Spain’s worst national blackout was caused by solar farms shutting down en masse after a sharp drop in electricity prices, according to an official investigation.
A government report into the continent’s largest recent power outage revealed that on April 28 — an exceptionally sunny day — solar farms produced an excess of electricity, causing prices to turn negative and effectively wiping out any profit for operators.
The resulting mass shutdown triggered severe voltage and frequency fluctuations that rippled through the national grids of both Spain and Portugal. Crucially, back-up systems designed to stabilise the grid failed to activate.
The blackout left more than 60 million people across the Iberian Peninsula without power, according to the Spanish government’s report.
The outage brought cities to a standstill, with widespread traffic gridlock and thousands of people trapped in trains and elevators. Several deaths have also been linked to the incident. In the aftermath, energy experts warned that the heavy reliance on net zero energy sources had made Spain and Portugal vulnerable, due to the inherent volatility of renewable generation. Despite this, Spain’s left-wing government has repeatedly denied that green energy was at fault.
Alberto Núñez Feijóo, leader of the opposition People’s Party (PP), criticised the government, saying ministers were “so intent on being the greenest in the world that you have led Spaniards into the dark,” as reported by the BBC.
The findings are likely to raise concerns in the UK, where Energy Secretary Ed Miliband is spearheading a push to make Britain’s energy system carbon-free by 2030. The proposed shift would see the country depend almost entirely on renewable sources such as wind, solar, and nuclear to keep the lights on.
Critics argue that more time is needed to strengthen grid resilience before making such a dramatic shift to renewables.
The Spanish government’s report, released on Tuesday, detailed how the blackout—just after midday—was preceded by unusual voltage fluctuations starting around 10am. These fluctuations were closely linked to sharp drops in solar output, likely caused by solar farms disconnecting from the grid as wholesale electricity prices fell.
The instability was compounded by other factors, including a sudden reduction in power exports to France, which further disrupted the balance of supply and demand across the network.
While the sudden solar switch-off was identified as the immediate trigger for the blackout, investigators placed broader responsibility on Spain’s grid operator, Redeia, for failing to accurately forecast the correct energy mix needed to maintain system stability. Redeia rejected that conclusion, insisting that voltage levels remained within approved limits throughout.
The report also criticised several power plant operators. Some had received payments to keep nuclear and gas-fired plants running as a safeguard, but chose to shut them down as well—allegedly to cut costs—further weakening the grid’s ability to absorb the shock.
