Apples and Oranges MIck Sagrillo c. 1993 Mick Sagrillo You'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 include the detailed information, specifications, and power curves for a number of wind systems. Background This article will review all of the commercially available wind systems that are sold in the United States by bona fide manufacturers. An explanation is in order. In the late '70s and early '80s, the federal and state governments offered tax rebates and incentives to folks who bought renewable energy systems, including wind generators. The objective of the program was to help a fledgling RE industry get off the ground, while weaning the United States from foreign energy supplies by growing more of our own. While the intentions of the tax incentive program were good, the results for the wind industry were nearly devastating. (Similar results occurred with the other renewables, but this article will be restricted to wind electric systems.) Scores of companies opened shop and began building wind electric equipment. Virtually all of these companies failed. Customers, however, were left with wind generators that didn't work, plus a bad taste in their mouths for RE. The Vantage Point Lake Michigan Wind & Sun, of which I am owner, is in the business of rebuilding and making parts for dozens of different models of wind generators that were manufactured by now defunct companies. We do a lot of reverse engineering. That is, we try to figure out where system design flaws are so we can correct them. By making the necessary upgrades, customers can turn a poorly designed wind generator into a usable piece of equipment. Because of the services we perform, we have a unique perspective as to where the wind energy marketplace is. We have no allegiance to any one manufacturer. We are in business primarily because all but a handful of wind generator manufacturers failed to build reliable equipment. As we found out a decade ago, anyone can make a wind generator. But making one that will work for years is another matter entirely! So when I say "bona fide manufacturers", I am not trying to slight anyone. I do, however, want to inform readers who the successful manufacturers are. I have tried to fairly represent their products in relation to all others reviewed. They are the survivors, because they have learned how to manufacture reliable products that have withstood the test of time. Addenda Two more points before we start. First, this article does not include either the Survivor or Soma wind generators, both of which have received press in Home Power. Neither machine is commercially available in the United States at this time. Second, a word on failures is in order. You may know someone who has or had one of the wind generators reviewed here that has suffered 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 systems. Paul Gipe of the American Wind Energy Association reminds us to only look as far as the automotive industry for a comparison. The auto industry is a multi billion dollar industry spanning over nine 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 wind generators 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. However, as stated earlier, those systems have not been included in this article. I have extensive experience with all of the systems reviewed here, with the exception of the Rutland Windchargers. This machine is a newcomer to the U.S. (We recently installed a test machine at our shop. An article on our Rutland Windcharger test will appear in a later issue of Home Power.) However, Marlec, the manufacturer, has sold more than 20,000 of these units worldwide. They obviously have a proven design. The Envelope, Please The following table summarizes all of the various features that you should seriously consider when shopping for your wind system. Explanations for the column headings follow. All of the specs have been provided by the manufacturers. 2 page spread TABLE Manufacturer and Model The various models are listed in ascending (i.e., increasing) output to help with comparisons. Manufacturers (or their major distributor) addresses and phone numbers appear 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. Even though the old Jacobs has not been made for 40 years, it is still considered by many to be state-of-the-art technology. They have been "remanufactured" (that is, rebuilt with all new components and put back onto the streets with a warranty) by various companies for at least two decades. The Jacobs wind generator is the yardstick by which many judge today's wind equipment. Rated Output, in general, refers to the maximum power output of the system. Any wind generator may peak at a higher power output than the rated output. This is because 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 safely below the point of self-destruction. Rated Wind Speed is the wind speed at which the wind generator reaches its rated output. You will notice that there is no standard rated wind speed, although most companies rate their systems somewhere around 25 to 28 mph. With regards to rated wind speed, note that not all wind generators are created equal, even if they have comparable rated outputs. In the past, some manufacturers have abused the concept of rated output by fudging on the rated wind speed. For example, a wind generator that reaches its rated power at 50 mph is obviously not the same animal as one which hits that same rated output at 25 mph. How often do you see 50 mph winds? Rated rpm refers to the alternator or generator rpm at which rated output occurs. Generally, the smaller the rotor, the faster the blades spin. Rpm will have an effect on the amount of noise that the wind generator produces. We'll consider noise later. Cut in Wind