The Wind on Grandpa’s Knob

creaking, squeaking, converter of solar energy became a thing of
the past. Not until we realized that we were running out of cheap
energy and some of our popular forms of fuel did we again look
around to see if we could resurrect something useful from the
past.

Everything from geothermal energy to the power of the
ocean’s tides was scrutinized. Among the many projects funded
from the taxes that we pay was a program to develop our available
wind energy.

From time to time in our national history, we tend to
‘re-invent’ the wheel, in that media exploitation of daily
events, tends to over emphasize things that seem to be new
developments. But, in reality, these are old files revisited. Thus
it is with the wind powered electrical generator of the size
suitable for a power system. In 1941 the General Electric Company
built a 1600 horsepower (1,250 kw) windmill generator for a Vermont
public utility. It was erected on a mountain top in Vermont known
locally as Grandpa’s Knob. This machine was technically a
success and ran until around 1945 at which time one of the blades
was broken and the project was abandoned. The idea has remained
fallow until recently.

Just what are the possibilities for supplying our energy needs
from the natural and renewable forces of the wind? Potentially, of
course, there are far more kilowatts of wind energy flowing across
the contiguous United States than we could ever use if we could
just harness them. That is the problem. Let us take a look at where
things stand if only for the fun of knowing.

The cool wind that we feel blowing in our face on a warm summer
day is the outward manifestation of solar energy at work, in one of
its forms. I like to explain the phenomena in terms of my sailing
days along the East Coast. On a warm summer morning the air is
still and there are only the long low swells from far across the
ocean hinting of things happening far away. As the sun gets up in
the sky and the land begins to warm, the air rises over it. This
upward thermal current would leave a vacuum at the surface if it
were not for the cool air above the water area moving in to fill
that space. And so it is that around noon on these days along the
coast a sea breeze will spring up. As the sun sets, the reverse
takes place. Measuring the velocity (as I have many times) it will
run about 15 miles per hour.

For the same technical reasons, daily breezes will blow across
inland areas. The sun warms the air and it rises. Cooler air moves
in and thus creates the breeze that for generations has turned
country windmills and pumped water or done other useful work. As
long as our star in the Milkey Way galaxy appears to rise every
morning and set every evening, we can look forward to this form of
energy. But, how do we capture it? Windmills are a possibility.

Probably the most familiar to all of us is the ‘bicycle’
wheel rotor windmill. These can pump water when the wind is only 2
miles per hour. Most of the machines contemplated for today’s
use will not function until the wind gets up around 10 mph. These
very large windmills are merely large two-bladed propellers on a
horizontal shaft. One such installation might be of interest. It
will have a tower 260 feet high with a 260 foot diameter propeller
for an overall height of 390 feet. It is rated at 4,000 kilowatts.
It will take a field full of these about a hundred to come close to
just a single generator in one of today’s coal burning power
plants.

Navajo ‘bicycle’ type windmill in Monument Valley, Utah,
pumping water. Thousands of these machines dotted the landscape at
the turn of the century with many still seeing active service.

There is another, however, that comes closer to what a farm
might use. It is the Darrieus or vertical shaft machine named after
the French inventor, G. J. M. Darrieus and patented in 1931. It
looks like an egg beater upside down. There is still another
vertical axis machine called the Savonius rotor. It is named after
the Finnish inventor, S. J. Savonius, who patented his device in
1929.

Although the Savonius rotor is not currently undergoing further
development, it is interesting to note that it was used to power a
‘three masted’ ship in the Carribean trade in the 1930s.
For the ‘handy-man’ interested in a do-it-yourself project
these rotors can be made by cutting a cylinder lengthwise into two
pieces and arranging them between two circular disc end pieces as
shown in the sketch. For size think of a 55 gallon oil drum.
Several of these sections can be stacked one atop the other on a
common shaft. That is the arrangement used in the experimental
ship. All three rotors (masts) were connected to the propeller
shaft.

Darrieus windmill under development by the Department of Energy
at Sandia Laboratories near Albuquerque, New Mexico. This 55 foot
diameter rotor will generage 50 kilowatts at 50.6 rpm and a 28.7
mph wind. Note spare blade in left foreground its airfoil section
is 2 foot across.

For our examination of the subject we shall use the horizontal
shaft design since it lends itself to our demonstration and is the
design most favored in the current program sponsored by the
Department of Energy and aided by NASA. We can use the unit of
energy, watts per square foot. This implies that we have a mass of
air passing through our propeller. And, it implies that we know how
fast it is moving. From this we might project just how much power
we could generate supplemeriting that which is being supplied by
the local electric utility system.

Let us start with a wind motor that has a five foot diameter
propeller. The projected area swept by this propeller then is 19.6
square feet and we can use a power figure of 30 watts per square
foot of wind energy potential. This gives us a total potential of
589 watts or a better unit would be watt-hours per hour. The
efficiency of our propeller is not 100%, but is somewhere around
40% at best. Over a year’s time the 30 watt per square foot
potential exists, on average, for 40% of the time. So, in one year
we might expect to generate about 825 kilowatt-hours. On a monthly
average basis this would only be about 10% of the requirements for
a residence with the usual appliances. We still would need the
power company for the difference and for those times when the wind
didn’t blow.

Many small wind powered generators of the type just described
are actually a direct current (dc) machine capable of charging a
battery which would get us over the time when the wind didn’t
blow and we could have, maybe, a steam or oil powered generator to
make up the difference if we were not hooked up to power lines.
But, let us not overlook the fact that if we go the battery route
we are on a dc system and there really are no appliances
manufactured today for such a system without the added piece of
equipment called an ‘inverter.’ We would have to be
satisfied with having only electrical lights.

