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Published on September 2nd, 2011 | by Guest Contributor


Harvesting the Energy in Intermittent, Gusty Winds

September 2nd, 2011 by  

by John Saavedra of Look for the Power

Almost every available article on wind energy has, at its foundation, the assumption that the winds must be relatively strong, constant, and from one general direction.

This closely correlates with the assumption that to generate electricity, a shaft must be rotated within a magnetic field, and that this rotation has to be in one direction (for example, clockwise).

These two assumptions are so universally held and widely believed that they are never explicitly stated, and to question them would be almost heretical, if not anarchist.

So, boldly going where no geek has gone before, let’s get in touch with our revolutionary roots, channel some leftover teenage angst, and look at them.

Remember the generator set you had on your bicycle growing up, the one that clamped against one of the tires and generated enough electricity to light a headlight and taillight?  That setup works regardless of the direction of the rotation of the tire.  Assuming you were dare devil enough to ride backwards, the output of the generator and lights was the same as going forward.

Wind atlases of the USA, and the world, are readily available.  When looking at them, one quickly realizes that:

  1. Obviously, preference is given to locations with relatively strong winds (Classes 5-7).
  2. Most of the USA, and the world, has only Class 1-3 winds, not considered viable for the production of wind energy.

Here is a representative statement from the National Renewable Energy Labs website:

          There is little wind energy potential in the Southeast region for existing wind turbine applications (Zabransky et al. 1981)

Is this true?  Does this mean that the Southeast doesn’t get wind?  The answer is obviously “No,” but rather that using existing technologies, the projected outputs do not have enough promise to recover installation costs.

Let’s move a moment from the scientific method to an anecdotal method by taking a simple, four-question quiz:

  1. Have you ever had to change a flat tire beside a busy Interstate highway with regular vehicle traffic and 18-wheelers moving past at 70+ mph?  Feel anything?  I use the word ‘fearsome’ to describe the turbulence generated.
  2. Have you ever carried a 4 x 8 sheet of 3/4” plywood on a roof?  Did you notice how strong the force of even a light wind was on the flat, rigid surface of the plywood?  It is easy to get blown off the roof by even a moderate breeze.
  3. Ever securely tied a mattress and box springs in the back of a pickup truck for moving, only to have them blow off at 30 mph, which usually correlates to “about halfway up the busy Interstate entrance ramp”?
  4. Ever tried to erect a tent or install an outdoor sign or canopy in a breeze, or wind?

If you scored even a “D” on this quiz by answering “Yes” just once, you’ll not be surprised to learn that of the energy contained in a gallon of gas burned by a vehicle travelling at highway speeds, approximately 25% is used overcoming the rolling resistance of the tires, 15% is used overcoming inertia, but the bulk of the energy — 60% — is spent overcoming aerodynamic drag.  This leaves aerodynamic turbulence in its wake — all of which is currently wasted.  None is harvested.

Here is a draftsman’s rendition of an electrical generator I built in my backyard that captures intermittent, gusty winds, the types found over much of the surface of the USA, and beside every Interstate highway (click to enlarge):

This is a perimeter frame of 3” DWV PVC pipe, holding a 4 x 8 sheet of ¾” plywood, hanging vertically, suspended from an axle/shaft along its top edge.  In an intermittent, gusty breeze, the panel rocks back and forth, like an old-fashioned gas station sign.  As it rocks, it turns the large central pulley bolted to its axle/shaft.  This drives a V-belt, which in turn drives two much smaller pulleys (44 and 46) at higher RPM’s.  These two small pulleys are bolted to permanent-magnet alternators, which generate current whenever the large plywood flap is in motion.

In a constant breeze, or no breeze, no energy is produced.  This system requires intermittent, gusty winds, as it is the reciprocation of the plywood ‘flap’ that generates electricity.

OK, now that you’ve let go of some of the constraints you’ve lived under ever since you were involved in energy, consider this picture, taken near my home in South Carolina (although it could easily represent the signs near you):

Can you just FEEL the turbulence?  Good — it’s working.

The horizontal portion of the sign support doubles as a walkway for service personnel to work on the signs.  Federal highway standards require that all such Interstate signs withstand 120 mph winds so as not to fall down during hurricanes, tornadoes, thunderstorms, etc.  So, both the vertical and horizontal portions of the support are sized accordingly.  In non-technical terms — big and heavy.

What if we borrowed the basic design from old-fashioned gas station signs and:

  1. Built a perimeter frame around the green signs
  2. Suspended the green signs from an axle/shaft located and fixed along their top edges (again, think of a gas station sign)
  3. Bolted this shaft to a cam or elliptical gears to limit the rotation so the sign would not go horizontal (unreadable)
  4. Designed the cam/elliptical gears so that the stronger the wind, the higher the low-speed torque on the shaft, and the smaller the rotation off of vertical
  5. Bolted the shaft to a gearbox/transmission to convert the high-torque, low-speed rotation of the signs to lower-torque, higher-RPM rotation required by permanent-magnet alternators
  6. Stored the resulting current in either capacitors or deep-cycle batteries
  7. Used the current to power LED lights to illuminate the signs at night/low light
  8. Sold any excess, leftover current to the existing utility (notice the electrical lines along both sides of the picture)…

Careful readers, what am I missing here?

Answer — funding to research materials, sizes, sites, outputs, and to build prototypes.

Here are some immediate advantages:

  1. Take existing signs off the grid for night-time illumination
  2. Address problems with glare by allowing small, constant changes to the vertical/viewing angle of the signs
  3. Reduce signage costs by allowing for lighter materials to be used in the supports.

This idea may have particular appeal to the one in four people on Earth currently living off of any electrical grid, which closely correlates to poverty, illiteracy, disease, hunger, unsafe drinking water, infant mortality, and other problems.

My website — lookforthepower.com — describes this and several other projects in more detail, if you are interested.

Your comments, feedback, reactions, and suggestion are all welcome.



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