Speed is the wind speed at which the wind generator begins producing power. For all practical purposes, there is no usable power in the wind below 7 mph, even though the blades may be spinning. This holds true unless you greatly oversize the rotor to allow it to capture power in low wind speeds. But then you open up all sorts of worm cans when trying to control generator output at higher wind speeds. Rotor Diameter is the "fuel collecting" part of the wind generator. The bigger the rotor diameter, the larger the collecting area and therefore, the greater the wind system's output, or the lower its rated wind speed. Number of Blades refers to the number of blades in the rotor. This is primarily a design consideration for the manufacturer. The greater the number of blades, the more torque the rotor can produce. A certain amount of torque is necessary to get the rotor spinning from a stopped position. However, torque is inversely related to rotor conversion efficiency. When you are trying to generate electricity competitively with the power company, efficiency is of prime concern. The fewer the number of blades in the rotor, the more efficient the rotor becomes. One blade is the ideal, but poses some dynamic balance problems. Two blade or three blade rotors are seen most often. The question arises, why use three blades if two blades are most efficient? Time for a digression! "Yaw" is a term that refers to a wind generator pivoting on its bearings around the tower top to follow the continually changing direction of the wind. Two bladed rotors pose a problem as the wind generator yaws. A two-bladed rotor actually sets up a "chatter" as it yaws, which causes a strain on all of the mechanical components. Chattering occurs during yawing because of the continuous changing of the position of the blades in the plane of rotation. When the blades are in the vertical position (that is, in line with the tower) there is little resistance to the rotor yawing around the tower. However, when the blades rotate 90 degrees so that they are in the horizontal position (that is, at right angles to the tower, or parallel to the ground) they pose maximum resistance (or inertia) to any yawing motion. The result is a rhythmic starting and stopping of the yaw twice per revolution of the rotor. This starting and stopping of the yaw is what is seen as blade chatter. Three-bladed rotors eliminate the chattering problem because there is never enough inertia from the one blade in the horizontal position to set up a blade chatter in the first place. The horizontal blade is more than counterbalanced by the other two blades working somewhere off on their own. Well- balanced three-bladed rotors operate very smoothly with no noticeable vibration or chatter. World Power Technologies has come up with a unique solution to the two-blade problem on their Whisper wind generators. The blades are mounted on a spring plate. The spring plate flexes to absorb some of the yawing vibration and therefore helps mitigate the yawing chatter on the Whisper wind generators. Blade Material refers to what the blade is constructed of. Within the last decade, blade material has fallen into one of two categories: wood or extruded fiberglass. While more expensive for materials and labor, wood is still considered by many as the material of choice for blades. Blades do a lot of flexing. That's what trees did as a side job for most of their lives. There is no question that sitka spruce is the "primo" material for wood blades. Sitka has one of the highest strength to weight ratios of any materials ever used by blade makers, as well as airplane and boat builders. Done properly, however, extruded fiberglass also makes an excellent blade material. Bergey holds the secrets with extruded fiberglass. Airfoil refers to the shape of the blade. Two types of airfoils are used by wind generator manufacturers: true airfoils and single-surface airfoils. The cross section of a true airfoil blade would look much like an airplane wing, that is curved on one side and more or less flat on the opposite side. Single-surface airfoils have matching curves on both sides. They are easily formed by the extrusion process. The differences between the airfoils occur in three areas: performance, noise, and manufacturing cost. True airfoils are quieter and perform better than single-surface airfoils. But single-surface airfoils are cheaper to manufacture than the more complex true airfoils. Lateral Thrust at the Tower Top is mainly a design consideration for tower manufacturers. Lateral thrust, the horizontal force vector, is a function of swept area of the rotor, the resistance the tower presents to the wind, and wind speed. The greater the lateral thrust, the stronger (and therefore, more expensive) the tower must be and the larger the concrete footings must be. Governing System refers to the manner in which the wind generator protects itself from high winds and rotor overspeed situations. Governing is necessary for two reasons: to protect the generator itself from overproducing and burning out, and to protect the entire system from flying apart in high winds. The governing devices used on all of these wind generators fall into two general categories: those that reduce the area of the rotor facing the wind and those that change the blade pitch. Changing the swept area of the rotor is accomplished by either tilting the rotor up and out of the wind (NEO and Whispers) or by side facing the rotor out of the wind by moving it around the tower (Rutland and Bergeys). In either case, the rotor is offset either above or to the side of a pivot point. Wind pressure on the rotor causes it to pivot out of the wind. These governing mechanisms are almost a foolproof method of controlling