Most people are not aware of the great increase in electric
power consumption that has occurred in the last 10 or 20
years and which is now leading to energy shortages and
environmental disaster. The trend in power consumption is
ever upward and fuel combustion, generating plants and
utility lines increasingly mar the landscape in even remote
and otherwise unspoiled parts of our land. We must curtail
our energy consumption first, then turn to alternate
sources of power–such as the wind–if we want to
live in tune with nature on this planet.
Before considering the wind as a source of power for your
domestic needs, however, you should take a look at the
electrical appliances you now have and decide which you
consider essential and which are just conveniences. Wind
power can be useful, but a very large and expensive
windmill would be needed to operate such greedy consumers
of electric energy as clothes dryers, space heaters, hot
water heaters, electric ranges and large, color TV sets.
If, on the other hand, you can live with reasonably modest
lighting, radios, shavers, a small black and white TV, a
refrigerator and perhaps an oil burner motor and circulator
. . . you may find that the wind can supply all or part of
your electric energy needs.
Factors to Consider When Switching to Wind Power
Let me, however, point out some aspects of wind power that
must be taken into account before embarking on any such
home energy generation project. First and most obvious is
the intermittent nature of this resource. Wind power is
extracted from the kinetic energy of moving air and the
power available from any mill at any given time is
proportional to the cube of the wind velocity. Which is to
say that if you can get, for example, 160 watts from a mill
at a wind speed of 10 mph . . . then you can obtain 1,280
watts when the air velocity is 20 mph (if the generator has
the capability), but only 20 watts at a wind speed of 5
mph.
Remember too that–depending on your
location–you may find there are long intervals during
which the wind will be relatively calm. If this is so, your
wind generator will not put out any appreciable power for
long periods, during which you’ll have to resort either to
energy stored in batteries, or to a standby gasoline or
diesel-driven generator. If you are fortunate in having a
windy site, this will be less of a problem . . . but it
cannot be overlooked.
Another aspect to be considered is that of excessive winds,
such as a severe storm, hurricane or tornado. Provision
must be made for feathering the mills’ blades, tilting the
attitude of the propeller so that the wind hits the ends
and edges of the fan instead of the airfoil surfaces or
applying some kind of brake or aerodynamic spoiler.
Automatic as well as manual operation of such a device is
desirable.
The intermittent nature of wind as an energy source makes
it most useful for those applications where the effect or
result is easily stored. Pumping water for irrigation or
domestic use with power extracted from moving air is a
natural. Windmills have been used for this purpose in the
Low Countries for many centuries, and were commonly
harnessed for the same work on this continent only a few
decades ago.- Today such American farm windmills are found mostly in Amish areas. Elsewhere the machines are
often seen in a state of disrepair on abandoned or unused
homesteads.
Windmills
If you’re interested in pumping water with wind power you
may be able to find an old American farm windmill and
refurbish it with new vanes and mechanical parts. Or you
can purchase one brand new, as they’re still made in a
variety of sizes from 6 to 16 ft. in diameter, mounted on
steel towers as high as 80 ft. tall. The manufacturer
gives performance in terms of pumping rate ranging from 100
to 3,000 gallons per hour. Construction is sturdy,
self-lubricating, and the designs are dependable through
many decades of experience in production and usage.
Building a Windmill
The most comprehensive description of a home-built windmill
is contained in a report prepared for an organization
called Volunteers for International Technical Assistance.
The paper describes a 16-blade mill with a diameter of 4
meters (13 ft.). The machine employs an automobile rear
axle and differential as both the shaft and support for the
fan . . . and the means for transmitting the mechanical
energy to the bottom of the tower.
Detailed descriptions of sheet metal blade construction and
regulating mechanism are given in Bossel’s report and the
only tool required which may not be readily available to
most MOTHER readers is welding equipment. Any body and
fender shop or blacksmith (check the yellow pages) should
have both the necessary equipment and skill, however,
or–in lieu of welding–other fastening methods
such as screws & nuts or rivets can be used.
This mill is primarily intended for pumping water and doing
other mechanical duties rather than for generating electric
power. Its tower and elevated turntable platform are of wooden construction. The machine’s output
in a 10 mph breeze is 1/3 horsepower, it produces 1 hp in a
wind of 15 mph and over 2-1/2 hp when spun by air moving 20
mph.
But what about electric power generation? Such energy is
not easily stored (a bank of automotive-type storage
batteries may supply a few hours’ needs . . . but then
you’re either out of power or you crank up a
gasoline-driven generator). I would strongly recommend such
a gasoline-powered standby unit for any winddriven
generator if you want reliable power without tying into the
utility line. At some future date, perhaps, the fuel cell
will serve as the alternate source, thereby avoiding the
noise and pollution problems of the internal combustion
engine.
