CLEAN TECHNOLOGY HASN'T BEEN RAKING IN the cash of late. Last year venture capital flows to the global cleantech sector plunged 33 percent, to $6.46 billion, San Francisco–based research and advisory firm Cleantech Group reports.

This slide may suggest that the skeptics are right about cleantech as an investment: It was a fad whose day has come and gone. But many experts contend that cleantech isn’t dying, it’s transforming. Helping to drive that change, and the current dip in funding, is the arrival of cheap, abundant natural gas on the U.S. energy scene.

Although the numbers frequently change, the U.S. Energy Information Administration recently estimated that there are 2,203 trillion cubic feet of recoverable natural gas in the U.S., enough to meet all of the country’s energy needs for 92 years at 2011 consumption levels. Through early February this year’s average contract settlement price was $3.35 per million BTU, the standard measurement unit for natural gas, compared with $9.04 in 2008. Natural gas thrills major energy companies with the promise that the U.S. could become a net exporter — in 2010 oil giant Exxon Mobil Corp. paid $35 billion for Houston-based producer XTO Energy — but it’s also helping to recast cleantech’s winners and losers.