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.

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. 

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

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.

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:

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.