Vertical Axis Wind Turbine (VAWT) Project
Not all wind turbines are like the conventional "wind mills" with a horizontal shaft. There is also the vertical axis wind turbine, or VAWT, that operates like an anemometer, the device used to measure windspeed. This project has taken quite a bit of time. You can see a previous blog entry that described the fabrication of the aluminum "wings."
Now the wings are attached to an aluminum cross piece and held rigidly in place with a system of hardened steel tubes that slip through holes in the ribs and the ends of the cross piece. The outside diameter is 8 feet. The height of the wings is 6 feet. The rectangular area of 48 square feet converts to about 4.46 square meters. The turbine is connected to a permanent magnet alternator by means of a chain and sprocket that uses a 5:1 ratio.
The alternator has two 12 inch diameter rotors that each have 12 neodymium disk magnets measuring 1.47 inche in diameter and .6 inches thick. Between the rotors is the stator consisting of 9 coils of awg #20 wire, 200 turns each. The coils are arranged to produce 3-phase ac. Each phase has 3 coils wired in series. There are 3 full wave bridge rectifiers, one for each phase. Each is isolated from the other. All three rectified dc outputs are wired together in parallel and the dc is sent via cable to the battery bank.
The stator is made by sandwiching the coils between two pieces of epoxy fiber glass board, the kind used in the manufacture of printed circuit boards. The top and bottom sheets, each 1/16 inch thick, are held together with bolts. They have reinforcing ribs added for stiffness. Power is brought out by means of stainless steel machine screws.
You can download an avi video clip of the turbine working in a 4 mph breeze (caution! almost 4 megabytes!) At the time the clip was made, the turbine was charging the 12 volt battery bank at about 0.5 amp, or about 6 watts. I have taken some information on computing the energy in wind from a very interesting fellow named Charles Morrison in hopes of comparing it with the energy actually produced to estimate the turbine's efficiency. Maybe some expert readers will comment on the appropriateness of my calculations.
The power density, or watts per square meter, at sea level is .05472 * V^3
The product of the power density and the swept area in square meters equals the total energy available in the wind that passes through the turbine. Not all this energy can be extracted. In fact, the Betz limit states that only 59% can be extracted. So in the 4 mph wind, the total energy that could be extracted by a perfect wind turbine with a swept area of 4.46 square meters would be 9.2 watts. Since the turbine actually puts out about 6 watts, it is operating at an efficiency of about 65% at this time. This is extremely high by most standards. It makes me wonder about my methodology or the accuracy of my anemometer.
Here are some photos of the stator assembly.
The epoxy-fiberglass board, called G10 board, is available in various thicknesses. This photo shows how reinforcing ribs were glued to the sheet using epoxy.
The stator was made in two halves. This facilitates experimentation by allowing for easy set-up and knock-down of various configurations.
The two halves go together. Stainless steel machine screws are used as connection points for each coil.
This is the underside showing the screw lugs which will connect the coils for 3-phase. Each phase consists of three coils wired in series. Starting with one coil and moving around the stator, a phase is every third coil wired together.
Top and bottom sheets are screwed together using stainless machine screws. Aluminum angle stock around the perimeter adds a great deal of stiffness to the G10 board.
The schematic diagram below portrays the circuitry that rectifies the 3-phase ac into dc voltage. Each phase represents three coils in the stator. Each group of three series-wired coils is connected to a full wave bridge rectifier. The dc outputs of the rectifiers are parallel-wired together. To achieve higher voltage, the dc outputs of the three bridge circuits could be series-wired.
A wind turbine like this experiences large forces at the point where the airfoils are attached to the rotor arm. There are centrifugal forces which tend to pull the airfoils apart; there are twisting forces caused by the wind pushing more on the top half of the airfoil than on the bottom half. It is extremely important to make the connection at this point a solid one. In this design hardened steel tubing fits through holes in the ribs of the airfoils and in the rotor arm. The tubing has steel plates welded to each piece. These plates facilitate bolting the parts to the airfoil ribs and to the rotor arm. Two outside pieces, A and B, of tubing slide down over the center piece. Using bolts to hold the tubing in place makes it possible to easily disassemble and remove the airfoils from the rotor arm.
The sketch below may clarify the tubing arrangement and show how it fits on the rotor arm. Parts A and B are identical and are made of slightly larger tubing than C.
UPDATE March 6, 2007
The weather cooperated and gave me a day of steady winds 11-13 mph, and I was able to test the VAWT.
I watched the analog ammeter reach 5 amps during the gusts. Assuming the charge voltage was 14 volts, that represents about 70 watts of power produced. How does that compare with the theoretical formula?
Watts = Conversion constant * Betz limit * efficiency * area in sq. m * wind^3
In a perfectly efficient turbine,
Watts = .05472 * 59% * 100% * 4.46 * 13^3 =316 watts
The 70 watts actually produced suggests an efficiency of 22% at this windspeed, considerably less than the 65% computed above in the 4 mph wind. This certainly needs more investigation to better understand what is going on.
