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4 5% per year

5 Vs. gas turbine

6 Avoided cost

YY7 hen I put this sign together for A /my booth in a local fair, it was

\_A_Ian attempt to rebut the time-

worn argument that we've all heard— solar electricity is too expensive.

As a newbie solar contractor, I was appalled at the negative attitude of my more experienced peers regarding cost. As an experienced remodeling contractor, I knew that cost was not necessarily a factor. For example, my clients would spend US$1,500 on a bathroom faucet, or US$20 per square foot on tile.

The products of the auto industry are never subjected to the kind of scrutiny regarding cost effectiveness to the purchaser that renewable energy products must endure constantly. Let's get over it! PV gives a tax-free return on investment (ROI) of 4 percent over the life of the system (50 years) in Seattle, Washington, right now. Compare that to a passbook savings account that presently yields around 1 percent.

If you don't remember anything else about my sign, remember that if you can afford a car, you can afford a solar-electric system. Perhaps PV module manufacturers could take a hint from the auto industry and offer zero percent financing.

What if we selected our mode of transportation the way we are told that we must select our source of electricity? Those of us who live in cities would all be using public transportation or bicycles, unless we were hauling loads. (How often do you see an SUV on the road with more than one or two occupants?)

In the comparison chart, the Jeep values are Blue Book prices, Jeep emissions were based on 10,000 miles per year, and Jeep cost is incremented by the cost per mile allowed by the IRS. The PV is devalued 0.5 percent per year. RETScreen (from Natural Resources Canada) was used to compute ROI and emissions saved compared to a modern gas turbine generator, and to decrement the PV cost based on a current utility rate of 8.7 cents per KWH. The installed cost of the PV system is US$6 per watt. We do 'em for as low as US$5.75, give the purchaser a 50 year product, and still make money, all without rebates.

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Choosing a Home-Sized Wind Generator

Mick Sagrillo

©2002 Mick Sagrillo ou're about to make the big decision: should a wind generator be in your future? You've analyzed your resources, both environmental and monetary, and weighed the pros and cons of having a wind generator. The only question left is: which system should you choose?

I can't answer that question for you. However, I can give you the tools to help you make that big decision. Those tools are the detailed information and specifications for a variety of wind-electric systems, along with some personal observations based on 22 years of working with home-sized wind-electric systems. An appendix with additional discussion and technical commentary can be downloaded from Home Power's Web site.

Apples and Oranges (A&O) was originally published in 1993 and updated in 1995 and 1998. Meanwhile, a lot has happened in the small wind turbine industry. One company went out of business, two more entered the field, and one manufacturer bought out a competitor. A number of wind generator models went out of production, and some new models were introduced. While it's been a tumultuous four years since A&O was last published, perhaps the shakeout in the marketplace has at last ended, and things have settled down for the U.S., small wind turbine consumer.

Background

This article will review most of the wind generators that are sold and supported in the United States. One European manufacturer and one African manufacturer are represented by U.S. distributors. A number of new turbines are on the drawing boards, but they are not included here. In addition, at least six non-U.S. manufacturers are considering exporting their wares to the U.S., but have not yet done so.

Several wind turbines currently available on the Internet are not covered by this article. The reason for their exclusion is the outlandish claims made like, "Get a kilowatt for only $250." When compared to other commercially available wind generators, this sounds too good to be true. As the old adage leads us to conclude, it probably is.

As another example, I ordered and paid for a new turbine back on November 1, 2001 from a manufacturer trying to enter the business. As of June 2002, that turbine has not been delivered, and the manufacturer is impossible to get ahold of by phone or e-mail. While their turbine is a promising design, some companies just aren't ready for prime time yet. So, if it's not covered in this article, you'll have to draw your own conclusions.

This article diverges from past articles in covering only "home-sized" wind generators. In the past, A&O has included a large number of microturbines, those wind generators whose primary niche is sailboats, RVs, remote telecommunication sites, and other specialty markets.

While microturbines certainly provide valuable electricity to many remote applications, the intended user of this version of A&O is the homeowner who wants to install a wind-electric system on an adequate tower for either on-grid or off-grid production of substantial amounts of electricity for a home.

A word on failures is in order. You may know someone who has owned one of the wind generators reviewed here, and has experienced a failure of some sort, maybe even a catastrophic failure. Don't prejudge all wind generators based on a few isolated instances. Sure, there have been failures, even with the best of wind-electric systems. Paul Gipe, author of Wind Power for Home & Business, reminds us to look only as far as the automotive industry for a comparison. The auto industry is a multibillion dollar industry, spanning more than ten decades. Yet they still don't always get it right, as evidenced by the numerous annual recalls of their products.

What you should be interested in is trends—not the occasional failure. Problems with a wind generator usually occur early in the system's life. All wind generator manufacturers have experienced some failures, as have all other RE equipment manufacturers. Numerous reports of problems with a particular manufacturer should raise a red flag in your mind.

