Restarting a power grid after a massive collapse—known as a “black start”—is one of the most technically complex operations in power engineering. Here’s why it’s so difficult, especially in light of the recent blackout in Spain, Portugal, and southern France on April 28, 2025:
- No Power to Restart Power
When a grid collapses, most power plants go offline, and they cannot restart without external electricity. This creates a paradox: you need power to generate power. Only certain generators—typically hydroelectric or small gas turbines—are capable of starting without grid power.
- The Grid Must Be Rebuilt in Stages
Restoring the grid isn’t just about turning things back on. It’s a step-by-step process:
- Operators must synchronize frequency and voltage
- Balance generation and demand in real time
- Prevent overloads that could trigger further blackouts
If this balance is off by even a small margin, it can lead to grid instability or secondary failures.
- Limited Black Start Resources
Only a few power stations are equipped with black start capabilities, and they are often spread far apart. In regions like the Iberian Peninsula, where interconnections with the broader European grid are limited, this makes restarts slower and riskier.
- Communication and Coordination Challenges
During a massive outage, real-time data and communication systems may be down, making coordination among grid operators extremely difficult. Crews must rely on backup systems or manual protocols.
- Local vs. Regional Grids
Modern power systems are highly interconnected, meaning a failure in one part can quickly cascade. In the case of Spain and Portugal, a failure in the connection with France triggered the disconnection of the Iberian Peninsula from the rest of Europe’s grid.
Role of wind and solar in restoring the grid
Wind and solar are typically not used in the initial black start phase because they depend on weather conditions and lack the consistent, controllable output needed to stabilize the grid; instead, operators rely on hydroelectric dams, diesel generators, or gas turbines to establish baseline power.
Once the grid is stable, wind and solar can be gradually reintroduced, but their integration requires careful management to avoid frequency and voltage imbalances, a challenge highlighted by Spain’s limited interconnections and the 60% demand drop during the blackout.
Comparison to April 28, 2025 Blackout
- Spain lost 60% of its demand within seconds (~15 GW), a massive and sudden drop.
- Portugal saw 85 of 89 substations go down.
- With few interconnections to the rest of Europe, both countries had to restart from within, a difficult and slower process.
- By late evening, only partial restoration had occurred.
- France’s interconnect disruption likely triggered the collapse.
Conclusion
Restarting a power grid is like rebuilding a delicate machine with many moving parts—all at once and under pressure. The recent blackout shows how fragile even advanced energy systems can be, and how vital robust planning, backup power sources, and cross-border coordination are for energy resilience.
Vir: Cata Paul
DAMIJAN blog 