Increasing power demand to cool homes in Spain is putting pressure on energy prices after the country’s grid boosted its reliance on gas generation in the wake of a massive blackout.

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.

A government investigation found that efforts by Red Eléctrica de España, Spain's grid operator, to address a small instability in the system actually led to more severe issues, causing a self-reinforcing cascade where high voltages caused power plants to drop off the grid.