REN stated this Wednesday, 17th, that it is not possible to guarantee that new blackouts will not occur and argued that the priority of the electrical system must be the ability to recover quickly in the face of technical, climatic or cybersecurity risks.
At the hearing at the Environment and Energy Commission, within the scope of the Working Group on the blackout of April 28, 2025, the executive president of REN, Rodrigo Costa, stated that the national grid operator does “everything to avoid” these events, but stressed that “there is nothing that can prevent” them from happening again.
“Our service is one of the best in Europe and things are fine, but we are subject to accidents, we are subject to cybersecurity and we are subject to natural disasters,” he said. “The only thing that needs to be done is to be well prepared to recover” in the event of another blackout.
Rodrigo Costa argued that this preparation cannot be limited to the transport network operator, but must involve “the army, the police, all critical services and telecommunications operators”.
REN’s presentation, made together with executive director João Conceição at the start of the working group meeting, began by characterizing the state of the Iberian system before 11:33 on April 28, when the collapse occurred. In Portugal, renewable production represented around 62% of consumption, while in Spain it reached 92%, with a strong weight of solar energy.
According to REN, southwestern Spain concentrated very high production — around 16,000 megawatts of solar and wind power — for reduced consumption, with a large part of the energy being exported to other areas of Spain and Portugal.
Those responsible also highlighted that Spain operated with a European derogation that allows voltage levels of up to 435 kV, above the standard practiced in Portugal, where very high voltage networks operate up to around 420 kV.
According to João Conceição, both systems met the minimum levels of inertia defined by the European Network of Electricity Transmission Network Managers (ENTSO-E), but voltage control in the Spanish system was not following the objective curve at several times.
According to João Conceição, Portugal and Spain complied with the minimum levels of inertia required by the European Network of Electricity Transmission Network Managers (ENTSO-E), but the Spanish system was not responding adequately in controlling voltage, one of the factors that led to the collapse.
“The main cause that has been identified is a very high voltage problem, which clearly starts in the Spanish system and spreads to the Portuguese system”, he stated.
At 11:33, the sudden loss of around 2,200 megawatts of solar production in southwestern Spain triggered a cascading imbalance that led, in around four seconds, to the total collapse of the Spanish and Portuguese systems.
During this period, the National Electric System’s emergency plans came into effect and REN phased out around 4,200 megawatts of consumption, starting with water pumping and progressing to progressively more critical consumption.
The Portuguese system, which was importing energy, momentarily began exporting around 2,400 megawatts, in an automatic attempt to support the Spanish system, an effort that was not enough to avoid collapse.
The recovery began autonomously, with the start-up of two plants in ‘blackstart’ mode, in Castelo de Bode and Tapada do Outeiro, and the creation of energy islands, in a process that REN described as “very meticulous”, due to the permanent risk of new system loss.
External support only began to arrive at the end of the afternoon, through the interconnection of Douro Internacional, allowing energy replacement to be accelerated and ensuring supply to priority consumption, such as hospitals and security services.
REN highlighted that it has been applying a conservative approach to restoring the commercial capacity of interconnections and that national and European measures are underway to reduce the risk of new events, although it reiterated that the increasing complexity of the system makes it impossible to completely eliminate this risk.
The blackout on April 28 was classified by the European Network of Electricity Transmission Network Managers (ENTSO-E) as “exceptional and serious”, with immediate consequences including the closure of airports, transport congestion and lack of fuel.
In the preliminary report released on October 3, the group of experts confirmed that the blackout originated in Spain and was caused by a succession of sudden shutdowns of renewable production, and subsequent loss of synchronization with the European continental grid.