Trust us, the feasibility of this car has been discussed almost to death (see this, this or this). Still, the idea of going directly downwind, faster than the wind (DDWFTTW) will generate a bit more explanation and discussion here, we're sure. Here's the deal.
A DDWFTTW vehicle moves using wind power, but not in the way a sailboat does (i.e., directly for propulsion). Instead, the wheels are what spin the propeller, and the thrust from the propeller moves the vehicle. The inventor, Rick Cavallaro, promises that there's no perpetual motion being claimed here, just that it's possible to go around three times the speed of the wind in a vehicle with no stored energy while traveling directly downwind.
As Richard Jenkins, the man behind the Greenbird, told Wind Car designer Dale Vince:
Oh, and if people have a problem with the time it takes to recharge an electric car, we certainly don't think a car that can only move with the wind is reasonable for people to drive. But it's still kind of cool, no? There's a video of the car after the jump.The video speaks for itself. These guys are not idiots, but sincere, genuine, technical people who took a myth and made it real. It works. It starts from rest, trundles to true wind speed, then powers to a multiple of about 3 times the true wind speed.
[Source: Zero Carbonista]