The world has become increasingly dependent on renewable energy sources such as solar, wind,
biogas etc. We chose to work on wind energy for this project. In this context, we focused on
developing a product that can generate electricity using the kinetic energy of the wind. All the
conventional wind mills have a simple phenomenon of doing the same. A typical wind mill has a
rotating device called “turbine” which rotates when wind flows over it. The shaft is coupled to a
dynamo and thus electricity is generated. This process sounds pretty good. But, when we try to
apply it on a small scale level, for example lighting a LED or charging a mobile phone etc., there are
a lot of problems involved. Rotation‐based wind turbines don’t scale down well due to friction and
he lower energy of lower wind speeds. So, there is a need to develop a new innovation which does t
not use rotary equipment, to achieve the required targets at the small scale.
By applying TRIZ techniques (TRIZ is a theory of inventive problem solving), one can easily say that
turbine is the part that is causing all the trouble. So, we simply eliminated it! Now, we need some
mechanism to capture the wind energy. After rotation, one can think of vibration. So, let there be a
membrane vibrating due to the wind. If we place magnets at its ends and make them oscillate in and
out of a copper coil, electricity can be produced! Shawn Frayne, an MIT graduate was the first
person to discover this idea and he created something called “Windbelt”. He started a company by
the name “Humdinger” which sells these Windbelts. Inspired by him, we tried out working on the
same principle in this course.
Until recently, the only viable wind harvesting device was the turbine. Humdinger’s Windbelt is the
first non‐incremental innovation beyond this century‐old approach. Instead of using conventional
geared, rotating airfoils to pull energy from the wind, the Windbelt relies on an aerodynamic
phenomenon known as “aeroelastic flutter”. This phenomenon is a well‐known destructive force.
However, it can also be used as a powerful mechanism for catching the wind at scales and costs
beyond the reach of turbines. At its heart, The Windbelt uses a tensioned membrane undergoing a
flutter oscillation to pull energy from the wind.
To picture how this works, think of how you held a blade of grass between your fingers as a kid and
made it whistle—or how the strapping on a truck can be seen moving in the wind. That is roughly
how the Windbelt can pull energy from the wind—then, it’s a second step to turn that energy of the
moving membrane into electricity, which is done by actuating new types of linear generators.
The Tacoma Narrows Bridge callapse is a famous example of the destructive power of aero elastic
flutter. The bridge across Puget Sound opened on July 1, 1940. Four months later a strong
continuous wind induced oscillation into the structure, which showed torsional and longitudinal
flutter, eventually causing its collapse. The photos given below are stills from video footage of that
flutter and collapse. Structural engineers studied the failure; newer suspension bridges were built
differently to avoid such oscillation.
How does the Windbelt turn its “flutter” into electricity? A pair of magnets is fastened to the belt, so
as the belt moves up and down the magnets follow the same motion. This motion of the magnets
takes place directly next to the stator (coil). A magnetic field moving next to a coil of wire induces a
current to flow. As generated, the electricity is alternating current (AC). This AC may be converted
o direct current (DC) with the enclosed rectifier. t
The Windbelt consists of a taut membrane made of Mylar coated Taffeta, 2 cap magnets, copper coil
and a frame to hold these equipment. Apart from this, it consists of an electrical unit that gives the
desired output power.
3D Model of our product:
This figure shows a basic model of our Windbelt. There is a lot of scope for improvement and more
ower can be obtained using multiple belts in parallel. p
Important materials involved in this project are Cap magnets, Copper coil and of course, a belt
• Magnets – Disc Magnets NdFeB / Neodymium
Stator coils – Cu
• Belt material – Mylar coated taffeta tape, Gun tape, Duct tape, Polystyrene ribbon, Packaging
tape, Video disc tape
Rough cost of the project we carried out:
Object Quantity Dimensions Co `) st (
Belt 1 1 meter long 15
Wooden frame 1 Slightly longer than belt 25
Magnets 2 1cm diameter 60
Stator coils 2 ‐ 20
‐ Differe t sizes n 20
Rough cost estimates of a final useful product:
Object Quantity Dimensions Co `) st (
Frame 1 1m x 5cm x 2cm 25
Belt 1 1m x 2cm 30
Magnets 4 80
Stator coils 4 30
Rectifier 1 ‐ 15
Nails, Nuts and Bolts ‐ Different sizes 10
hus, a basic model of a wind belt costs less than `200 to manufacture. T
Our work (in photographs)
We played around with tools and materials in CFI (Center for Innovation), IIT Madras and finally
built a Windbelt prototype!
