Facts and lessons learned from the Iberian blackout

The Iberian blackout on April 28, 2025, has sparked a heated debate about its root causes and consequences, with discussions often shaped by competing perspectives. In this article, we first explain the basics of electricity grid transport, providing a foundation to analyze the facts and some of the opinions surrounding this unprecedented event. We then compare the Iberian situation with the circumstances in the Netherlands, highlighting key similarities and differences. Finally, we offer our perspective on the potential changes that must be made in the energy sector based on the lessons learned from the blackout.

An electricity system consists of three main components: electricity generation (power plants, wind farms, solar PV, etc.), load (industry, households, exports, etc.), and a power grid that transports electricity and connects the two (see figure 1). These components must operate together seamlessly to ensure reliable electricity delivery.

Electricity system operation is highly complex. Electricity production and consumption must continuously match, transmission must stay within grid limits, and voltage and frequency must remain stable. For example, standard household outlets consistently deliver 230V at 50Hz. However, producers and consumers independently decide when to generate or use electricity.

To maintain stability, electricity supply, demand, and transmission are coordinated through multiple markets and grid services. Failures within these systems can create imbalances, potentially leading to power outages or blackouts.

Imbalances between supply and demand cause deviations in voltage and frequency, prompting parts of the grid to shut down. Usually, shutdowns are intentional to avoid infrastructure damage, with service restored quickly. Severe deviations, however, can physically damage grid components, resulting in extended outages.

Outages stem from various issues, including excessive demand, infrastructure damage, severe weather, or cyberattacks. Typically, localized faults are isolated, allowing the broader grid to remain operational. Blackouts occur when the broader grid cannot absorb a disruption, either due to simultaneous multiple faults or insufficient operational safety margins. A cascading series of outages can escalate into a total blackout.

The integration of renewable energy sources, such as wind and solar, increases operational complexity due to their intermittent nature. Matching supply and demand becomes a greater challenge for grid operators. Additionally, solar and wind installations lack inertia, a natural property of conventional fossil-fueled power plants that helps absorb sudden imbalances. These factors increase the likelihood of grid imbalances and potential power outages.

To address these challenges, grid flexibility is crucial. Electricity storage systems, such as pumped hydro and battery energy storage, can partially offset variability and reduced inertia by storing excess energy during periods of abundant renewable generation and releasing it during peak demand. Batteries are particularly effective at rapidly injecting and extracting electricity, allowing them to mimic the inertia provided by traditional generators. Additionally, interconnectors – transmission lines linking different electricity grids – —provide further flexibility by facilitating the transfer of surplus energy between them. Many countries are increasingly investing in these flexibility measures to accommodate higher shares of renewable energy.

The Iberian electricity system features a high share of renewables, limited interconnection capacity, and a relatively slow rollout of battery energy storage systems, as we describe in this article. This combination increases the overall risk of power imbalances and potential outages. However, it is important to note that these factors alone do not necessarily cause blackout, and each incident must be evaluated based on its specific context and contributing events.

The blackout led to a heated debate

At 12:33 on April 28, 2025, the Iberian Peninsula suffered a blackout that left both Spain and Portugal without electricity for a half a day. In response, the two network operators carried out an exceptionally complex technical operation to restart their electricity systems in record time, managing to restore service to meet nearly 85% of expected demand by midnight. For the rest of the article, we will focus in Spain, where the critical events originated.

The blackout triggered intense debate across media channels about its cause, with opinions deeply polarized. Some placed the blame on renewables, arguing that the operation of the Spanish grid was overwhelmed by too much variable renewable generation. Others claimed that nuclear plants experiencing disconnections from the grid could be behind the oscillations detected before the blackout. Somewhere in the middle of these opposing views were a range technical partial explanations, each shaped by the corresponding expert’s own area of knowledge. The real experts all agree on one point: The reaction of such a complex system cannot be understood simply by analyzing the behavior of one of its individual components.

