Electricity-generating windmills churn out free energy as long as the wind is blowing. So strapping one to the roof of your car where there's always a breeze as long as you're driving just seems obvious. The Transport Turbine — seen here as a 3D-printed proof of concept — puts four small wind turbines on the roof of your car that generate electricity as long as you're driving at least 40km/h, with minimal drag so as not to affect your gas mileage.
When available later this year, they'll come in a simpler 25-watt version, and a more industrial 1000-watt model which can be used to keep a battery perpetually charging in an electric car. The extra power can also be used to run in-vehicle electronics like a Wi-Fi hotspot or an elaborate entertainment center, and just like their larger counterparts these turbines don't mind a little bad weather. At least anything below an F1 tornado or category one hurricane.