Sharing the Wind

Sharing the Wind
Fairfield Neighborhood Wind Project
Lawrence A. Gamble
©1999 Lawrence A. Gamble

The wind blows, the sun shines. Many dream of using the sun and wind to provide energy for their homes. In Fairfield, Iowa, people are making this dream a reality.

Fairfield is home to Maharishi International University and about 4,000 people who do transcendental meditation, among other things. Several thousand people get together to meditate twice a day in two large domes. We experience a deep silence and connection with natural law during meditation. This translates into a deep interest in living in tune with natural law, in ways that do not harm the earth or ourselves.

Fairfield is a hotbed of natural building and renewable energy (RE) activity. There are 25-30 RE-powered homes in this small southeastern Iowa town of 10,000. Visitors are welcome almost anytime, and internships are available for people who would like to learn about sustainable agriculture, energy, or housing projects.

Solar Neighborhood Adds Wind

For the last five years, my neighborhood in Fairfield has been getting all of its electricity directly from the sun, using photovoltaic panels. Photovoltaics is a bit like magic-sunlight is converted directly into electricity, with no moving parts and nothing to wear out. In contrast, 99 percent of the electricity supplied by electric utility companies in Iowa comes from coal, oil, and nuclear power.

We're now taking an exciting new step in my neighborhood-the installation of a shared wind generator to supplement the power obtained from our solar panels.

The Sun and Wind in Iowa

Iowa is truly blessed with an abundance of renewable resources-sun, wind, biomass, and even falling water in some places (of course, these seemingly separate energies all have their source in the sun). It's obvious to anyone who has spent any time in Iowa that if the sun isn't shining, often the wind is blowing. The combination of sun and wind here can provide an abundance of energy, whether you look at shorter daily and weekly weather cycles or at longer seasonal cycles.

Over the last five years, the homes in my neighborhood have demonstrated the joy of getting by comfortably on solar energy. Many times during the year, we have an overabundance of energy. And once in a great while (usually less than 1 percent of the time), we run a little short. Then we have to conserve a bit, or run a small backup generator. This year we've discovered that when you supplement solar electric generation with wind power, the result is the bliss of a real abundance of energy.

Two Curves

To confirm this intuition and informal observation about the complementary nature of the sun and wind in Iowa, I obtained daily sun and wind data from the airports at Ottumwa and Burlington. The result is graphed below.

The important thing about these graphs is not the exact value at any point, but the shape of the two curves. As expected, the amount of energy available from the sun has a peak in the summer months and a minimum in the winter months. The wind has a peak in the winter months and a minimum in the summer months. As you can see from the shape of these two curves, the wind and sun are complementary; the peak for one is the minimum for the other. Combine the two and it's easy to have an abundant source of energy year 'round.

Four Solar Homes

My neighborhood is in a new subdivision, which does not have utility power or water available. There are now four households-Gamble, Lafrancis, Munson and Wright-all of which have obtained their electricity from solar power for the last five years. Two homes have their own solar electric systems. The other two homes share a single system. Ultimately, all four homes will probably have independent solar electric systems.

My system has 1,140 watts of PV, configured for a 24 volt system. There are six groups of seven Carrizo laminate PV modules, a Trace 2624 quasi sine wave inverter, and twelve 6 volt, 220 amp-hour Exide batteries. I have a Power Pulse desulfation system and a Bobier Electronics OmniMeter.

My appliances include a Sun Frost RF-12 refrigerator, compact fluorescent lights, computers, 30 inch (76 cm) TV, and stereo. I also have a water pump and a large variety of tools (drill press, bench sander, radial arm saw, worm drive skill saw, drills, belt sanders, etc.).

I also run the Lafrancis house, which is about 500 feet (150 m) away. They are connected by a #10 (5.3 mm [SUP] 2) wire to the AC output of the inverter, and have lights, TV, stereo, and two compact refrigerators.

The Munsons have 760 watts of PV, also at 24 volts. They have four groups of seven Carrizo laminate PV modules, a Trace 2624 quasi sine wave inverter, and twelve 6 volt, 220 amp-hour Exide batteries. They have a Power Pulse desulfation system and a Cruising Equipment Amp Hour +2 meter. Their appliances include an apartment size refrigerator, compact fluorescent lighting, and other standard appliances, plus a mini dish TV system.

