡± says the ETH scientist.

Nuclear power and hydrogen

New nuclear power plants only make economic sense in the scientists¡¯ model calculations if a complete breakdown of electricity imports every two years is assumed and gas imports are not possible. ¡°The very high investment costs of new nuclear power plants would only be offset by their relatively low operating costs in this unrealistic scenario,¡± explains ZHAW scientist Darudi.

The scientists base their conclusions on assumed investment costs of EUR 10,000 per kilowatt (kW). This is roughly equivalent to the costs assumed by many other studies for the construction of new nuclear power plants in Europe. The scientists have also drawn similar conclusions when testing scenarios featuring lower costs.

Sustainably produced hydrogen is only deployed as an offsetting power supply in those shock scenarios in which electricity and gas imports break down completely every two to ten years. Altogether, however, it would amount to a maximum of just 2.5 TWh of electricity generation, which is equivalent to around 3% of Swiss demand. If, on the other hand, gas imports are available, it is not worth relying on hydrogen, which is expensive to produce.

Robustness of the analysis

The scientists also tested the findings of the study in another modelled energy system. They assumed that the targets set out in the Federal Act on a Secure Electricity Supply from Renewable Energy Sources would be met.

In this case, around 60 percent of demand is produced by photovoltaic systems in Switzerland, with the remainder coming primarily from hydropower and wind energy. This reduces the role played by electricity imports from neighbouring countries, and Switzerland would export roughly the same amount of electricity as it imports throughout the year.

In this system, too, the researchers came to the same conclusions: reserve power plants fuelled by gas or liquid fuels are also in this case the most efficient solution for dealing with rare shocks.