Spain finally says what caused its huge nationwide blackout

The blackout had "multiple" causes, Ecological Transition Minister Sara Aagesen told reporters following a cabinet meeting, adding the system "lacked sufficient voltage control capacity" that day.

Overvoltage is when there is too much electrical voltage in a network, overloading equipment. It can be caused by surges in networks due to oversupply or lightning strikes, or when protective equipment is insufficient or fails.

When faced with overvoltage on networks protective systems shut down parts of the grid, potentially leading to widespread power outages.

Aagesen singled out the role of the Spanish grid operator REE and certain energy companies she did not name which disconnected their plants "inappropriately... to protect their installations".

She also pointed to "insufficient voltage control capacity" on the system that day, due in part to a programming flaw, stressing that Spain's grid is theoretically robust enough to handle such situations.

Due to these misjudgements "we reached a point of no return with an uncontrollable chain reaction" that could only have been managed if steps had been taken beforehand to absorb the overvoltage problems, she added.

Authorities had scrambled to find answers after the April 28th outage cut internet and telephone connections, halted trains, shut businesses and plunged cities into darkness across Spain and Portugal as well as briefly affecting southwestern France.

Spanish Prime Minister Pedro Sánchez announced the formation of an inquiry commission led by the ecological transition ministry shortly after the blackout, urging residents not to speculate until detailed results were available.

He had warned that the probe's conclusions could take several months, given the complexity of the incident.

Following the incident, several hypotheses were considered to explain the blackout, including a cyberattack and a grid failure caused by excess renewable energy production -- both quickly ruled out by the authorities.

These theories were again dismissed on Tuesday by Aagesen, who nonetheless acknowledged that "vulnerabilities" and "deficiencies" had been identified in Spain's power grid security systems. She said corrective measures would be proposed.

The right-wing opposition has questioned the Socialist-led coalition government's phase-out of nuclear energy and reliance on renewables, saying they made Spain more vulnerable to blackouts.

But the government says there is no evidence to suggest "an excess of renewables or the lack of nuclear power plants" caused the crisis.