The massive blackout in April 2025 that left millions in Spain and Portugal without power was an illuminating wake-up call. It exposed the challenges of managing power grids that rely heavily on solar energy but lack enough stable, grid-supporting base load.  

The failure originated with a cascade of breakdowns in power plants across southwestern Spain, just as solar photovoltaic (“PV”) systems, which convert sunlight directly into electricity, were supplying the bulk of the region’s power. The incident spotlights the pressing need for advanced grid control technologies in renewables-dominated systems, as well as the importance of infrastructure upgrades. 

The April blackout, as noted by an international investment banker, taught us a dark truth: the challenge isn’t simply generating enough electricity but managing how all these different sources work together on the grid. The banker from a prestigious financial institution pointed out that although there are built-in redundancies, “Transmission System Operators (“TSOs”) today struggle to fully control output from the wide variety of energy sources feeding the system.” One major hurdle? Many renewables like solar and wind are asynchronous, meaning they don’t naturally sync up with the grid’s heartbeat. That’s very different from traditional synchronous generators, like hydropower or thermal plants, which inherently help keep the grid stable and balanced. 

“Transmission System Operators (“TSOs”) today struggle to fully control output from the wide variety of energy sources feeding the system.”

Investment banker, Madrid

Because asynchronous generators require power electronic equipment to “convert” their output to synchronous grid power, and since this equipment itself relies on electricity failures, it can cascade rapidly when the system is overly dependent on these sources. In the Iberian blackout, existing backstops failed to isolate issues locally, causing a broader grid collapse. The investment banker elaborated, “More work can probably be done on how we convert asynchronous generators like solar and wind to synchronous generators that provide baseload power.” There is a core vulnerability in grids heavily dominated by asynchronous renewables without sufficient synchronous inertia or control mechanisms. 

To address these risks, the system needs enhanced control technologies alongside infrastructure upgrades. Battery storage is a critical part of the solution, especially given the intermittency of solar and wind power. As a renewable energy consultant emphasised, “the higher your reliance on intermittent renewables like wind or solar, the more you need reliable battery storage systems.” Batteries can provide fast-response frequency regulation and supply power during generation shortfalls, smoothing out fluctuations. 

Moreover, integrating grid-forming inverters that provide synthetic inertia will help solar and wind plants behave more like synchronous generators, enhancing frequency control and grid synchronisation. This operational upgrade, combined with real-time advanced monitoring and predictive analytics, can enable TSOs to better anticipate and respond to disturbances. 

Our sources also highlighted the importance of having sufficient backup and redundancy. While transitioning away from fossil fuels is necessary, phasing out non-renewables must be balanced to maintain system reliability. Backup generation and ringfencing (isolating parts of the grid to prevent cascading failures) can serve as vital “backstops” to contain disruptions. 

The blackout also throws into sharp relief the role of cross-border interconnections. Spain’s grid is interconnected with Portugal and France, but its links to France, in particular, have been historically limited. Interestingly the investment banker argued “that the cross-border infrastructure worked very well, at least in the case of France” and helped shorten the blackout durations there. However, Portugal’s weaker infrastructure meant it couldn’t disconnect quickly from Spain during the event, resulting in longer outages. 

The consultant also agreed that existing cross-border infrastructure is largely adequate, noting that European Transmission System Operators already work closely together to coordinate grid demand through the European Network of Transmission System Operators (“ENTSO”). The renewable energy consultant added, “The time it took to jumpstart the system again means there is at least some chance of foul play, perhaps through a cyber-attack.” 

“The time it took to jumpstart the system again means there is at least some chance of foul play, perhaps through a cyber-attack.”

Renewable energy consultant, UK

Policy-wise, Spain and Portugal must love thy neighbour and continue working closely with European partners to enhance grid resilience through coordinated planning, shared reserves and emergency protocols. Expanding High-Voltage Direct Current (“HVDC”) interconnectors to France and beyond will provide additional security buffers, especially as renewable capacity grows. 

The April 2025 Iberian blackout offers valuable insights into managing grids with high solar PV penetration. A key lesson for energy players, as noted by the international investment banker, “is that there isn’t a lack of generation sources but a lack of control over the grid infrastructure.” To ensure grid stability, energy systems must adopt advanced operational tools such as battery storage, synthetic inertia and real-time monitoring, alongside maintaining balanced backup capacity during the transition away from fossil fuels to stay out of the dark age.