Wind Energy Facts: Is Wind Power For You?
How Wind Energy is Used on Your Site Will Determine Return on Investment
By Dan Fink – My interest in wind energy facts started with a particularly brutal winter up here off-grid in the Colorado mountains at 8,200 feet elevation. It howled, it roared, the windows rattled, the snowdrifts piled up and we all felt those little jets of piercingly cold air through every crack around every window and door we hadn’t sealed properly. “There must be some way to put all this energy to good use,” I thought, while hauling yet another sled load of firewood to the stove. And as it turns out, small wind turbines can be very effective in generating electricity—if you install the right one at the right location in the right area for the right reasons.
A decade later, I’m still an advocate of small wind energy, and have thoroughly researched wind energy facts. In many situations, it’s an extremely effective complement to solar energy. But nowadays when I talk with potential clients, I find myself spending more time talking about wind energy facts, and usually end up talking them out of wind power entirely instead of designing a system for them. Why? Most people overestimate how much wind power potential they have available, are interested in it for the wrong reasons, and underestimate both their own electricity needs and the scope of the project required to meet those needs. You should always evaluate wind energy pros and cons thoroughly before deciding to invest in wind energy.
Wind Energy Facts: Are You a Good Candidate For Wind Power?
When evaluating wind energy facts to see if you’re a good candidate for wind power, you should start by taking a look at where you live.
• Live in an urban or suburban area;
• Buy electricity from the utility and don’t have a battery backup system;
• Want to use wind power just to reduce your household utility bill;
Then you’ll likely be disappointed in the expense and long payback time of wind power. I’ll be trying to talk you out of the whole idea, and talk you into a solar electric system instead. Wind energy would not be your best renewable energy source.
On the other hand, if you:
• Live in a remote or rural area on a property of at least four acres;
• Have battery backup electricity for your home or business;
• Live off the grid or are planning to do so;
• Already generate some of your own electricity from solar;
Then you might be a good candidate for a wind turbine.
Wind Energy Facts: Location, Location, Location
You wouldn’t mount a solar panel in the shade, would you? It would cost you a lot of time and money, with very little energy output to show for it. Just as solar arrays need bright, direct sunlight to live up to their potential, wind turbines need smooth, fast-moving air. Friction with ground cover and turbulence from nearby obstructions slow down moving air, and wind speed is the number one factor in how well a wind turbine performs.
As far as wind energy facts go, these are the primary reasons that small wind power in urban and suburban areas has never been very effective, and likely never will be. Anyone from a cold, windy climate has seen strategically-placed snow fences that cause drifts to form around the fence instead of on the road, and in desert climates, sand fences are used the same way. The fences are obstructions to slow down the wind and make it turbulent, so that snow and sand drop out. Buildings and trees work the same way with wind turbines, drastically reducing power output and causing extra wear and tear on the turbine (photo 1).
The only solution is to fly the turbine well above any obstructions. A general rule in the small wind industry is 30 feet above anything within 500 feet in any direction, measured from the lowest point of the rotor. That presents a variety of problems in more populated locations! Many local statutes limit the height of towers for any purpose to 30 or 40 feet without a variance—not nearly high enough to meet the 30/500 rule—and a variance usually requires a lot of red tape, a hefty fee and permission from all your surrounding neighbors. Local statutes often include setback rules, too: a tower must be located so that if it falls, everything lands at a minimum distance from any structures, roads or property lines, and that required distance may be up to 200 percent of the tower height.
A tower tall enough to get you above the 30/500 rule is also a significant investment. Plan on spending at least as much on building and installing the tower and foundation as you spend on the wind turbine itself. There are a variety of tower types, each with advantages and disadvantages. See the “4 types of towers” sidebar for more details about how to get your spinning hardware up in the smooth air where it needs to be. Off the grid, we can cheat that 30/500 rule a bit, to maybe 30/300 or 20/300, but also remember—trees grow!
Wind Energy Facts: How Much Wind Do I Really Have?
Thanks to decades of sun intensity monitoring data (which factors in weather patterns) solar site assessment has become a very simple and precise science, to the point that some solar installers will even offer performance guarantees in kilowatt-hours per month for the systems they design and install. Not so with small wind power. Thinking about wind energy facts, factors like terrain effects and the difficulty of measuring wind speed and turbulence at different heights above the ground makes wind site assessment is far more tricky.
