Spain in last April suffered a mysterious blackout. You probably heard about the case, but not about the investigation. Despite some things remain unclear, I have some details.

A big commercial photovoltaic power plant in the region of Badajoz in the southwest of Spain on April, 28th in 2025 supplied 250 MW into the grid, when seconds after twelve o’clock at noon, as the responsible company Red Eléctrica España figured out, this photovoltaic power plant caused an oscillation of 0.6 Hz. How or why remains unclear. {I wonder whether an undiscovered oscillation already existed in the EU power grid due to the Baltic countries only few weeks beforehand switching from the ex-Soviet power grid to the EU power grid.} The oscillation was curbed successfully, seemingly without any problem. But to the purpose of curbing, additional phase shifters got activated and export to France and to Portugal was reduced.

The power grid seemed to be stable again, when minutes later an inter-area (which means it was caused somewhere else in the EU power grid and seemingly wandered from an unidentifiable location) oscillation of 0.2 Hz occurred. This oscillation, too, was curbed. Yet reactive power occurs in a circuit, when current and voltage aren’t in phase, so the operational headquarters of Red Eléctrica España added 760 Mvar and noticed a sudden 845 MW increase in demand. This demand in truth was a lack of supply caused by small photovoltaic power plants suddenly stopping their supply. Roughly seven-hundred Mega-Watt shall have missed from power plants smaller than one Mega-Watt and one-hundred-and-two Mega-Watt shall have missed from small power plants able to supply more than one Mega-Watt. Why the small power plants stopped their supply also remains unclear.

Due to the inexplicable outages, the operational headquarters at 12:30 decided to order supply from gas-and-steam power plants. But these needed one and a half hour for going online, so didn’t play a role in the further events. The power grid already was successfully stabilized again at 12:30.

At 12:33, a transformer substation in Granada in the south of Spain went offline. This transformer substation had supplied 355 MW and absorbed 165 Mvar. Why it went offline again remains unclear. But the power grid nevertheless shall have been stabilized again and within milliseconds. Until 1.5 seconds later Sevilla and Badajoz, too, for an unclear reason went offline. They together had supplied 727 MW into the power grid. Five seconds after Granada had went offline, a cascade of photovoltaic power plants and also of wind farms in the southwest of Spain going offline followed. Thus the missing power supply summed up to two-thousand Mega-Watt. Conventional power plants in the south, southwest, and middle of Spain (Andalusia, Extremadura, La Mancha) should have absorbed the reactive power, but weren’t able to do what since the year 2000 would have been their legal duty! The investigation revealed that every fifth power plant in Spain is unable to absorb the reactive power, which it is by law expected to absorb. Excess reactive power led to excess voltage and this led to load-shedding, for which photovoltaic power plants and wind power plants went offline, while a high-voltage direct current (HVDC) electric power transmission line to France continued to export one Giga-Watt. The load-shedding summed up to a lack of two Giga-Watt of power supply. Other power lines tried to import the missing supply from France.

In consequence of the described chain-reaction did the frequency of the power grid fall below 49.5 Hz and this is a threshold for shedding big consumers like pumped storage hydro power stations. A conventional power plant in the east of Spain also went unexpectedly offline. Though at that time consumers, pumped storage hydro power stations also absorb reactive power and hence cutting them off from the power supply further increased the voltage and further decreased the frequency.

When the frequency fell under 48.5 Hz, it had passed other thresholds. First the power lines to Morocco were interrupted and then also those power lines, which imported electricity from France. But the high-voltage direct current (HVDC) electric power transmission line, which still exported electricity to France was interrupted only after the frequency fell below 48.0 Hz. This at the same time caused the Spanish nuclear power plants to go offline. This was the complete collapse of the Spanish power grid at 12:33:24, less than thirty seconds after the transformer substation of Granada had went offline.

A blackout also occurred in large parts of the northwest of the Czech Republic for around three hours since noon on July, 4th. The police reported that hints to sabotage or cyberattacks weren’t found. The blackout shall have been caused by a broken phase shifter (an identified one in power line V411), which caused eight transformer substations to function improperly. While the investigation report excludes a connection with photovoltaic power plants, some people, who live in the Czech Republic, presume a connection with the weather or more precisely with a drop in temperature. Due to the three preceding days having been very hot, temperatures between 27°C and 38°C had been expected. But the temperature on July, 4th ranged only between 17°C and 28°C. This shall have led to many people switching off their air conditioners (Czech people can afford them much easier than Germans could) and in consequence to an excess import of electricity, which shall have been like in the preceding three days 1.55 GW from Poland and 2.76 GW from Germany. This could have been too much for the phase shifter.

Already during (not after) the blackout in Spain and later also during the blackout in the Czech Republic had religious zealots become very loud about the blackouts having nothing to do with photovoltaic or renewable energies. Such a claim at such a time already was very suspicious! The blackout in the Czech Republic seems to be explained, while the blackout in Spain still has many mysterious elements. So the blackout in the Czech Republic is much less thrilling and I reported about it here only because it perhaps could give a hint to the mysterious outages of small photovoltaic power plants in Spain. Although the blackout occurred during a sunny day in Spain, the small photovoltaic power plants could perhaps also have been somehow influenced by weather conditions.