The European investigation into the blackout calls it the "most serious" on the continent but does not point to blame.

The European Association of Electricity Grid Operators (ENTSO-E) attributes the cause of the power outage across the Iberian Peninsula on April 28 to voltage control problems in Spain. The investigation, which has not yet concluded, considers the incident "the first of its kind" and "the most serious to occur in Europe in the last twenty years." According to the account of the events, the problem began "in southern Spain" and "in less than two minutes spread to the Portuguese grid" and was contained at the connection to France.

The main objective of their proposals is to "prevent something like this from happening again," for which they believe it is necessary to improve "the system's voltage control capacity," which is a well-known and accessible technology, but which in Spain has different legal regulations than the rest of Europe. Regarding the role of renewables in this problem, Entso-e sources affirm that this is a phenomenon "independent" of the characteristics of the generation, but that at the same time, "they all require voltage control."

Spain has one of the highest proportions of variable renewable generation, especially wind and solar, which creates greater challenges in voltage control, especially in rural distribution networks or in areas with many solar plants.

Entso-e's final report won't be published until the first quarter of next year, and the organization believes its role "is not to assign responsibility , but to determine what needs to be done to ensure something like this doesn't happen again."

A report by three professors from the Technological Research Institute (IIT) of Comillas Pontifical University and published last week found that "synchronous generation (mainly combined cycle and nuclear power plants) in the southern and central regions was unusually low , with only one combined cycle plant in Andalusia and one nuclear plant in the center. Furthermore, more than a third of the 400 kV grid was offline for maintenance or voltage control, leading to poorly damped oscillations."

The authors consider that what happened was "an unprecedented phenomenon" in Europe, linked to "the uncontrolled increase in voltage when renewable generation was disconnected" and that "the maneuvers carried out by Red Eléctrica de España between 12:00 and 12:30—connecting lines to try to dampen the oscillations—further reduced the safety margin, accelerating the collapse of the system."