The idea sparking the latest technology rush is as old as the sun: solar cell energy.

After years of shying away from funding solar cell energy start-ups because of high costs, venture capitalists are almost tripping over themselves to sign up the most promising companies, many of them in Silicon Valley.

Breakthroughs in solar technology, favorable policy proposals by Democratic presidential hopeful Sen. John Kerry, disgust about dependence on foreign sources of oil, and skyrocketing demand for energy worldwide are all playing a role.

``There's clearly something going on here,'' says Erik Straser, a partner at Mohr Davidow Ventures who is prowling for possible investments, after he was asked by his firm to get up to speed in the sector.

Straser recently considered investing in San Jose's Miasolé, a hot solar cell start-up, but hesitated after extensive research. But another venture capital firm, Vantage Point, had been eyeing the deal and moved in to snag it. Vantage Point now has a team of partners focused on solar and other clean technologies.

This year, State Treasurer Phil Angelides has announced a $1.5 billion plan to use the state's pension funds to invest in environmental technologies, and $200 million has been earmarked for start-ups. And there's new buzz from Sacramento about a legislative proposal by Gov. Arnold Schwarzenegger, which would pay $1 billion in rebates for solar cell technology to be used on a million California rooftops beginning next year.

Solar investment still makes up a tiny part of overall VC investing, but money going into clean technologies is growing. While data on venture investments to solar start-ups is sketchy, money committed to clean technology companies is increasing. It reached about 2.4 percent of the total venture capital invested last year, compared with 0.8 percent in 1999, according to Ron Pernick of Clean Edge, a research group. About $300 million was invested in clean technologies during the first quarter of this year, with $59 million going to energy-related deals, according to Cleantech Ventures.

New fundings

The deals in solar cell technology, anecdotally at least, are on the rise. Over the past few months alone, a slew of companies boasting new solar technologies are announcing new fundings.

It's all attracting a new generation of entrepreneurs. One is 39-year-old Sunil Paul, founder of anti-spam company BrightMail, which he sold recently for $390 million. He has since invested in two solar cell companies and can't get enough. He wants to build companies, he says, that go ``beyond just making money.''

He has started a Bay Area energy forum for entrepreneurs and others called the ``Power Lunch,'' with the aim of exploring solar and other alternative energy ideas.

Driving much of the excitement is a risky quest by several newer companies to bring about drastic cost reductions. All solar companies rely on the same photovoltaic process: Sunlight in the form of photons hits a light-absorbing semiconductor material in the solar cell, exciting electrons and thus allowing them to flow out of the cell in the form of an electrical current.

Alternatives to silicon

Traditionally, solar cell manufacturers relied on costly silicon as the semiconductor. But the physical limits of silicon -- its crystal form is bulky and inflexible -- have kept solar cells three times more expensive than traditional sources of energy for the power grid.

To overcome the cost, subsidies and government regulations have helped support growth in the solar cell industry output of about 35 percent a year. Economies of scale are reducing costs up to 7 percent a year, but the progress is too slow to make solar truly competitive without subsidies.

So scientists are exploring some more revolutionary techniques, and they're making progress.

The new companies are doing away with silicon. One is Miasolé, which uses thin films of a copper alloy (called CIGS) deposited on a flexible metal. The process has already been used successfully to produce cheap, high-quality hard disks for disk drives.

Chief Executive David Pearce -- who looks the part of environmental executive with green shirt, hazel green eyes and a green and yellow business card -- used the technology at a previous optical-components company he founded. Now, he says, he's ``supremely confident'' he can apply it to solar and expects a product to be on the market by the first quarter of next year.

Then there are more radical efforts, including those of Nanosolar, Konarka and Nanosys, using nanotechnology materials to create flexible solar cell sheets that can be mass produced and promise to rival the cost of traditional energy sources. The first products should be on the market in about two years.

Their semiconductor cells are one-thousandth the width of silicon, made instead of particles of titanium oxide or CIGS. These are then printed on a metal roll in the form of a thin flexible film.

Arno Penzias, a Nobel Prize winner for physics, who is now a partner with New Enterprise Associates, and has invested in Konarka, realizes the bet is risky.

``More people have lost money in bets against silicon than I know,'' he says.

But then you're talking a huge possible payback: The power market is about $1 trillion.

The companies that are busy recalibrating the multiple sensitive chemical processes are sure to argue that their way is best. Expert Pernick says it's too early to say: ``We don't know yet which one is going to win out at the end of the day,'' he says.

Nanosolar, for instance, has developed a semiconductor paint, which saves it from the disadvantages of the usual wet electrolyte that could start leaking on a rooftop after a few years. Konarka, in response, says it has made good headway on creating a sealant for its electrolyte.

Both plan to print out their cells on large swathes of foil. Martin Roscheisen, chief executive of Nanosolar, hopes to drive the raw uninstalled cost of solar electricity down to about 40 to 60 cents per watt by 2006, from the $2.75 per watt cost reached by traditional solar manufacturers. This would bring the price of solar below most other grid sources, such as natural gas.

``The demand would be infinite,'' says Nanosolar investor Marty Lagod. ``We think its achievable. That's why we're excited about the area.''

Also driving the lower cost would be Nanosolar's ability to print cell foil in large quantities. It could cover whole parking lots, or be painted on the side of buses and cars. And by 2006, Nanosolar could have the capacity to produce enough energy to make up 20 percent of the global solar cell market, according to Roscheisen.

Worldwide, solar is a $7 billion a year business, according to industry experts. The world's largest player, Japan's Sharp, controls about a third of total solar cell output.

Other big players are making moves. General Electric recently bought Astropower, a solar power leader, and last month said it hopes to boost solar energy sales to $1 billion by the end of the decade.

Nanosolar's Roscheisen embodies the new interest among Silicon Valley veterans in solar. Roscheisen, 35, was an early dot-com pioneer, having sold Internet company eGroups to Yahoo for $432 million in 2000 during what he says was ``my other life.''

Kicking around for his next business idea, he found most software and Internet technologies were well covered by other companies. But he noticed how much he was paying for inefficient heating bills and at the gas pump to fill up the guzzling Mercedes-Benz G500 he bought from Sequoia venture capitalist Michael Moritz. Traveling the world, and inquiring about how to develop better energy sources, he fell upon the idea for Nanosolar.

For Roscheisen, the change of industries is a family tradition. His great great grandfather founded the Germany's first regional electricity utility, still powering Bavaria today -- but only after he first built a construction company.

Roscheisen says it was almost impossible to raise money from VCs back in 2002 when he first came up with the solar idea. ``Most considered solar uninvestable,'' he says. Now he's gotten backing from big-name VC firms, and Monday plans to announce a $10 million grant from the Department of Defense's research arm, DARPA.

To the contrary, he says, the industry plays to Silicon Valley's strength -- taking a technology developed first outside -- in this case, Japan and Germany -- but adapting it in a more cost-effective way: ``This is what Silicon Valley is great at.''