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Alphabetical Article List
- Average Us Wind Speeds By Region
How To Buy A Wind Electric System
by Ian Woofenden and Mick Sagrillo (Home Power - December 2007/January 2008)
There’s a lot of preparatory work to do before you get to see your wind turbine’s blades spin. It includes understanding how much energy you need (or want), how to use energy efficiently, how much wind energy you have available at your site, and how to match your needs with your resource. After you’ve covered this ground, you can start to consider which wind turbine and what balance of system components to buy, and how to install them.
Energy Analysis First
If you want to install a wind-electric system, the first step is to determine how much electricity you use. Electrical energy is measured in kilowatt-hours (KWH), and one way or another, you need to discover how many of them you use per month. You could learn to read your utility meter and check it multiple times over the year. But it’s easier to simply contact your utility, which will usually supply a summary of the past year’s electrical usage.
If you’re planning a new home, you’ll need to estimate your electrical use. Reviewing utility bills from your current home may give you a good estimate if you’re going to use a similar range of appliances. But in the end, this will only be a guess, since your actual usage may vary considerably.
The goal of the analysis is to come up with the number of KWH per year that you want your wind system to generate. Without this number, you’re guessing, and may end up being unhappy with your investment in wind power. If you say you want to make “a lot” of electricity, wind energy experts will tell you that the system will cost “a lot” of money. If you say you want to make 150 KWH per month, your renewable energy installer will be able to suggest a few turbine options and give you a cost in dollars, or at least an informed estimate.
Once you know how many KWH you use or expect to use, you could proceed to “Go” and start shopping for wind-electric system components. But your time and money will be better spent by first focusing on energy efficiency. Typical Americans can reduce their home’s energy use by 20% to 50% (or more) by using more efficient lighting and appliances, defeating phantom loads, and simply by being determined to use less.
Reducing your electrical loads will reduce the cost of your system considerably. A smaller wind generator will be needed, and that means you won’t need as stout of a tower. The family of an acquaintance recently reduced their electric bill by about 50%—just by using compact fluorescent bulbs and changing their habits. The $60 per month they are saving is going into the kids’ college fund—and the youngest has become a real ”turn the lights off” fanatic since she saw the savings. They had been using 700 KWH per month, and they’re now down to 350 KWH.
At an 11 mph average annual wind speed, they just reduced their turbine needs from an Eoltec 6 KW at $25,200 to an ARE 110 at $11,500, a savings of nearly $14,000—plus the savings from the lighter tower needed for the smaller turbine. A smaller battery bank (if batteries are used) may also be in order. All the way down the line, implementing energy-efficiency measures will reduce the size and cost of your wind-electric system.
While you’re doing the energy-use groundwork, start assessing your wind resource. Home wind-electric systems rarely justify a full-scale wind resource assessment with wind datalogging and analysis, but you must at least get a general idea of the amount of “fuel” you have available before you start reaching for your wallet. It’s a little too common to hear of people spending thousands of dollars on a wind-electric system only to discover that reality didn’t support their unscientific analysis that “it’s always very windy.”
The ideal situation is to have several years of wind data from your site, at the proposed turbine height. But small turbine buyers rarely do this, and for good reasons. Installing a tower and wind datalogging system of this sort might cost half as much as the wind-electric system, as well as delay the project. The going rate for such a monitoring project
is about $15,000. More often, if any wind measurement is done, it is of shorter duration and at a lower height. Taking this data and extrapolating to turbine height, while comparing it to data from nearby monitoring sites, might give you a reasonable guesstimate of what to expect. However, this kind of analysis is more complicated than it appears, and is a good place to seek a wind expert’s guidance.
The best wind resource data presently available for most states is the high-quality wind maps available on the Wind Powering America Web site (see Access). The few states without wind maps have some data available, from airports, universities, wind energy users, weather hobbyists, or government agencies. Look around to see what you can find there, but do track down where the data came from, since some data may come from monitoring equipment that is not installed high enough in the wind to produce reliable and useful information.
More subjective analytic methods can be used, though they should be used with a great deal of caution. Long-time residents can give you impressions about how windy it is and has been—apply lots of salt. Your own observations on your property can be better than nothing. And the way vegetation is deformed by the wind can be an indicator of the presence or lack of a wind resource. There’s even a scale that correlates tree deformation with wind speed—the Griggs–Putnam Index.
The goal of all this analysis is to come up with your site’s average annual wind speed. You want to know this number at your proposed tower height because it represents the “fuel” available to your wind generator to turn into electricity. This is most often in the 8 to 13 mph range for home-scale systems. Sites with an average below 8 mph may not have enough wind energy to justify the investment in a system, unless the site is off-grid and you’re replacing engine generator fuel.
Selecting Your Turbine
Now that you know your needs and you’ve determined your resource, it’s time to go shopping. Any wind turbine manufacturer worth buying from can supply you with annual energy output (AEO) numbers for various average wind speeds. You simply need to choose a turbine that will produce the amount of energy you need with your wind resource. If you determine that you want to generate 2,100 KWH per year in your 11 mph average wind regime, check out the manufacturers’ output predictions to see what’s available.
