The idea of boosting vehicle fuel economy by using windmill components might sound a little Quixotic, but here goes.

Mazda is working on a new braking system called i-ELOOP. It captures energy from the vehicle's inertia and produces an electric charge from the alternator just as the driver lets off the gas pedal. This energy is captured quickly in a Electric Double Layer Capacitor, which are commonly found in wind turbines. The system will debut on the 2014 Mazda6 and is part of the company's Skyactiv fuel-economy boosting efforts.

Under the most optimal conditions (i.e., when running every imaginable battery-draining component in the car), Mazda's new system can boost fuel economy by as much as 10 percent. More typically, though, fuel economy will increase by about one mile per gallon.

In 2011, the Japanese automaker said it was aiming to boost fleetwide fuel economy by about 30 percent over the next three years through its Skyactiv program. That effort starts down the fuel-saving path by using improvements in engine design, aerodynamics and weight-reducing parts. Later, bigger changes to the powertrain (i.e., plugs) go into effect. You can read about the general timeline here.
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Regenerative Braking System
Regenerative braking systems convert a vehicle's kinetic energy into electricity as the driver applies the brakes. The electricity is then stored for later use. It can be used to power the headlights, climate control, audio system, or any other electrical equipment. This reduces the need for the engine to burn extra fuel to generate electricity, thereby improving fuel economy.

Mazda's i-ELOOP is a unique regenerative braking system that uses a capacitor instead of a battery to store the electricity. Capacitors can be charged and discharged extremely quickly, enabling electricity to be supplied as and when it is needed. By efficiently recovering, storing and reusing energy, i-ELOOP improves fuel economy by approximately 10 percent in real-world driving conditions.

i-ELOOP's New Technologies
A variable voltage alternator (12V-25V) for efficient electricity generation as the vehicle decelerates

A high-capacity Electric Double Layer Capacitor that rapidly stores large amounts of electricity and efficiently redistributes it. (i-ELOOP is the world's first passenger vehicle regenerative braking system to use a capacitor)

i-ELOOP starts to recover kinetic energy the moment the driver lifts off the accelerator pedal and the vehicle begins to decelerate. The variable voltage alternator generates electricity at up to 25V for maximum efficiency before sending it to the Electric Double Layer Capacitor (EDLC) for storage. The alternator can fully charge the capacitor in just a few seconds. A DC/DC converter steps down the electricity from 25V to 12V so it can be used for the vehicle's electrical components.

Providing there is sufficient charge stored, all the vehicle's electric components are powered by the capacitor and the battery, thereby removing the need for the engine to generate electricity through the alternator by burning extra fuel. The alternator is switched off when the accelerator pedal is depressed and when the i-stop idling stop system is active, and switched on only when the vehicle is decelerating. During city driving with frequent acceleration and deceleration, charging mostly recommences before the capacitor is fully discharged. Therefore, i-ELOOP can provide nearly all of the vehicle's electricity requirement. This combination of minimizing the amount of fuel needed for electricity generation and efficiently recovering, storing and reusing energy enables Mazda to deliver significantly improved fuel economy.