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Flexible circuit wind generator

A new way to generate wind energy using only polyester film based flexible circuits

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This project involved the development of a brand new type of wind generator called a FLAG; a Flexible Linear Aeroelectrostatic Generator. It uses the motion of a flexible circuit to generate electricity.

A FLAG is made by cutting thin polyester film into the required shape, surfacing
it with a pattern of conductive areas that make it work as an electrostatic machine, and then folding the plastic into the final shape of the generator. When exposed to the wind, the generator oscillates, and the relative motion of the conductive areas extracts work from the wind, allowing the circuit harvest electricity continuously.

This demonstration prototype requires only plastic film, conductive tape, and three diodes (no 3D printing required). Imagine a future with lightweight power generating kites, flags, and leaves!

A FLAG is one of the first thin film technologies successfully prototyped for outdoor wind power.  It is essentially a self-actuated-air-valve made of thin plastic film, combined with an electrostatic machine.  This simple, lightweight, inexpensive, easily manufactured, and recyclable technology is a new way to generate small scale electricity.  FLAGs can have the appearance of flags, or leaves, and are light enough for airborne wind power.

The generator is surfaced with conductive areas called "sectors", that generally act as variable capacitors.  Either mechanical contact switches, or diodes are also used to strategically transfer charges between sectors, so that the mechanical work of pulling the oppositely charged sectors apart can generate electricity.  A number of different harvesting circuits have been successfully prototyped in combination with the aerodynamic oscillator.  This particular FLAG build uses diodes, and the circuit used is depicted below. 

C1 is essentially a variable capacitor consisting of three sectors, each mounted onto one of three layers of the polyester film. The inner sector can move back and forth between the other two, and the charge on C1 is increased by a factor of 2 each reciprocation (if connected to ground).  This design is not connected to ground for ease of construction, so the factor is likely reduced to 1.6.  C2 is an energy storage capacitor, which is not absolutely necessary but improves the reliability of the machine and size of the output current pulses.  The circuit is similar to one described in De Queiroz, A. C. M. (2016). Energy harvesting using symmetrical electrostatic generators. 2016 IEEE International Symposium on Circuits and Systems (ISCAS). doi:10.1109/iscas.2016.752732, except this circuit uses the equivalent of a three plate variable capacitor, instead of two synchronized variable capacitors, and there is no true ground connection.

The generator is made of one piece of polyester film, cut and folded into three layers.  The outer layers have holes which cause the inner layer to oscillate in the wind.  The inner layer of film blocks one set of holes, causing air to flow through the opposite set of holes, ultimately creating a very stable and repeatable oscillation over a wide range of windspeeds.

The FLAG prototypes operate at windspeeds in the approximate range of 15-50 km/h.  The thinner films are lighter, and have a lower cut-in speed, but theoretically cannot operate at as high of voltages.  At 20 km/h, the oscillating frequency is in the range of 10 Hz.

Since the conductive surfaces are open-to-air, the output is affected by humidity.  The generator is self-starting and works well up to 60% humidity, depending on the materials used.  At low humidity they have run at up to 2 kV (occasionally causing breakdown of the polyester film).  Higher operating voltages result in significantly higher power outputs, so future improvements should include fully enclosing the conductors in polyester. 

The two other thin film technologies that have been attempted for wind power applications are piezoelectric films, and TENG (triboelectric nano generators).  FLAG has some advantages over these technologies including the use of non-specialty materials, low cost, and relative insensitivity to humidity. 

NOTES TO HACKERS/MAKERS:

 ● Recently, the circuits needed to cheaply and efficiently convert pulses of high-voltage-low-current to more useful voltages have been invented, using only diodes and capacitors: Fractal converter circuit

● It might seem like a good idea to insulate the conductive surfaces with an insulating tape.  Insulating the generator with tape instead has a negative impact on the performance.  I believe this is because charges migrate past the adhesive after a few seconds or minutes, creating an electret like effect.  I've tried...

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FLAG Instructions.pdf

Detailed instructions with photos explaining how to make a thin film wind generator.

Adobe Portable Document Format - 6.73 MB - 09/26/2021 at 16:37

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ms-excel - 1.33 MB - 10/10/2021 at 22:44

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  • 1 × polyester film .002" - .005" thickness, at least 7" x 24"
  • 2 × conductive tape 3M 3190 - 10.3x10 sheets
  • 3 × diodes 1N4007, or M100FF3
  • 1 × load T4 fluorescent light bulb

  • FLAG Project History #6

    Stuart MacKenzie4 days ago 0 comments

    Trying to identify the causes of success and failure, I built over 200 prototypes, using different designs and materials.

