More thunderstorms could hamper efforts to restore power to thousands of residents who have had to cope with the oppressive heat for several days.  DTE Energy is reporting that about 50,000 homes and businesses in metro Detroit are still without power after powerful storms from Wednesday and Thursday.  Consumers Energy says approximately 23,700 of its customers are without electricity from the south side of the state to several northern Michigan counties.  Both utility companies expect to have the majority of their customers back on line by Sunday evening.