1. Harnessing Hydrogen

Hydrogenics: Building markets for fuel-cell tech. A big bonus: byproducts can quench a thirst.

Pierre Rivard compares critics of hydrogen power to those who could never fathom color television, portable phones or the Internet. "They just lack vision," says Rivard, cofounder of Hydrogenics, an Ontario-based company. "People couldn't have imagined the advances we have made years ago."

Granted, we're still a long way from a hydrogen-powered car in every driveway, but Hydrogenics is working on other applications to build a market for the technology. (Hydrogenics produces fuel cells that fit together like LEGOs and extract electricity from the chemical reaction of hydrogen and water.) Last December it installed a hydrogen refueler inside a General Motors car-assembly plant in Canada to power two forklifts. And this summer, Hydrogenics technology started fueling a Purolator truck in Toronto and a transit bus in Winnipeg. GM, which holds a 20 percent stake in Hydrogenics, deems its trial a success.

Hydrogen fuel cells aren't just clean—they're also silent, and they produce water as a byproduct. That's creating defense applications that can capitalize on a stealth approach. Another upside: in —desert settings like Iraq, the technology produces drinking water for soldiers. The U.S. Army recently started a yearlong trial using Hydrogenics to power a few of its Stryker light armored utility vehicles.

When this technology will move into mass markets is unclear. GM says it may happen in the auto industry over the next decade. (Hydrogenics helped develop a "neighborhood car" prototype that looks like a street-legal golf cart.) Hydrogenics' sales fell by 37 percent last year, but it has a big backlog of orders. David Smith, an analyst at Smith Barney, remains bullish on the company, and ABI Research estimates the fuel-cell market could reach $2 billion by 2012. For now, Rivard is content to focus on smaller projects. "It is important for us to go after these low-hanging fruits," he says.

—Jessica Silver-Greenberg 

6. A New Power Paradigm

Ion America: Developing solid oxide fuel cells that could put a power plant in your basement

Imagine, for a moment, a future where electricity is generated not in big power plants but behind your home or in the basement of your office building. High-efficiency, low-polluting fuel cells the size of minivans provide all your power needs. They take hydrogen-rich natural gas or propane and then chemically strip the fuel of its electrons to produce electricity. One byproduct is hydrogen, which can then be funneled into your new, clean- running hydrogen car. While the fuel cells run hotter than anything else in your home, perhaps as high as 1,000 degrees Celsius, that's OK, too—the extra heat is captured and warms the water tank.

Ion America is a quiet Silicon Valley firm pursuing this coveted power paradigm, using solid-oxide fuel cells. The three-year-old start-up, based at NASA's Ames Research Center in Mountain View, Califor—nia, is still developing its technology. But the company's first fuel cells are now being tested and the prospects are exciting some energy experts. The U.S. Navy gave Ion America a $2.7 million contract to test its fuel cells in submarines, where another byproduct, oxygen, can be used as breathable air. A Chattanooga, Tennessee, university will install a five-kilowatt prototype early next year, and the city is asking for a more powerful, 100- to 200-kilowatt version to use downtown by 2008.

Ion's founder, Indian-born KR Sridhar, started his fuel-cell crusade while heading the Space Technologies Lab at the University of Arizona in the 1990s. He worked for NASA on ways to make breathable air from the carbon dioxide in the Mars atmosphere. When NASA terminated the lab's contract in a late '90s purge, Sridhar looked at the technology from a different angle, wondering if he could make electricity from hydrogen efficiently, which drew him to fuel-cell research.

Sridhar has said he hopes to begin selling products next year. That will help answer questions raised by skeptics. The fuel cells run at such high temperatures, for example, that reliability and stability could pose problems. But if Ion can answer them, old power sources will look like the dinosaurs whose remains they consume.

—Brad Stone