    What I eventually realized, was that plastic film materials intended for printing cannot be used.  The pre-treatments given to plastic for printing seem to cause adsorption of humidity from the air, giving them poor surface resistivity.  I also discovered problems with insulating the generators with tape.  My theory is that charges migrate through the tape adhesive, and build up there-  creating a parasitic capacitance with the sectors that eventually stops the machine.

    Using no insulating tape, and only insulating using polyester film, I started to get consistent results.  I carefully designed the generator so that all the oppositely charged conductors are on opposing film surfaces, or have a large distance between them.  These two things combined allowed the generator to be self-starting at up to 60% relative humidity, and with a "jump start", it will run at higher.  I believe the power output can be increased significantly by encasing the sectors within the polyester, but this sort of manufacturing is beyond what I can do at my desk.

  • FLAG Project History #5

    Stuart MacKenzie4 days ago 0 comments

    The poor humidity performance and unreliable switching was persisting, so at this point I decided to get rid of the surface contact switches altogether and replace them with diodes.  I also changed the design to get better separation of the oppositely charged areas, and started trying different materials and insulating the generators with tape.  I also bought a Cricut cutting machine to make the generators more quickly with the time I had available.  I tried some designs with the diodes housed in a 3D printed mast, and very simple 3 or 4 diode harvesting circuits.  This is a 3-sector design, with no storage capacitor:

    The design later progressed to having the diodes mounted in small 3D printed swivel rings that can slide over the fluorescent light itself, or over a piece of acrylic tubing if I want to try powering some other kind of load.  The rings are 2-pieces, and are put together with a small zip-tie, which squeezes the ring a little bit and pinches the electrical connections between the diodes and the conductive film.  You can see on these generators, I'm using small elastic bands to restrict the distance that the generator opens in the wind.  One nice thing about this design, is that the electrical connections are secure, and there are no sliding contacts or subject to repeated stress.  The use of diodes instead of surface contact switching allowed for a design with all the oppositely charged surfaces to be very physically separated, which really improved the performance in ordinary air humidity.  Variations of this overall design are still among my favorites, but they require a high resolution 3d printer:

  • FLAG Project History #4

    Stuart MacKenzie4 days ago 0 comments

    After the first successful prototype, I started making more generators in this style, mostly by hand.  I refined the design a little bit;  I gave it some supports so it could be hung from an acrylic rod or directly from a fluorescent light.  I also put the power output on those supports, so I would no longer need to use alligator clips when testing.  Here is an example, where you can see the power outputs (+ and -) on the outside supports, and the "ground" connection (approximately equivalent to a "neutralizer" on a Wimshurst machine) on the center support.

    As the generators oscillate very quickly, whenever one wouldn't work I often couldn't tell what the problem was. For troubleshooting, I built a "stroboscope" by hacking into an automotive timing light and adjusting the strobe timing with an arduino.  With my stroboscope, I could turn out the lights, and adjust the frequency of the strobe light to be close to the oscillating frequency of the FLAG.  This would create the optical illusion of the FLAG moving in slow motion to help me troubleshoot it.  The light beam was a little too narrow to make the illusion perfect, but it was good enough to be helpful.

    The slow-motion on the newer iPhone models has become so good, the stroboscope was quickly retired. 

  • FLAG Project History #3

    Stuart MacKenzie4 days ago 0 comments

    It was May 2018 when I had the first successful test of a FLAG, oscillating in the wind to power a light.  Despite trying many different variations and circuits, you will notice the design still looks very similar to the original 4-sector 3-layer acrylic test shown in the last log.

    In order to make the generator oscillate in the wind, I took a rectangular piece of polyester transparency, folded it in half, and cut out rectangular vent holes.  A second piece of polyester goes inside the "V", and when held in the wind, the center film oscillates at a fairly high frequency.  The center film covers one set of holes, causing the air to pass through the opposite holes, which essentially sucks the center film to the opposite site...  over and over, at high speed.  

    The harvesting circuit and sectors stuck onto the film was made using ordinary aluminum foil tape, with the tips folded over wherever an electrical connection was needed.  Alligator clips were connected from the bottom two connections to power a fluorescent light.  The tabs of tape sticking out were what I used to hold it in the airflow from my "wind tunnel", and holding it relatively fixed like this makes the generator oscillate at much higher frequency.  This is something I still wish to experiment with further, as the latest FLAG designs run at a much lower frequency.  Generally speaking these sorts generators will theoretically make more power per unit volume at higher frequencies, with less travel, and more layers.

    After all the effort in getting to this point, I had the first working FLAG framed. 

    The generator still had some problems to be sorted out.  It still seemed to be sensitive to humidity, and the mechanical contacts were still unreliable.   More to come in the following logs.

