The technical reports published by the Ministry for the Ecological Transition and the Demographic Challenge (MITECO) and by Red Eléctrica de España (REE), 50 days after the 28 April blackout, share common ground in their core findings but diverge in their technical criteria, timeline definitions and implicit allocation of operational responsibilities.

Both documents confirm that the peninsular electricity system collapsed at 12:33:30 due to an uncontrolled overvoltage phenomenon and cascading disconnections, but they differ on when the instability began, how premature disconnections are interpreted, and the role of generation assets responsible for voltage control.

Temporal criteria: cumulative failure or sudden event?

The 28-A Committee report, presented on 17 June by Minister Sara Aagesen, traces the origin of the crisis back to instability events as early as 22 April, with prior overvoltages, undervoltages and oscillations which, according to the report, progressively weakened the system’s resilience. On the 28th, voltage showed stress indicators from 9:00 am, and by 10:30 relevant oscillations were already recorded.

In contrast, the REE report, released on 18 June in compliance with Operating Procedure 9 (P.O.9), narrows the analysis window to events after 12:00 noon on 28 April, dismissing earlier anomalies as “commonplace in real-time operation” and without “causal relevance” to the collapse. This scope excludes over three hours of abnormal tension events mentioned by the Committee.

Premature disconnections: shared diagnosis, divergent emphasis

Both reports note that several generation plants disconnected before exceeding regulatory voltage limits. Aagesen stated that “some disconnections were triggered without technical justification,” a view that the Committee links to the aggravation of overvoltage and cascading outages.

REE concurs with this diagnosis and explicitly details that disconnections were caused by incorrect tripping of generation plants, before voltage thresholds set out in P.O.1.1 and Order TED/749/2020 were reached. It also identifies two “forced oscillations” possibly caused by internal anomalies in certain plants, and three events involving generation loss due to erroneous tripping.

Voltage control: breach of P.O.7.4

Both texts highlight a breach of Operating Procedure 7.4, which mandates that certain installations regulate voltage dynamically. According to the Committee, some plants scheduled via technical constraints failed to follow instructions—one even injected reactive power when it should have been absorbing it, further increasing the voltage.

REE specifies that generation units subject to P.O.7.4 failed to absorb reactive power as required, emphasising that its calculations assumed all plants complied with technical obligations—thus placing responsibility on the service providers.

Operational availability: a critical omission

The MITECO report indicates that of the 10 units scheduled for dynamic voltage control (three nuclear, seven combined cycle), one was declared unavailable on 27 April due to a fault and was not replaced, reducing effective capacity at a critical time. This operational gap is not acknowledged by REE, which asserts that the active units provided sufficient inertia, power flow control and voltage support.

Inertia and frequency: a point of consensus

Both reports agree that the collapse was not caused by frequency or inertia issues but by a severe imbalance in reactive power. REE confirms that, thanks to technical constraints, the system had inertia levels above ENTSO-E recommendations, ruling out a frequency dynamic failure.

Interconnection role: effective measure according to OS

REE underscores the effectiveness of the HVDC link between Santa Llogaia (Spain) and Baixas (France), which was switched to fixed power mode per its protocol with RTE, the French operator—an action that mitigated oscillations without severing European support. This operational measure is not detailed in the MITECO report, which instead highlights the structural need to reinforce the interconnection with France.

System defence and evacuation grids

System defence mechanisms activated as expected, though REE warns they are not designed to isolate incidents of this scale. It recommends reviewing overvoltage protection settings in generation evacuation networks to avoid incorrect tripping. These aspects are not discussed in detail in the ministerial report.

Recommendations: contrasting approaches

The Committee proposes regulatory actions to reinforce technical oversight, implement P.O.7.4, expedite the rollout of storage and demand response, and improve system governance. The document will be forwarded to the CNMC and other regulatory bodies, potentially leading to judicial procedures over technical responsibilities.

REE puts forward 15 operational recommendations, including:

• Creation of a universal dynamic voltage control service
• Review of overvoltage tripping settings
• Expansion of system observability
• Mechanisms to mitigate sudden energy fluctuations

The release of both reports reveals a shared technical diagnosis of critical factors, yet exposes a clear methodological and narrative divergence. 

The 28-A Committee adopts a broader, preventive perspective, while Red Eléctrica defends its procedures and shifts the focus to non-compliance by certain generation facilities.

Both versions are now under CNMC review and may trigger technical and regulatory reforms with direct implications for the market, generators, and the system operator itself.

Sector reactions to MITECO and Red Eléctrica reports

The simultaneous release of the Government and System Operator’s reports has triggered intense technical and institutional debate. Energy sector academic Alejandro Diego Rosell summarised the differing approaches succinctly: “Same causes, different culprits.”

While MITECO portrays a systemic failure—insufficient synchronous generation, poor voltage management, massive renewable tripping and lack of real-time data—REE attributes the origin to a forced oscillation caused by a photovoltaic plant in Badajoz, and flags non-compliance with regulations and misconfigured protections.

The exchange of blame extended to the media: Iberdrola labelled REE’s management “reckless and negligent,” following statements by REE’s president Beatriz Corredor and technical director Concha Sánchez, who claimed that power companies submitted incomplete or confidential data, obstructing the investigation. 

At the heart of the dispute is the enforcement of P.O.7.4 and the activation of backup thermal generation in response to early alerts.

From the private sector, Carlos Martín Graña, Operations Manager at Enerjoin Spain, criticised the confidentiality of the ministerial report and the lack of named accountability. He also pointed to uncontrolled self-consumption, an overly meshed grid, and sluggish regulation on voltage control via power electronics in solar plants as factors contributing to system fragility.

These reactions reflect a shared technical consensus around voltage imbalance as the root cause, but also reveal a schism in anticipation, management and institutional response. With the CNMC now assessing the reports and possible sanctions under review, the debate moves into a regulatory—and potentially judicial—phase.