The number of homes and businesses without power in southern Louisiana continues to pile up. More than half a million electricity customers are now in the dark, and are likely to remain so throughout the duration of the storm, utility officials say, with Jefferson and Orleans parishes continuing to bear the brunt of the impact from the slow-moving Hurricane Isaac. Entergy Corp., the New Orleans utility giant, reported that the storm had knocked out power to more than 572,000 of its customers throughout the state, according to the Entergy Storm Center website, which provides updates on power outages in New Orleans and across the region.