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On 04/28/2025, Spain experienced a major grid collapse that affected large swaths of the country and raised important questions about how far and fast we can push toward 100% renewable energy without overhauling the underlying infrastructure that supports it. While investigations are ongoing, initial data suggests a confluence of high renewable penetration, technical misconfigurations, and insufficient grid resilience played key roles in the blackout.
As of the incident, Spain was running with more than 60% of its generation from solar energy — an impressive milestone on paper, but one fraught with hidden risks. Renewable sources like solar and wind lack the physical inertia that traditional baseload assets (like gas, coal, or hydro with large turbines) provide. This inertia is critical for stabilizing frequency and absorbing short-term shocks. In its absence, even a small disturbance — be it from a voltage oscillation, cloud cover, or equipment misfire — can trigger a cascading system failure.
That appears to be what happened here. Reports and data from Spanish grid operator REE and third-party frequency monitoring indicate that frequency oscillations began building in the minutes before the event. When a voltage excursion occurred near the Aragon-Catalonia corridor, inverter-based solar generators — many configured in grid-following mode rather than grid-forming — began to disconnect en masse. This sudden loss of generation pushed the system into freefall. Protection relays tripped. Transmission lines disconnected. Even Spain’s nuclear fleet shut down to avoid damage. France and Portugal islanded themselves to avoid being pulled down with it.
So while the proximate cause appears to be inverter misconfiguration and lack of inertia, the root issue is broader: Spain’s grid was carrying a structurally unbalanced portfolio of resources. Over 60% of supply was tied to non-firm, inverter-based generation, without sufficient baseload supply, dispatchable spinning reserve or hybridized assets to buffer it. The volatility of the top tranche of solar output — especially in good weather — creates a “tail risk” scenario where small forecasting or control failures can quickly snowball.
Spain is not alone. We’ve seen similar events in Texas, South Australia, and Brazil. In each case, over-reliance on inverter-based renewables without supportive grid architecture led to instability. It is not a condemnation of renewables — but a clear signal that we must treat renewables as a fundamentally different class of generation, one that demands better orchestration, smarter markets, and investment in firming capacity.
According to data from Spain’s grid operator, Red Eléctrica de España (REE), the electricity mix at the time of the outage was approximately:
• Solar photovoltaic (PV): 59%
• Wind: 12%
• Nuclear: 11%
• Other sources (including hydro): 13%
• Natural gas: 5%
We warned about the possibility of such events in our previous writeup back in January of this year:
- “The bad news — As more wind and solar farms are added, the challenges associated with renewable integration worsen. Additional peak supply is often pushed into illiquid short term markets, leading to curtailment when equivalent demand cannot be shifted within the available time window. Under current market structures, achieving high Renewable Portfolio Standards (RPS) of 30% or more could become increasingly difficult without significant changes to grid infrastructure and market mechanisms.”
- “Grid upgrades present another major challenge. Modifying the grid is both economically and politically sensitive, requiring careful planning over a long timeframe. A shift from a baseline-load-focused market to one that prioritizes on-demand flexibility would require massive investments in transmission capacity, spinning and non-spinning reserves, and other ancillary services. Such a transition carries risks, including grid instability issues like Area Control Error (ACE), brownouts, or worse.”
So what should have been done differently?
- Curtailment protocols: Operators should preemptively curtail the riskiest 20–30% of solar output during times of low demand and high renewable penetration. Not all MW are equal — tail production is disproportionately volatile.
- Portfolio (re) structuring: Solar and wind bids should be aggregated and structured with complementary assets (like hydro, batteries, or demand response) to create stable, dispatchable blocks as well as allow for participation in baseload supply.
- Increased reg up and reg down capacity: Increasing regulation up and down capacity is necessary, but it comes with trade-offs. Unfortunately, much of the ancillary services market — including these regulation reserves — is still dominated by non-renewable sources like natural gas, which can conflict with Renewable Portfolio Standard (RPS) targets.
- Increase the overall inertia of the system: Similar to previous point, operating a grid with solar or other renewables making up 50% or more of the supply stack requires a corresponding increase in spinning reserves to provide the inertia needed for grid frequency stability under such conditions. Inertia requirements should be well known and maintained for system stability prior to scheduling and dispatch of renewables.
- Inverter standards: Grid-forming inverters must become the default, not the exception, especially as systems cross the 50% renewable threshold.
- Infrastructure modernization: Market mechanisms and SCADA controls must be upgraded to accommodate second-by-second balancing needs.
At Digital Wind, we view this not as a failure of clean energy, but an opportunity to improve overall system design. Our mission is to enable a firm, dispatchable and reliable renewable grid — one where events like Spain’s blackout become less likely, not more.
In summary, the future isn’t just about adding more renewables. It’s about building the systems that can handle them.
