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Blackout in Spain | Vulnerability of electricity systems and the critical role of back-up power systems

The massive blackout, which took place on Monday 28 April, affected 60 million people in Spain and Portugal, as well as a multitude of infrastructures, leaving the inhabitants of the entire peninsula without power supply.

The massive blackout, which took place on Monday 28 April, affected 60 million people in Spain and Portugal, as well as a multitude of infrastructures, leaving the inhabitants of the entire peninsula without power supply.

At 12:33 a power outage occurred due to a severe fluctuation in the power flows within the electrical grids, resulting in a drop in electricity generation. At that moment, 15 gigawatts of electricity generation suddenly dropped out of the system: according to government sources, this represents 60% of the electricity being consumed across the country.

Since the event occurred, several hypotheses have been proposed regarding the root cause of the outage. Described as an unprecedented “energy zero” in Spain, the Director of Grid Operations Services at Red Eléctrica, Eduardo Prieto, classified the incident as an “absolutely exceptional event—something that had never happened before.”

This crisis has exposed the inherent vulnerability of electrical systems and underscored the critical need for reliable and readily available backup power solutions. In this article, we examine the international regulatory context, available technological responses, and industry best practices aimed at ensuring continuity of electrical supply during grid failure events, drawing upon the real-world insights gained from this incident.

Timeline of the crisis

The power supply was progressively restored during the early afternoon of April 28 in specific areas of northern Spain. According to sources from Red Eléctrica, the entity responsible for managing the national electricity supply, work on restoring the power supply began in areas of northern Spain close to France.

12:56	14:30	14:50	17:30	18:45	23:00	7:00
Red Eléctrica releases an initial technical statement via its official social media channels, providing early insights into the outage.	Eduardo Prieto, Director of Grid Operations at Red Eléctrica, holds a press conference announcing that full restoration of service could take between 6 and 10 hours.	Prime Minister Pedro Sánchez convenes an emergency meeting at Red Eléctrica’s headquarters along with key cabinet members.	Power supply is gradually restored in several regions including Catalonia, Aragon, the Basque Country, Galicia, La Rioja, Asturias, Navarre, Castile and León, Extremadura, and Andalusia.	Electrical service resumes in portions of the Region of Murcia, the Valencian Community, Madrid, and Castile-La Mancha.	51% of national electricity demand has been successfully restored.	99.95% of the country’s electricity supply is fully operational.

What Happens When a Large-Scale Grid Failure Occurs?

During the blackout, the only facilities that remained operational were those equipped with UPS (Uninterruptible Power Supply) systems or standby generators.

The UPS system provides instantaneous, interruption-free power, although its autonomy is limited.
The generator starts operating after a short delay (approximately 10 seconds), taking over critical loads with unlimited autonomy.

In highly sensitive applications such as hospitals or data centers, the UPS + generator combination is essential to ensure uninterrupted operation during power outages.

Technical Flow of Events During the Blackout

Global Context: Is There a Common International Standard for Emergency Power Provision?

Currently, there is no globally unified regulation, nor even a pan-European standard, that mandates the generalized installation of backup generators in critical infrastructure. Each country, and in some cases each regional authority, defines its own backup power requirements.

In Spain, critical infrastructure is regulated under Law 8/2011 and Royal Decree 704/2011. The Low Voltage Electrotechnical Regulation (REBT) stipulates mandatory emergency systems for "public occupancy facilities", but grants flexibility in other cases.
Internationally, ISO 8528 governs sizing parameters, testing, personnel safety, and genset design criteria.
Countries such as France and the United States have their own national standards: NF E37-312 and NF S61-940 (France), and UL 2200 (USA), addressing safety levels, generator reliability requirements, and minimum operational autonomy. This latter factor is critical for the effectiveness of any backup system: it is generally recommended to store sufficient fuel for at least 24 hours of operation, with easy access for refueling.

The Role of Alternative Energy Sources: Solar, Wind, Nuclear... Were They Also Affected?

During the blackout, all grid-connected power sources, including renewable (solar, wind) and conventional (nuclear, hydro, thermal) generation, were affected either directly or indirectly.

