How can the power grid of a country like Spain collapse in five seconds?

Why is the cause not yet clearly identified?

The power grid is a backbone comprised of thousands of interconnected components. "Grid operators must carefully analyze huge amounts of real-time data," such as frequency changes, line failures, and the status of generating stations, "to trace the sequence of events," Pratheeksha Ramdas, an analyst at Rystad Energy, told AFP.

What are the usual causes?

Outages are often caused by the sudden shutdown of a production plant due to a technical hazard or a shortage of fuel to power thermal power plants.

In recent years, events such as storms, earthquakes, wildfires, extreme heat or cold, sometimes intensified by climate change, have damaged infrastructure or created spikes in demand for heating or cooling.

Other possible causes include overloads on high-voltage lines, which force excess electricity to be transferred to other lines, and cyberattacks, a threat increasingly cited due to increasingly digital networks. The Spanish justice system has announced an investigation into possible "computer sabotage," while the Sanchez government has emphasized that "no hypothesis" has been ruled out.

Imbalance between supply and demand?

In Spain, on Monday evening, the network manager REE reported "a strong oscillation in power flows, accompanied by a very significant loss of production."

In Europe, the electrical frequency on the network is calibrated to the standard of 50 hertz (Hz).

A frequency below this level means that not enough electricity is being produced relative to demand; above this level, it means that less power is needed. It is the job of the operators to order the power plants in real time to produce more or less, depending on demand, and to maintain the frequency.

"Maintaining this frequency is a question of balance," Michael Hogan, an advisor to the Regulatory Assistance Project (RAP), told AFP.

If the frequency deviates from 50 Hz, automated protection systems are triggered to shut down parts of the network to prevent damage to equipment. A chain of disconnections led to the widespread outage.

"Once power plants start shutting down to protect themselves, the situation can quickly spiral out of control. But it's very rare for it to reach the stage we saw on Monday," Hogan said.

How did it all begin?

"One of the factors that most likely contributed to the instability was the poor interconnection between the peninsula and the rest of the Western European network, meaning there wasn't much inertia in that part of the network to dampen the oscillations" on the Spanish side, according to Michael Hogan.

But this is a possible factor, not the primary cause. "It will likely be the failure of one or two major transmission facilities, which then spread to other connected parts of the network, but the cause of this initial failure remains to be determined," he adds.

What impact do renewable energies have?

In Spain, approximately 40% of electricity production comes from solar and wind power. As of midday on Monday, this figure was around 70%, at a time of low demand.

However, unlike gas-fired power plants, which "take a few minutes to start up," "solar and wind power cannot be controlled on demand and often has to be reduced," Rystad Energy points out.

The European electricity transmission system operator (ENTSO-E) warned on April 18 of the risks of overproduction of solar energy as the warmer weather approaches.

Monday's outage is a "warning," according to Rystad: "without stronger resilience at the national level and better regional coordination, future network outages could have even more serious consequences."

"Without sufficient flexibility measures, such as storage, fast-start plants, or robust interconnections, large swings in renewable energy generation can destabilize the grid," said analyst Pratheeksha Ramdas.

Criticism of renewable energy immediately surfaced on social media after the outage, but Hogan points out that massive blackouts of this type in the past have "almost always" been caused by transmission problems, not generation.

Lion Hirth, professor of energy policy at the Hertie School in Berlin, however, believes it is "likely" that "a system with very little 'conventional' generation (nuclear, gas, coal, hydroelectricity) has less damping inertia, that is, it is more prone to such oscillations becoming uncontrollable."

While remaining cautious, he believes "that the fact that the Iberian system was operating mainly on wind and solar energy on Monday midday did not help."