HAVANA — Cuba said it was generating only enough electricity to cover about 1/6th of peak demand late on Wednesday, hours after its national grid collapsed leaving millions without power. The National Electric Union (UNE) said it was producing 533 MW of electricity by evening, still just a fraction of typical dinnertime demand of between 3,000 and 3,200 megawatts, leaving a majority of Cubans in the dark as night fell across the Caribbean island. Earlier, the communist-run government said it would prioritize returning power to hospitals and water pumping facilities. Schools and non-essential government services were closed until further notice.