9 Things to Know About Small Wind Power

Published by Green by Design under Renewable Energy

Vertical wind turbines are ideal for generating power in tight spaces

By Amy Berry

Used to be if you wanted to put a wind turbine up at your house you either had to live on a remote farm, or grow your hair long and pledge allegiance to an aging group of touring musicians. Thanks to major improvements in technology and a general awareness of the benefits of making your own energy from clean and free wind, small wind power is going mainstream. According to the American Wind Energy Association (AWEA), the US small wind market grew by 78% last year with many new turbines hitting the market. But more options don’t make finding the right wind power solution easy. If you are interested but not sure how to even get started, here are 9 things to know as you consider wind power.

1. Small wind turbines can be broken into two main technologies: Horizontal Axis Wind Turbines (HAWTs) or Vertical Axis Wind Turbines (VAWTs). HAWTs are propeller based turbines that are traditionally mounted on tall poles and are commonly used in large wind farm settings. HAWTs have blades which rotate vertically around a horizontal axis, similar to a propeller on an airplane. VAWTs include two main classes: a tall vertical airfoil style (Darrieus), and a solid winged style (Savonius). Darrieus Turbines come in a few varieties. Some have rotors with curved blades that look like an eggbeater and rotate about a vertical axis. Another variation uses straight-sided airfoils and is called a Giromill. Like propeller turbines, Darrieus turbines utilize some lift to capture wind energy. Savonius Turbines have rotors with solid vanes or “scoops” which rotate about a vertical axis.

2. There is no precise definition for “small wind” but it usually applies to machines with less than 100 kilowatt (kW) ratings. The “ratings” refer to how much power the turbine can instantaneously generate at a specific wind speed. There are no standards in the small wind industry, so manufacturers are able to set their ratings at varying wind speeds. It is not uncommon to find one turbine rated at 25mph and another one rated at 48mph. Obviously the higher wind speed used will result in a higher kW rating, so its not a completely useful figure to go by.

Example of kWhs used per month on energy bill

3. While kW ratings will give you a general sense for the size of a turbine, what really matters is how much energy it will produce over a period of time. Wind turbine companies provide energy curves that tell how many kilowatt hours (kWhs) you can expect to generate at specific average wind speeds. You can check your monthly electric bills to gain an understanding of how many kWhs you use. Electricity use varies by season and time of day, so ideally you should add up the kWhs of the last 12 months.

4. This should go without saying, but you need wind to create wind power. All turbines have a minimum required wind speed at which they will start to generate power, this is also known in the wind world as the “cut-in” wind speed. It is possible for a turbine to spin at speeds below the cut-in speed, but those rotations won’t be fast enough to actually create energy. The majority of small wind turbines require a minimum of 10mph average annual winds to generate significant energy. Wind power is a cubic function of wind speed. For all you non-math people out there, this means that a little more wind can create a lot more power. When determining average annual wind speeds, a 10mph average annual wind does not mean it blows 10mph all day everyday. Because of the cubic function, a day of high wind can generate enough power to make up for multiple days of low wind. For you math geeks, average wind speeds follow the Rayleigh distribution curve http://en.wikipedia.org/wiki/Rayleigh_distribution)

Horizontal wind turbines work best with a large tower

Horizontal wind turbines work best when there is room to put up a large tower

5. So, how do you know if you have enough wind to make wind power a feasible option? The most ideal way to know is to install an anemometer where you want to place your turbine. You can get a very good anemometer for around $500 from www.madgetech.com. If you don’t want to wait a year, you can do shorter anemometer tests but you need to realize that wind speeds change with the seasons. Not ready to invest $500 in your research? Check out local weather sites which should provide data on average wind speeds. Local airports are also wonderful resources for this information. The DOD provides wind maps, but these are measured at 50 meter heights (for use by the big wind guys) and are not always localized enough for small wind installations which are very site specific. You can also call a local wind turbine dealer and request a site visit.

6. What about a site? A “site” is the place on your property where you install your turbine. Site location is a crucial element, and will have a major impact on which turbine you can consider. Turbines are best placed with enough open space to allow the wind direct access to the rotor. This does not necessarily require a specific lot size or a totally open and clear site. Many small wind turbines are designed to work in various settings, for instance HAWTs will work if you can put up a large tower and have consistent wind direction. A VAWT maybe a better option if your wind changes directions and you cannot put up a structure taller than 30 feet. Wind speed can also vary drastically on one piece of property due to structures and topography. Always choose the site with the most access to wind.

