Solar inverter company Enphase Energy priced shares at the low end of its range on Thursday night, while selling more shares than expected. Clean fuel company Luca Technologies is expected to price shares later in the day.

Those offerings could pave the way for other, similar IPOs in coming months, analysts said.

The sector is still reeling after the large-scale bankruptcies last year of solar-panel maker Solyndra and energy storage company Beacon Power. Shares of other clean tech companies have performed poorly since their listing. In addition, the sluggish economic recovery is dampening enthusiasm for emerging industries.

Yet, investor appetite is slowly coming back in the sector, thanks in large part to a new crop of companies based on clean technologies, from biofuels to solar, that have matured much more than their predecessors.

Relatively high oil prices - $4 a gallon gas - and concerns about supply disruptions also are helping create an opening where numerous deals are expected to be launched this year.

"There's a push going on and a window right now for IPOs that we haven't seen in 18 months," said Ben Kallo, a clean tech equity analyst at Baird.

Adds Jay Spencer, Ernst & Young LLP's Americas Cleantech director: "We've been talking about clean tech for years, but now there are products out there so people are finally starting to use them and experience them."

But this time around, investors are becoming more careful and looking for companies with proven technology and solid business plans, rather than those breaking into markets so nascent they barely exist today.

"In the past, certain companies have gone public with technology that was only proven in a lab or at lab scale, but now investors are more discerning and are looking for young companies that have proven their technology at least near commercial scale," said Jim Schaefer, global head of renewable energy and clean tech and Americas head of power & utilities at UBS AG.

"Investors say: ‘I don't want to hear about a unicorn — I want to see a unicorn.'"

VENTURE CAPITAL INFLOWS

Last year, there were 54 clean tech IPOs globally, which raised a total of $9.6 billion, according to clean tech research firm Kachan & Co.

That was down from 98 IPOs, which raised $16.4 billion in the prior year. The majority of these offerings both years, however, were from China, where companies are looking to improve energy efficiency and reduce greenhouse gases in a country that is considered to be the world's largest polluter.

However, more venture capital money has been flowing into the sector. Global clean tech investment from venture capital topped $9.1 billion in 2011, up from $8.2 billion in the year prior, according to industry research firm the Cleantech Group, which tracks clean tech investment.

"It's all about having a critical mass of these companies make it through the pipeline to the point where they make sense to the public markets," said Andy Garman, a managing director with New Venture Partners who focuses on energy and environmental technologies. "The next wave of clean tech might have more technologies that look like traditional IT companies."

The upcoming IPOs will further test the waters of an already fragile market.

"Some investors are saying ‘why do I want to invest in a market where I've already been burned?'" said one banker who works with clean tech companies. "For some of these companies, it's going to be a tough sell."

Clean tech skeptics have long pointed to the sector's overdependence on government subsidies and massive amounts of capital for technologies to become functional.

PayPal founder and Facebook investor Peter Thiel is one outspoken critic of today's clean technology companies.

"Clean tech is an increasingly large disaster that people in Silicon Valley aren't even talking about any more," Thiel said last year during the TechCrunch Disrupt conference in San Francisco.

Netscape co-founder Marc Andreessen has also publicly said that his venture firm Andreessen Horowitz will not look at the clean tech sector as it requires a different skill set than investing in IT companies.

Enphase, based in Petaluma, California, priced its shares at $6 a piece, at the low end of its range. It sold 9 million shares in the offering, above the 7.3 million shares it expected to sell.

Enphase was forced to slash its range earlier this week to between $6 and $7 a share from $10 to $12 apiece. The company's products convert solar-generated electricity to standard AC electricity.

Luca Technologies, based in Golden, Colorado, has not cut price expectations. It is looking to raise about $100 million by selling 8.5 million shares at a range of $11 to $13 a share. The company's products help draw more useable methane from hydrocarbon deposits in the earth.

Both trash-to-bio fuel company Enerkem and solar thermal company BrightSource Energy also set the terms for their public debuts last week, seeking to raise as much as $137.8 million and $182.5 million, respectively.

Additional IPOs this year are likely to come from a range of industries including smart-grid network providers, LED lighting companies and energy-efficient material makers, say bankers and analysts.

BIOFUEL IPOs

Biofuel companies will also continue to tap the public markets on high oil prices, and as people look for alternative energy plays.

On Thursday, President Obama addressed the concerns many Americans are facing with rising gasoline prices, calling on Congress to repeal tax breaks for big oil firms. Investors are hopeful that a crop of new biofuel IPOs will perform better than past offerings did. Biofuels companies Gevo, KioR and Solazyme, which went public last year - and all of which were unprofitable at the time of their offerings - traded below their IPO prices on Thursday.

Yet, despite this weak performance, interest in clean tech remains strong among some investors, who see the sector maturing from its early days in 2007 with more established companies.

"It's been a challenging space broadly since mid-2011 but there are certain investors who want to play in clean tech still and have the risk profile to do it," said Terry Schallich, head of equity capital markets for Pacific Crest Securities who works with clean tech companies.

"They're perhaps risk adjusting a bit more but there's still a high level of interest."

(Editing by Carol Bishopric and Muralikumar Anantharaman)

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