The critical number from which you can make monthly and annual energy output predictions is called “annual average wind speed,” which also factors in all the hours each year the wind is not blowing at all. An annual average of 10-12 mph or better is considered good, though in remote, off-grid situations lower average speeds might still be useful. If you are planning a significant investment in wind power, it pays to hire a trained wind site assessor for an evaluation. But there are a few tactics you can use on your own to get a reasonable idea of how much energy you’d be able to produce from a wind turbine at your site and to best evaluate the wind energy potential at that particular location.
Wind maps: The U.S. Department of Energy publishes detailed wind maps for every U.S. state, and these can give you a general idea of your wind potential (#1.5). But remember, these maps are usually for 50 to 80 meters (164 to 262 feet) above the ground—much higher than your tower will likely be—so actual wind speeds closer to the ground will be much lower.
Anemometers: Inexpensive home weather stations that include a logging anemometer are available at your local big box store, and can also give you a general idea of what to expect. More capable professional loggers are available too (#2) in the $600 range. But unless they are flying at the intended height of your prospective turbine, the data won’t be very accurate. On the bright side, if data from near your rooftop shows good wind, it will get much better as you go higher. Also keep in mind that there are good years and bad years for wind; one of the reasons solar site assessments are so accurate is all the decades of ground station data, while your anemometer might only be logging for a year or two at most.
Tree “flagging”: Sometimes the best wind site assessment information is just plain common sense. If there are conifer trees near your proposed turbine that look like photo 3, you can be quite sure that’s a windy site, and from which direction the prevailing winds blow! More subtle tree flagging (photo 4) is still a good indication of steady winds. There’s even a chart, called the “Griggs-Putnam Index,” (#5) that predicts annual average wind speed based on conifer tree flagging.
“Wet-finger” wind prospecting: “It’s always windy around here.” This gets many folks into trouble by overestimating their wind potential, as they tend to remember only those times the wind is blowing strongly, and forget all about the far longer periods of calm air.
Wind Energy Facts: Off the Grid or On It?
When evaluating the wind energy facts and potential for your particular location and needs, think about whether or not you are off the grid or on it. If you live in an off the grid home, or are planning to move or build there, wind power can be an excellent complement to solar. The farther north you are, the more important it can become. On the grid, electricity use and generation are usually combined into a net figure, with excess solar generation during the flush summer months credited towards excess usage during winter. Off the grid, though, what’s most important is having enough power to keep the lights on right now, tonight, and for the next couple days. The combination of reduced solar gain plus more lighting and heating loads is a real double whammy in the winter off the grid.
Take a look at #6, showing a solar versus wind case study for an off-grid home in upstate New York, which has few sun hours in the winter due to high latitude, and many days with poor sun intensity due to the “lake effect.” The shaded area shows those times of year when the existing two-kilowatt solar array couldn’t keep up with energy usage, and lots of generator run time was needed. Adding more solar would have helped, but would have also resulted in excess energy in summer with nowhere to store it when the battery was full. Now, add a wind turbine instead of doubling the solar, and look at #7. An off-grid wind power success story!
On the grid, I’m afraid the tale told with wind energy facts is vastly different. The wind turbine needed to power a typical American home (1,000 kilowatt-hours per month) on a site with good wind resources and a tall tower would need a rotor 23 feet in diameter, and cost over $60,000 installed. Smaller turbines, like a 12-foot diameter model typically used off the grid, are far less expensive (under $10,000 installed) but at a 10-12 mph average wind speed site on a tall tower would typically produce only 250-350 kilowatt-hours per month—$25 to $30 worth of electricity at an 11 cents per kilowatt-hour rate. Not a very impressive payback against your utility bill. But off the grid, those kilowatt-hours are pure gold dust! They often come in exactly when you need them the most, and they are competing against very expensive energy from your gas-fired backup generator instead of cheap, subsidized utility rates.
There are some exceptions to the poor prospects of on-grid small wind. The first is if you have a battery backup system for critical loads. The wind turbine may not make a significant difference in your monthly utility bill, but if there’s a grid blackout—and even more crucially an extended blackout that effectively puts you off-grid for days or weeks—it could be a key element to keeping your homestead running until the power comes back on.
Another exception is if you have an agricultural application that uses a whole lot of power each month, racking up an extensive bill. An investment of $60,000 to $100,000 and up in wind power (photo 8) might seem extreme, but if your monthly electric bill is over $5,000, the return on investment can be relatively rapid if you have a good site with steady wind. In fact, the small wind industry has been rapidly moving towards larger, more expensive wind turbines for just this sort of application, as “grid-tied backyard small wind” with the intention of offsetting household utility bills turned into a boondoggle of dissatisfied customers and bankrupt wind turbine manufacturers over the last few years.
