On 8 May, Redes Energéticas Nacionais (REN) announced the partial resumption of electricity imports from Spain, setting a limit of 1,000 MW until 12 May. The measure followed the preventive disconnection triggered by the 28 April blackout and was adopted as part of a gradual and coordinated recovery strategy.

At the time of the incident, Portugal was importing 33% of its electricity from Spain, within a broader context in which 20% of its annual demand historically depended on that interconnection. The disruption had an immediate and direct impact on wholesale electricity prices in the Portuguese market.

Daily price effect: Portugal pays more

The interruption in energy flows led to a stark contrast in prices between the two countries. On 29 April, the average daily price in Portugal was €18.26/MWh, compared to €18.5/MWh in Spain. However, on 30 April, this difference widened significantly: Portugal paid €20.54/MWh, while Spain paid €31.83/MWh.

Following the blackout and suspension of imports, Portugal faced consistently higher wholesale electricity prices. Between 1 and 9 May, the average daily price in Portugal stood at €32.03/MWh, more than double the €14.06/MWh average recorded in Spain over the same period.

The data reflects a sustained decoupling in the Iberian electricity market, driven by Portugal’s precautionary limitation on imports from Spain. Although daily variations occurred, the trend clearly shows how restricted cross-border flows can elevate costs for consumers.

Although the variations were not drastic every day, they clearly illustrate the impact that import limitations have on price formation.

“This leads to higher electricity bills, as significant use of natural gas is required to stabilise the grid,” notes Alejandro Díaz González, renewables consultant and CEO of Energy Green Data, in conversation with Strategic Energy Europe.

An unprecedented blackout on the peninsula

As explained by João Moura, Grid Connection Manager at Iberdrola, the blackout began at 11:33 am on 28 April (Lisbon time), causing a total power failure across mainland Portugal and also affecting Spain, Andorra and parts of southern France.

“It was a serious and rare event: essential infrastructure such as transport, hospitals and communications collapsed,” the expert highlights.

The most likely cause identified by operators was the sudden disconnection of 2 GW of electricity generation in Spain, which caused a sharp frequency drop and triggered automatic cascade protections.

According to Moura, “The grid tried to respond, but the imbalance was so severe that more plants and loads were automatically shut down.”

In Portugal, the recovery was gradual. The northern and central regions began receiving power around 9:00 pm, and Lisbon regained a stable supply overnight. The black start procedure was implemented, restarting power stations from zero and gradually synchronising the network.

In its official report dated 5 May, Red Eléctrica de España (REE) confirmed that the system registered three prior generation losses, occurring approximately 19, 5 and 3.5 seconds before the blackout.

Jorge Antonio González Sánchez, Director of Energy and Projects at Losan, explains: “What we saw was a successive drop in generation that the system failed to contain – unlike other occasions, such as 9 January, when a nuclear plant outage was successfully absorbed.”

The executive and analyst also clarifies that the Spain–Portugal interconnection remained technically open for exports from Portugal to Spain, allowing night-time flows of surplus energy.

“What was not allowed was importing electricity from Spain, a decision made by REN due to the lack of confidence in grid stability until REE clarifies the event’s cause,” he states.

Looking ahead

“We cannot operate under these conditions for much longer. The market signals are not good, especially for solar investors,” warns González Sánchez.

Adverse weather — rain and cloud cover — reduced solar generation during the affected days, which helped prevent local oversupply. However, if the weather improves, “we may end up with excess solar energy and no market to absorb it, especially with Portugal’s import restrictions still in place,” he cautions.

The event has delivered operational and market lessons, but the final outcomes of ongoing audits in Spain and Portugal are still pending.

For now, the Iberian electricity system continues to operate under restrictions, in a context where regional coordination remains essential for system efficiency.