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Long before there was an international crisis in the Middle East and when our lives were paced by the steam trains and not the jet planes, our landscape was dotted with windmills. Before long though, cheap energy in the form of oil and gas began to take over their chores. Then came the rural electrification program and that 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: Kh = 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 Kh 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.