7. You’ve done your research and know you have a good source of wind. Now it’s time to pick a turbine or turbines. It’s very common for people to put up multiple turbines to meet more of their energy needs. Two big factors to initially consider are the expected power output and the cost of the unit fully installed. Consult the energy curve of each wind turbine to determine how much energy it is likely to create with your average wind speeds over the course of a year. Compare the kWhs at the same wind speeds across wind turbines, while keeping in mind total cost of the unit. A wind turbine that generates 400kWhs for $2,000 is a lot more expensive than a wind turbine that generates 2,000kWhs for $6,500. Also, don’t be fooled by energy curves that show amazing results at 30mph average winds. It is very unlikely that you live in an area with wind speeds of that level and will ever reach those energy levels.

Example of a wind turbine power curve

8. The other big factors to consider are the look of the wind turbine and the sound it creates while operating at moderate wind speeds. Try to visit the wind turbines that you are considering (or at least view on video) so that you can see and hear what they sound like when they operate. There are many designs on the market, all with varying looks and sounds. Find a local dealer or contact the manufacturer with questions. This is a big purchase decision, so you should feel comfortable working with the company and its local representative.

9. A final note on independent testing. As I mentioned above, there are no standards for small wind at this time. AWEA is currently putting these together, but it will be at least a year before they are finalized. Until then, we recommend focusing your search on independently tested wind turbines. Power curves, which turbine companies use to estimate power ratings and energy curves, can be supposed from complex calculations. But, the truest power curves are created from units being independently tested in real world scenarios. It is very easy for manufacturers to create their own power curves, so it is important to look for wind turbines with independently tested data. I recommend avoiding any turbines that do not have their data verified by an independent test facility.

Amy Berry can be found on twitter @wind2power tweeting about small wind power and the Windspire wind turbine.

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Lacrosse EA-3010U Handheld Anemometer

This nifty gadget is a must-have for keeping tabs on current wind conditions. The tiny handheld anemometer comes in a sporty, yellow, plastic, weather-resistant casing, making it ideal for use during water activities or rainy weather. About 5 seconds after powering up, the anemometer reports the current wind speed in either miles per hour, kilometers per hour, meters per second, or Knots plus, displays wind speed on a Beaufort Scale bar graph. The module also records the maximum and average wind speeds for any 2- to 10-second period of time, and recalls them at the user’s prompting. This anemometer also measures current temperature in Fahrenheit or Celsius and wind chill. The LCD screen has a backlight, making the display easy to read even in low-light conditions. The display automatically turns off every 8 seconds in order to preserve the life of the 3-volt lithium cell battery.

2 Responses to “9 Things to Know About Small Wind Power”

Lawrence Baker says:

