HANOI, March 25 (Reuters) – Vietnamese private firm Trung Nam Group said on Wednesday it will at the end of this month start building a 450-megawatt solar farm in central Vietnam that will be the largest of its kind in southeast Asia. The 14-trillion-dong ($593.22 million) facility in Ninh Thuan province is scheduled to start power generation in the fourth quarter this year, the company said in an emailed statement.