Max Wright is out of town for a year, and we haven't connected him to the wind generator, although we will when he returns. His system is also at 24 volts, and he has 760 watts of PV. He has four groups of seven Carrizo laminate PV modules, a Trace 4024 sine wave inverter, and four 6 volt, 220 amp-hour Exide batteries.

The Wind System

In 1997, my neighbors and I got together and decided to install a wind generator that we could all share. After much thought, I recommended a Whisper 3000 (3,000 watts, 24 volts, and a 15 foot (4.5 m) diameter rotor). Much thanks to Elliot Bayly at World Power Technologies for helping think the system design through. My neighbors and I shared the US$4,000 cost of the machine.

With the machine chosen, the next step was to pick the spot for the wind generator tower, and to size the wires going to each battery bank. To minimize cost, and losses in the wire, it was essential to pick a central location. The location we chose is less than 300 feet (90 m) from each house.

The three-phase AC power from the Whisper is changed to DC by a device called a rectifier. Rectifiers use diodes (one of the most simple electronic devices), which are like a one way valve for electricity. They let electricity flow in one direction but not in the other. In our system, the diodes perform an additional trick. In addition to changing AC to DC, they allow power to flow from the wind generator to each battery bank, but they block the flow of power from one battery bank to another.

We have a separate rectifier at each battery bank. The rectifiers isolate the battery banks from each other and keep each battery bank from draining or charging the others. The power from the wind generator automatically flows to the battery bank with the lowest voltage. When all battery banks are full, the controller turns on a large resistive load that comes with the Whisper 3000 and absorbs all the excess power.

I initially thought that we would have to use a higher voltage model and a transformer at each location. It turned out to be cheaper to use the lower voltage model, and to use larger wire to each battery bank rather than using transformers. We ended up with three #0 (53 mm [SUP] 2) cables to one location and three #00 cables to the other (the wire in #00 (67 mm [SUP] 2) cable is about 1/2 inch (13 mm) in diameter-this is big, heavy wire!).

Controlling the Wind Generator

With solar panels, when the batteries are full, you can simply disconnect the panels. With a wind generator, some method must be used to control the machine if the batteries are full and the wind continues to blow. If the wind generator is allowed to turn in the wind without a load, it will overspeed and may damage components.

There are three methods for controlling wind generators: keeping some kind of electrical load on the system, mechanically spilling wind from the blades, and using a brake to stop the machine. World Power's Whisper machines do all three. Their machines are regulated by a controller that can connect a resistive load large enough to take the full load of the generator if the batteries are full.

The Whisper also controls output in high winds by tipping the blades back to a horizontal position. In high winds it looks a more like a helicopter than a wind generator. This is necessary because the power available in wind is related to the wind speed cubed-double the wind speed and you get eight times the power. The energy available in a 40 mile per hour (18 m/s) wind is 64 times greater than the energy available in a 10 mile per hour (4.5 m/s) wind. The Whisper simply spills this extra energy by tipping back the blades, a technique that has been used to govern wind generators since at least the 1930s.

As a final safety measure, shorting all the leads of the generator together can shut down the Whisper. This puts a huge load on the generator and keeps it from starting up. The down side of this method of stopping the generator is that it is not always successful in high winds.

Managing a Shared Resource

The controller and dump load for the wind generator are located at my house. There are shut-off switches (which simply short out the three-phase AC coming in from the generator) located at the Munson house, the tower base, and at my house. If a storm is coming, or there is some reason to shut off the machine, any of us can do it. I generally watch and manage the wind machine. If all our battery banks are full, we usually shut the wind machine off.

I usually check with the Munsons to make sure that their batteries are also full before shutting the wind machine off. It turns out that I am a larger power user than they are and that if my batteries are full, most likely their batteries are full too. In cold weather, I sometimes let the machine run just to get the extra heat. We have extra energy about 70 percent of the time.