The divided responses are not surprising, given Spain’s politicized path to renewable energy. As far back as 2000, following the approval of Spain’s National Plan for the Promotion of Renewable Energy, alarmists were insisting that the Spanish grid would never be able to accommodate more than a 10% share of wind generation. Since the blackout, those voices, which had been consistently renewing their call that it is “impossible to accommodate this share of renewables” have resurfaced, claiming they “had warned us.” Now, with more than 80% variable renewable penetration during specific hours during the day, grid operators may indeed need to reconsider its limits.

What are the facts?

The timeline in figure 2 presents the key confirmed facts at the time of writing. There have been reports of various operational conditions occurring from some days to just before the incident: faults in power generation plants (including a nuclear plant in France (link in French)), voltage oscillations, frequency variations across the European grid, and even some industrial customers being disconnected.

Source: ENTSO-E, Spanish Ministry for the Ecological Transition, Polytechnic University of Madrid, RaboResearch 2025

As shown in figure 2, prior to the critical fault sequence, a substation in Granada experienced the first loss of generation at 12:32:57. Normal operation apparently resumed quickly. The subsequent three events, which are currently being investigated as the root cause of the blackout, resulted in the loss of three critical elements in succession (N-3). No grid is designed to withstand such a rare sequence of critical failures, since the likelihood of this happening is extremely low, and the costs of safeguarding against such an occurrence would be prohibitively high.

The sequence began at 12:33:16 with a loss of generation capacity in the Spanish province of Badajoz. Unable to recover, the system suffered a second loss just two seconds later in the region of Sevilla. These events resulted in a combined loss of 2.2 GW within 20 seconds, causing the system frequency to drop below 48Hz. This frequency drop triggered automatic protective mechanisms, leading to the disconnection of the French grid from the Iberian Peninsula. The separation then cascaded into a widespread generation failure, ultimately resulting in the total blackout.

While the urgency to explain the blackout has led to various theories linking any anomaly to its root causes, analyzing such phenomena in isolation carries a high risk of misdiagnosis. Only coordinated agents with combined access to all of the data can establish whether there is a causal relationship between the operational data and the true sequence of events. For instance, say a factory connected to the high-voltage network detected grid oscillations. Only a central operator confronting that signal alongside the others in the system, with their respective timestamps, could identify that those oscillations in sequence had triggered the system protections or other deviations.

At the time of writing, the root causes of the Iberian blackout remain under official investigation by Redeia and monitored by ENTSO-E, according to the European protocol. To fully understand the reasons behind the blackout, this complete systems analysis will be essential.

The operation of the Spanish network, carried out by Redeia, has been an extreme and, so far, successful case. Despite Spain’s very limited interconnection to the EU grid, the Spanish transmission system operator (TSO) has been consistently integrating the highest share of renewable energy with the lowest share of curtailment, as the IEA found. Moreover, according to BloombergNEF’s Energy Transition Investment Trends in Europe 2025 report, it has done so with one of the lowest grid-to-clean-power investment ratios in the EU, as illustrated in figure 3. While this efficient use of resources may be approaching its limits, history has shown that a high share of renewable energy is often hastily blamed for blackouts. A notable example is Germany’s 2006 blackout, where initial assumptions incorrectly pointed to high renewable penetration as the cause.

While we wait for the results of the official holistic investigation, it is clear that this event will prompt important reflections on grid operation in Spain. The country’s remarkable efficiency in variable renewable integration – despite minimal investments and limited interconnection – may have reached a turning point. But, history has proven that further renewable integration is possible with the right investments, a review of technical procedures, and increased interconnection capacity.

While the Iberian Peninsula faces operational challenges due to its low interconnection capacity with the central European grid, that doesn’t mean that countries in central Europe are shielded from events like blackouts. Compared to Spain’s 8% interconnection capacity, a central European country like Netherlands reaches almost 48% of its peak demand as interconnection capacity from neighboring countries. But even this level of integration within a greater network does not guarantee that blackouts are impossible.

A nationwide, long-duration blackout in the Netherlands is very unlikely, but not impossible

The Dutch electricity grid is among the most reliable in Europe. In 2023, on average, households and businesses only experienced 22 minutes of power outage.[1] To date, a nationwide blackout has never occurred, but that doesn’t mean it could never happen.