rotor speed. They do come with a cost though. Once the rotor governs by tilting up or side facing, it produces little power. Blade-activated governors work by pitching the blades out of their ideal alignment to the wind. The greater the rotor speed, the greater the degree of pitch. Having more moving parts than either the tilt-up or side-facing mechanisms, they are considerably more complicated governing devices. However, they offer much better power curves, as we will see later. Governing Wind Speed is the wind velocity at which governing mechanism is fully operational. Shut-down Mechanism refers to the manner in which the rotor can be stopped and the generator shut down. This is desirable for maintenance or repairs, or whenever else you do not want the rotor to be turning. The most common system used is to fold the tail (all of these systems have tails) so that it is parallel to the blades. This takes the rotor out of the wind, and it will cease to rotate. Folding the tail involves either cranking or uncranking a cable which will furl or unfurl the tail, depending on the system. The cable winch is at the base of the tower, meaning you must go out to the tower to accomplish the shutdown. Wind Turbine Industries uses the winch to activate a mechanical brake which slows the rotor to a stop on the 10 kW Jakes. Dynamic braking is unique to permanent magnet alternators. Dynamic braking works as follows: if you short out the three phases of a permanent magnet alternator, it will overpower the ability of the rotor to spin the alternator (i.e., stall the blades) and the rotor will come to a stop. this can be done from the comfort of your home! Tower Top Weight refers to everything that goes on the tower: generator, governor, rotor, tail, and turntable assembly. You'll notice that there is wide variation in tower top weights. Based on my experience I side with the "school of heavy metal", manufacturers who believe that beefiness of components is directly related to the longevity of equipment life. Marine Option indicates whether the unit is suitable for use in a marine climate (within one mile of an ocean or on an island) or if this option is available for an additional price. Generator Type describes the electrical generator that is used in the system. Three types are used: permanent magnet alternators, DC generators, or brushless alternators. A little about the pros and cons of each is in order. But first, another digression! Electrical generating devices work by having a wire (or series of wires) pass through a magnetic field. The movement of the wire through the magnetic field causes a current to flow through the wire. It's the flowing current that we are after for our batteries and grid intertie inverters. Permanent magnet (PM) alternators use, as the name implies, permanent magnets for the field. PM alternators are lighter in weight than generators that use copper wire-wound fields. Alternators produce three phase "wild" ac current. "Wild ac" means that the frequency is variable with the wind speed. As rotor speed increases, so does the frequency. Wild ac cannot be used by standard 60 cycle appliances, and must be rectified to DC before it can be used in either a battery bank or a utility tie-in synchronous inverter. DC generators simply produce DC current. Some manufacturers claim that PM alternators are better in wind systems than DC generators, primarily because there is less maintenance involved with an alternator than with a generator. DC generators have brushes, which have to be replaced periodically, maybe every six years or so. PM alternators do not have brushes. (From my perspective, replacing brushes twice a decade can hardly be construed as a maintenance problem.) The real advantage of permanent magnets to a manufacturer is that the magnets are cheap. Compared to the cost of the copper wire needed in a wound field, permanent magnets are a bargain! Cheaper materials means that a manufacturer can be more competitive in pricing his product. The advantages to a system owner of PM alternators are two. First, you can take advantage of dynamic braking, described earlier. Second, three phase ac current can be transmitted through wires more efficiently than DC current, meaning that you can keep your wire costs down. However, PM alternators have a disadvantage compared to generators with a wound field. Because the magnets in a PM alternator are permanent, the amount of magnetism they exude, or their flux density, is fixed at the magnet's maximum amount. The amount of flux density in a wire-wound field magnet, however, is proportional to the amount of voltage present. (I'm going to simplify this greatly, so all you electrical engineers out there, please don't drop your teeth!) In other words, the higher the voltage present in a wire-wound field, the more current the field will draw, and therefore the stronger the magnet will be. However, as the rotor speeds up, the flux density of the field increases accordingly. The nice thing about this arrangement is that the magnets in a wire-wound field generator put very little magnetic drag on the spinning armature when little wind is blowing. But there's plenty of magnetic drag available when the wind is cranking, and the generator is peaking. The power curve of a DC wire- wound field generator nicely follows the power available in increasing wind speeds (the cube law). That's just the way you want it. PM alternators, on the other hand, always have maximum magnetic drag on the current generating stator. This means that performance is at its peak at really only one spot on the entire power curve. All other points on the power curve are a compromise, especially at the low wind speed end of the curve, the part of the curve where