Fortunately for those of us who live off the grid and have modest energy needs, a few of those companies still remain and still build relatively inexpensive small turbines for the relatively small off-grid market. You can even consider building and flying your own wind turbine (“Build your own,” page 30), though it’s not a project for the faint of heart. In addition to lower cost, though, one big advantage of building your own turbine is that if it breaks, you already know exactly how to fix it and can easily get replacement parts!
Wind Energy Facts: How to Choose a Wind Turbine
If you’ve done your homework and evaluated the wind energy facts that apply to your particular location and needs, and you have decided that wind power will help your power situation, that you have a windy site, figured out how big a wind turbine and how tall a tower you need to meet your energy needs, the next step is to see if you have enough room for the tower type of your choice, and get approval from local authorities if needed (and don’t forget to talk to neighbors, too). Then it’s time to consider which turbine to purchase. There is a daunting array of choices, and I hope these guidelines will help you quickly winnow out the wheat from the chaff.
• Choose your turbine size by swept area, not manufacturer’s “rated output”;
• Ask a professional small wind installer what brand of turbines he installs and why, and which brands and models to avoid;
• Check to see if the turbine has been certified by the Small Wind Certification Council (www.smallwindcertification.org), and if not ask the manufacturer why;
• Find out how long the manufacturer has been in business and how many turbines they have operational in the field;
• Ask the manufacturer to put you in touch with a happy customer who can show you at least a year’s worth of energy output data and maintenance records, or maybe even let you visit the site to see and hear the turbine in operation;
• Inquire about the length of the warranty, plus what is covered and what is not.
Wind Energy Facts: 4 Types of Wind Towers
There are four basic types of towers for small wind turbines: Monopole, freestanding lattice, guyed lattice and tilt-up. However, the most important question to ask yourself is if you are trained and willing to climb a tower, or would you rather be trained in how to tilt a tower up and down? Many experienced turbine techs will tell you that climbing is far safer if you have the proper training and equipment. Training is needed for tilt-up towers too, as they can be very unpredictable and must be laid out and rigged very precisely to be safe when raising and lowering.
Monopole: These are the most aesthetically pleasing of all the tower types, with their smooth, tapered lines and no guy wires, and take up the smallest “footprint” of land when viewed from above (#8). Some can be tilted up and down, others require a crane and are designed to be climbed. They are also by far the most expensive type of tower, and require a massive pour of steel-reinforced concrete for a foundation. They also become exponentially more expensive as you go higher, compared to other tower types.
Freestanding lattice: This design also needs no guy wires, and is designed to be erected with a crane and climbed. The footprint is larger than a monopole but the foundation can be less massive, with a smaller steel-reinforced concrete footing under each of the four tower legs. Less expensive than a monopole, but more expensive than other types.
Guyed lattice: The least expensive tower type, still with a relatively small footprint (photo 10). Most are designed for climbing only, though some can be tilted up #8: Monopole#9: Freestanding lattice#10: Guyed lattice#11: Tilt up and down. A crew of two (a climber and a ground support person) can erect these towers with no crane needed by using a movable davit as each tower section is lifted by a pulley from the ground. Thanks to the three guy wires and anchors, no concrete is required, not even for the tower base, though in some situations (for example rocky ground) concrete is needed if helical guy wire anchors cannot be driven into the ground or the base is on uneven terrain. These towers are popular with ham radio enthusiasts, and so are often available used as surplus.
Tilt-up tube: Despite their dangers and disadvantages, most people installing small wind turbines prefer tilt towers for the simple reason that the wind turbine can be installed and maintained on the ground. The danger comes during raising and lowering; a change in wind speed or direction, or a poorly laid-out base, guy anchors or guy wire lengths can cause a disaster in the blink of an eye (I’ve been there and done that.) Tilting towers have the largest footprint of any tower type, and the entire area must remain clear of brush or other obstructions for raising and lowering (#11). No concrete is needed except in the same special cases as guyed lattice towers. Raising and lowering is usually done with an electric or hydraulic winch, though a truck or tractor can be (perilously) used in a pinch for shorter towers.
I advise getting professional training before tackling a tower project, no matter if you’ll be climbing or tilting. There are dozens of trainers offering tower climbing classes across the U.S. thanks to the proliferation of cell phone towers and big wind farms. There are a smaller number of outfits offering tilt-up tower training, but classes are still available. If you can’t find one in your area, try contacting a local small wind installer and ask if you can tag along and learn the next time they raise or lower a turbine. The crew might appreciate your presence, even if just for fetching tools and keeping bystanders away.
