TOPIC #6
SEPA Portugal Factfinding Mission and Lessons from a Blackout
An energy system factfinding visit generates thoughts on requirements for a high inverter-based resource grid.
SEPA Portugal Factfinding Mission
The Smart Electric Power Alliance (SEPA) is a leading industry organization focused on accelerating the electric power sector’s transformation to a modern energy future through convenings, education, research, collaboration, and insights.
- One recurring activity is the annual factfinding mission, which involves member visits to selected regions of the world and learning from grid operators, utilities, and regulators about trends in grid development.
- In October 2025, ScottMadden and a delegation of SEPA members went to Portugal, seeking to learn about impacts of its rapid and growing integration of renewable energy.
Renewable electricity supplied 85% of Portugal’s energy demand in 2024. Significant solar and wind capacity as well as 8 GW of pumped storage hydropower comprise much of the resources, with natural gas playing a limited and flexible role.
A major blackout on the Iberian Peninsula on April 28, 2025 (the “Iberian blackout”), dominated the discussion during the factfinding trip. Originating in Spain, the Iberian blackout lasted more than 10 hours in some areas and affected 55 million people. A summary of key events is shown at Figure 1.
FIGURE 1
Timeline of the Iberian Power System Disturbance (Apr. 28, 2025)
Sources: SEPA and ScottMadden, Operational and Market Design Lessons from a High-IBR Grid (Mar. 2026)
Key Takeaways
ScottMadden joined SEPA in traveling to Portugal and studied how a high inverter-based grid operates.
The visit took place within months of a spring blackout on the Iberian Peninsula in which voltage control and a lack of reactive power led to cascading grid failure.
A key theme from the Portugal factfinding was that in low-inertia environments, conventional methods of grid operation must change, requiring new tools and models, increased visibility into local systems, and increased resource flexibility with compensation and requirements to incentivize it.
Final Expert Report Findings on the Blackout
The European Network of Transmission System Operators for Electricity (ENTSO-E), created under European Union law, provides technical coordination among European transmission system operators. ENTSO-E released a detailed study of the events and causes of the Iberian blackout and provided recommendations (ENTSO-E Report). Root cause events were largely concentrated in Spain.
The report identified the critical issue of voltage control and the failure of or lack of conventional resources to deliver reactive power that would absorb voltage changes (and no economic consequences). The report identifies several other causes that affected response to system conditions, including:
- Manual operations: Manual shunt-reactor switching, which required decision-making and processing time
- Less flexible resources: Fixed power-factor operation for many renewable energy sources, which negated reactive power provision on voltage changes by those resources
- Unaligned designs: Local generation-network voltage-control designs not aligned with system needs and contributed to disconnections while the network was within limits
- On the edge: A narrow margin between Spain’s 400 kV wider operating range (than other EU countries) and generator disconnection thresholds
The system had reactive resources but not enough fast, visible, controllable, and effectively deployed dynamic voltage response. The report also noted that system inertia could have slightly dampened inter-area oscillations, but additional inertia would not have avoided the loss of system synchronism considering the sequencing of events.
ENTSO-E Recommendations on the Blackout
ENTSO-E prepared a set of recommendations grouped into two categories: those directly linked to root causes of the incident and those not directly linked to root causes.
As mentioned previously, the operational issues were largely within the Spanish grid operator’s purview, but this illustrates the potential adverse effects on adjacent, interconnected regions such as Portugal.
The summary table at Figure 2 shows high-priority recommendations made by the ENTSO-E expert panel. In the introduction to the recommendations, the panel stated:
“The increasing penetration of variable renewable and distributed generation, further market integration, broader electrification, and evolving environmental and geopolitical risks place the European electricity system under increasingly challenging operational conditions, requiring higher levels of resilience. The recommendations address voltage control and reactive power management, oscillatory stability, and generation disconnection behavior. They further aim to enhance the effectiveness of system defense mechanisms and the robustness and preparedness of restoration processes.”
FIGURE 2
High-Priority Recommendations of ENTSO-E Expert Panel Related to Blackout Root Causes
Note: The panel also had high-priority recommendations for non-root cause events, including improved post-event simulations and mandating realistic and periodic black start tests.
Sources: ENTSO-E
Panning Out: Lessons Learned from Portugal
While the events of the April 2025 Iberian blackout were not precipitated by the Portuguese grid, it shares characteristics of the adjacent Spanish grid with high and growing levels of inverter-based resources (IBRs).
As the SEPA/ScottMadden report on the factfinding trip observes: Portugal’s high-IBR experience demonstrates that renewable growth changes reliability needs, not just the resource mix.
- Resource adequacy alone is insufficient: stability depends on voltage control, inertia, and local system strength.
- Operators need updated models, protection schemes, situational awareness, and training for low-inertia conditions.
- Flexibility is now a reliability requirement, including storage, demand response, aggregation, and fast response.
- Markets must explicitly value reliability attributes such as reactive power, inertia, voltage support, and ramping.
- Local constraints still drive outcomes, even within integrated markets and shared operations.
For U.S. utilities, Portugal highlights the need to modernize operations, planning, and market design alongside renewable resource deployment (see Fig. 3).
FIGURE 3
Lessons for U.S. Utilities
Sources: SEPA and ScottMadden
Implications
The Iberian Peninsula’s recent experience shows that decarbonization efforts can drive rapid renewable integration but may require new tools, models, and market reforms to ensure reliability in low-inertia, high inverter-based resource (IBR) systems. Conventional grid management approaches must adapt to fast dynamics and local system strength. As IBR penetration increases, markets will need to explicitly require and value stability attributes.
With significant solar capacity in U.S. interconnection queues and some jurisdictions and utilities promoting their deployment, some regions risk facing similar system challenges as Portugal. The North American Electric Reliability Corporation (NERC), North America’s electric reliability organization, has parallel work streams under way, addressing issues such as voltage/frequency ride-through for IBRs.
Utilities, regulators, and NERC will need to continue to project, monitor, and proactively prepare for system changes as IBRs grow in penetration in the U.S. bulk electric system.
CONTACT OUR EXPERTS
On SEPA Portugal Factfinding Mission and Lessons from a Blackout
Kevin Hernandez
PARTNER
klhernandez@scottmadden.com 919.781.4191
Gerardo Morales
Partner
gjmorales@scottmadden.com 404.814.0020
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