FORTUNE — Bright ideas about how to help the environment and in the process make a few bucks — or perhaps even a few billion bucks — abound. But which of them could actually work?
Might it be billionaire Tom Siebel’s new venture, the mysteriously-named C3, which aims to use clever software to radically improve big companies’ energy use and carbon output?* Or perhaps it will be Global Thermostat, which says its “carbon negative” technology can suck carbon dioxide right out of the air. (For power the company uses the excess heat generated by existing industrial processes such as smelting, energy that currently goes to waste.) Carbon capture technology would look especially appealing if Japan’s recent catastrophe sends zero-carbon nuclear power into a long-term decline.
Many of the contenders will get a chance to reveal their plans at Fortune’s annual Brainstorm Green conference, which starts today and brings together a who’s-who of the green movement from government, the Fortune 500 and all manner of newcomers.
Siebel, who made his fortune in database software, is one eco-neophyte. He plans to talk about C3, which has been in stealth mode since 2009. In October the company raised $48 million in a private offering, according to a filing with the SEC, roughly doubling its total funding. Siebel has recruited a blue chip board, including former Secretary of State Condoleezza Rice and former energy secretary Spencer Abraham.
While the company’s minimalist web site remains vague, someearly speculation centered around the idea that Siebel would use his software knowledge to create an easy, automated way for companies to track and trade their carbon emissions. That would likely work best under a cap-and-trade or carbon tax system. Neither policy seems politically viable in the U.S., at least for the time being. (Whether the idea of carbon-trading markets is doomed will likely be another major topic at the conference.)
How will the ongoing crisis at Fukushima reshape the environmental debate?
Beside Global Thermostat, a New York City based company called Kilimanjaro Energy also says it can capture carbon dioxide out of the air. Yet that company is thinking of nothing so small as merely making up for the potentially diminished use of carbon-free nuclear power. It wants to change the way people think about carbon dioxide, from a liabiity to an asset: “Atmospheric CO2 is a vast resource whose transformation into useful products can help humanity close the carbon cycle.”
Another company with big dreams, Transphorm, says it can effectively match the current output of all renewable energy sources at no harm to the environment. Its secret: eliminate the vast amount of electricity that is now lost by the electric grid as it transforms it from one form to another (say by stepping its voltage up or down.) That’s an efficiency breakthrough that could work no matter what form of fuel — coal, natural gas from shale, solar — ends up powering the grid in the coming century. Perhaps there’s no green magic bullet that can help clean up the radioactive material spewing from the Fukushima plant, but there are, in other words, lots of alternatives to nuclear emerging from the green energy space.
Then again, perhaps the quest for a cleaner environment shouldn’t rely on the hunt for a game-changing technology. There are lots of little ways for making green decisions pay. A company called ecoATM has designed a machine that can accept old cell phones and spit out cash for turning them in. Its plans may be relatively small, but they are real. Less toxic materials go in the landfill, more money goes into consumers’ wallets. Their strategy should serve as a reminder to greentech thinkers that all change, no matter how big, generally starts quite small.
*Editor’s note: An earlier version of this sentence characterized C3’s plans as secretive when in fact several details about the startup are public. The sentence has been revised to reflect the information.