A Lowell-based solar technology company that received $1.5 million in state loans when Mitt Romney was governor has filed for bankruptcy, opening the presumptive Republican presidential nominee to charges of hypocrisy. Konarka Technologies revealed Friday that it had filed for Chapter 7 bankruptcy protection and would fire its 80-member staff and liquidate its assets. Romney has chided President Obama for investing $535 million in a different solar company that failed and insisted governments should not pick winners and losers in the private sector.