In addition, Joe Schwartz of Home Power magazine suggests checking out the customer service reputations of the manufacturers or distributors before buying. Your best bet is to discuss the wind generator you plan to purchase with as many owners as you can, not just your dealer or the manufacturer. Remember that manufacturers and dealers have something to sell. A pleased or disgruntled user doesn't.

The comparison table summarizes all of the various features that you should seriously consider when shopping for your wind-electric system. This article explains how to interpret the information in each row of the table. All of the information in the table (except where noted) has been provided by the manufacturers.

Manufacturer & Model

Contact information for manufacturers and major U.S. distributors listed in the table appears at the end of the article. All of the wind generators presented are new equipment, with the exception of the remanufactured Jacobs Wind Electric generators (short case and long case Jakes). The Jacobs 31-20 is a new machine, based on another Jacobs design.

Even though the old Jacobs has not been made for 50 years, they are still considered by many to be top-of-the-line technology. As such, they have been remanufactured (that is, completely rebuilt with many new components and put back onto the streets with a warranty) by various companies for at least the last 28 years. The Jacobs wind generator is the yardstick by which many judge today's wind equipment.

Swept Area & Rotor Diameter

To help with comparisons, the various wind generator models are listed in ascending order of swept area and rotor diameter. This is a radical departure from the way most manufacturers rate their various turbine models, as well as from previous versions of A&O.You'll see why when you read my comments on cost.

The "rotor" is defined as the entire spinning blade assembly, including the hub to which the blades are attached. The rotor is essentially the collector of the wind generator—gathering fuel in the form of wind, and converting it into electricity by driving the generator.

Think of the rotor in the same terms as we describe a solar water heater. One 4 by 8 solar hot water panel (32 square feet) will collect a certain amount of sunlight and produce a proportional amount of hot water. If you double the number of panels, you double the collector area (now 64 square feet), thereby doubling the amount of sunlight you can collect and the amount of hot water you can produce. Swept area works much the same way.

The rotor converts the movement of air passing through the two or three blades into the rotational momentum that turns the generator, thereby generating electricity. Just like a solar water heater's area, a wind generator's rotor size is a pretty good measure of how much electricity the wind generator can produce. The larger the swept area of the wind generator's rotor, the more electricity it can produce.

While manufacturers rate their products at different peak wattages, the output of a wind generator is primarily a function of its swept area. Other features will influence output, such as high-tech airfoils and more efficient generators. However, they pale when compared to the overall influence of the size of the rotor.

Mike Klemen, a seasoned wind generator user and tester in North Dakota says, "Ultimately, we must realize that energy production comes from square feet." Hugh Piggott of Scoraig Wind Electric in Scotland contends, "Swept area is easier to measure and harder to lie about than performance. What we'd like to know is KWH per month, but until we get more independent testing done, swept area is a good guide." Swept area is the most critical feature that will help you compare the output of one wind generator with another.

Jacobs 31-20:

754.0 sq. ft. swept area 31.0 ft. rotor diameter

Proven WT 6000:

Jacobs, Short & Long:

Proven WT 2500:

Proven WT 600:

Jacobs 31-20:

754.0 sq. ft. swept area 31.0 ft. rotor diameter

Proven WT 6000:

Jacobs, Short & Long:

Proven WT 2500:

Proven WT 600:

Whisper 175:

African Wind Power 3.6:

wept Area Diameter

Whisper 175:

African Wind Power 3.6:

Cut-in Wind Speed

This is the wind speed at which the wind generator begins producing. For all practical purposes, wind speeds below about 6 to 7 mph (3 m/s) provide little or no usable energy, even though the blades may be spinning. From my perspective, a few watts does not result in usable energy. At best, this minimal output only overcomes the power losses caused by a long wire run or the voltage drop due to diodes.

We are beginning to see high-tech controllers that are able to "store" the small amount of energy available at low wind speeds in the alternator windings. This energy is then pulsed to the batteries in a manner similar to a pulse width modulated charge controller. The new Bergey XL.1 uses such a controller.

Rated Wind Speed

This is the wind speed at which the wind generator reaches its rated output. Note that not all wind generators are created equal, even if they have comparable rated outputs.

There is no industry standard for rated wind speed. "So what?" you ask. The listed wind generator companies rate their turbine output at anywhere from 18 to 31 mph (8-14 m/s). This may not sound like such a big deal until you understand that there is potentially 511 percent more power in a 31 mph wind than in an 18 mph wind.

To drive home the example, let's use 16 and 32 mph instead of 18 and 31. The power in the wind available to a wind generator is defined by the equation:

Where P is power, d is density of the air, A is the swept area of the rotor, and V is wind speed. Notice that wind speed is cubed. In other words, the equation really reads P = 1/2 d x A x V x V x V.

