The wheels are powering the fan blowing rearward I assume at a 1 to 1 ratio into the wind. The cart requires an initial "push" from the human. The wind pushes

The wheels are powering the fan blowing rearward I assume at a 1 to 1 ratio into the wind. The cart requires an initial "push" from the human. The wind pushes both the fan blades and the cart. So the net push from the wind > net drag with the wheels powering the fan. The faster the cart goes, the faster the blades spin, so the cart is being perpetually pushed by the wind on the spinning blades no matter how fast it goes. The spinning blades appear to be stationary from the perspective of the wind. The blades spinning tax the speed of the vehicle, but the payback is that the spinning blades are stationary relative to the ground. This cart would not move if the ground was moving at the same speed and direction as the cart. First law of thermodynamics has not been violated, the cart is simply using the energy from the wind on a virtual stationary object to power itself.