There is no magic-bullet fuel crop that can solve our energy woes without harming the environment, says virtually every scientist studying the issue. But most say that algae—single-celled pond scum—comes closer than any other plant because it grows in wastewater, even seawater, requiring little more than sunlight and carbon dioxide to flourish. NREL had an algae program for 17 years until it was shut down in the mid-1990s for lack of funding. This year the lab is cranking it back up again. A dozen start-up companies are also trying to convert the slimy green stuff into a viable fuel.

GreenFuel Technologies, of Cambridge, Massachusetts, is at the head of the pack. Founded by MIT chemist Isaac Berzin, the company has developed a process that uses algae in plastic bags to siphon carbon dioxide from the smoke-stack emissions of power plants. Algae not only reduce a plant's global warming gases, but also devour other pollutants. Some algae make starch, which can be processed into ethanol; others produce tiny droplets of oil that can be brewed into biodiesel or even jet fuel. Best of all, algae in the right conditions can double in mass within hours. While each acre of corn produces around 300 gallons (1,135 liters) of ethanol a year and an acre of soybeans around 60 gallons (227 liters) of biodiesel, each acre of algae theoretically can churn out more than 5,000 gallons (19,000 liters) of biofuel each year.

"Corn or soybeans, you harvest once a year," says Berzin. "Algae you harvest every day. And we've proved we can grow algae from Boston to Arizona." Berzin's company has partnered with Arizona Public Service, the state's largest utility, to test algae production at APS's natural-gas-burning Redhawk power plant just west of Phoenix. Algae farms around that one plant, located on 2,000 acres (809 hectares) of bone-dry Sonoran Desert, could double the current U.S. production of biodiesel, says Berzin.

The energy farm, as GreenFuel calls it, isn't much to look at, just a cluster of shipping containers and office trailers next to a plastic greenhouse structure longer than a football field and perhaps 50 feet (15 meters) wide. Outside the greenhouse, rows of large plastic tubes filled with bubbling bright green liquid hang like giant slugs from hooks. After making a few calls to his boss, GreenFuel's security-conscious head of field operations, Marcus Gay, allows me to inspect this "seed farm," which grows algae for the greenhouse. Everything else is off-limits. The company guards its secrets closely.

With good reason: Only perhaps a dozen people on the planet know how to grow algae in high-density systems, says Gay. Algae specialists, long near the bottom of the biology food chain, are becoming the rock stars. Two of Arizona's largest universities recently started algae programs. Their biggest challenge, as with cellulosic ethanol, is reducing the cost of algae fuel. "At the end of the day for this to work, this has to be cheaper than petroleum diesel," says Gay. "If we're one penny over the cost of diesel per gallon, we're sunk." (In July, rising costs and technical problems forced GreenFuel to shut down the Redhawk bioreactor temporarily.)

Hard numbers—supply, efficiency, and, most important, price at the pump—will determine the future of ethanol and biodiesel. But for now green fuels have an undeniable romance. In the garage of his office complex in downtown Phoenix, Ray Hobbs, a senior engineer for APS who is leading the company's fuel initiative, walks past a small fleet of electric cars, hybrids, even a hydrogen-powered bus. He climbs into a big diesel Ford van and turns the key. The exhaust, unlike a typical diesel's, is invisible, with just the faintest whiff of diesel smell from the algae biodiesel made at the Redhawk pilot plant. The superslick plant oil has also quieted a little of that annoying diesel rattle.

"The way I think about these things is I'm sitting in a river in a canoe," says Hobbs. "Now do I want to paddle upstream, or do I want to go with the flow? Algae is downstream, with the flow. We have processes in nature that are honed for us, that have evolved. So we can take those processes and make them faster and more efficient and harness that power. We can't wait generations to screw around with this. We have to do it now."

Hobbs says he has fielded dozens of calls from power companies interested in building an algae plant of their own to scrub emissions and help meet their renewable fuels mandate. The lure of plant fuels even seems to have reached the petroleum-rich sands of the Middle East, where the United Arab Emirates has launched a 250-million-dollar renewable energy initiative that includes biofuels—perhaps a sign that even the sheikhs now realize that the oil age won't last forever.