Why Wind??? Mick Sagrillo c. 1993 Mick Sagrillo Wind power has taken a lot of bashing in recent years, for a variety of reasons. Some of the criticism has been justified, but most of it is completely unfounded. A fresh look at wind power and its place in a renewable energy (RE) system is in order. Dispelling Myths Let's take the most frequently used excuses for not considering wind power in an RE system and analyze the whys and why nots. By the time we're finished, you will have clearer understanding of wind's place in the whole RE picture. "Wind doesn't work" One reason given for not wanting to use wind power is that the equipment apparently doesn't work. "I drove past this wind generator and the blades weren't spinning." Well, maybe the wind wasn't blowing, or maybe it was blowing too hard. Maybe the wind system was shut down for routine maintenance. Maybe the owners' batteries were charged up and the power was not needed. Maybe...I could go on and on, but I'm sure that you get the picture. We humans are very visual yet blind creatures in that first impressions are often the most lasting impressions. When one glances quickly at a PV array, a solar hot water heater, or even a hydro plant, you have no idea if it's operating or not. You can't see what's going on inside. But it is always obvious when a wind generator is or is not operating. This isn't to say that wind generators always work. In the late '70s and early '80s, there were scores of companies who set up shop building wind generators. In many cases, their motivation was greed. They were attempting to cash in on the 40% federal tax credit that was granted to buyers of RE equipment. Most states also offered tax incentives for RE purchases. Homeowners could get up to 70% of a $10,000 investment back from the government. The problem was that there were no standards for most of the RE equipment that folks bought. Consumers were in the mood to spend lots of cash, and manufacturers were all too willing to take their money. No standards, lots of money, and the tax credits all combined for what would ultimately be a major setback for renewables. There is no question that a lot of junk was being sold. Many of these travesties still hang from their towers as a dismal reminder that their owners had been had. Not only wind power, but all forms of renewables got a black eye that is now just healing. Unfortunately, many people developed a sour taste for RE. Ronald Reagan even got a laugh at one of his State of the Union speeches by poking fun at wind farms and Jimmy Carter's solar water heaters. Six years after the sunset of the tax credits, virtually all of the 80 or so wind generator companies doing business in the U.S. are gone. Only a handful of manufacturers have survived the shake-down. And these survivors are still cranking out the same reliable equipment that the fly-by-nighters tried to emulate a decade ago. There is no question that the equipment available today is reliable, and their manufacturers stand behind their designs. These people know that a wind generator manufacturer is in the business to help generate renewable electricity, not just build and sell RE equipment. Today's wind generators work! "No Power!" Many folks have the misconception that there is no real power available in the wind. Therefore, why bother with a wind generator. Let's look at this more closely. The equation for determining the power available to a wind generator is as follows: P = 1/2 d AV3 where P is the power in the wind, d is the density of the air, A is the swept area of the rotor, and V is the wind speed or velocity. What we are interested in here is V3 or V x V x V. When we double the wind speed for a given location, say from 5 to 10 mph, we increase the value of V3 by a factor of eight! Multiply 5 x 5 x 5 and you get 125. Double it to 10. Multiply 10 x 10 x 10 and the result is 1000, an 800% increase. There are two lessons here. The first is that even small gains in wind speed can result in enormous increases in the power in the wind. As the wind steadily increases, the power in the wind increases exponentially. The second lesson is that, because the power gets so large so fast, it must be awfully difficult to build a wind system that will survive high winds. Any do-it-yourselfer who has tried to design a wind generator has learned this lesson, probably the hard way. So have all those bankrupt manufacturers that were mentioned earlier. But today's wind generators know how to behave without self-destructing in high winds. "No Wind?" A lot of people have the idea that wind power is so site specific that they probably have little or no wind at their site. Richard and Karen Perez even fell into this category, until a manufacturer gave them a wind generator to test at their home. Lo and behold, they now have more power than they oftentimes know what to do with! The chief culprit here is that wind power has been saddled with a very poor yardstick: average wind speed. Dealers will ask a prospective buyer what their average wind is. If it's down around eight or nine miles per hour, the dealer will usually disregard the wind system in favor of photovoltaics (PVs). But average