The biggest energy unicorn left standing By: CNBC.com News June 01, 2015 at 09:55 AM EDT A cleantech moonshot company that has attracted deep-pocketed investors like the Walton family is ripe for an IPO. Is 2015 the year it goes public? Read More >> Related Stocks: Adobe Systems Apple Coca-Cola Company Google, Inc. Wal-Mart Stores, Inc. eBay