Generating Electricity From the Wind Using a Plastic Film That Flaps in the Breeze

Generating electricity from wind

When discussing how we can effectively harness the free, clean energy coming from the wind as a solution to our current climate crisis, most people probably imagine a large wind farm dotted with turbines. These are great for centralized power production, but their massive size and unsightliness can be a problem to many. So rather than attempting to reinvent the windmill, Stuart MacKenzie came up with the Flexible Linear Aeroelectrostatic Generator, or FLAG for short, which can be placed in discrete locations for transforming the wind's energy into small amounts of electric power that can be used in embedded devices.

Theory behind the circuit

A wind turbine operates by pointing a propeller against the wind's direction and using its force to rotate a shaft connected to a generator. As it spins a copper coil within a magnetic field, an electric current is produced and sent for distribution.

MacKenzie's FLAG system, on the other hand, relies on a three-plate variable capacitor where a middle conductive surface oscillates between the two outer conductive surfaces. Due to the presence of diodes creating opposing charges, this movement creates a current which can then be passed through an attached load and an additional diode to maintain a single polarity. MacKenzie also included a small energy storage capacitor which helps to smooth the resulting power.

Cutting the film and layering conductors

For a base layer, MacKenzie went with a single, thin film of polyester because, unlike other plastics, it lacked surface treatments that would otherwise cause it to become too conductive or too stiff. The polyester piece was then precisely cut with the intent of being folded into three layers.

The outer layers have holes, whereas the inner layer selectively blocks a few of them depending on which direction the FLAG is currently pointing. By cutting the sheet in this manner, stable and repeatable oscillations can be achieved over a wide gamut of wind speeds.

Final assembly and testing

After attaching the conductive tape strips to all of the correct locations, folding the FLAG a few times, and adding diodes, MacKenzie was able to light several LEDs in series each time there was an oscillation. At a wind speed of 20 km/h, this worked out to be 10Hz. But because the outputted power was at a high voltage and low current, it was not conducive for powering embedded devices or charging a battery. To achieve a high efficiency conversion without much voltage drop, MacKenzie created a 96-unit fractal switched capacitor converter that charges many capacitors in series, yet discharges them in parallel.

Results

Now with a working power generation system and a way to convert its output into something more manageable, MacKenzie connected several LEDs again, except this time in parallel to test current delivery. Much to his delight, the system worked as expected, although he did acknowledge that increasing the oscillation frequency and number of layers would go a long ways towards improving power generation even further.

You can read about this project in much greater detail here in MacKenzie's Hackaday.io write-up, which also has instructions for those who wish to build their own versions of the FLAG system.