Europe's Largest Blackout Exposes Grid Vulnerability
A story about Renewables, Grid Inertia, Cross Boarder Capacities and more
Executive Summary
On Monday, April 28, 2025, Spain and Portugal were hit by a complete power outage, leaving trains stranded in tunnels, office workers stuck in lifts and mobile phone services cut, in the biggest blackout in Europe for two decades and is expected to have a measurable impact on the GDP of both countries.
While the exact root cause is still under investigation, with cyberattack officially ruled out at the time of writing, a leading hypothesis is emerging: the blackout was likely triggered by critically low system inertia due to exceptionally high wind and solar penetration. This left the grid acutely vulnerable to frequency disturbances—regardless of their origin—and enabled a cascade of failures.
Just prior to the collapse, wind and solar accounted for 22 GW of Spain’s 32 GW total generation capacity. While renewables are central to decarbonization efforts, wind and solar do not contribute rotational inertia—the stabilizing force provided by the spinning mass of conventional turbines. As the share of inertia-less generation increases, the system becomes less capable of managing sudden frequency changes—which are key to maintaining grid stability and avoiding widespread outages, also known as a blackouts.
Conventional power plants—particularly those powered by nuclear, coal, gas, or oil—naturally stabilize the grid through their large rotating masses. This inertia reserve acts as a shock absorber during disturbances, buying critical seconds for system operators to react. Without it, even minor disruptions can escalate into grid collapse within one or two seconds.
The blackout’s effects were not limited to the Iberian Peninsula. France, still operating a large fleet of nuclear power plants, experienced the same frequency swing. However, its reactors’ inherent inertia absorbed the disturbance passively and immediately—preventing a wider collapse. Without this buffer, the blackout could have spread across Europe, including Germany, the Benelux countries, and beyond.
This event exposes a growing systemic risk. Countries like Germany, the Netherlands, Belgium, Denmark, and the UK have significantly reduced their grid inertia by phasing out nuclear and other conventional baseload plants. Their grids are now similarly exposed to the kinds of disturbances seen in Spain and Portugal. Without sufficient inertia reserves, frequency fluctuations can become uncontrollable—posing a clear threat to energy security.
European policymakers and voters must now confront a critical truth: the ongoing energy transition—while aimed at meeting EU climate goals—has introduced structural vulnerabilities into the grid. Without the reintroduction of large-scale, inertia-providing generation—preferably nuclear—Europe’s synchronized electricity system remains dangerously exposed to future blackouts.
As is often overlooked, electricity is not just about generating energy—it’s about timing and location too. Wind and solar technologies, while important, fail to meet the full operational requirements of a stable and affordable grid due to three fundamental challenges: (a) their intermittency, (b) their lack of inertia, and (c) their inability to provide reactive power.
We explore most of these challenges in detail in the sections below and remind our audience that this remains a preliminary assessment based on incomplete data.