the wind system spends most of its life. In order to overcome this problem, manufacturers using PM alternators have to design more torque into their blades just to get the rotor spinning in low winds. But remember, torque is inversely related to efficiency. So while PM alternators are simpler (no brushes) and cheaper to build than DC generators, the simplicity comes at a price. To be fair, DC generators come at a price, too. They are more expensive than PM alternators. Brushless alternators offer the best of both worlds. The fields are wire-wound rather than permanent magnets, but there are no brushes to replace. Their power curve is similar to a DC generator. On the down side, brushless are considerably more complicated, and therefore more expensive to replace than either DC generators or PM alternators. Tower Top Cost is the cost of the complete wind generating device. In most cases, it does not include the cost of any controls, except where noted in "special notes." Different end uses require different types of controllers, and some end uses don't require any controller. $/Watt refers to the tower top cost divided by the rated output in watts. This figure is included so that you can make direct comparisons with the cost of PV panels. Available Systems refers to the wind generator's end use. Different end uses will utilize different control systems, which are not interchangeable. Battery Systems is self explanatory. The voltages available for the battery systems are listed. UTI Systems refers to utility tie-in systems, that is, using the utility grid as your storage. Resistance Heating means that the wind system is used for space heating. These controls are the simplest and least expensive end use option. Water Pumping means that a control package is available to pump water with an electrical pump run off the wind generator directly. No batteries! This category designates whether an ac or DC pump is used. Because of the wide variety of controllers available, prices have not been included. Contact the manufacturer with specific needs and for price quotes. Estimated Monthly Output at Sites with Average Wind Speeds of 10 mph and 12 mph is included so that you have some idea what a wind system will produce at your site. For comparisons, a very efficient home or small cabin would use 75 to 200 kiloWatt-hours (kWh) per month. The "average home in the U.S." (whatever that is) uses 600 kWh/month, as might a small business or farm. These are manufacturers' numbers, not mine. Be aware that "your mileage may vary"! The number in parenthesis is the calculated capacity factor for the system based on estimated monthly output. Capacity factor refers to the amount of kilowatts that the generator produces over a given period of time compared to its potential if it were running at full output all of the time. Note that different systems boast different capacity factors. Capacity factor for wind generators is a function of the swept area of the rotor and the rated wind speed of the system. Generally, the larger the swept area and/or the lower the rated wind speed, the greater the capacity factor. Warranty All the manufacturers warrant their products for parts and labor (that is, in house repairs) against defects in materials or workmanship. This means that you must return the defective part to the factory for evaluation and repair or replacement at the discretion of the factory. Standard practice is that you will pay shipping both ways, just as with any other consumer good. Warranties do not cover improper installation, neglect, use of unauthorized components, abuse or "acts of God" (this is why you have homeowners' insurance). Manufacturer liability is for the defective part only, and does not include incidental or consequential damages. Time in Business is included so that you can see that these manufacturers are not fly-by-nighters. All of these folks have established businesses and have done extensive business in, as well as outside of, the U.S. Footnotes: 1. The NEO is formerly the Windseeker 2. While the Windseeker wind generator has been available for 8 years, the Wind Baron Company, which has been in business for 15 years, has had a relationship with Windseeker for only three years. 2. Whisper wind generators have been available for only four years. Prior to that, the company was known as Whirlwind and manufactured a different line of wind systems. Routine Maintenance refers to what needs to be done to the wind generator to keep it in prime operating condition for a long life. How long? That's hard to say. I recently took down a Jacobs that had seen 60 years of nearly continuous duty. Properly cared for, any one of these systems could match that. This doesn't mean that you will never have to replace parts or do some major repairs. Blades will need repainting and probably a new leading edge eventually. Bearings wear out and need replacing. Some systems, as noted, need annual greasing or oil changes. Bolts might loosen and need tightening. Adjustments might be needed here or there. It is unrealistic to expect something as complex as a wind generator operating continuously in the harsh environment that it lives in to work flawlessly with no maintenance. If that's your belief, then don't buy a wind generator. Some manufacturers recommend only a visual inspection as their maintenance. Bergey Windpower Company, for example, suggests that after you install one of their units, once a year you need to go out to the base of the tower and look up to see if it is still running. That's it for another year! There is no question that Bergey builds the most maintenance-free wind generators available in the industry. However, I am a little more conservative than they are. Many of the catastrophic