Regardless, a notable footnote in the most recent quarterly portfolio update from Soros was that while the hedge fund manager was amassing his big stake in the natural gas vehicle stock, he was closing out a 60,000 share stake in a volatile U.S. wind energy stock, Broadwind Energy ( BWEN). Soros continues to dabble in solar stocks, too, with a minor 3,600 share stake reported in U.S. solar stock bellwether First Solar ( FSLR) at the end of the first quarter. Yet even that small First Solar stake represented half of the First Solar shares that Soros hedge funds had held at the end of 2009. "Institutional investors have become much more aware of the fact that there are lots of ways to play the evolving energy efficiency story, and it is not just solar," says ThinkEquity analyst Shawn Severson. Westport Innovations is a small-cap stock -- and like its alternative energy peers, Westport shares can be up or down 30% in a heartbeat -- but a look at its top shareholders indicates that some brand-name growth investors believe in the natural gas vehicle story as more than a quick-flip profit, or a fingers-crossed retail investor gamble on the most volatile edge of the stock market. Equity fund managers Lord Abbett & Co. and Driehaus Capital Management are also among the top five shareholders of Westport Innovations, and the only managers joining Soros with more than one million Westport shares owned. Lord Abbett and Driehaus Capital are also among the top ten shareholders in natural gas vehicle play Clean Energy Fuels ( CLNE). Westport Innovations operates in two key markets within the natural gas space, and it has some well-known partners joining in its bet that the migration of the trucking industry away from diesel and toward natural gas is going to be a major transportation trend. Westport has a 50-50 joint venture to develop natural-gas vehicle engines with Cummins ( CMI) for the medium-sized truck market, Cummins Westport. Cummins is the fourth-largest truck engine manufacturer in the world. Westport also has a patented technology to convert heavy duty (HD) diesel truck engines to natural gas as a fuel source, the Westport HD division. Last November, Westport inked a deal with Volvo ( VOLVY) to supply the second-largest truck and truck-engine producer in the world with its HD truck natural gas engine technology.