“It’s not a good time to go out,” she said. “No one’s going to appreciate the value you’ve created, and it’s such a high bar.”

Ms. Pfund is an investor in a number of alternative energy start-ups, like Solar City, which does solar panel installation. She said the company had blossomed and was on pace to more than double last year’s revenue of $26 million, but she said that it, like a lot of energy start-ups, was simply too early in its development to go public.

Indeed, some venture capitalists are arguing that the pipeline for public offerings has dried up in part because of the considerable shift in the industry’s interest in the last three years into “green” technologies, which was taking time to bear fruit.

But Paul Kedrosky, an investor and the author of Infectious Greed, a venture capital-centric blog, said that there were deeper, more systemic problems for venture capitalists in addition to the cyclical challenges. He said part of the problem was that the industry was backing companies that lack widespread investor appeal, like YouTube clones and dating and social networking sites.

“There is nothing that the industry is producing that investors want,” Mr. Kedrosky said. “The stuff they’re investing in is idiosyncratic  it’s fun and appealing to them but Wall Street doesn’t care.”

“The Valley is operating in its own little world, and the capital markets don’t care about the things that are getting the Valley excited.”

Over all, the market for public offerings has been in a funk. So far this year there have been 36 offerings, down from 130 during the same period last year, according to Renaissance Capital, a research firm based in Greenwich, Conn.