July 16, 2009 at 8:24 pm

The Baker Wind Turbine is a major breakthrough in wind energy technology. The super quiet, Low Pressure Turbine is enclosed and 100% bird and people safe which allows the turbine to be installed and operated in close proximity to people. This eliminates the need for long transmission lines because the electricity is consumed close to where the electricity is generated. The 12 feet in diameter Model #3 Baker Wind Turbine is mounted on a car trailer and the unit is easily transported. Set-up is easy. The outriggers lift the turbine foundation and stabilize the turbine so that it can rotate 360 degrees. The fenders and tires are removed. No tower is needed; all that is necessary is a 6’ by 6’ wind flow. More efficient and powerful than a single dimension propeller driven windmill, this multidimensional wind energy turbine dynamic has never been seen before. Of course, the multidimensional turbine dynamic does not even resemble a single dimension propeller driven windmill. Google Baker Wind Turbine and two videos will appear; the longer video demonstrates the Low Pressure Turbine Dynamic.
Let me explain to you the basic turnaround in wind energy science and technology demonstrated by the Baker Wind Turbine. You don’t have to be a genius to understand wind energy.
First, the maximum amount of energy in the wind is directly in front of the wind. This is the basic and simple premise and is easily proven to anyone logically. (Aristotelian logic is the foundation of all science.) While standing in the wind, face the full force of the wind which is directly in front of the wind. Now, form both hands into a cup which represents a ½ round, cupped turbine vane with volume. Now, cross over your hands and form a blade with no volume representing a propeller driven wind mill. Which of the two forms catch more wind and has full thrust from the wind?
The first part of the equation is solved: The maximum amount of energy in the wind is directly in front of the wind and the best surface form to catch the wind and consequently, has more thrust and power, is a ½ round aluminum turbine vane with volume.
The second part of the equation is as logical. Which direction will the maximum wind catch area turbine vane turn? Naturally, the turbine vanes and rotor turn harmoniously in the same direction as the wind is blowing. This eliminates wind noise caused by turbulence. A propeller blade rotates sideways to the wind energy airstream which results in less power produced, noise from propeller turbulence and high stress on bearings and blades creating high maintenance cost. Propellers are so big; birds can’t see them and they have devastated wild bird populations. Check out the out of control wind propeller explosions on You Tube.
The third part of the equation is that the more cupped wind catch surface area that is directly in front of the wind, the more powerful the turbine. A single dimension propeller can only expand in size and power by increasing its’ diameter. The multidimensional Baker Wind Turbine can not only increase its’ power by increasing its’ diameter but can expand horizontally and add exponentially more wind catch surface area and power.
The Baker Wind Turbine has 144 cupped turbine vanes that are 3 inches wide (5 ½ inches of surface area). The 3 inch aluminum vanes give us 11 inches of weld at the cupped base. Each turbine vane has 1 1/2 sq. ft. of cupped surface area. This is important because the stress per catch area unit is low as apposed to a large catch area with a high stress attachment to the hub. No one turbine vane pulls by itself but pulls together with the other turbine vanes in a “gang”. This spreading of wind energy over the rotor maximizes the wind catch area and spins the rotor smoothly without vibration. Each turbine hub has 6 turbine vanes that are 6 ft. long. There are 24 hubs (6ft. wide) and there are 18 rows. Each row has 8 members that contain 48 lineal ft. of turbine vanes. At any given moment, the top section contains 108 sq. ft. of cupped wind catch surface area. As each row is assembled, they are progressively stepped which forms a horizontal twist. Twist is torque and torque is horsepower. The more twist, the more horsepower. Dividing the diameter into 18 lateral rows creates massive torque that is visible. For example take a wood screw and hold it sideways and turn it. You will notice that the screw is made up of one helix and 8 or more twists (or flights). The Baker Wind Turbine is Like the Archimedean screw but made up of 6 helixes with 8 twists which torque from right to left six feet. The overall dynamic of the Baker Wind Turbine is germane to High Pressure Turbine Dynamics but adapted to Low Pressure Turbine Dynamics which I am the inventor of and the Baker Wind Turbine is the test prototype. Just as Mr. Parsons’ invention of the high pressure steam turbine revolutionized steam power; the Baker Wind Turbine will revolutionize low pressure wind power.
The Baker Wind Turbine rotor has a lower surface to weight ratio than a propeller windmill so the rotor and shaft which weigh 660 lbs. begins turning on 1 or 2 miles an hour of wind and will operate smoothly and quietly in a 100 mile an hour wind at an estimated (920 R.P.M). High pressure steam and gas turbines operate at 20,000 to 50,000 R.P.M or higher; so in high winds the low pressure turbine dynamic is figuratively just loafing along. The Baker Wind Turbine not only has a wider range of operation but also produces more power at any given wind speed than a propeller driven wind mill and therefore the new turbine wind energy technology should rightfully outmode the old propeller driven windmill technology. The Baker Wind Turbine, like all major inventions, has a wide range of applications that will change roof top architecture, bridge design, ship design, high speed train (forced air) electric grid locomotives, forced air/ electric cars, parks, backyards, airports and all areas where the wind can be utilized in a natural or forced air environment. The turbine is enclosed so the housing can be easily painted to blend in with the surrounding area.
