Today Derek Muller posted a video about a wind-powered vehicle that can go downwind faster than that downwind itself.

The vehicle has three wheels, I estimate about 5 meters from front wheel to back wheels, and and a two-bladed propellor is mounted about 5 meters up.

The mechanical connection between the propellor and the wheels is such that when the vehicle is rolling forward the propellor is moving air from the front of the vehicle to the rear of the vehicle.

Speculation: It may be that the connection between the wheels and the propellor is fitted with a ratchet mechanism, such that the wind is prevented from causing the propellor blades to turn with the wind. If the wind would turn the propellor blades then the vehicle would start rolling into the wind. The propeller blades must only be free to turn against the wind.

The vehicle is as lightweight as possible for its size, so it's quite flimsy. This is definitely not a practical device, it is a proof-of-concept device.

Previous question about that vehicle:
Details about mechanics of directly-downwind-faster-than-wind vehicle