There is a wind-powered generator called the
Wincharger available for about $400 from
Dyna-Technology, Inc. of Sioux City, Iowa 51102. It uses a
6-ft. two-bladed propeller with a patented air-brake
governor to limit its speed in high winds, and comes with a
10-ft. steel tower. Although of small capacity (it produces
20 to 30 kilowatt-hrs. of energy per month and charges a
12-volt battery at rates up to 14 amperes) the unit is very
reliable and has been produced for many years. A 7 mph
breeze is sufficient to start charging, and full output is
reached in a 23 mph wind. For a cabin, campsite, trailer,
camper or boat the Wincharger would be adequate to serve
the electrical needs of 12-volt lighting, radio, shaver and
portable TV.
It should be noted that when 120-volt AC appliances are to
be accommodated, an electrical device called an inverter
must be used to convert a wind generator’s 12-volt DC to
the higher AC current. The size and cost of this stationary
converter depends on the maximum wattage of the various
loads which may be connected at any time and there is a
certain loss of power in the inverter (typical efficiency
being 80 to 90%).
If you’re looking for a windmill which will serve needs up
to a few kilowatts, you must consider larger machines. One
source for them is Elektro gmbH of Winterthur, Switzerland.
This manufacturer’s units employ three-bladed propellers
ranging from 3.5 to 5.0 meters in diameter with output
ratings from 2,000 to 5,000 watts. The equipment produces
110-volt DC current and, as usual, is employed in
conjunction with a bank of storage batteries.
The Elektro units are of sophisticated design with blades
which may be adjusted or “feathered” to compensate for
varying wind speeds. The propeller shaft is coupled to the
generator by gears running in an oil bath. As might be
expected, the price of these machines runs to several
thousand dollars, but–if you add up all your electric
bills over a few years–that’s not so unreasonable.
And what about building your own wind-driven electric
generator? Well I’d advise that you first arm yourself with
all the information you can get and ask yourself if your
site is suitable. You might even record daily air
velocities at your location with an inexpensive wind gauge.
Designing Your Windmill
Figure that the mill should be situated at a higher level
than any obstructions nearer than a few hundred feet. This
may require a high tower, or running a line out to a
hilltop location. Remember that the power you’ll get is
strongly dependent on average air speed, so make sure you
pick the spot most exposed to prevailing winds.
Next, decide on the approximate-sized machine you need or
can readily build, bearing in mind that power output varies
as the square of propeller diameter (a 6-ft. diameter
propeller yields four times as much power as one of the
same design but only 3 ft. across). Construction costs also
go up sharply with increased size. With 3 ft. or less, all
you can expect to do is trickle charge batteries or carry
very small loads such as a single radio or small light.
Then again, building and operating a generator of this size
might be worthwhile before undertaking a larger unit.
You’ll find a 6-ft. diameter mill to be a good practical
size if you can really limit your consumption of
electricity. Even more useful is a 10 or 12-ft. diameter
power plant unless you find the difficulty and costs of
construction prohibitive. I would not recommend fabrication
of any larger units until some experience is gained with
one of these smaller sizes.
Choice of propeller style and design has a strong bearing
on the efficiency of a windmill. All modern electric
generating mills have two or three very slender blades
resembling aircraft propellers. Such
designs feature a high rip speed ratio which is a
comparison between the velocity of the blade tips and the
wind speed. Tip speed ratios between 5 and 8 are not
uncommon for efficient high-speed mills . . . as compared
to the ratios between 1 and 3 which are typical for the
slower-running multiblade machines such as the American
farm water-pumping windmill. On the other hand, although
the latter design is less efficient, its higher starting
torque and better performance at low wind velocities gives
it a steadier pumping action in light breezes.
Ideally, the propeller of a wind machine used for
generating electricity should have a cross-section
resembling that of an aircraft wing . . . with a thick,
rounded leading edge tapering down to a sharp trailing
edge. It should be noted, however, that the most efficient
airfoils for aircraft propellers, helicopter blades or
contoured fan blades (all designed to move air) are not the
most efficient airfoils for windmills (which are intended
to be moved by air). An old airplane propeller, in
other words, has neither the proper contour nor angle of
attack to satisfactorily extract energy from the wind.
The Generator
The generator itself is of vital importance in any
windelectric system. Unfortunately, most generators which
would seem to be suitable suffer from the requirement that
they be driven at high speeds (most are built to be turned
by gasoline engines at 1,500 to 3,600 rpm) and windmills,
especially in larger sizes, seldom exceed 300 rpm. This
means that one must either find special generators, or
resort to step-up gearing to achieve the high rotational
speed needed by the generator. Brushless permanent-magnet
rotor alternators give reliable, troublefree operation and
require no electric power for a field winding but;
unfortunately, are hard to come by. One possibility is to
adapt an automobile alternator by replacing the field
winding in the rotor with a permanent magnet.
