The financing was led by Warburg Pincus, a private equity firm based in San Francisco. Core Innovation Capital and Obvious Ventures, Twitter (NYSE: TWTR) founder Ev Williams’ venture firm, also contributed to the round. The company last raised $200 million in debt financing in April 2016, and has previously raised about $23 million in addition to a grant from the U.S. Department of Energy in 2012. The company was founded in 2010.
