The end of federal subsidies for residential solar would devastate an industry that’s already been struggling with bankruptcies, sluggish sales and high borrowing rates, executives and analysts have said. Last year, residential solar installations dropped 31% from the year before, according to research firm Wood Mackenzie. SunPower Corp., a pioneer in solar, filed for bankruptcy last year and home solar financial provider Sunnova Energy International Inc. is teetering on the edge of insolvency.