Tight credit and equity markets are particularly hurting growth-stage clean tech startups, say analysts and venture capitalists. But other more recent factors, such as the strengthening dollar and a decline in fossil-based energy prices, have also hurt even established clean tech companies.

Growth-stage clean tech startups often need hundreds of millions of dollars to build commercial plants, such as for a new biofuel or solar technology. But the product, even if proven in pilot plants, is still too risky for banks to finance in this environment, said Jim Watson, managing director of San Francisco-based venture firm CMEA Ventures.

Initial public offerings and hedge funds, also traditional sources of funding for these types of companies, are effectively closed.

The list of startups affected is long. Wind company First Wind, advanced battery developer A123 Systems, and biofuel producer Codexis filed to go public this year to raise cumulatively hundreds of millions of dollars, but not one of them launched an IPO.

Solar system maker Solyndra, which is backed by CMEA Ventures and other top-tier venture firms, relied on “unconventional” financing sources to expand its manufacturing capacity, said Mr. Watson. Among those sources are the Walton family’s private equity fund and Masdar, an Abu Dhabi fund that seeks to turn the emirate into a clean tech power.

“The companies that do find that capital, it will be Darwinian. They will have to be best of breed in their area or it will be difficult to find scale-up money,” said Mr. Watson.

Some venture and private equity firms are shifting to fill that finance void. Venture heavyweight Kleiner Perkins Caufield & Byers has launched a $500 million fund to focus on clean tech companies entering their growth phase. Industry observers say, however, that these moves will not be enough to compensate for the funding sources that have evaporated.

And it’s not just startups that are feeling the pain of the credit crunch. Big players, especially in the solar industry, are being affected as well. Tight credit means consumers are less willing, or able, to buy renewable energy systems, said Lux Research analyst Paul Karayan.

T. Boone Pickens, the oilman now enthusiastic about renewable energy, said at an energy conference on Wednesday that the difficulties in the debt markets have slowed his plans to build the largest wind farm in the United States, according to a report from The New York Times.

But other factors, like the strengthening dollar and declining fossil fuel prices, have added to the pressure in clean tech industries. Europe accounts for about 75 percent of global solar demand, and a strengthening dollar has made solar systems less affordable.

“There is a flight to quality,” said New Energy Finance analyst Nathaniel Bullard. “The second tier companies will be pushed the hardest on declines in their module selling prices and ability to raise money.”

Chinese solar cell maker JA Solar lost $21 million, or 36 cents per share, in the third quarter, compared with a profit of $24.4 million, or 17 cents per share, a year earlier. Its stock plunged 29 percent on news of the loss on Wednesday, though it recovered more than 7 percent on Thursday.

Mr. Karayan said the solar industry is moving from supply limited to demand limited as a result of all these pressures.

“The people trying to build out can’t, and the established companies are pushing through production that can’t be consumed on the other end,” he said.