Table 1 shows that the Netherlands, like Spain, has a lot of installed renewable energy capacity (solar and wind). However, the Netherlands has more installed battery energy storage system (BESS) capacity and interconnector capacity than Spain. This makes the Dutch electricity grid more robust. Also, the Netherlands has higher installed thermal capacity than peak demand, which is not the case for Spain.

[1] Source: Energienet ook in 2023 99,99 procent betrouwbaar | Netbeheer Nederland

*Note: Dispatchable production includes thermal power plants and hydro, excluding nuclear.
Sources: TenneT, CBS, ENTSO-E, Red Eléctrica, RaboResearch 2025

Chances of local, short-term power outages are increasingly likely

There are some concerns about the security of supply of the Dutch electricity system in the longer term, as some existing thermal capacity is likely to leave the system. TenneT says it is possible that after 2030, non-solar and wind capacity will be insufficient to meet demand for some hours a year. If this happens, system operators could temporarily shut down electricity to supply to some consumers to balance supply and demand. The Netherlands has an energy-only market and not a capacity market, which makes it less interesting for thermal power plant owners to keep their facilities on standby.

Additionally, the Netherlands is suffering a lot from power grid congestion. In certain regions, the problem has become so severe that system operators have warned that regular, short-term power outages are no longer unlikely. This is specifically the case for the Utrecht province. The provinces of Gelderland, Noord-Holland, and parts of Flevoland are also dealing with severe offtake power grid congestion.

No matter the outcome of the official analysis of the Iberian blackout event, some consequences can be certainly expected.

While future blackouts cannot be entirely ruled out anywhere in the EU, their likelihood is expected to decrease due to anticipated preventive measures and lessons learned from past incidents. The operation of the Spanish grid will be reviewed and adjusted with a more conservative approach. Data from the ENTSO-E platform already suggests an increasing share of generation contributing to system stability.

We are likely to witness an accelerated rollout of BESS and other grid-supporting technologies, such as synchronous condensers equipped with flywheels. In Spain, the regulatory pipeline already includes several significant proposals that are nearing approval. Recent developments will only expedite their implementation. In particular, we expect the establishment of a capacity market to gain urgent priority, with the introduction of fast-responding capacity now appearing more likely than ever.

Regarding energy prices, the operation of the grid after the blackout is expected to increase the cost of technical restriction resolution’s mechanism. These are corrections that the TSO implements in the market’s results for the day ahead, to ensure safe operation of the grid. However, this is unlikely to impact the European power price benchmark for the Iberian Peninsula. Renewable energy projects currently in the pipeline may undergo review. However, due to the evolving market conditions, we anticipate that only those facing significant challenges will not hold up to scrutiny.

Support from national and European policies – particularly through power purchase agreements (PPAs) and contracts for difference (CfDs) – is unlikely to weaken. On the contrary, it may even be strengthened. These developments will likely add to the growing body of evidence supporting the need for comprehensive reform of the electricity market, including changes to adequately compensate for the varying systemic value of different generation technologies.

Pressure on France to significantly expand interconnection capacity will be stronger than ever. However, France has demonstrated steadfast resistance in this area, often going to great lengths to protect its national nuclear interests.

As widely reported in the press, the Iberian blackout has reignited the nuclear energy debate – even though, without knowing the root cause of the blackout, it remains unclear whether a greater reliance on nuclear power could have prevented this blackout or future disruptions. Energy companies are likely to explore new opportunities in this space, which may also lead to spillover effects for natural gas combined-cycle plants, some of which are nearing the end of their technical lifespans.

Overall, we do not foresee a significant negative impact on the renewable investment pipeline. If anything, we expect a positive effect on grid-supporting technologies. Variations in these investment flows are more likely to be driven by changes in domestic demand than by fears of lasting deterioration in grid operations. As with previous disruptions, we hope this rare event will ultimately serve as a catalyst for positive change in the ongoing energy transition.