We can simplify the relationship by stating that P ~ V3, that is, P is directly proportional to the cube of the wind speed. If we double the wind speed (V), the power (P) increases by 800 percent. So there is 800 percent more power available to the rotor at 32 mph than at 16 mph. Viewed in reverse, there is 1/8 the power in a 16 mph wind compared to a 32 mph wind.

Let's say we have two wind generators, both rated at 1,000 watts. Lots-o-Watts is rated at 16 mph and Mighty-Watts at 32 mph. At 32 mph, they're both producing 1,000 watts, right? But at 16 mph, Lots-o-Watts is still producing 1,000 watts, whereas Mighty-Watts is only producing 1/s that amount, or a paltry 125 watts!

All of this means that the lower the rated wind speed, the more energy a wind generator will produce, given its rated output. As a consumer, therefore, you should be particularly interested in machines with low rated wind speeds.

Rated Output

This measurement is taken at an arbitrary wind speed that the manufacturer designs for. It tends to be at or just below the governing wind speed of the wind generator. Any wind generator may peak at a higher output than the rated output. The faster you spin a wind generator, the more it will produce, until it overproduces to the point that it burns out. Manufacturers rate their generators at a safe level, well below the point of self-destruction.

You are not necessarily interested in the rated output of a wind generator. A turbine with a high rated wind speed will invariably cost less than one with a lower rated wind speed, for the same rated output. How can this be? Refer back to the power equation mentioned above. A higher wind speed gives a certain wattage to the manufacturer at a smaller rotor diameter, smaller physical size of the generator, and subsequently less weight. All of this means less cost for the manufacturer, and less cost to you.

But remember, it takes a higher wind speed to achieve that rating. In a 12 mph (5 m/s) average wind speed site, you will see 18 mph (8 m/s) winds a mere 3 percent of the time. Not much, you say. But you will see 31 mph (14 m/s) winds for less than 0.2 percent of the time.

Rated output comes to us from the photovoltaic industry, where panels are tested for output at a fixed light intensity and a fixed temperature. The wind industry has no such fixed standards. So, while comparing PVs based on rated wattage makes for great cost comparisons, comparing rated outputs is a poor way to compare wind generators. You are far better off comparing swept areas, or the KWH per month of electricity the different systems will produce at different average wind speeds.

Peak Output

This figure may be the same as rated output, or it may be higher. Wind generators reach their peak output while governing, which occurs over a range of wind speeds above their rated wind speed. Although widely touted by some marketers, it has limited relevance to the buyer. To quote Hugh Piggott, "Peak or rated output specifications for small wind turbines can be red herrings unless you take the rated wind speed into account, and yet these specs are all the customers seem to want to know about."

Wind turbines are not PVs, don't operate in the same manner, and should not be rated in the same way. What you should be asking is what wind energy engineer Eric Eggleston asked, "What will this wind generator do at my site in my average wind speed?"

Maximum Design Wind Speed

Bandied about by marketing departments, this term has little bearing on the expected life of a wind generator. Wind generators are designed by engineers, on paper, to survive wind speeds of 120 mph (54 m/s) or more. Unfortunately, wind turbines are not tested for these survival speeds because, quite frankly, it's a very difficult thing to test for, or to test repeatedly.

Much of the survival speed documentation we have is not from actually testing turbines at those speeds, but from anecdotal situations. Bergey Windpower might boast that their machine survived a hurricane in Kansas that blew Toto away from Dorothy. Great, but what have we learned?

I don't mean to demean claims like this, but again, they are difficult to test, and everybody supposedly designs their turbines for extreme winds. In fact, Bergey Windpower has actually had very good success designing their turbines to survive such high winds. How? By making their wind generators very robust, very heavy duty.

Does that mean that any turbine will survive a 100 mph (45 m/s) storm? Maybe, maybe not. A 100 mph wind that is coming straight on is fierce, I'll grant that. But have you ever watched a wind generator sited on a short tower near trees and buildings? The poor thing hunts around continuously, all the while buffeted by the turbulence caused by the short installation height, along with the nearby ground clutter. I have seen more wind turbines destroyed by turbulence than I have seen destroyed in survival-rated high winds.

Furthermore, a 100 mph wind packs an awesome wallop, and while wind generators and their towers can be designed to withstand those winds, there's no guarantee that they will. I live in dairy country in northeast Wisconsin. During our last 100 mph wind, cows were flying through the air! If a cow, or a 2 by 4, or a sheet of plywood hits the wind generator or tower, it will probably crumble, regardless of what wind speed the system was designed for. Flying debris is what takes out many turbines in high winds. You can't design for flying lumber or livestock.

So what should you look for if not maximum design wind speed? I look for tower top weight, which is a pretty good indicator of reliability. My experience is that heavy duty wind generators survive, and light duty turbines do not. While all of the units listed are rated for 120+ mph (54+ m/s) winds, in-field experience indicates that many of the lighter turbines cannot handle sites with heavier winds or turbulence. Be forewarned! Weight, by the way, will be reflected in the price. You'll only get what you pay for.

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