Fidel Castro once called Cuba’s power plants “prehistoric.” But the country still relies on them, contributing to the longest blackout since the collapse of its former patron, the Soviet Union.

Cuba's efforts to restore power to the island were derailed for a third time late on Saturday, Cuban authorities said shortly before midnight, leaving millions in the dark and raising fresh questions over the viability of the government's bid to reestablish electrical service.

Cuba’s electrical grid went down Friday after one of the island’s major power plants failed, a day after a massive blackout swept across the Caribbean island and with no official estimate for when service will be restored.