But having appeared to be negative about wind power let me take
another approach and show you just how you might supplement your
household electrical system. We will get away from batteries and
from complicated synchronous generators that need to run at exact
speed and a lot of other troubles.

I would like to introduce you to the simplest electric generator
ever built the induction generator. You have seen them many times
but probably didn’t know what you were looking at. What are
they? Simply put they are a squirrel cage induction motor driven by
an engine or wind mill at greater than synchronous speed. Lets put
that into other terms. Take an induction motor whose nameplate says
that its rated speed is 1750 rpm, for example. Synchronous speed
for this machine is 1800 rpma multiple of the 60 cycles of the
power system. The difference between the 1800 and the 1750 or 50
rpm is called the ‘slip speed.’ If now we drive this
machine at 1800 plus the slip speed or 1850 rpm and it is connected
to a 60 cycle power system it will generate power equal to its
nameplate rating. That is, a 1 horsepower motor will generate one
horsepower (746 watts) of electrical power. BUT, and this is a very
big BUT, the motor MUST be connected to a regular power system
because an induction generator requires something that it can not
provide for itself known as ‘magnetizing current’ and this
it gets from the synchronous generators of the system to which it
is connected.

Smaller Darrieus rotor is about 15 foot diameter and develops
about 7 horsepower which is quite suitable for many farm or ranch
applications. Note guy wire system to prevent overturning in strong
winds.

In a way that helps us. Let us take a windmill case. The wind
isn’t blowing today and our needs for power are being supplied
by the power company and our electric meter’s disc is turning
around merrily and adding up kilowatt-hours consumed. Now the wind
starts to blow and the mill turns the motor faster and faster and
faster until it is up to 1800 rpm. If now we close the switch that
connects the motor to the power system there will be a momentary
‘blip’ as the motor self synchronizes with the system, but
noting else happens. So the wind blows a little harder and the
motor is reved up to 1825 rpm. If you had been watching the
electric meter disc it has a black dot for easy revolution counting
and had noticed how fast it was turning before then now that the
wind generator is working the disc would be turning more slowly.
Some of your power needs are being supplied by the windmill.

Let us say that the induction generator is generating more than
the load on your system. The disc will reverse and begin to
subtract some of the kilowatt-hours that you had used previously.
No batteries! No fuss!

I am no legal expert on the rules and regulations of your local
power company. If you don’t run the meter all the way back so
when it is read at the end of the month it looks as if they owe you
money, then you should not have any difficulty. This is a way to
integrate your efforts at wind power with your present system.

Unless you want to hire a small boy to close and open the switch
when the wind blows and when it doesn’t then we have to find a
way to automatically connect the induction generator when the
breeze is favorable. What we need is a centrifugal switch. Some
types of induction motors (single phase) have a centrifugal switch
that disconnects a starting winding when the motor is up to speed.
Something similar to this could be used to connect the induction
generator when the windmill has gotten up to synchronous speed.
Unfortunately, once connected, the machine will operate
continuously either as a generator or as a motor depending upon how
hard the wind is blowing. If the wind stops blowing then you will
have a most beautiful electric fan until the switch is opened.
Actually, there are reverse power flow relays that can be purchased
that will do the job. However, that gets to be a bit more
complicated. If you go this route perhaps you have a friend who is
an electrician that can help.

Here is another trick. Lets say that you would like to know how
much power you are using and you don’t have a watt-meter. But,
you do have the electric meter provided by the power company. Look
at the face of the meter. There will be a lot of information about
the meter on the face. One of these pieces will read like this:
K_h = 7.2, for example. That means that for each
revolution of the disc on your electric meter you will have used
7.2 watts (if that is the number on your meter). Look at your watch
and count the revolutions of the disc that take place in one
minute. Multiply the number of revolutions in one minute by 60 to
get revolutions per hour and multiply that by the K_h
value shown on your meter. The result will be the watt-hours per
hour or simply the watts. Divide by 1000 if you like kilowatts
better. And, if you prefer horsepower instead of kilowatts we all
need some standard of experience to judge by then divide the
kilowatts by 3 and multiply by 4. OK, you in the back of the room,
yes, the factor is 0.746 but 0.75 is near enough and I don’t
have to take my shoes off to do the calculation.

After you have rigged up your induction generator you can run it
as a motor to make certain that everything is turning in the right
direction. That is, when the motor is running the windmill as a fan
the air has to be flowing in the same direction as it would have
had the wind been turning it. Even if you don’t save much in
electric bills it should be fun just to build the system. Start
small may be a half horsepower motor and see how you make out.

Notes for those that would look further: ‘Wind Catchers,
American Windmills of Yesterday and Tomorrow,’ by Volta Torrey,
the Stephen Greene Press, Brattleboro, VT and ‘Electric Power
From the Wind’ by Henry Clews, East Holden, Maine 04429.

Carl Lathrop, author of this article, notes that
Atlantic Electric will pay $500 each to first 100 residential
customers who install equipment for generating electricity from
wind-powered devices. The New Jersey utility’s program was
described in McGraw-Hill’s ‘Electrical World’
magazine.

David V. Boney, an Atlantic Electric VP, told Lathrop
that at least ten have gone into operation. Equipment must be
approved and the company must be notified before work is started.
Technology of the induction generator is described in Lathrop’s
article ED.