At just after midday last Monday, electricity grids across the Iberian Peninsula failed almost simultaneously, cutting off power to tens of millions. Trains ground to a halt, mobile networks dropped, hospitals switched to backup generators, and entire cities were plunged into darkness. The exact answer isn’t yet clear as to what the cause was, but there appears to have been a chain of events or a single issue that lead to a sudden, massive imbalance in how power was flowing through the grid. As renewables take up a bigger share of electricity generation, and as countries become more interconnected, experts say incidents like this could become more likely. So how exactly does a grid collapse like that happen—and could it happen here? We're joined by Dr Paul Deane, senior lecturer in Clean Energy Futures at the MaREI Research Centre of UCC's Environmental Research Institute.