Why?

Automatic Grid Protection Mechanisms

When a severe voltage or frequency drop occurs, power plants, regardless of type, disconnect automatically to prevent major equipment damage. This mechanism, known as “islanding protection”, ensures that generators do not operate under unstable or off-limit conditions, which could compromise expensive infrastructure.

Lack of Independent Synchronization

Large-scale renewable energy systems such as solar farms or wind parks are mostly, not designed to operate in island mode. They require a grid reference (voltage and frequency anchor) to function correctly. Without it, electronic inverters also trip offline automatically.

Nuclear and Thermal Plants

Nuclear and conventional thermal plants also disconnect when grid stability is lost. With no loads to supply and no stable grid to synchronize with, operators are required to reduce output or shut down completely. A controlled shutdown ensures a faster and safer restart process.

In the case of the blackout in Spain, only a few exceptions were reported, such as small solar installations for self-consumption or off-grid battery-backed systems. Likewise, certain critical facilities such as hospitals or data centers equipped with hybrid generation systems (e.g., photovoltaic + battery + generator) managed to stay operational by relying on their internal energy infrastructure.

Mitigating the Consequences of a Blackout: Backup Power Systems

Could expanding the use of generators beyond traditionally defined critical infrastructure be a solution? The blackout has sparked debate over the advisability of broadening the deployment of backup power systems:

Small businesses: Could benefit from generators supporting essential services (lighting, point-of-sale systems), tolerating short interruptions in non-critical loads.
Residential areas, schools, non-critical industries: Generators could sustain minimum services and prevent economic losses, even where there is no threat to human life.
Continuous-process or refrigeration-based industries: Any halt in operations could result in massive financial losses or irreversible damage, making full backup systems a justifiable investment. Properly sizing the backup system in line with the criticality of the load is key to optimizing both cost and reliability.

The Critical Importance of Preventive Maintenance

The reliability of a generator is directly tied to its maintenance status. In exceptional events such as this recent blackout, it is essential that gensets have been correctly maintained throughout their service life. A well-maintained generator can make the difference between operational continuity and irreversible damage during an abrupt grid outage. Recommended maintenance practices include:

Periodic test runs: At least once a month, to ensure proper lubrication of bearings and readiness.
Preheating systems: To ensure fast and efficient start-up under controlled temperatures.
Inspection of auxiliary systems: Including batteries, chargers, heating elements, and fuel transfer systems.

Conclusion

Massive power outages, such as the one experienced in Spain in April 2025, highlight the vital importance of having robust systems in place to mitigate their impact. While such events cannot always be prevented, their consequences can be minimized through proper planning and the use of alternative energy solutions, ensuring basic communication and critical services remain active in times of crisis.

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A key factor is infrastructure redundancy

Systems must be designed with multiple automatic supply routes capable of taking over during a failure. This concept is particularly critical for hospitals, transport systems, data centers, and telecom networks.

Generators play an essential role in emergencies by enabling autonomous electricity generation while the main grid is restored. While their use is already widespread in healthcare and public infrastructure, expanding their deployment to other strategically important sectors such as education, rural areas, or cultural and residential facilities could ensure continuity and resilience. Alternative energy solutions emphasize the importance of a generalized adaptability strategy for scenarios that can affect all of society.

Properly dimensioned and maintained backup systems (generators and UPS) should not be seen as additional expense, but as fundamental infrastructure for an increasingly electrified society. Preventive planning, strong regulation, and sector-wide awareness are crucial to building a more secure and resilient future.

HIMOINSA’s Response to the Blackout

During the incident, HIMOINSA, an international company specialized in energy technology solutions with its headquarters in Spain, activated two priority response fronts:

After-Sales Service: Reinforced on-site technical assistance at critical facilities. Most incidents were resolved swiftly and were primarily related to installation deficiencies.
Rental Service: Through HIMOINSA Energy Services (HES), the company provided emergency backup generators both directly and through its network of rental partners, ensuring energy support across multiple sectors.