Shares of solar firms Enphase Energy ENPH.O and First Solar FSLR.O were also down 15.6% and 5.2%, respectively. By Shubham Batra and Shashwat Chauhan Oct 20 (Reuters) - Futures tracking Wall Street's main stock indexes fell on Friday as U.S. Treasury yields hovered near multi-year highs following hawkish comments by Federal Reserve Chair Jerome Powell. Speaking at the Economic Club of New York on Thursday, Powell said the U.S. economy's strength and continued tight labor markets could require tougher borrowing conditions to control inflation.