wind speed is the wrong question to ask. An example is in order. Let's assume two locations, each with an average wind speed of 10 mph. We are only interested in the average for one month, and we are going to take readings on a weekly basis. The wind speeds for our two imaginary sites are as follows: INSERT TABLE 1 It should be clear that while both sites have the same average, they have not been created equal! Let's develop the example a little further. Remember the power equation, P = 1/2dAV3? Let's plug in the weekly values for wind speed from sites one and two, and then add them up to determine the monthly value for V3. Note that the units for the numbers don't matter here. What we are interested in is the numbers themselves. INSERT TABLE 2 Obviously, when we plug the value of V3 into the power equation, 64,000 times something is going to be a lot more than just 4,000 times that same thing. While both sites look the same with regard to their average wind speeds, one site has a lot more fuel than the other! Even though your site may appear to be poor for a wind system based on the average wind speed, a low average wind speed is not enough in and of itself to disregard a wind installation. Another major problem with the average wind speed readings that we have for the vast majority of the U.S. is that these averages are not representative of our wind resources. Wind speed data is usually collected by people like the National Weather Bureau or a local airport. The trouble lies in the location and height of the recording equipment. Weather bureaus are interested in wind speeds at street level, where the people are. But wind generators live 80 or so feet up in the air, far above the obstacles and turbulence found at ground level. A similar situation exists with airports. Traditionally, airports were located in sheltered areas, because, traditionally, airplanes had trouble coping with cross winds when landing. While modern jets and planes have much less trouble with the wind, we're still stuck with wind speed readings from traditional airport locations. Airports don't spring up like strip malls. The bottom line: average wind speeds at hub height, the height where the wind generator will be installed, are always substantially higher than those recorded by weather bureaus and airports. "For how long?" We have been told that in order to get a reasonable idea of the wind resource for a given location, that the site must be monitored for at least a year. Longer if possible. But why bother, you say. After all, if you have to wait a year to see if you even have any wind, why not just install PVs? This seems reasonable. All you need to do is look in a book to find what the weather bureau tells you is your solar resource. This is nonsense! All this kind of talk does is dissuade one from even considering a wind system. There is a way to make weather bureau and airport data useful. Let's say you were to install a recording anemometer at your site and take daily readings for a month. During that month, you also called the weather bureau or airport for their readings once or twice a day. At the end of the month, you would see a relationship between your data and their data. As a matter of fact, you could extrapolate your data as far back as you wanted to, using the relationship between the two sets of data. You now have an excellent set of numbers describing your site's wind resource. In order to make these numbers useful, the readings that you take at your site must be at hub height. This may entail getting up 60, 80, or 100 feet. Remember, wind generators spend their lives up above the trees and buildings, out of the turbulence. Taking the data at roof top level is about as useful as relying on weather bureau readings. "Not Reliable" Photovoltaic converts often point to the arrays and ask how a wind system can possibly compare to photovoltaics for reliability. After all, PVs have no moving parts. There are wind systems out there that are just as reliable as PVs. Let's look at a few examples. I recently took down a Jacobs wind generator that had been in service for nearly 60 years. At one point it had been moved from one farm to another. At that time the bearings were replaced. One blade was replaced after being hit by lightning. And periodically, the brushes were replaced. Sixty years of service is why the old Jakes have earned the reputation as being the "cadillac" of wind generators. Today's technology has comparable machines. Bergey wind generators are known to operate year after year with little or no attention. This is why Bergey is a frequent choice of power supplies at remote telecommunications and coast guard sites. "Expensive" Another criticism leveled at wind is that the systems must be expensive because a generator has to be installed on a tower. The tower is certainly an added cost. However, when one compares the costs of a wind generator tower with a PV array tracker, an interesting fact arises. For a given generating capacity, say 3 kiloWatts of PVs versus a 3 kW wind generator, towers come in at approximately the same cost as trackers. All of the other system components used Ä the batteries, the wire runs, the