FOR Andrew Beebe, the light bulb went off almost two years ago at a computer technology conference in the Arizona desert. Mr. Beebe, who had just sold his profitable Internet start-up and was wondering what to do next, picked up a book on harnessing the sun's energy — or, as he saw it, "how to hack photosynthesis."

At the time, March 2001, the computer industry was suffering from post-bubble shock and California was being racked by an electricity crisis. The normally zealous attendees at the annual gathering seemed dazed. After reading the book, Mr. Beebe, 31, was convinced that the almost-within-grasp promise of solar-, biomass-, hydrogen- and wind-generated power was "the new new thing." After returning to San Francisco, he became a partner at Clean Edge, http://www.cleanedge.com/ a firm in Oakland, Calif., that is a consultant to energy start-ups.

With the threat of war in Iraq refocusing public attention on the United States' dependence on oil from the Middle East, renewable energy is regaining some of the buzz it had when Mr. Beebe was in diapers. It is attracting the attention of entrepreneurs and venture capitalists who not long ago were dreaming of riches on the Internet.

For now, the size of venture funds that are focused solely on energy is relatively small. About $2 billion is available to invest — as much as in two good-size computer-focused funds. About $488 million of that was actually invested in 2002. That is off from a peak of slightly more than $1.2 billion in 2000 but up significantly from the early 90's, when less than $25 million a year was being invested, says Nth Power http://www.nthpower.com/ a venture capital firm with a long history of energy investing.

"The tech refugees are moving in," said Martin Lagod, managing director of Firelake Capital Management http://www.ch2bc.org/bulletin/bulletin20030102.htm, an investment firm that specializes in energy, advanced materials and communications companies. And he says that's a good thing. "They are technically savvy, know how to build companies and access capital," Mr. Lagod said.

"Some of the hopes and expectations about how quickly energy would be liberalized and how fast distributed generation would catch on have been dampened," said Nicholas Parker, a longtime investor in alternative energy and chairman of the Cleantech Venture Network www.cleantechventure.com which brings together so-called clean-technology entrepreneurs and investors.

But advocates of alternative energy say things are different this time.

"Twenty years ago, a lot of the technology just wasn't ready," said Dan W. Reicher, an assistant energy secretary in the Clinton administration. He is now the executive vice president of Northern Power Systems www.northernpower.com energy engineering company, and a partner at New Energy Capital http://www.newenergycapital.com/, which invests in alternative energy projects.

Today, he said, energy technology is more reliable and is often backed by giants like General Electric, which bought Enron's wind power business, and BP, which is pursuing several projects in solar energy, wind power and alternative fuels like hydrogen.

The market potential is certainly large. Electricity alone is the third-largest industry in the United States, worth about $300 billion annually. And of the two billion people in the world who the United Nations estimates are without electric power, some may be candidates for off-the-grid renewable sources of energy.

Governments are helping to drive demand, which could spur innovation. About 30 states encourage renewable energy; New York and California, for example, require that 20 percent or more of their energy supplies come from renewable sources in the next decade and a half. Mr. Reicher said, "It's a convergence of technology, policy and market forces that make clean energy such a terrific investment."

ENTREPRENEURS' and venture capitalists' enthusiasm for alternative energy stems partly from the continuing slump in the computer and telecom industries. "There's nothing much else to look at," said Ivor Frischknecht, a co-founder of Angara Database Systems of Palo Alto, Calif. He is investigating opportunities to invest in clean technology.

Venture capitalists are starting to follow the entrepreneurs into this unfamiliar terrain — with an estimated $90 billion in venture capital idle, they are looking for places to invest it. Kleiner, Perkins, Caufield & Byers, Silicon Valley's top venture fund, is reviewing deals in energy and clean technology. Draper Fisher Jurvetson, another well known venture firm, in October led a $13.5 million investment in Konarka Technologies, a start-up in Lowell, Mass., that is working on less-costly thin-film solar panels.

Many entrepreneurs see in alternative energy that rare and desirable condition — a disruptive technology that could transform entire industries, from energy to transportation. "This is really the Internet 10 years ago," Mr. Beebe said. "We're on the verge."