On a much smaller scale, there is available at reasonable
cost (about $11) a bicycle generator which will produce a
useful output of one to two watts at low rotational speeds.
This is the English-made Sturmey-Archer Dynohub
generator. With a 2-ft. diameter
propeller it can deliver its rated output without any
modification. All that’s required is the attachment of
propeller blades.
The Dynohub unit is made for use as the hub of a bicycle
front wheel and comes equipped with ball bearings and spoke
holes . . . which make it possible to construct sheet
aluminum or fiberglass blades and secure them to the hub at
two points. At the perimeter a bicycle rim can serve as the
supporting ring. The Dynohub is available in two models,
with holes to accommodate either a 32 or a 36-spoke wheel.
One model is suited to 4 or 8-bladed fan and the other to a
3 or 9-bladed propeller.
Practical applications of this design are limited to
trickle charging batteries, such as for a boat at a
mooring, or for a two-way radio at a remote campsite or
cabin.
Inspiration for my Dynohub mill came from a wind-powered
generator developed about 1964 by the National Bureau of
Standards for use by the Navy or Weather Bureau on the
MAMOS automatic weather reporting station. The
Tri-GEN wind power units which supply
power to this buoy, use three modified Dynohub generators
on the shaft of the windmill to produce a threephase output
and reduce cogging effect. Both 30″ and 36″ 20-bladed mills
are used to reach peak outputs close to 7 watts at wind
velocities between 23 and 25 knots. Their low tip-speed
ratio of 1.7 is typical of mutibladed mills. The propeller
blades are fabricated of sheet aluminum and are supported
at their tips by a double ring and at half-span by a
smaller ring.
The design of a windmill involves decisions as to the size
of the generator as well as the size and style of the
propeller or rotor. Since there are no fuel costs, the cost
of construction and maintenance are prime considerations
and it’s best to start with an electric generator of
adequate power rating at relatively low speeds (a few
hundred rpm).
Once a suitable machine is selected, a decision must be
made as to what wind velocity will be necessary to achieve
full output of the generator. If you decide to get full
electric output at low wind speeds, you’ll need a larger
propeller . . . whereas a small fan will be adequate if you
want full electric output only in very high winds. The
question to ask when designing a mill, then, is: how
frequently do winds blow with a velocity greater than X
mph?
Statistical studies made of wind records at Dayton, Ohio
show that each month there is a well-defined group of wind
velocities which predominate. These are called the
prevalent, or frequent winds. There is also a
well-defined group which contains the bulk of the energy
each month called, appropriately enough, energy
winds. Energy winds blow 2 out of 7 days; prevalent
winds 5 out of 7.
Many working wind machines are designed to reach full
output in air velocities of 20 to 25 mph, and deliver no
appreciable output in breezes of less than 6 or 8 mph. At
winds higher than those required for maximum output,
governors or spoilers limit the rpm of the mill, thereby
throwing away large quantities of energy but protecting the
machine against damage. Lack of good performance at low
wind velocities is not a serious drawback, since there is
very little energy available from the wind at these calm
conditions anyway.
It should be noted that wind velocity will vary
considerably even in a local area, as the figures for New
York City indicate. At any rate, figures and tables aside,
nature has free power available for you to use, without
polluting Mother Earth or consuming her resources. Think
about harnessing the wind and give it a try . . . you’ll
like it!
Bibliography:
1. PROCEEDINGS OF THE UNITED NATIONS CONFERENCE ON NEW
SOURCES OF ENERGY. Volume 7: Wind Power (408 pages),
published 1964. UN Sales No. 63.1.41, $3.50 . . . an
excellent resource; contains texts of 40 papers presented
at the 1961 Rome conference under categories of:
a. Studies of Wind Behaviour and Sites for Wind-driven
Plants
b. The Design and Testing of Wind Power Plants
c. Recent Developments and Potential Improvements in Wind
Power Utilization
2. LOW-COST WINDMILL FOR DEVELOPING NATIONS by Dr.
Hartmut Bossel, Mechanical Engineering Dept., Univ. of
California at Santa Barbara 93106 . . . a 35-page report
prepared for Volunteers for International Technical
Assistance (VITA), College Campus, Schenectady, N.Y. 12308.
This report describes construction of a 13-ft. diameter
mill using readily available materials and basic tools.
3. Marks’ STANDARD HANDBOOK FOR MECHANICAL
ENGINEERS, Theodore Baumeister, Editor . . . contains
a 6page section by E.N. Fales on wind power; chock full of
vital information. Check it out at your library.
4. ALTERNATE SOURCES OF ENERGY – a new publication
privately produced by Donald Marier of 300 S. Taylor Ave.,
Oak Park, Ill. 60302 . . . the Sept. 1971 issue contains an
extensive bibliography on wind, solar, tidal, and
geothermal energy.