I own the wind generator. The Munsons had a well drilled, and I get access to the well in exchange for them getting access to the wind generator. I was initially more worried about the social issues than the technical issues with this shared system, but everything seems to be working smoothly.

The Lafrancises (the people connected to my system with a 500 foot (150 m) long AC extension cord) also watch the wind machine. If there is going to be bad weather and no one is around, they can shut the machine off at the base of the tower. They don't currently have a way to monitor the battery voltage at their house, so they are not usually involved in shutting the machine off if the batteries are full.

Nelson Lafrancis designed and built the tower. He also has a truck with a crane rig that we can use to safely raise and lower the tower. We all share in the duties involved in operating the wind system, and it works out pretty well.

Power on High

We had to choose a tower design. You can increase annual output of a wind generator by increasing tower height. Due to friction of air moving across the ground, wind speed increases with height above the ground. It's pretty easy to go up another 20 feet (6 m) or so and get another couple of miles per hour of wind speed. Because the power in the wind is related to the wind speed cubed, there is almost twice as much energy available in a 12 mph (5.3 m/s) wind as there is in a 10 mph (4.5 m/s) wind.

Also, it's important to be above turbulence created by the wind flowing around trees and houses on the ground. There is a lot less wear and tear on the machine if it operates in smooth air. Picture water flowing and swirling across the landscape, around trees and buildings, and you get an idea of what wind turbulence looks like.

Typically, the optimum height is 80 to 100 feet (24-30 m) above the ground. Our location is on top of a hill. I felt that 60 feet (18 m) was a minimum, and our tower should ideally be 80 feet (24 m) tall. We ruled out a guyed tower because the guy wires would take up too much space, and we didn't want to look at them. We wanted a tower that would tilt down for installation and repair.

Temporary Tower

Nelson Lafrancis is a genius metal fabricator, so we left the design and fabrication of the tower to him. The tower is by far the most complicated and difficult part of the whole installation. While we were planning for the permanent tower, we put the wind generator on a temporary tower 40 feet (12 m) tall made of 5 inch (13 cm) schedule 40 steel pipe.

We installed the foundation for the permanent three-legged tower. The footings for each leg have five yards (15,000 pounds; 6,800 kg) of concrete in the foundation. My neighbor Bill Munson and my friend John Freeburg helped place the concrete. Each footing is on the corner of an 18 foot (5.5 m) triangle.

For the temporary tower, we used the leg foundations as guy wire anchors, and placed another block of concrete in the middle of the triangle to set the pipe tower on. The pipe pivots at the bottom, and can be lowered or raised using a crane hoist on the back of Nelson's truck. The arrangement works pretty well, although I am glad to have someone as experienced as Nelson when we raise and lower the tower.

Now that we have had almost four seasons of experience with the shorter tower, and have had excess power for most of that time, we see little reason to go to the taller tower. I should point out that the wind generator is located on a very exposed hilltop site. I expected more turbulence at this height, but the machine seems to run very smoothly.

A Beautiful Machine

The big moment finally arrived. The generator had been installed on the top of the tower, the blades and tail attached, the connections made, and the tower raised. I stepped back to look and thought it was one of the most beautiful machines I had ever seen. The blades are much longer and the airfoil is more developed than on the smaller Whispers I have installed. The final step was to remove the brake and see what would happen.

Nothing happened for half a minute or so, but then the blades began to spin, slowly at first. At the end of another half minute the individual blades became invisible as they began to spin around at 300 rpm (at that speed, the speed at the tip of the blades is 160 miles per hour (70 m/s)). The wind speed was a modest 10 mph (4.5 m/s) or so, and I eagerly went inside to see how much was being put into the batteries.

When I looked at the ammeter on the Whisper power center, it was reading about 0.7 amps or so, which I thought was a little low. Then I discovered that the power center amp reading has to be multiplied by 10, so we were really getting 7 amps. That's more like it! 7 amps at 24 volts is approximately 164 watts, which is really quite a lot of power at such a low wind speed.