Wind Energy Facts: How Wind Power Works
The phrase may be “light as air,” but air does have mass. At sea level, a cubic meter of air weighs about 1.2 kilograms. As the sun shines on different areas of the earth, large masses of air are heated unevenly, and they move to try and achieve equal temperatures. That’s wind—and in fact, you could say that wind power is just a roundabout way of collecting solar power.
A wind turbine works by slowing down this moving air, and transferring its energy into a spinning shaft that drives an electrical generator, pump or grain mill. But it can’t do the job with 100 percent efficiency, because…that would stop the wind! In 1919 Albert Betz proved that at most we could harvest 59.26 percent of the power available in the wind; beyond that point air simply moves around the collector instead of through it. That number is called the Betz Limit.
The formula for how much power is available in the wind is very simple, but has some interesting effects. It is:
P = ½ · d · A · V³ · cP
where P = power in Watts, d = air density in kg/m³, A = rotor swept area in m², V = wind speed in m/s and cP = coefficient of power, which can never exceed the 0.526 Betz Limit. (Most small wind turbines operate at a cP of 0.25 to 0.35, or 25 to 35 percent efficiency)
Notice that “cubed” for wind speed? It’s the most important number in wind power, as it means that if you double the wind speed, you get eight times the power. That shows the importance of flying wind turbines on tall towers, where wind speeds are faster and less turbulent, and also shows why wind turbines must have a system to protect themselves in high winds. A wind turbine that hums along at 1,000 Watts output in a 30 mph wind will have 8,000 Watts driving the shaft in a 60 mph wind, which would burn that 1,000 Watt alternator to a crisp.
Swept area is also extremely important. Because of the “squared” in area, doubling the diameter of a wind turbine rotor gives you four times the power. That shows the fallacy of tiny, rooftop-mounted wind turbines whose manufacturers claim “it can power your whole house!” Nope, the collector is too small unless you live in a doghouse.
Note that “swept area” refers to the area of the circle that the blades and rotor spins in, not the actual surface area of the blades themselves. The latter is called “solidity,” and while it may seem counterintuitive, less blade surface area is actually far better for generating electricity. Rotor designs with many blades—like common farm water pumping windmills—spin at slower speeds but with more torque. That’s great for moving a heavy pump shaft up and down, but very inefficient for generating electricity, where faster rotation means better efficiency and a lower-cost generator.
I’m often asked about converting old farm windmills into electricity-producing wind turbines, but unfortunately, it’s a thankless task. Gearing is required to boost the RPM, and the friction from that robs the turbine of most of its low-wind performance. Since low winds be-tween 7 and 20 mph are by far the most common, that’s a significant reduction in energy output. Best to leave farm windmills to the job they are best suited for: pumping water. In fact, you’d actually be hard-pressed to find a successful wind-electric water pumping system, as farm windmills do a better job at lower cost.
KidWind: Wind for Kids!
If you’re interested in wind energy facts, there’s a good chance your kids will be too. The Kid-Wind Project (www.kidwind.org) can provide you with a plethora of free educational material, and even better, a whole bunch of inexpensive parts from which your kids (or your class) can build and experiment with safe, tiny wind turbines that can run in your backyard or in the wind from an electric fan. They hold the “KidWind Challenge” at schools across the country each year, but beware—oftentimes, the kid’s little turbines out-perform those designed by their teachers!
Vertical Axis Wind Turbines
If you’re an avid boater, what would you say if someone came up to you on the dock and told you they’d invented a radical new boat propeller design that:
• Is far more high-tech than this old-fashioned kind #13.
• Is slow and quiet;Works in both calm and rough water;
• Doesn’t kill fish;
• Pushes more water;Is revolutionary and patented;
• Will change the world of boating forever;
And finally, all you have to do is invest some money now so they can build their first one to test, so you’ll be “in on the ground floor” and get rich when it hits the market?
If you’re like most boaters I know, the response would be “Go jump in the lake.”
Unfortunately, exactly such claims spring up like crabgrass each year for new Vertical Axis Wind Turbine (VAWT) designs, mostly on “tech” websites that purport to show the latest and greatest upcoming gad-gets. Just substitute birds for fish in the claims above. These turbines spin on vertical shafts as opposed to more typical Horizontal Axis Wind Turbines (HAWTs) and use different blade designs. They purport to be the new high-tech replacement for “old-fashioned” wind turbine designs like #14.
