Estimated Increase in Windspeed (mph) with Height

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Estimated Increase in Wind Speed (mph) with Height

Wind Speed

mph

30 ft.	80 ft.	100 ft.	120 ft.

10 mph	11.6 mph	11.90 mph	12.20 mph
11 mph	12.76 mph	13.09 mph	13.42 mph
12 mph	13.92 mph	14.28 mph	14.64 mph
13 mph	15.08 mph	15.47 mph	15.86 mph
14 mph	16.24 mph	16.66 mph	17.08 mph
15 mph	17.40 mph	17.85 mph	18.30 mph
16 mph	18.56 mph	19.04 mph	19.52 mph
17 mph	19.72 mph	20.23 mph	20.74 mph
18 mph	20.88 mph	21.42 mph	21.96 mph

Note: Figures based on readings taken at 30 ft. tower and extrapolating power to other tower heights.

This table represents the power output that may reveal the average wind speed at a property owners site. The column that has a 30 foot tower, could be the tower height found at your local airport. Most airports have a tower of 30 feet tall--on which they monitor the wind speed. The airport usually is in a wide open space. Wind speeds are constantly being monitored at the airports. The interval that is being recorded by the anemometer can vary. But, typically, the wind speed can be determined at the airport by the day, week, month and year with the data that they keep on record.

The wind speed data that is recorded by the airport is free to the public--via the FAA administration. The information that is compiled by the FAA is in the form of table data. One can determine which months out of the year are the slower wind speed months and which are the higher speed wind months and so on.

Now and then, people call or write to me about their concern to determine their average yearly wind speed. Some people want to put up an anemometer tower to determine this data. These survey towers are guy wired. That means that the tower will have at least four guy wires from each section of tower for every 90 degree quadrant. This is rather large area to consume to put up an anemometer to record wind speed data. (I am presupposing that this meteorological tower will be the same height as the center hub of the wind machine that one plans on putting up.) The decision to put a MET tower like this up is a good idea if the property owner was planning on putting in a wind farm; but, certainly not a wise investment if the property owner is thinking about buying a small, 20 kw wind machine!

So, short of putting up a MET tower, a property owner may want to view how Bay Winds can help them determine their average yearly wind speed. From the table, one can surmise the increase in wind speed at one's property with a taller tower verses the 30 foot tower data that the airport would use. However, each property owner is located some distance away from the airport. Thus, each person has to determine how useful the above table is to their own environment. Siting issues become very important locally, when the data from the airport is suspect to differences in expectations of the property owners site.

If an anemometer at the airport yields a yearly wind speed of 11.06 mph, then the property owner could expect an average yearly wind speed at his site of more then 13 mph with a tower of 100 feet. This derived value of annual wind speed means something when correlating it to expected output from a Jacobs 20 kw wind machine. From the table that provides expected outputs for given wind speeds, the expected output from a 20 kw wind machine with a 13 mph average annual wind speed would yield in the ball park of 39,300 kwh in a year. Does this mean that this output should be written in stone? Of course not! Once again, siting is very important. One must look over topographic maps to determine relief patterns which places the airport at a specific site and look at one's own particular place and compare and contrast upwind obstructions. If the local airport is not really that local, then one must determine just how useful that data is to making an informed opinion of the wind speed at his or her site.

From the charts that are provided on the 10 kw - 17.5 kw link, the bottom right image is what this table is all about. Starting at the 30 foot tower increment, the increase in wind speed yields higher outputs as one progresses upward in elevation. The increase of tower height is some multiplier of an increase in wind speed for the tower heights that can be acquired for the Jacobs wind turbine.

Each property owner has to decide how much value can be arrived at for a given tower height to install a wind turbine on. Keep in mind, the rotor height is where the height is from the ground. When the blades sweep in the lower most position, there would be less wind speed there verses being in the upper most position. Any obstruction upwind of the rotor will cause a diminished return of power output of the wind machine--especially when the blades swing in the lowest part of the arc. And, if the obstruction is close enough, all kinds of turbulence can and will be manifested by the wind turbines output.

Be sure to review the siting aspects of this web site. And, perhaps even buy a book found on my web site to learn about siting issues and more about issues pertaining to small wind machines written by Paul Gipe.

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