Will the falling price of oil have a negative impact on investments in the alternative energy sector?

Venture capitalists speaking today at the Renewable Energy Finance Forum in Seattle think it might.

"If we see oil in the $50, $60 or $70 range, a lot of these technologies don't make a lot of sense," said Raj Atluru, a director at Draper Fisher Jurvetson.

The price of oil has been on a rapid descent in the past three months, losing more than half of its value. It closed Tuesday at $64 per barrel.

With oil prices falling, Atluru predicted that there will be some "high profile losers" in the clean tech space. Still, Draper Fisher remains bullish on clean tech and renewables, with Atluru noting they are taking a long-term view with plans to "double down" in the sector. He said they are trying to take a 10 to 20 year view, adding that it could take close to a decade to make real money.

The falling price of oil certainly resonated with the crowd. Over a lunch discussion, an Indiana entrepreneur who was looking to finance a wind farm near South Bend wondered if the financing would be there for his project if oil stayed at current levels.

Another problem facing clean tech investors is the global economic crisis, which is leading to some very delicate conversations between VCs and the large financial institutions that back them.

"it is painful," said Pivotal Investments' Brad Zenger of the interactions with limited partners. "You time your phone calls to what the market is doing."

Large project finance deals are tougher to complete and many biofuel projects are languishing, panelists said. There are fewer dollars to spread around at this moment, which means some of the "swing-for-the -fences" type of companies are facing tough times, said Atluru.

But Zenger expressed optimism that roughly 80 percent of the global venture capital pie in the clean tech sector went to U.S. companies last year. Global investors may not believe in Wall Street anymore but they still believe that the U.S. is the "heart of innovation," he said.

That led Zenger to offer his advice to clean tech entrepreneurs who face an unusual set of tough circumstances at the moment.

"Don't give up," he said. There may be a "huge hiccup" on Wall Street, but "this is the time to invest in the next cycle."

That thought was echoed by Anup Jacob of the Virgin Green Fund, who reminded attendees that over the past 50 years the "best returns have been made during recessions."

"We have never been more excited as an investor as we are now," he said.