Even as most in the solar industry remain tight-lipped about the ongoing investigation into the blackout that plunged the Iberian Peninsula into darkness at the end of April 2025, a palpable undercurrent of unease over any potential long-term fallout can be detected.

Brussels and other national capitals could come under immense pressure to fast-track stricter technical and regulatory requirements for solar photovoltaic (PV) systems to reduce grid instability risk. “The blackout issue is on everyone’s mind; there is awareness now,” a solar-industry source said at the Intersolar conference held in early May.

The Iberian event undeniably raised concerns of a public backlash against renewable energy and exposed the vulnerabilities of a modern power grid operating with high levels of inverter-based renewable generation that provides limited traditional inertia to act as a shock absorber, further compounded in Spain and Portugal by structural limitations like weak cross-border interconnection.

The solar industry is pushing back, pointing out the need for grid reform.

Compliance Cost

Expect swift moves to mandate “grid-forming” inverters to stabilize renewable energy connections to the grid. This technology is already being embraced by London and Berlin to force renewables to act less like a disruption and more like a dependable power player, said Marc Cheah Mane, an academic researcher from the Universitat Politècnica de Catalunya in Spain.

“As far as I know, they are not being implemented at large Spanish power plants,” Mane said.

The device will provide intermittent solar with “inertia” that will help it resist quick changes to grid frequency and run at a steady pace (typically 50 Hz for the Continental Europe Synchronous Area), acting as a shock absorber when disturbances occur. Otherwise, it is possible to overload equipment and trigger safety shutdowns.

The question is whether the lack of that traditional inertia made the Spanish grid more vulnerable to frequency changes, that is, “oscillations” on April 28, and flipped those cascading safety switches one by one. Experts note that renewable integration without these inverters is just one potential reason for grid instability. Others include weak links within the grid itself or a sudden loss of power generation.

In contrast, Spain’s widely deployed “grid-following” inverters passively follow the grid’s existing frequency, leaving the grid to manage its own stability during sudden oscillations. Meanwhile, power oscillation damping controllers to damp existing low-frequency modes are another option and already part of the Spanish grid code, Mane said, but they proved not to be enough to prevent the blackout.

Brussels’ reluctance to mandate grid-forming inverters bloc-wide stems from a confluence of factors, including the nascent technology’s cost, the heterogeneity of member states’ grid infrastructure, and a preference for slower but market-driven adoption. But this could be set aside after the recent incident.

There definitely needs to be market incentives for ancillary services. “In the UK, renewables and storage providers are increasingly expected to participate in services like frequency response, voltage regulation, and even synthetic inertia,” Pratheeksha R, a power and renewables analyst from Rystad Energy, said. “Recently, the UK connected its first grid-forming battery in Scotland as part of the Stability Phase 2 Pathfinder programme.”

Germany’s BSW-Solar expressed confidence in its grid’s stability earlier in the year, citing existing regulatory (System Stability Ordinance, Solar Peak Act) and technical (advanced inverter functionalities and smart meter rollouts) measures.

A potential surge in EU grid stability compliance, though transforming solar from a potential grid challenge into a stabilising asset class, will also likely elevate capital expenditures for solar operators. Stability requirements are, therefore, bound to become a critical initial investment consideration.

Energy storage is another provision required for grid stability. “Spain has already launched an investment subsidy scheme for storage projects co-located with wind and solar, and plans to launch the capacity market auctions later this year,” Pratheeksha R said.

Open Investigation

The Spain-Portugal blackout prompted Europe’s grid operators’ association ENTSO-e to order an expert panel investigation into the incident’s root causes, as mandated by EU law for “such an exceptional and grave incident.”

Spain-Portugal Blackout Investigation

• Initial Catalyst
  • Power generation was disrupted twice in southwest Spain (details under investigation by ENTSO-e)
• System collapse (3.5 seconds later)
  • Major oscillations emerged (Possibly exacerbated due to a lack of inertia from majority renewables grid mix, details under investigation by ENTSO-e)
  • Oscillations potentially threatened to overload equipment
  • Grid instability triggered safety shutdowns
  • French interconnection is disconnected by France’s grid operator RTE
  • A large portion of renewables is disconnected, resulting in final blackout

Sources: Marc Cheah Mane, academic researcher, Universitat Politècnica de Catalunya; Pratheeksha R, renewables analyst, Rystad Energy

Furthermore, ENTSO-e will provide regular updates to the EU Commission and EU Member States, including progress reports of the investigation to the Electricity Coordination Group.

Regarding what happened to cause the blackout, one description comes from Spain’s utility provider Iberdrola, which states that at the time of the incident: “…detected anomalous oscillations in the grid that made it difficult to stabilize, which led to the automatic decoupling of various installations in the system.”

However, it is noted that the initial disruption that acted as the catalyst of this domino effect is still under investigation and is expected to take months to uncover. “In the southwest of Spain, in particular Extremadura, there are large PV power plants. However, we don’t know yet if one of those plants tripped,” Mane said. The root cause might have even been outside of Spain, as a large 0.21Hz oscillation observed between the Iberian Peninsula and the Baltic countries before the event needs to be investigated.

Defending Solar

Regarding the Spanish grid’s renewable electricity share at the time of the blackout, trade association SolarPower Europe stated: “At the moment of incident, solar PV and wind were only supplying 80% of the Spanish electricity demand.” They also noted that the level of renewable contribution was not unusual for Spain, and solar and wind have often reliably served the Iberian Peninsula at equivalent or higher levels.

Mane emphasized that grid operators like Spain’s REE and Portugal’s REN conduct extensive modelling studies to account for scenarios with a high level of renewables, and therefore, this incident was probably caused by a specific and maybe unforeseen cause.

Generally speaking, despite the technical vulnerability due to lack of inertia, the chances of such an event happening because of the nature of renewables are actually considered low, he said.

“I would characterize the risk as medium, especially in systems with high renewable penetration and limited interconnection capacity,” said Pratheeksha R. The generation mix in each country played a significant role in the blackout, Rystad Energy maintained in an analyst’s note. “France’s nuclear fleet, however, provided steady baseload generation throughout the event, giving it the ability to respond swiftly once interconnectors were re-engaged.”

Nonetheless, ENTSO-e highlighted the rapid restoration efforts by national grid operators REE and REN. The real-time monitoring done by the European Awareness System platform was also crucial.

In a joint statement, big players in the solar world such as SolarPower Europe, Spain’s solar association UNEF, and the Global Solar Council asserted that photovoltaic technology is mature, fully compliant with grid codes, and capable of providing stability services. They emphasized that solar plants did not “voluntarily disconnect” but were disconnected by the grid instability resulting from the initial, still unexplained, generation loss events.

The big solar players are, in turn, pressing Brussels to mandate policies that empower renewables, like solar, to actively manage grid voltage and frequency – coupled with a bloc-wide EU Storage Action Plan and faster permits for hybrid solar PV-energy storage facilities – as technology evolves fast amidst these challenges that threaten investor confidence.