On 28 April 2025, at 12:33:30, a system-wide blackout left the entire Spanish and Portuguese mainland grid without power, following a sequence of uncontained voltage events.

The final technical report on the crisis, presented by Minister Sara Aagesen on 17 June, was compiled over 49 days by a multidisciplinary committee and confirms that the blackout had a multifactorial origin.

However, the analysis identifies specific operational errors, technical breaches and shortcomings in foresight, particularly concerning the system’s voltage management.

“Some of the generator disconnections occurred before voltage thresholds set by regulations had been exceeded,” stated Aagesen during her address.

“These disconnections were triggered without technical justification, worsening the problem,” she added, aligning with the Committee’s conclusions.

Insufficient voltage control capacity

One of the report’s most decisive findings is the confirmation that the grid lacked sufficient dynamic voltage control capacity on the day of the blackout.

This shortfall was not due to a structural lack of resources, but to the low operational availability of synchronous power plants. 

Of the ten units scheduled by the System Operator (Red Eléctrica de España) to provide voltage control—three nuclear and seven combined-cycle plants—one was declared unavailable on 27 April due to a fault and was not replaced, reducing effective capacity at a critical time.

These units were activated outside of the day-ahead electricity market, via remunerated technical restrictions, and were tasked with supplying or absorbing reactive power to regulate voltage across different parts of the country.

Despite this programming, the report reveals that some units failed to respond correctly to operating commands. In one case, reactive power was injected when absorption was required, increasing voltage instead of stabilising it.

A system under strain days before

The technical document provides information not included in Aagesen’s public remarks or the government communiqué. It shows that in the days leading up to 28 April, several voltage instability episodes were recorded, such as overvoltages on 22 April and undervoltages on 24 April, along with isolated oscillations. 

These precursors were considered by the Committee in identifying an accumulating trend that progressively undermined system stability.

The technical analysis mapped the blackout into five phases: an initial instability phase from 09:00, followed by an oscillation phase between 12:00 and 12:30, a third phase of progressive disconnections between 12:32:57 and 12:33:18, the critical blackout phase between 12:33:18 and 12:33:30, and a final restoration phase, which reached 99.95% recovery by 07:00 the following day.

“From as early as 10:30 in the morning, we observed increased amplitude in voltage instability,” Aagesen noted. “Various companies reported oscillations in their control centres, which clearly indicated stress on the system,” she added.

Premature disconnections and cascading failure

The report notes that, between 12:32 and 12:33, voltage rose rapidly, triggering successive generator disconnections in multiple provinces.

“What’s important is that some disconnections occurred before reaching regulatory limits, while others were automatic due to self-protection mechanisms,” explained the minister. Voltage limits on the transmission grid range between 380 kV and 435 kV.

These disconnections sparked a chain reaction: each disconnected installation contributed to a further voltage increase, prompting more generators to trip offline.

The simultaneous frequency drop led to loss of synchronism with France and the isolation of the Iberian Peninsula from the European interconnected grid.

Structural measures and regulatory consequences

The report not only diagnoses but also proposes short- and medium-term measures. Firstly, it underscores the urgency of reinforcing oversight of technical compliance among system agents.

It also advocates the effective implementation of Operation Procedure 7.4 (PO 7.4), which would allow power electronics solutions to be deployed for voltage control in asynchronous installations.

Other proposed measures include:

• Reviewing the technical restrictions and balancing services scheme.
• Increasing electricity storage capacity and demand-side flexibility.
• Strengthening interconnection with France as a structural stabilisation measure.

Additionally, the report indicates its findings will be referred to the National Commission on Markets and Competition (CNMC) and other competent authorities to initiate the appropriate administrative proceedings. This could result in partial judicialisation of the case, depending on how the relevant bodies interpret the legal framework.

An unprecedented crisis as a turning point

“This report is a tool for analysis and action,” summarised Aagesen during her presentation. “It does not seek to assign blame, but rather offers the best available technical diagnosis to reinforce what works and improve what has failed.”

With over 300 GB of data analysed, the work of the 28-A Committee represents the largest investigation into cybersecurity and grid operation in Spain’s history. No evidence of cyberattack was found, but technical vulnerabilities and coordination issues were identified that compromise the grid’s resilience in high-tension scenarios.

This report lays the groundwork for a profound review of Spain’s power system in a context of increasing renewable integration and operational complexity. The Council of Ministers is expected to announce a legislative package shortly to implement the recommendations and safeguard the grid from future systemic risks.

Energy sector calls for operational accountability and accelerates push for structural modernisation

The report’s publication has triggered technical responses and institutional positions across the energy sector.
Experts and associations stress that the failures identified do not undermine the role of renewable energy but reinforce the need to modernise the grid, improve planning, and optimise voltage control systems.

From a technical perspective, expert Jorge Antonio González Sánchez notes the report confirms voltage oscillations days before the incident, and from 09:30 on 28 April itself. He warns that the System Operator “failed to anticipate or adequately correct the issue in time.”

He also questions the effectiveness of grid meshing and the management of the interconnection with France, pointing out that reduced availability of thermal plants left the system with minimal reactive power control.

Sectoral bodies such as UNEF highlight the report’s confirmation of insufficient dynamic voltage control and stress that while solar PV technology is technically capable of providing this function, “regulations still do not permit it.”

This limitation stems from existing rules that do not recognise solar PV as a voltage-regulating agent, reserving this role for conventional synchronous generators. Moreover, PO 7.4—which would allow voltage control through power electronics—has yet to be approved.

In this context, UNEF welcomed Aagesen’s announcement that the procedure will be fast-tracked, a longstanding demand from the sector. UNEF also calls for regulatory adjustments to enable hybrid storage deployment and use of grid-forming inverters, technologies essential for a stable high-renewables grid.

Similarly, organisations like Fundación Renovables, Renovem-nos and the Global Solar Council argue that the blackout cannot be blamed on renewable generation but rather on planning and operational failures.

They see the incident as an opportunity to redesign the power system architecture, integrating storage, digitalisation, and stronger interconnections.

From Redeia, CEO Roberto García Merino publicly acknowledged that “the risk of another blackout is there” and announced sustained annual investment increases in the grid, reaching €1.5 billion per year.

He also emphasised the need to expand international interconnections to improve system security, which currently stands at 3%, compared to the 15% EU target.

Stakeholder reactions converge on one key idea: the system’s resilience must grow in line with the energy transition. The 28-A report marks a starting point to accelerate that process.