At times, it seemed like 1999 all over again. More than 350 venture capitalists, corporate investors, and CEOs of cash-seeking technology firms schmoozed at a buzz-filled conference in San Francisco, while each day's headlines trumpeted news about the year's hottest IPO, a Silicon Valley tech firm expected to fetch $2.7 billion. Alas, the forthcoming IPO is Google's, but there was no ignoring the positive energy at the Cleantech Venture Forum conference in San Francisco's Fairmont Hotel late last month. Many of high-tech's heaviest hitters were represented, including VC firms Kleiner Perkins and Rockport Capital Partners, and law firms Heller Ehrman and Wilson Sonsini. It was by far the best-attended of Cleantech Venture Network's bi-annual Forum series launched 18 months ago. The investor momentum and enthusiasm for clean tech were palpable, but of course it isn't 1999, and you needn't worry about a repeat of the Internet bubble in clean tech. Instead of irrational exuberance, the mood around investing in renewable energy and other clean technologies seems to be guardedly optimistic. I think we're on the verge of a major (and long-awaited) infusion of capital into this sector, but there are still significant hurdles and challenges to overcome before it happens. The timing of Google's IPO news was coincidental, but the Web search company's unconventional IPO statement is quite relevant to investors in clean tech. Warning their prospective shareholders not to get in for the quick buck, Google's co-founders wrote, "A management team distracted by a series of short-term targets is as pointless as a dieter stepping on a scale every half-hour." They're not going to run their company like many did in the IPO Class of '99 -- the dot-com days of "built to flip." In terms of investment returns, Google is trying to manage timeframe expectations. So it is in the world of clean-tech financing. Lee Bailey, a partner at VC firm Rustic Canyon Partners, told a Forum questioner that hydrogen fuel cells, to cite one example, are still too much of a long-term investment play for his firm. "Those of us who manage money in order to feed and clothe ourselves need returns in two to four years of 5x [five times one's investment] or better," he said. The timeframe question remains a challenge, and it's directly related to the continued availability of low-cost fossil-fuel energy in the near term. "Whether we like it or not, energy today is cheap," said Ananth Ananthasubramaniam, vice president of Edison Development Corp., a unit of DTE Energy in Detroit. But upward trends in oil and natural gas prices could alter that formula in clean tech's favor, shortening investment horizons in the process. Investors also spoke of the lack of blockbuster success stories among clean-tech startups and their backers -- notwithstanding pioneers like PV manufacturer Evergreen Solar ($29.5 million in VC funding last year) or investment firm Nth Power (a $200 million clean- tech portfolio). "There are a lot of positive trends for money coming in," said Global Environment Fund president Jeffrey Leonard, "but money coming out will be the sign of industry maturity." To date, renewables and clean technology have not attracted much capital from the huge spigot of institutional investors. But that's about to change in a big way. At the behest of California state treasurer Phil Angelides and his visionary Green Wave investment initiative announced in February, two of the nation's three largest public pension funds are about to pour up to $500 million into clean tech. CalPERS (the state employees' pension fund) and CalSTRS (the pension fund for the state's teachers) will invest with a combination of private equity, venture capital, and project financing for two goals: to grow the clean-tech sector in California and, of course, to generate solid financial returns for their members. "This sector is now competitive with other high-risk, high-return sectors," Angelides said in his Forum keynote. "We believe [our initiative] will be proof that we can meet our green- eyeshade fiduciary duties and our green responsibilities to the environment. It's a new investment dynamic." And it could be a tipping point. CalPERS is the nation's largest pension fund not just in dollars, but in influence. In the long run, its vote of confidence in clean tech will turn out to be much bigger news -- with deeper implications -- than even Google's IPO. Because it ain't 1999 anymore. And that's good news. Wilder is Clean Edge's contributing editor. E-mail him at wilder[at]cleanedge[dot]com.