The blackout in Spain shows: Weather-dependent energies can destabilise the European electricity grid. Frequency fluctuations, a lack of reserves and poor networking led to domino effects – a warning signal for the whole of Europe.
by Björn Peters, 29th of April, 2025
On 28 April 2025, Spain and Portugal experienced one of the biggest power outages in Europe for years. Around 50 million people were affected. What are the causes and what are the implications for the energy policy debate?
The exact cause of the blackout is still under investigation, but there are several key findings. At 12:33 p.m., 15 gigawatts of generation capacity was lost within five seconds – this corresponded to around 60 per cent of the electricity consumption in Spain at the time. According to the Spanish grid operator Red Eléctrica (REE), there were two power outages just one and a half seconds apart. The grid was able to recover from the first, but not from the second, which led to the collapse.
The affected region in the south-west of Spain has high photovoltaic capacities, which supplied electricity on a large scale that day. As the Spanish grid was unable to absorb the overproduction, electricity had to be transported to France. It is highly likely that the sudden loss of large amounts of solar power – possibly due to automatic rapid shutdowns – triggered the domino effect. The Iberian peninsula’s low level of interconnection with the rest of the European electricity grid (only around two per cent interconnectivity) exacerbated the situation and neighbours were unable to help out.
It is still unclear what exactly caused the disruption. Initially, it was claimed that a fire in France had led to the emergency shutdown of a high-voltage line. However, pictures of the supposed site of the fire quickly circulated, showing no smoke at all. Others speculated as to whether cyber attacks had paralysed the solar installations. There was no evidence of this either. Instead, there is growing evidence that the emergency shutdown was caused by the operation of the power grid itself.
Local fluctuations built up, led to overvoltage and „blew fuses“ to automatically protect systems from overvoltage. Conversely, the automatic protection systems also quickly stabilised the grid again. While they initially switched off large parts of the grid and many large consumers automatically to prevent damage caused by overloads, the power supply was largely restored by Monday evening. Significant assistance was provided by foreign countries and black-start hydroelectric power plants. All substations are now working again.
Complex systems are vulnerable
The matter becomes interesting when you look at the state of the European interconnected grid in the hours before the blackout. The industry information service R2J Energietechnik, which deals intensively with grid stability and grid frequency in Europe and constantly measures the grid frequency, reported on the evening of the following day that there had been oscillations in the grid frequency in the hours before the blackout.
This is where it gets exciting. The European interconnected grid is by far the largest machine that mankind has ever built. It spans Europe from the Atlantic to Eastern Europe and from the North Cape to around the Mediterranean. In this huge area, the voltage, frequency and phase in the electricity grid must always be precisely regulated, no matter how high the electricity consumption is at any given time.
In the past, it was the large flywheel masses of the generators of coal, nuclear and gas-fired power plants that were able to compensate for small fluctuations in supply and demand. The more these flywheels are missing, the more „demanding“ grid control becomes. It now has to be regulated manually, which was previously achieved by simple physics. „Manually“ is not quite right, as numerous control mechanisms are implemented to influence the grid.
This is exactly where cybernetics comes into play. The more sensors (measuring devices) and actuators (control elements) a system contains, the more unpredictable it becomes. There is a whole discipline in physics that analyses such systems, called „non-linear dynamics“. My main focus during my studies thirty years ago.
Oscillations like the frequency oscillations here are a clear sign of instability. If they build up due to random events, threshold values in the grid frequency can easily be exceeded, above which automatic interventions take effect: if the grid frequency falls below certain values, large consumers or even entire sub-grids switch off automatically; if the grid frequency rises, power plants switch off. The PV systems in Spain also have such emergency measures built in. The crux of the matter is that these measures „on autopilot“ can cause even more instability elsewhere.
I think it is likely that after a thorough investigation of the blackout in Spain, the sole cause will not be found, but rather a chain of small but unavoidable events that led to the collapse of the grid.
In system design, such instabilities are recognised and damping or inertia elements are therefore built in. As mentioned above, these were the rotating masses, but these power plants are less and less in the grid as a result of the energy transition. On Monday, PV systems and wind power plants in Spain supplied three quarters of the power, and some of the energy had to be sent to Portugal and France. However, the weather-dependent power plants are not producing any attenuation, but are pushing inertia out of the grid in the form of thermal power plants.
Unfortunately, the Spanish nuclear power plants were unable to provide support. Only one of them (Prillo) is of a newer German design and could have gone into so-called island operation. However, it is currently being overhauled and disconnected from the grid. In contrast, the other nuclear power plants in Spain are older and of American design. They are not technically equipped for island operation. This would have ensured that the power plants were disconnected from the grid, but would have been able to feed power back in immediately when the grid was restarted from standstill. Incidentally, all German nuclear power plants had this capability for island operation – this was one of the reasons for the robustness of the electricity supply in Germany.
However, it is the declared aim of the federal government, which is currently in the process of being formed, to quickly expand the power plants that fluctuate due to weather conditions. In this country, too, we will therefore experience more and more situations in which small disruptions in the grid build up. Germany is in the comfortable position of having a much larger electricity grid than Spain, and the German grid is also better integrated into the neighbouring grids than the Spanish grid. On the other hand, Germany is pursuing the expansion of weather-dependent energies at least as rigorously as Spain and at the same time shutting down power plants that have always been able to stabilise the grid.
A „Chernobyl moment“ of „renewable“ energies is emerging here. The reactor accident at the Ukrainian nuclear power plant was much more of a catastrophe for nuclear technology than for the region around the power plant. Nature there has recovered perfectly, but myths about the lack of controllability of nuclear technology persist in the public debate to this day, even if they are downright absurd for Western-style nuclear power plants after so many thousands of successful years of operation.
In Germany, the Spanish blackout may finally lead to the systemic question being asked. The one-sided bet on a duopoly of solar and wind energy is clearly leading to risks which, if they materialise and last for several days, could lead to the complete collapse of society. According to reports from those affected on Platform X, some people in Spain lacked energy, telephones, internet, money, petrol and all the necessities of life for 20 hours. If a blackout lasted longer than a day, possibly not at an outside temperature of 25 degrees Celsius but in winter, homes would remain cold and chaos and violence would quickly spread in the cities.
Few people had previously realised that weather-dependent energies could cause a system collapse. The debate was limited to the question of where the electricity would come from in the event of a dark doldrums, when neither the sun nor the wind were providing power. Increasingly, attention is being drawn to the fact that the even greater danger arises during „light breezes“: solar and wind power plants generate high surpluses that can destabilise the grid and cause it to collapse. It will be interesting to see whether politicians finally dare to fundamentally question their energy strategy.