For the rest of the story…
Paddle wheels (#15) were a very early form of mechanical boat propulsion, dating back to the first century A.D. Their numerous disadvantages included: complexity, fragility and the very large size needed for adequate thrust, making them very expensive to build and maintain; poor performance in rough water; and poor efficiency due to their slow rotational speed and limitations in paddle design. Upon the invention of the far more efficient and inexpensive screw propeller, paddle wheels faded into history, and are now used almost exclusively for tourist ships because they are an aesthetically pleasing piece of the past. Their only advantage, shallow draft, was overcome with the invention of waterjet drive in the 1950s.
Vertical Axis Wind Turbines (#16) were a very early form of machine to harvest wind power, dating back to the first century A.D. and used for grinding grain and pumping water. Their numerous disadvantages included: complexity, fragility and the very large size needed for adequate power output, making them very expensive to build and maintain; poor performance in both turbulent and smooth winds; and poor efficiency due to their slow rotational speed and limitations in rotor design. Upon the invention of the far more efficient and inexpensive three-bladed, lift-based Horizontal Axis Wind Turbine, VAWTs faded into history, though working examples still exist in remote parts of Persia (now Iran and Afganistan) and few other parts of the world.
So why do VAWTs seem to be making a come-back now, while paddle wheels remain in obscurity? My theory is simply that we boaters are a far more cynical lot than the general public. I for one wouldn’t invest in a new propeller or stink bait formula without proof that it actually works, like watching my buddy using it to catch more fish. Always refer to the wind turbine buyer’s checklist here before pulling out your wallet—and do it even more carefully if the design is new, unusual or makes spectacular claims.
Wind Energy Facts: Build Your Own Wind Turbine?
When I first became interested in wind energy facts in the 1990s, there were only a couple turbine options available, and they were far beyond my budget at the time. “These things don’t look very complicated,” I said. “It should be easy to build one.” So I joined forces with neighbor, machinist and gearhead extraordinaire Dan Bartmann and we built a small wind turbine based on a surplus tape drive motor. And it worked! For about a week. Then it blew into pieces scattered about the yard. We kept trying, had some minor successes but never came up with anything that lasted more than a few months at best.
Then we finally got to meet Hugh Piggott of Scoraig, Scotland, took one of his classes in the U.S. and learned how to design and build a wind turbine that holds together for years (with regular maintenance). Hugh’s “secrets,” which he shares freely worldwide, are simple: Build a heavy, sturdy machine for durability, as the weight doesn’t matter once it’s on top of a tower. Design the rotor and blades carefully so the turbine spins at low RPM, making it both quiet and reliable. Build the permanent-magnet alternator from scratch so it generates good power at low RPM, instead of mucking about trying to adapt surplus equipment. And build in a very simple, (almost) foolproof “furling system” that automatically turns the turbine out of the wind when wind speeds get too high, then rotates it back into place when winds become more reasonable.
We took those ideas and ran with them, and ended up with our book Homebrew Wind Power (2009, Buckville Publications LLC, ISBN 978-0-9819201-0-8). It gives step-by-step, illustrated instructions for building your own wind turbine, in addition to all the relevant theory that explains how wind power works and how turbines are designed. If you are interested in building your own turbine, this book is an essential addition to your library. Also be sure to get copies of Hugh Piggott’s books Windpower Workshop and A Wind Turbine Recipe Book to complete your education.
You can look at Hugh’s work on his website www.scoraigwind.com, and ours at www.otherpower.com. Hugh offers week-long hands-on wind turbine building classes at his location in Scotland, as well as France; we offer our classes two or three times a year at various locations in the U.S. Consider these workshops “small wind boot camp,” and expect to come out exhausted, exhilarated and with all the knowledge and skills you need to build your own turbine at home.
Wind Energy Facts: At the End of the Day…
Small wind power is not for everyone, and you need to carefully evaluate wind energy facts before you decide to invest. In fact, I think it’s not for at least 99.99 percent of the population, who would be much better served by solar energy. But in the right off-grid location and working to complement solar energy, small wind turbines can be extremely effective. Plus, they are dynamic, exciting and fun to watch, making solar look pretty darned boring by comparison!
Do you have any other wind energy facts that you think should be taken into consideration when evaluating the potential for wind power at a given location? Leave a comment and share your wind energy facts with us.
Thanks to Dr. David Laino of Endurance Wind Power for the humorous inspiration behind this comparison, from the lecture he gave at the Small Wind Conference in Stevens Point, Wisconsin in June 2014 (www.smallwindconference.com)
Originally published in the November/December 2014 issue of Countryside & Small Stock Journal and regularly vetted for accuracy.