By Pietro Lombardi MADRID (Reuters) -Spanish grid operator Redeia blamed power plants for the massive blackout that affected the Iberian peninsula in April, as it disputed a government report that said its failure to calculate the correct energy mix was a key factor.

Spain’s government said Tuesday that the massive April power outage across Spain and Portugal that left tens of millions of people disconnected in seconds was caused by technical and planning errors that left the grid unable to handle a surge in voltage.

Spain has identified the causes of the historic April 28 electricity outage and signaled that it was due to a lack of capacity to control voltage changes.