Light breeze and dark doldrums: two sides of the energy transition

At the beginning of March 2025, a lecture series at the Collegium generale in Bern focused on the challenges of dark doldrums and light storms in the context of the energy transition. Dr. Christian Grams from MeteoSwiss explained how weather extremes with little or too much wind and sun affect electricity production and how they can be dealt with.

On Monday, April 28, 2025, there was a massive power outage in Spain, Portugal and parts of France. In cities such as Madrid, Barcelona and Lisbon, rail and subway traffic came to a standstill and caused considerable traffic chaos due to broken traffic lights. Mobile phone networks and internet connections were disrupted or failed completely. The power outage also affected ATMs, card payments, hospitals, supermarkets and security services.

Reasons for the power failure

While a cyberattack has been ruled out, several factors could have played a role. These include, for example, the sudden loss of power supply, grid instability due to renewable energy, weak international connections or technical faults.

Personal and economic damage

The economic damage is estimated at between 1.6 and 4.5 billion euros. Industrial companies such as Volkswagen and Seat had to stop production. In the food industry, large quantities of goods spoiled due to interrupted cold chains. Tragically, several people lost their lives, including through carbon monoxide poisoning as a result of improper use of emergency generators and fires caused by candlelight

Lessons learned and outlook

The incident underlines the need to make electricity grids more resilient, particularly in view of the growing share of renewable energies. Investments in grid stabilizers, energy storage and the expansion of international connections are recommended to ensure security of supply.

Two interesting aspects of the energy transition are repeatedly mentioned. A “light breeze” is a phase of high solar and wind power production with low demand, which leads to an oversupply and sometimes negative electricity prices. In contrast, the “dark doldrums” describe periods in which wind and solar plants hardly supply any electricity due to weather conditions.

Four-fifths of Swiss electricity from renewable sources

According to the Swiss Federal Office of Energy (SFOE), around 80 percent of electricity in 2022 came from renewable sources: 65 percent from hydropower and 14 percent from photovoltaics, wind power, small hydropower and biomass. 20 percent came from nuclear energy. Switzerland will remain well positioned in 2025 with almost 80% renewable energy in the sockets, with hydropower continuing to dominate. Nevertheless, the electricity supplied – the so-called supply mix – deviates from the production mix, as there is lively trade with other countries.

Solar energy as a great opportunity

Solar energy offers enormous potential: depending on the location, solar radiation is between 1050 and 1550 kilowatt hours per square meter – comparable to Tuscany or Provence. In total, solar energy exceeds 200 times Switzerland’s energy consumption. Wind energy mainly plays a role in the winter months, but accounts for less than one percent of electricity production.

Saving energy in everyday life

In addition to the expansion of renewable energies, energy-saving measures are important, for example by consistently switching off appliances in standby mode using power strips or smart technologies, without having to sacrifice convenience.

New risks due to light breeze and dark doldrums

However, the energy transition brings new risks: Not only dark doldrums, but also light crises pose challenges. Switzerland is well integrated into the European grid and has strong storage capacities thanks to hydropower. However, with the rapid expansion of solar plants, the risk of local overproduction is also growing. With the Energy Strategy 2050, the federal government aims to increase the average production of electricity to 37,400 GWh/year by 2035. By 2050, the target is 38,600 GWh.

Measures against grid overloads

Swissgrid, the national grid company, is already working with grid congestion management, flexible feed-in regulations and, if necessary, temporary curtailment of generators. Nevertheless, cooperation between grid operators, producers and large-scale consumers must be further improved.

Battery storage as a (still) inadequate solution

Battery storage could be a means of combating bright breezes. However, the existing capacities are not yet sufficient: Many batteries are full after just a few hours of full solar radiation. Planned large-scale storage projects in Valais and Ticino will only provide relief in the long term.

Improving the remote controllability of photovoltaic systems

Many existing photovoltaic systems cannot be controlled remotely. Only new systems must have the appropriate interfaces. Experts are therefore calling for existing systems to be retrofitted or for controllable switch-off options to be created via incentive systems.

Holiday plans and smart electricity tariffs as a strategy for the future

Some experts suggest developing specific measures for public holidays: For example, industrial companies could be given incentives to ramp up their production during solar-strong hours. Intelligent electricity tariffs could also help to adapt consumption to generation.

Intelligent control of surpluses

In future, we must learn to manage not only dark doldrums, but also light crises. Thanks to flexible hydropower, Switzerland currently still has an advantage over its neighbors. However, anyone who wants to successfully shape the energy transition will not only have to prevent bottlenecks in the future, but also intelligently manage surpluses.

Binci Heeb

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