Windbelt consists of two cap magnets, which move in and out of two copper coils connected in
series. So there is change in magnetic flux which produces electricity in the coil. The output from
the coil is AC, can be converted DC through a rectifier circuit attached between two terminals of
Voltage output from Windbelt V=20.19 mV and current output I=0.04A (measured using
belt prototype Therefore power output from Wind
P=V*I=0.81 mV ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ (1)
pproximating vibrations of the membrane (belt) to a parabolic shape A
Belt at stationary
Belt under vibrations
Here =1.0cm, equation of the parabola passing through 3 points (0,0), (47.5,1), (95,0) is
4.432 10 0.0421
So area swept by belt (under vibrations) across wind flow is
2 = 126.63
ned in wiPower contai nd can be found by
Here density of air, =1.23
Swept area, A=126.63
Velocity of wind, v=2 (Table fan setting 2)
Therefore power P=15.57mW ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ (2)
100Efficiency of Windbelt = = 5.20%
Advantages of a Windbelt
• The Windbelt is a light weight, low cost, portable, easy‐to‐use device.
• The 1 meter Windbelts are designed to work alone or in groups to provide power to
or any situation demanding 0.1 kWh to 1 kWh of lighting, WiFi nodes, micro‐base stations,
energy per month.
It can also be used for lighting bed lamps.
• a mobile A Windbelt can be kept on a moving car and the output can be used to charge
phone while travelling.
• A Windbelt can be placed on poles in high wind zones and used for street lighting.
• An array of Windbelts placed side by side can form a “Windcell” and it may be used to light
up an entire room!
The Windcell have a form factor similar to Solar panels and are designed for larger installations,
targeting applications with 5 kWh to several MWh of energy demand per month, with particular
attention to cost.
On larger installations, the Windcell panels have an initial projected production cost of Rs. 2.5 per
kWh (at 6m/s average wind speed).
Cost combined with modularity, safety and form factor gives the variation of the technology access
to many of the places that wind and solar cannot presently go.
Scope for further improvement
There is a lot of scope for improving the design of the Windbelt for a better performance.
• One straightforward improvement in performance efficiency would be to use magnets of
and length higher strength, coils with more number of turns and belt with optimum tension
to be in resonance.
The number of magnets and coils used can also be increased for a higher output.
• As mentioned earlier, a series of Windbelts can be used to form a Windcell, so that we can
get output for medium scale appliances as well.
• The design can be modified in such a way that the wind is directed on to the belts. One such
example is shown in the following figure.
Q: What if the belt does not vibrate?
A: The belt tension can be increased or decreased (as the Windbelt is in the moving airstream).
Make sure that the magnets are not stuck to the stator. If the belt is mounted so close to the stator
that the magnets are clinging to the stator, the Windbelt should be rotated so that the wind blows
hrough it from the other side. Otherwise, the belt should be remounted with proper spacing
etween the belt and stator.
Q: The belt is vibrating there is no electrical output.
A: The stator should be installed in the proper orientation and the pair of magnets is so close to—
but not touching—the stator. Otherwise, there will not be any electrical output.
Q: The belt is seems to be in torsion, and is generating very little output.
A: Measure the electrical output (if any) with a meter to have a comparison. Then flick the belt with
your finger. If that does not work, the belt tension can be varied with fingers. Try rotating the
indbelt so the air blows through from the other side. Torsional flutter often occurs when the belt
s incorrectly tensioned, misaligned on the bolts, or too close to the stator.
Q: Is it ok to hook up two or more units together to power a bigger load?
A: Yes, as long as they are hooked up in parallel (positive‐to‐positive, and negative‐to‐negative).
ote: If they are in series, the induced current from one Windbelt may flow through the coil of the
ther Windbelt, and potentially disrupt the induced current generation of that generator.
s it matter if the Windbelt is horizontal or vertical when it is in front of the fan?
Q: What is the expected electrical output?
A: 10mW to100mW (milliWatts), depending on wind speed. At 6m/s wind speed, around 50mW is
delivered to the load. Voltage, unloaded, will be around 2‐3 volts AC before rectification.
Q: How does moving a magnet past a coil generate electricity?
A: This process is called electromagnetic induction
Q: At what frequency does the wind usually vibrate?
A: The 0.5 meter Windbelts will vibrate at around 70‐100 Hz. The 1 meter Windbelt vibrates at a
lower frequency: 20‐50 Hz range ideally. Frequency varies depending on belt thickness, belt
ension, wind speed etc. t