inverter, the switches, fuses, and disconnects Ä will be identical in cost no matter what electron generator is employed. The real cost advantage is with the wind generator itself. Wind generators are 20-40% of the cost of PVs, watt for watt, depending on the economy of scale Ä the size system you buy. The exception is very small "micro" wind generators. "Too Erratic" Wind has often been criticized as being too erratic and inconsistent. No argument on this one. Well, maybe a little bit of a disagreement. The sun is pretty predictable. It comes up every morning, and goes down every night. You can bank on that one. The wind comes and goes. You never know when it might blow. But the wind is more predictable than you might realize at first. After all, the wind is a form of solar energy. "Capacity factor" is a term used by electric utilities for comparing different generating technologies. The term refers to the amount of time that a given generator type is producing its kilowatts compared to the total time available for production. For example, let's say you live in an area with an average of 4 peak hours of sunlight for PV production. Since there are 24 possible hours of production available in a given day, your PVs would have a capacity factor of 4 divided by 24, or a 16% capacity factor. Annual average capacity factors for fixed PVs in the lower 48 run from about 8% to about 25%. That number can increase for the northern tier of states by about half with the addition of a tracker. In comparison, annual average capacity factors for wind generators range from 10% to about 28%. Taller towers can do for wind what trackers do for PVs. While the weather bureau does a poor job with average wind speeds, daily and seasonal wind patterns are very well documented. For about 90% of the U.S., the wind is quite noticeable during the fall, winter, and spring. During the summer, the wind ceases to exist in many places. When you think about it, the wind usually blows when the sun doesn't shine. And the sun is usually really bright when the wind isn't blowing. These daily and seasonal patterns exist for the bulk of the U.S. Maybe we're onto something here! Comparisons Let's look at some of the advantages and disadvantages of the two technologies: PVs advantages include: ù No moving parts. This is PVs trump card, by far. ù They are on the ground. No dangling from 80 feet in the air when it's time to remove dirt or bird droppings. ù They're modular. If you don't have enough capacity, just add a few more panels. You can't do anything like this with a wind system. If you need more wind capacity, you get a bigger wind generator, or install a second unit. PVs only disadvantage: ù Cost! PVs are, by far, the most expensive of the renewable energy technologies. Wind power's advantages include: ù Cost. It is one of the more cost-effective renewable energies, coming in behind only solar hot water heating and some hydro electric generators. ù More power in the resource. Because of the cube law, P = 1/2 dAV3, wind generators can deliver awesome amounts of electricity in a brief period of time. For the folks with batteries, that means it's equalize time. Wind power's disadvantages are: ù Heights! Wind generators live on top of towers, making service and maintenance more difficult. Tilt-up towers make this disadvantage a moot point, because the generator tilts down to ground level. ù They have moving parts. Any device with moving parts will eventually need maintenance. By the way, don't let anyone tell you that their wind generator needs no maintenance. Any mechanical system with moving parts will need some attention eventually. However, recent improvements in materials science have eliminated many of the problem components in older machines. A Marriage The point of this exercise was to dispel a lot of misconceptions about wind power that exists in the PV community. But more than that, it was to get you to think about the possibilities that exist with a wind/PV hybrid system. Let's compare advantages and disadvantages of wind/PV hybrids. Advantages: ù The resources are quite complementary. Long sunny days and periods of good winds rarely overlap. ù Because the resources complement each other, their peak operating times occur at different times of the day and year. This means that the capacity factors are somewhat additive. A PV system with a 15% capacity factor and a wind generator with a 20% capacity factor may combine for a total system capacity factor of 30%. ù Higher capacity factors for the generating devices means less storage is needed with the batteries. This often results in a downsizing of the balance of the system's components. Higher capacity factor means that you can retire your stand-by gas generator, like the crew at Home Power did. [Editor's note: While we did give away the old generator, sometimes poor weather forces us to run the Honda Ä about 12 hours for this issue.] Less fossil fuel means that our atmosphere as well as the rest of us can all breathe a little easier! Disadvantages: None! Access Mick Sagrillo enjoys his wind generators at Lake Michigan Wind & Sun, E3971 Bluebird Rd., Forestville, WI 54213 ù 414-837- 2267