failures that I have seen over the years with various systems were due to something as seemingly inconsequential as a bolt loosening. I believe that the prudent wind generator owner should thoroughly inspect his/her system twice a year at a minimum; once on a nice fall day before winter hits and again on a warm spring day before thunderstorm season. As they say, prevention is the best cure! Preventative maintenance becomes more important as your investment in the system increases. Most of the great strides in reduced maintenance have come not from new designs, but from new materials. The designs for today's wind generators have been around for a long time. For example, the side-facing governing mechanism was patented in 1898 and used on waterpumpers. The tilt-up style of governing was patented in 1931. And the blade-activated governor was patented in 1951. However, such things as graphite impregnated nylon used in some bushings or the aliphatic resin tapes that are used for leading edge protection were just being developed ten years ago. Continuous upgrading by incorporating modern materials in wind system components has helped greatly in the maintenance arena. The manufacturer who cuts corners by using cheap materials is the one who is courting trouble with his customers. Power Curves The power curves for all of the wind systems reviewed have been put together so that you can more easily compare one system to another. The curves compare the power output of the various systems as a function of wind speed. However, be aware that this is still an "apples and oranges" comparison. To use the PV analogy, it is better to compare all panels of a given wattage than to put all panels made on the same chart. The problem with wind generators is that there are not that many models available to choose from. Because some equipment outputs are close, some reasonable comparisons can be made. POWER CURVES HERE Noise Questions often arise about how much noise a particular wind generator makes. For the most part, a well designed wind generator is relatively quiet. By the time the wind generator is cranking enough to cause some noise, trees are rustling and buildings are rattling as well. Noise from a wind generator can come from two sources: mechanical noise and blade noise. Mechanical noise would emanate from something such as a gearbox. Most of the systems reviewed are direct drive, meaning the blade is coupled directly to the generating device. Only the 10 kW Jacobs utilizes a gearbox. Blade noises can be caused by two things: rpm and/or the airfoil. Rpm should be obvious. The faster something spins, the more noise it is likely to make. The shape of the airfoil can also have an effect of the amount of noise the blades make. As a rule, true airfoils are quieter than single-surface airfoils. Installation The installation of a wind generator on a tower can be accomplished with either the use of a gin pole or a crane. A gin pole is like a boom that is mounted on top of your tower. Using cables and rigging, either the entire wind generator or its component parts are hoisted to the top of the tower, where they are installed. This is relatively easy to do with the smaller systems. However, only an experienced crew should attempt this with something as large as a 10 kW system. These wind generators are probably better installed with the help of a crane. An alternative is to install a tilt-up tower. Tilt-up towers tilt down to ground level, where the wind generator can be easily installed and serviced. Tilt-up towers are generally more expensive than either freestanding or guyed towers. My Choice? "So, Mick, what do you recommend?" is the most frequently asked question that I get. The answer: it all depends on your situation. I can honestly say that, properly specified and installed, any one of these machines will do a fine job of producing electricity for you for many years. They all have their own personalities and idiosyncrasies, just like the cars we drive. And, just like the cars we drive, they come in a variety of shapes and prices. Finally, just like the cars we choose, they will all get us from point A to point B. However, not all cars, nor all wind generators, are created equal. Quality comes at a price. I hope you now have all of the tools you need before you to make an educated choice. But make sure that you digest the facts and figures, as well as your needs and pocketbook, for a while so that you may choose well. The Manufacturers The manufacturers for the systems reviewed can be contacted for prices or more information. Or you can contact your favorite wind generator dealer. Bergey Windpower Company, 2001 Priestly Ave., Norman, OK 73069 ù 405-364-4212 ù FAX 405-364-2078 Manufactures the BWC 1500 and the BWC Excel. Lake Michigan Wind & Sun, E3971 Bluebird Rd., Forestville, WI 54213 ù 414-837-2267 ù FAX 414-837-7523 Remanufactures the Jacobs "short case" and Jacobs "long case." Trillium Windmills, Inc., R.R. #2, Orillia, Ontario, L3V 6H2, Canada ù 705-326-6513 ù FAX 705-325-9104 North American distributor for the Rutland Windchargers (which are manufactured by Marlec Engineering co., Ltd. of England) Wind Baron Corporation, 3920 E. Huntington Dr., Flagstaff, AZ 86004 ù 602-526-6400 ù FAX 602-526-5498 Manufactures the NEO (formerly the Windseeker 2) Wind Turbine Industries, Corp., 16801 Industrial Circle SE, Prior Lake, MN 55372 ù 612-447-6064 ù FAX 612-447-6050 Manufacture the Jacobs 23-10 World Power Technologies, 19 Lake Avenue North, Duluth, MN 55802 ù 218-722-1492 ù FAX 218-722-0791 Manufactures the Whisper 600, Whisper 1000, and Whisper 3000 Access Mick Sagrillo ruminates on wind generators at Lake Michigan Wind & Sun, E3971 Bluebird Rd., Forestville, WI 54213 ù 414- 837-2267