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 25 mph, with minimal drag so as not to affect your mileage.
When available in the US later this year, they'll come in a simpler 25 watt version, and a more industrial 1,000 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 centre, 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.