Experts say it takes about 5-7 kg of coffee grounds to get one liter of biofuel, which with a medium-sized production would yield a cost of about $1 per gallon. Plus, it's already used: you can just walk around to your local coffeeshops and convenience stores and stock up the same way you would on vegetable oil.

Creating fuel from the grounds uses the same procedure as other biodiesels, transesterification, which is sort of complicated to explain but fairly inexpensive. The US estimates we consume over 7 tons of coffee each year, which would yield about 340 million gallons of biodiesel.

But mostly, a subtle coffee scent might overcome the significantly less savory odors currently dominating my car. [The Economist]

Needless to say, we're being more than a little hard on the BioBot. In reality, it's a geek-worthy device that can produce almost 20 gallons of diesel per cycle. But unless you work at a french fry factory and have a BS in biochemistry, it's probably worth leaving this method to the pros.

If you're still interested, the BioBot runs $5000 and is said to pay for itself in two years. [BioBot via New Launches]

GSE Katana DA-20 Plane With Omnivore Biodiesel Engine

Awards Won: None

This modded Diamond Katana DA-20 plane was probably the most innovative and exciting plane in the challenge with its biodiesel capability, but due to a faulty inlet sensor, it was unable to compete. Designed by Greg and Geoff Stevenson and their aircraft engine company, GSE, the Omnivore only relies on biodiesel for auxiliary power during takeoff and landing. But the plan is to get it FAA certified step-by-step so that it relies more on the eco-friendly fuel. The engine also has an electric motor and fuel injection to help make the craft quieter and more fuel efficient. It was expected to win the Green Prize handily, which would have been awarded to any plane averaging over 30 mpg for the race, but none of the others could meet that requirement.

Pipistrel Virus

Awards Won: Safety Prize, Shortest Takeoff Distance, Quietest Cabin Noise, 400 Mile Race Winner, Best Angle of Climb

The Pipistrel Virus took home more awards than any other craft, but the team was still disappointed with their results, as it had performed better in some categories last year. The $100k craft has a constant propeller speed switch that helps with fuel efficiency (28.8 MPG for the competition), as well as heavy sound dampening where it tied the Lambada motoglider for lowest cabin noise at 91.5 db. The plane flew 145 miles per hour, and only required 924 feet for takeoff.

Pipistrel even flew out a team of engineers from Slovenia to install a new engine that was supposed to improve power and mileage, but it didn't quite work out. What did work out was the super high-tech dashboard, normally found in much more expensive planes, with the aforementioned three GPS modules and a panel that can take map data and can digitally recreate the surrounding geography when visibility is poor.

UFM-13 Lambada

Awards Won: Lowest Community Noise, Quietest LSA, Lowest Cabin Noise

Running as quietly as a pickup truck, the sexily named UFM-13 Lambada motoglider took home prizes for having the lowest community noise, at 62dB. According to team leader John Dunham, the plane would have also won the Best Glide Ratio award—this measures the amount a plane can move forward once it cuts power and eases back towards the ground, and the UFM-13 is apparently able to glide at a similar rate as a feather—but miscalculations due to human error prevented that from happening. Few mods were made to the plane itself, other than noise dampening measures. For the challenge, it managed to fly 130 mph, averaged 26.5 mpg and required 1011 feet for takeoff.

Flight Design CT

Awards Won: Best Glide Ratio

Spearheaded by freelance aircraft mechanic Bob Bashim, this Flight Design CT didn't have the resources of some of the other teams, but managed to snag the Best Glide Ratio prize. Bashim had some neat ideas to reduce noise and fuel consumption, including the use of a motorcycle muffler on his plane. Other measures taken for the challenge include adding noise dampening panels around the engine, and removing all unnecessary weight around the plane.

— — —

Though most of the participants started working on this only 6 weeks ago, they are already looking forward to next year, with more time to work on their planes. Pipistrel's team in particular is interested in the idea of shorter takeoff lengths, where people could have their own runways, and wouldn't have to use a regional airport to hit the skies. For more information on the challenge, check out the homepage of the [CAFE Foundation].

Creator Michael Sturtz started off with a BMW motorbike and a Beemer high-performance car engine only available in Europe (which shut down for four days after its computer thought it had been stolen, so Sturtz had to beg BMW for the security codes.) Its retro look comes from having engine and chassis wrapped in 3/4 aluminum fairing.

Die Bike cost $20,000 and took six months to build. As well as running on biodiesel, it can take both diesel and straight vegetable oil (SVO). Sturtz, who is Founder and Executive Director of The Crucible, is hoping that his creation will break the existing diesel motorcycle world record, as well as establishing new land speed classes for both bio-diesel and straight veggie oil. [Popular Science via CNN]

Q & A : Biodiesel Airplanes? [TreeHugger]