NEW YORK — Alternative energy has long been dismissed as too expensive to be practical, but with oil hovering around $65 a barrel, solar energy and fuel cells are starting to look positively affordable. As a result, alternative fuel companies' stock has soared this summer alongside oil prices.

While equipping your house with solar panels will almost certainly pay off in time, alternative energy stocks are riskier. Many are money-losing companies. All have uncertain futures.

"This is an emerging growth space that's been emerging for a long time," said Jack Robinson, president of Winslow Management Co., a 21-year-old investment firm focused on green investing. "There are companies that are much riskier than others."

Most alternative energy stocks are thinly traded. Several of the companies don't have a lot of cash.

"They are still consuming a lot of cash; there's a risk of them not being able to consume their way to success," said Timothy Woodward, managing director at Nth Power, a venture capital firm specializing in energy technologies.

"Many of these companies have to go back to the public markets on a fairly regular basis to support their operations," he said. "If they can't do a financing, they run the risk of having to shut the doors."

Recently, the financing hasn't been a problem.

Hurricane Katrina has shut an estimated 5 percent of the nation's oil refining capacity, which will send gasoline prices even higher.

For 2005, energy expenditures in the United States are expected to be $1.08 trillion, approximately 24 percent above the 2004 level, the Energy Information Administration, a division of the U.S. Energy Department, reported Friday. It said energy costs will represent 8.7 percent of the nation's annual gross domestic product this year, the highest percentage since 1985.

That's good news for Spire Corp., which makes solar cell manufacturing equipment. The company makes a profit and has solid sales, but it still received a letter from the Nasdaq Listing Qualifications Panel in April saying that Spire was no longer in compliance with the exchange's $10 million stockholders' equity requirement. That put it in danger of delisting from the exchange, which would make it harder for the company to raise cash.

Since June, however, Spire's stock has doubled. It's now in compliance with listings requirements, said Roger Little, Spire's CEO. "The issue's gone away," he said. A Nasdaq spokeswoman did not return calls for this report.

Why did the stock double?