What to look for in a Wind Turbine:Ī good design will quote power output at reasonable wind speeds…below 9 m/s or 20 mph. We can’t…but we can sure as heck avoid it! Since it is much harder to design an good efficient airfoil for low Reynolds numbers and because low wind speeds are prevalent over populated areas, here are some things to look for when choosing a wind turbine. There is no way to get around these basic physical concepts, no matter what a sales rep may say, so if you have a choice, always go bigger for a better return on investment. From the Reynolds number chart above, we can see how low the efficiency will be compared with larger wind turbines. Real numbersįor a 10 ft (3 m) diameter wind turbine spinning in 10 mph (4.5 m/s) wind, average Reynolds number will be 110,000 (1.1E5) based on a 6 inch wide blade (measured at 2/3 radius). What the plot tells us that at low Reynolds Numbers, we don’t have any hope of achieving reasonable efficiency…this translates directly to power output.
The Vertical Scale denotes L/D…which is an engineers way of denoting aerodynamic efficiency and the horizontal scale is Reynolds Number. Just look at the Reynolds Number Effects plot. The darkest side of small blade width is inefficiency. What do baseballs have to do with wind turbines?Ī wind turbine with small blade width (narrow blades & small diameter) needs to spin very fast to achieve good performance.twice as fast as a turbine with double the blade width. So what? Well, as we all probably noticed from riding in cars, noise tends to greatly increase with increasing speeds. Thus, an object half the size needs to go twice as fast to maintain identical aerodynamic behavior. Now, since the baseball is half the size, if we throw it at 120 mph, it will behave the same as a softball at 60mph, as far as the air is concerned. If we throw a curve ball with both at 60 mph, they will curve differently. To illustrate, lets compare a baseball and a softball, which is about twice big. Basically, what Reynolds number tell us is that if air is moving past 2 objects are at the same Reynolds Number, then it will behave identically. In simple terms, Reynolds Number denotes a relation ship between air speed and an objects size. Watch out for wind turbines which quote power output at high wind speeds (above 15 mph or 7 m/s) for the following reasons: Reynolds Number (Re) …say that again! On the flip side, if a wind turbine is placed in the wake (wind shadow) of an object, losses, turbine noise and vibration can result and will shorten your turbines lifetime and power output significantly.
Wind accelerates as it flows past most solid objects’ tallest/widest points (the top of a hill, edge of a cliff, roof line) as shown in the above computational fluid dynamics (CFD) simulation picture. Object’s shape, orientation and wind direction are critical to maximizing wind speed gains. Up to 30 % gains in wind speed are shown in the above image where red contours represent highest wind speeds close to 7 m/s when the prevailing wind speed is 4 m/s. If wind prevails from a single direction, the top of your house (or a hill) may be the best place. Stay at least 10x the house height downwind, ideally 20x. Stay at least 3x the house height upwind. Stay at least 5x the tree height downwind, ideally 10x.įor sparsely placed solid objects like houses: Guidelines for Anemometer or Wind Turbine Placementįor sparsely placed non-solid objects like trees:
Anemometer measurement free#
If you are unsure, feel free to contact us, and we will help you make the right choice free of charge. How do I tell which turbine is best for me? Watch out for the cheap propeller type wind turbines from China you will get what you pay for. The last thing you need, is to have to climb a pole or a roof in the middle of winter to replace worn bearings. Maintenance does not help the long-term financial picture, so choose quality over price. Will I save money?Īs you may already know, most wind turbines are expensive and if not situated correctly, they are a money loosing proposition. It does the math and shows you how two wind turbines will compare at your location. Calculator only requires that you know a manufacturers quoted power output at a particular wind speed and the average wind speed at your location. A calculator can help put in perspective two different wind turbines.
The hardest part for most people is comparing between different wind turbine systems because every manufacturer quotes power output at a different wind speed. Choosing and comparing different wind turbines
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