Power Center

The Whisper comes with a really cool power center that includes volt and amp metering and a place to hook up 40 amps worth of solar power as well. The power center has a place to connect the large resistive load (4,800 watts at 24 VDC-about the same power consumption and heat generation as 4 toasters). It also has the electronic intelligence to connect the load when the battery bank is full. It uses an algorithm that includes battery voltage to decide when the battery is full.

Our resistive load was connected for a different voltage when it arrived, so we had to rewire it for 24 volts. The factory gave us the wrong directions, and when the wind generator was first turned on, the resistive load was not connected. Eventually, we took the box with the resistors in it apart and figured out how to wire the resistors for the proper voltage. Everything is very well made-the power center and resistor box are made of stainless steel. The power center is 17 by 18 inches (43 x 25 cm) and the resistor box is 17 by 17 inches (43 x 43 cm).

A Quiet Gift

The machine lives up to its name and makes very little noise. At very low wind speeds it really is a whisper. At higher wind speeds it makes more noise, but there is also more noise from trees and bushes and grass moving in the wind. At no point is the noise objectionable. As my friend John Stanley says, it's the sound of God giving you free energy.

Initially the winds were very light. I decided to leave the machine up in light winds for a couple of days and then take it down to retighten and adjust everything. All day long the wind speed increased. It wasn't possible to tell if the resistive bank was working because the battery voltage did not rise high enough to turn it on. Soon the machine was putting out 30 or 40 amps, with peaks to 80 amps.

I began to worry about shutting the machine down. To use up the extra energy being generated, I turned on an electric heater, generally a big no-no with solar electric systems. Still the wind increased. At its peak, the machine put out 150 amps, well over its rated output. Previously the most amperage the battery bank had seen was about 40 amps from the PV panels. The batteries were merrily gassing away getting the equalizing charge of a lifetime. The wind became so strong that I could not shut the machine down with the brake.

The Whisper uses "dynamic braking," which simply shorts the three-phase AC leads from the generator to stop the machine. But in very strong winds, shorting the leads does not shut it off. At the time, I was not very familiar with the operation of this machine. I now know that I can usually wait for a slight lull in the wind by watching the ammeter. If I shut the switch off during a lull, I can usually brake the machine even in a storm.

Use it Up!

I went on a mission to use up the extra energy. I made bread in the bread maker. I bought some inefficient incandescent lights to replace my compact fluorescents and left them on all night. I asked the neighbors to leave their lights on. I ran the heater all night. I turned the stereo up loud. I got through the night, and the next day the wind had calmed down enough so that I could shut the machine down. The Whisper 3000 is like a 500 pound gorilla. In the wrong circumstances, it's not easy to control.

We have found that most of the time we only have to run the wind generator for a few hours every couple of days to keep the neighborhood batteries topped off. Everyone is thrilled with the extra power. It is very comforting to come home and see the wind generator working away in combination with the solar panels, providing an abundance of energy. The machine even has a little red light on it so you can see if it is producing power at night.

Complementary Power Sources

Although we have found that, watt for watt, the sun is a more reliable source of energy in Iowa than the wind, the power of the wind makes a great supplement to the power of the sun.

I'd like to thank the following for their help and support with the project: Nelson and Mary Lafrancis, Bill and Joyce Munson, John Freeburg, Michael Havelka, John Stanley, Adam Cargill, Cecelia Connerton, Phil Scot, and Jeff Albrecht (and many others who I may have forgotten to include).

Access

Author: Lawrence Gamble is consultant for solar, wind, and hydroelectric projects. He has a degree in electrical engineering and is a registered professional engineer * 1860 Woodland Dr., Fairfield, IA 52556 * 888-SUN-ENERGY * lonniegambleyahoo [dot] com * www.sunfarm.com

World Power Technologies, 19 North Lake Ave, Duluth, MN 55802 * 218-722-1492 * Fax: 218-722-0791 * salesworldpowertech [dot] com * www.worldpowertech.com ---

Ian Woofenden ian [dot] woofendenhomepower [dot] com, Fax: 360-293-7034 Associate Editor, Home Power magazine The Hands-On Journal Of Home-Made Power Editors are Professional Idiots - We misunderstand text so our readers won't.

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