The last part of the equation is a little harder to grasp, even some engineers don’t get it straight. Those who defy convention and who can think individually in multidimensional terms get it right away.
First the single dimension. One assumption in Betz’ Law is that a solid wall is considered 100 % efficient in the wind and a propeller is considered 50% efficient because half of the wind flows through the propeller which causes the propeller to turn. So, 6 feet by 6 feet swath of airstream at, lets say, 10 pounds pressure per square foot (pounds is air speed and density) would give you 360 pounds of pressure thrust overall. A 50% efficient propeller would have 180 lbs. of thrust available. A three blade propeller with 5 ½ inch wide blades and 6 foot in diameter (4 1/2 sq. ft. surface area or 40.5 lbs thrust) produces but a fraction of one horsepower. The reason for this is a small surface area propeller rotates on a flat plane sideways to the energy source, has little torque, and is of a single dimension.
The multidimensional Baker Wind Turbine wind in-take is 6 feet high by 6 feet wide by 12 feet deep. The wind travels laterally across the turbine top section 12 feet to the other side which creates rotary power. The turbine rotor vanes are denser close to the center of the hub and wider at the tips and spaced such that the wind passes through the turbine to the other side. Again, hold up the wood screw. Notice by looking across the top half of the screw that there are air passages to the other side? Remember the Baker Wind Turbine has 6 helixes and 8 twists and the air passages move from right to left six feet? Now, look at the down wind side of the screw and you will notice that the flight is open and fanned out and is not drafted by the spiral? The turbine spirals leading edge is made up of many turbine vanes from many different rows so they do not draft one another. Of course, the leading edge of the opening is constantly changing as the rotor turns. At the apex of the turbine, as observed directly in front of the wind in-feed, the vanes form a continuous wall dimensionally. Because there are dimensional openings between the turbine vanes, and air is highly fluid, the wind powers all nine rows at any given moment from one side to the other. Each row is one dimension under wind power and there are 9 rows. There are 48 lineal feet of 3 inch cupped turbine vanes per row and 108 cupped sq. ft. total under power. If we figure out our total surface area in the top section it would contain 198 sq. ft. of surface area under wind power. At 10 pounds per sq. ft. that would be 1,980 pounds of thrust overall. That is 49 times more than the estimated efficiency of 40.5 pounds thrust for a single dimension propeller operating in the same 6 feet by 6 feet airstream! The Baker Wind Turbine is even more powerful than just converting speed and density of air into rotary power, the traveling torque creates even more horsepower, however, digging into traveling torque equations at this time is not necessary. My point has already been proven in science that Baker Low Pressure Turbine Dynamics is at least 49 times more powerful then a propeller driven wind mill dynamic and my 12 feet in diameter low pressure turbine proves it. That is why I built model #3 so that people could see the powerful turbine dynamic operate even though they do not understand how it works or all of the ramifications of it working. Now you know how it works and basically the breakthrough technology of Baker Low Pressure Turbine Dynamics. Did you get it? Or was it to much for your wee mind? For those who get it, read on. For those who don’t get it; drive down the road at 65 mph. and cup your hand into the wind and let it jerk your arm back (lever) and each time ask yourself “where is the power and energy in the wind”?
The reason the modern American Green Energy Economy is not moving forward is because independent scientist and individual inventors, like me, are without funding. The reason there is no funding is because the economic powers that be, the status quo, has snuffed any State or Federal funding programs for independent green energy inventors. Are you surprised there is no level ground? Do you know what scares the hell out of the multinational Big Oil and energy barons? The answer is the advancement of science with new inventions that they can’t control (their economy) that would outmode the use of fossil fuels for energy (their product). That is the cause of man made Global Warming.
Logically, one would think that the first government action would be to utilize our national talent by holding a national green energy science contest thereby acting free from Big Oil. I am not the only independent inventor; there would be thousands of qualified applicants with new concepts. The winner would receive a one million dollar reward to further develop the new green energy concept. Ten million a month could finance and develop ten new grass root industries employing thousands in green energy jobs. Out with the old and in with the new, let the best win in science and the lesser fold or be outmoded by something even better. That is fair competition and free enterprise. A modern American Main Street Capitalism based on a green energy economy would grow from the bottom up and not be dominated and controlled by multinational corporations from the top down. Great inventors were individuals not controlled universities; they should be funded as well.
Lawrence Baker
650-218-9434 windcatch@gmail.com

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Dave Astley says:

October 23, 2009 at 5:03 pm

Really good guide on initial considerations for people considering a wind turbine.

2 points I would like to add in support of the above article.

If any readers are in the UK the wind speed maps available online are at 3 heights (10, 25 and 45 metres above ground level) and are averages of kilometre grid squares so much more use for small wind.

If anyone wants to do the Rayleigh distribution, Green Jury have a free calculator on site which you can use for your average wind speed and then compare to the power curve of the turbine. available at http://www.greenjury.com/ralsure.php and no registration required.

Hope this is of use

Dave Astley

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