“This blackout will not stop renewables; on the contrary, it will bring positive developments,” states Javier Revuelta, Senior Principal at AFRY, referring to the “zero voltage” moment on 28 April, when electricity demand dropped to zero nationwide, causing unprecedented operational and economic impacts.

The value of the unserved energy losses was estimated by AEPIBAL analysts at up to €3 billion.
This figure is based on a valuation of €22,000/MWh applied to a loss of around 138 GWh.

“Unserved energy in a single day justifies filling Spain with batteries and synchronous compensators,” says Jose Manuel Menendez, AEPIBAL advisor and executive at Alantra.

Total blackout: causes, consequences and solutions

Among the conclusions shared by experts during AEPIBAL’s Open Session, one key point stood out: at the time of the event, the system was operating under conditions considered stable for spring—high renewable penetration, low demand and reduced synchronous generation.

“From a technical point of view, the system was not experiencing anything extraordinary,” clarifies Chema Zabala, advisor at Alantra.

While the exact causes of the blackout have yet to be confirmed, experts agreed that it likely involved a combination of frequency and voltage oscillations, as well as cascading disconnections of photovoltaic inverters. “What has been ruled out is that PV itself was to blame,” Revuelta adds.

From a technical standpoint, inverters—especially grid following types—cannot initiate oscillations, as they follow the frequency and voltage of the existing grid. However, their ability to respond to disturbances is limited.

“Without firmware updates or enabled services, they simply disconnect,” explains Eugenio Domínguez, Vice-President of AEPIBAL and CEO of Hesstec.

The role of storage and grid forming

Storage is emerging as an essential component for avoiding similar blackouts. Experts distinguished between two types of battery needs: large-scale batteries for renewable integration, and smaller, smarter, distributed batteries for responding to critical oscillations within milliseconds.

“We must distinguish between volumes, location and type of response. Spain needs both: batteries for renewable integration and others for local, fast-acting stability,” argues Revuelta.

Grid forming technology is central to this equation. Unlike current systems (grid following), it allows the inverter to act as a generator of voltage and frequency, providing synthetic inertia and active control.

[Recommendation: Grid Forming: the key to a stable and secure 100% renewable system]

“These solutions can prevent the system from drifting in frequency or voltage, and avoid cascading effects like those of 28 April,” stresses Domínguez.

In this context, both reconfiguring the system’s operation and updating the existing inverter fleet appear increasingly urgent.

New markets for new services

To enable the implementation of these technologies, it will be crucial to create dedicated remuneration mechanisms, warns Pedro Basagoiti, Director of Technology, Innovation and New Developments at OMIE.

“Storage can act as both generation and demand, which is essential in critical moments,” he highlights.

There are already international precedents, such as in the United Kingdom, where grid forming projects participate in inertia and stability markets. 

In contrast, Spain still lacks a defined framework for remunerating services like damping, synthetic inertia, and local voltage control.

The creation of a specific stability market and the development of appropriate price signals are essential steps.

“Storage cannot rely solely on energy arbitrage—it must be recognised for delivering advanced, localised services,” assert sources at Alantra.

Unanimous opinion: renewables are not the problem

All the experts were clear in exonerating renewables as the cause of the blackout. 

“The issue is not having 18 or 27 GW of PV capacity. The issue is which tools we have to ensure it behaves properly during a fault,” explains Revuelta.

The system’s vulnerability stems from a lack of stability tools—not from renewable generation itself. The technology, they insist, already exists. What is missing is its implementation, scaling and funding.

“The energy transition needs both technical and financial support. It’s no longer just about integrating renewables, but also about keeping the system running during critical events,” concludes Domínguez.