For off-grid applications, you’ll need to consider seasonal energy usage. If your windiest season matches up with your heaviest use of energy, you’ll make the most of your system. But in other cases, you may need to oversize your wind turbine to cover the seasonal load variation. And with off-grid systems, you will almost certainly need a second source of energy, like solar electricity.
You’ll find only a couple dozen selections in the small wind turbine market, and in any given size range, just one or a few choices. Other parameters may further limit your options, such as system voltage, batteryless versus batterybased machines, and machine durability. If you have to choose between two turbines that straddle your target energy need, buy the larger one—it’s much better to end up with more energy than less.
But don’t just think about the present. Never buy a turbine solely on its up-front cost, but rather on what it will cost you over the long haul—in money, time, and aggravation. Windelectric systems are the toughest renewable energy systems to maintain, with the highest failure rate. Why? Because wind turbines live in a brutal environment atop 80- to 120-foot (or so) towers not readily accessible if you don’t climb, or if it’s minus 30°F outside with a 30 mph wind.
Avoid these pains by buying the highest-quality system you can afford. Unlike a car, you won’t be able to drive your “bargain” down to the dealer for warranty repair. You’ll have to pay someone to climb your tower and fix it, or do it yourself—neither is cheap nor easy.
Balance of Systems
A wind turbine is just one part of a system. You’ll need other components to actually make electricity. Though the wind generator is a critical component to buy well, you should give similar attention to the other parts of the system. Your tower design will be determined by the weight and swept area of your wind generator, the specifics of your site, and your preferences and budget. (See the tower article referenced in Access for more information.) The best suppliers of wind generators also supply towers, knowing what is appropriate for their machines.
System electronics include charge controllers, inverters, and metering. Sometimes these are included with the turbine, and other times you have some choices—depending on whether your home is off-grid or on, battery-based or batteryless. Make sure you understand the options, as these components must be matched to the turbine and to other parts of your system. Batteries are a big subject, and if you intend to use them in your system, you should educate yourself. Off-grid users must carefully consider how much storage they want, and whether they will use backup or other energy sources like PV.
On-grid users who want utility outage backup must analyze the critical loads they’ll want to power. We recommend that you work with an experienced supplier who can help you make the important decisions of battery type, size, and system design and installation. Other components in a system include wiring, disconnects, overcurrent protection, and grounding. These are issues that require electrical expertise and experience. Either hire a qualified person or take the time to get enough education to do a safe, code-compliant job.
Do It Right!
If you’re a novice at electrical and mechanical installations, don’t even consider taking on a wind turbine installation yourself. Because of gravity and the tower heights involved, this is serious business—fraught with potential danger to life and limb, as well as the opportunity to make poor design and installation decisions that could affect performance and safety over the life of the system. If you have any doubt about your abilities, hire a professional. Think of this system like an automobile. Most of us don’t even do our own auto maintenance; much less would we would even consider designing and building a vehicle. Wind electricity is not an easy DIY project, and may never be, since it requires tall towers to get the turbine up into its “fuel.”
Wind-electric systems are not easy, simple, cheap, or perfectly reliable. But if you do your homework, buy quality equipment, and get the help you need, you can end up with a long-lasting and satisfying system. Thousands of families have done just that, and they look up regularly to see their turbine spinning, making electricity from the wind!
Ian Woofenden (firstname.lastname@example.org) has been living
with wind electricity since the early 1980s, and teaches, consults,
and writes about wind energy from a real-world perspective. He is
a supporter of successful wind-electric systems, steering people
away from hype and unrealistic expectations.
Mick Sagrillo consults (currently as the wind technology specialist
for Wisconsin’s Focus on Energy), teaches, and writes about small
wind based on almost 30 years’ experience installing and operating
nearly all the turbines covered in this article. He reminds folks that
it’s not about “cheap,” but about reliable renewably generated
- “Wind Turbine Buyer’s Guide,” Mick Sagrillo & Ian Woofenden, HP118
- “Anatomy of a Wind Turbine,” Ian Woofenden & Hugh Piggott, HP116
- “Wind Generator Tower Basics,” Ian Woofenden, HP105
- “Estimating Wind Energy,” Hugh Piggott, HP102
- Explanation of Jim Green’s AEO formula can be found on page 9 of Wind Powering America
- Wind resource maps
- For more detailed information on the topics raised in this article, see the technical appendix, available at www.homepower.com/promisedfiles
Wind Turbine Manufacturers/Importers:
- ARE, Abundant Renewable Energy
- Bergey, Bergey Windpower
- EMS, Remanufactured by Energy Maintenance Systems
- Endurance, Endurance Wind Power
- Entegrity, Entegrity Wind Systems Inc.
- Eoltec, Pine Ridge Products
- EWP, Endurance Wind Power
- Halus, Remanufactured by Halus Power Systems
- Kestrel, Imported by DC Power Systems
- PGE, Énergie PGE
- Proven, Imported by Alaska RE
- LakeMichigan Wind & Sun
- Solar Wind Works
- SWWP, Southwest Windpower
- WTIC, Wind Turbine Industries Corp.
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