That is a great construction job ! ! I love to see other people proceeding
with their own ideas. I see you as a person who has great self confidence.
Very interesting project. I will get some of our studets to give it a go in
the energy project.
Hi your wind project looks great and am very interested in your comments
and stats you may already know this but I read somewhere that if you pour a
mixture of carbon powder and fine iron fileings mixed with a quick setting
resin like car body fillers and fill up the space in the middle of your
coils this is supposed to greatly improve the efficiency of the generation.
Regards
Tom
The setting of wings is very important. You can try modify the angles of
wings. It's possible at 4 mph wind the angles are good but at stronger
wings those are not good. Try multifarious of angles.
Sorry, I haven't good English!
I've just come across your web page and was encouraged to see other DIYers
generating electricity.
A few months ago I made myself a neodymium magnet generator out of 16
small round magnets with 16 coils of very thin wire (29 SWG?). I can light
a 60W mains bulb with it when I connect it to my cycle trainer. My measured
voltage was over 150V.
I'd really like to make a VAWT now but am having problems working out the
values for magnets, wire gauge, number of turns etc to give me a generator
that gives good outpur at low revs. How did you work it out?
Keep updating your pages. Good luck.
Good job. I think your efficiency calculation has a math error:
I have always been fascinated by the VAWT. With that being said have you
considered making the air foils taller while decreasing the overall
diameter. This would increase RPMs while the increased heigth would
maintain torque. I would think this might enable you to get rid of the
gearing.
Dennis, I am sad to say my blades are lying in a pile on the ground. We
have had several fierce wind storms and the last one ripped apart the
wooden cross piece that held the blades in place. I don't think I'd want to
make my blades much taller than they were. It becomes hard to build them
strong enough. I think you will be better off than me with your three
blades. When I rebuild, I will make three.
I am building a vawt something like the one you show.Different H X W. and
larger mangnets.I tried to time the rpm's from your vidio.It came out to
about 16 rpm a miniute.Is that correct.
Have you tried to place your vains closer then 8 ft? If so what were the
results.
I made my 1 wing so far out of 12" and 10" round heating duck pipe
[21 ga.It is pre rolled.LOL
Have you ever did a 3 wing?
tks
Johnny
16 RPM is about right for a gentle breeze. 60 RPM is common for moderate
winds. I think a 3-wing unit would be better than mine in strong winds.
I've not tried it, however. The large diameter is not helpful in high
winds. In one really big windstorm the rotor was quite erratic in its
behavior. Shortening the diameter to about 5 feet increased the rpms and
improved the performance in high winds.
That cool rotor, but i am finding for schemes, does anybody know source?
Solar panels are use to make renewable energy from sun,Most places in the
high plains have plenty of solar energy available to meet some, or all of
your needs.
A solar system is ideal for urban areas where building codes prevent a
<a href="http://highplainswindandsolar.com/">wind turbine</a>.
A good article for DIY vertical wind turbine. I have some advices on the
blade shape design. This blade is the tradational shape. Actually there
are many new blade design for Vertical wind turbines. You may see the
Aeolos or helix websites. They have good design on the blades.
This type of turbine will work much better if the return side is completely
covered by a flap and it is possible to arrange them that the wind is
increased on the push side. I am planning to make one that is a lot wider
but also taller but with wind intake controlled by the flaps. I wonder
how important the size of the blades is. Only about 50% of the wind force
can be used but I wonder if there is a formula for the optimum blade size
to achieve maximum output. .
Horizontal axis wind turbines (HAWTs) are the most common wind turbines
used. Consisting of one to three blades that spin around a rotor, these
turbines look like giant propellers jutting from the landscape atop an
aerodynamic tower on a hillside. Wind passes through the blades, affecting
the pressure on either side. This pressure creates a lift force that causes
the blades to rotate around the rotor. The rotor converts the power of the
wind into usable energy. Both cost effective and efficient, these turbines
harness the power of the winds that blow several meters above the ground.
The problem with horizontal systems is that they have to cope with all wind
speeds and produce practically nothing in ordinary wind conditions. I
want a system that produces .5 to 2 KW works in 3-5ms prevailing winds but
gradually closes down at higher wind speeds. The large commercial
systems cope with varying wind speeds by changing the angle of the blades
but this is not possible for small systems.
1, certain type of batteries (if used) has higher speed on charge and
recharge, on given straight line of power produced from sources. LiFePO4
(or, Lithium ion batteries) has quite efficient rate of charge and
discharge. and would have more power given equal amount of power generated
from source.
2, Threshold of electric potential absorption givern longer time of
contact between ends of electrode (or wire), the longer time builds higher
threshold and also affect the rate of reading and the power capacitance.
3, Other factors such as loss through friction, fluctuation of power and
speed also give an uneven (not a straight line ) power generation and
absorption.
4, loss through the air-blade fliction, moisture and static
charge in the moist/dry air (humidity) also a factor....
I am not a electrician. I am a doctor that happen to be very interested in
alternative energy and about the electricity read from inserting cardiac
pacemakers. Please teach me more from what you know. Much thanks
hjc, M.D.