  • FLAG Project History #2

    Stuart MacKenzie4 days ago 0 comments

    Sometime around 2010, I unpacked a box and found what was still a sorry excuse for a wind generator.  After a few years of thinking about it, I decided that it might have a better chance of working if the motion was simple reciprocation instead of the wave-like motion that was required in the previous iterations.  I had an idea for something a little more basic, and just to try it out, I built a test out of 1/8" acrylic.  This was a new 4-sector machine, with unique flat contact switching on it.  Back and forth action causes the inner sectors to alternately approach the other sectors, and the switches connect the sectors to each other and ground in such a way that the charges double each cycle (though I don't think a true doubling is possible without a good connection to ground-  in this case I think the charge multiplier theoretically approaches 1.62).  After a minute or so of shaking the generator, the compact fluorescent light would blink with every shake.  The wires were very well insulated with silicone fuel line tubing.

    This was encouraging enough to bring the FLAG project back to life.  I started making new generators out of thin films that were more similar to this acrylic test, and started experimenting with ways to make something like this reciprocate in the wind.  Progress was very slow- now having 3 kids I would work on it whenever I had a little bit of spare time.  I moved the blower I had been using from the previous experiments from my workplace into my garage for occasional wind tunnel testing.  

  • FLAG Project History #1

    Stuart MacKenzie4 days ago 0 comments

    The idea for this project first started after seeing a demonstration of a Wimshurst machine, a type of rotary electrostatic machine known as an "influence machine".  These machines use electric fields, not friction, to generate electricity.  It might be easiest to think of these machines as charge copiers.  Starting with whatever tiny charge imbalance there is between two conductive "sectors" when they are close together, the sectors are physically pulled apart from each other, causing the capacitance to decrease, and the voltage to increase.  The higher voltage makes it possible to move the charges around, and with at least 3 sectors and by repeating the motion, there are switching operations that can be carried out that will copy the charges over and over, until the machine is operating at thousands of volts.  A description of the design and operation of the Wimshurst machine can be found here:  Wimshurst machine - Wikipedia, though the electrical circuit used on the latest FLAG prototypes is more similar to a machine called Wilson's Machine, or another one called Bennet's Doubler.  

    Virtually all the historical electrostatic influence machines were invented in the late 1800's or early 1900's, and the invention of today's common electromagnetic generator quickly made them obsolete.  They were mostly made of glass, and since that time, plastic materials with superior electrical performance now existed.

    I was very interested in wind energy, and it seemed to me like it might be straightforward to make a linearized version of the Wimshurst machine into a new sort of wind generator without many parts.  I imagined this a little like unwrapping the two plates of a Wimshurst machine into straight lines, and that the two layers could flutter against each other in the wind in a wave-like motion to make electricity.  I proceeded to make many, many failures, from approximately the years 2000-2005 before focusing on a family generators that looked like the one shown below.  These were being made using polyester transparencies, and hardware store aluminum foil tape.

    It has multiple sectors, cascading switches, and grounding on the inside in the center.  The sectors naturally each charge to the opposite polarity of the adjacent sector, and a rythmic wave motion would cause the machine to accumulate charge, until crackling with arcs and the smell of ozone!  The machine electrically worked very well if you were to make it move by hand (and it delivered some nasty shocks), but I eventually ran into a few problems that seemed insurmountable.  As a separate effort, I was trying to get the required motion from two layers of film in moving air using a shop blower at my workplace.  The two layer design had a rather weak and unreliable reciprocating motion, and the surface contacts would not work reliably like this.  Electrically, this design also didn't work well in humidity, and it became obvious it would never make any electricity from the wind this way.  At this point I was getting married, moving houses, and starting to have kids.  The generator project was packed into a box and went to sleep for a few years...

View all 6 project logs

  • 1
    How to Build a FLAG

    Here are some detailed instructions on how to build a FLAG, with lots of photos. These instructions are for making one using a Cricut hobby cutting machine, and there are links to all of the Cricut files in the instructions.  A hobby cutter is easiest, but the patterns can also be cut out with a sharp knife and patience. 

    FLAG Instructions.pdf (hackaday.io)

    This is a demonstration design, intended to be as easy as possible to make and not requiring any 3D printed parts.  It is not intended for extended use or high performance.

View all instructions

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Paul McClay wrote 21 hours ago point

Persistence FTW

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Walker Arce wrote 3 days ago point

Impressive!  I look forward to seeing where your technology goes.

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Krzysztof wrote 3 days ago point

Fractal switched capacitor convertors - this is the thing I needed and I thought that such thing must exist already. Now, this will be the new hotness for ion - flyer drones :)

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