Login
Password

Forgot your password?

Wind Power: What Size Wind Turbine?

By Edited Aug 14, 2016 0 3
Wind Turbine

Wherever you install wind or solar power, there are site considerations that need to be taken into account in selecting the right equipment. Commercial power sites are usually selected only after a long term survey is completed using a logging anemometer. Large PV solar installations require the same level of certainty and data that proves the site is going to provide reliable sunlight. The same principles apply on a smaller scale to personal solar/wind power projects.

Site Considerations
I'm convinced that in most areas the best plan is to combine wind and solar (PV) power. The logic is that when the sun is not shining the wind is blowing, and the wind produces 24 hours a day, and PV only works a few hours per day. In our area the wind picks up when the weather is bad and the sun's light is limited. So combining sources results in a more consistent source of power and reduced stress on the battery system.

Assuming that you want a combined system, the next step is to think about your property's resources so that the right emphasis can be employed for your situation. If wind is less use more panels. If wind is abundant use fewer panels. Try to find the best match for your location. Remember that wind turbines make some noise, so you want to be aware of your neighbor when selecting a wind turbine. If you live in the country this is usually not a problem, but as lot sizes shrink the physical size of a wind turbine becomes an issue.

Power Of The Wind

Affect Of Air Speed

Take a look at the following table:

Miles/Hour 
Watts/Ft2
 Out/Rated Pwr
Meters/Second 
Watts/Meter2
0
0
 0
0
0
2.2
6.5
 .07%
1
0.6
4.5
52.7
 .6%
2
4.9
6.7
177.6
 2%
3
16.5
8.9
421.9
 4.8%
4
39.2
11.2
820.2
 9.3%
5
76.2
13.4
1424.1
 16.2%
6
132.3
15.7
2261.5
 25.7%
7
210.1
17.9
3375.6
 38.4%
8
313.6
20.1
4806.1
 54.8%
9
446.5
22.4
6592.9
 75.1%
10
612.5
24.6
8774.7
 100%
11
815.2
26.8
11392.5
 
12
1058.4
29.1
14485.0
 
13
1345.7
31.3
18090.9
 
14
1680.7
33.6
22251.2
 
15
2067.2
35.8
27004.5
 
16
2508.8
38.0
32390.8
 
17
3009.2
40.3
38449.8
 
18
3572.1
42.5
45220.3
 
19
4201.1
44.7
52743.2
 
20
4900.0

As you can see, a 2 mph difference in wind speed, (barely noticeable) makes a bigger and bigger difference in power as wind speed increases. This table illustrates why the proper site for a wind machine is so critical. Even a small difference in wind speed makes a huge difference in the power that extracted from the wind.

Affect Of Swept Area
The power that you get from the wind is a function of the power that wind can supply and the efficiency of the system. Wind turbines come in many shapes and sizes, and each has it's advantages. However the power you can extract cannot exceed the power in the wind.

The formula for area in pi * (radius2). To see the significance of size, all you need to do is calculate the area on a few examples and look at the results. Power output is approximated at 23 mph. The purpose of the table is just to show the effect of blade diameter.

Diam. in Feet Area in Ft2 Watts Power Out
3
7.1
 121
4
12.6
 214
5
19.6
 333
6
28.3
 481
7
38.5
 655
8
50.3
 855
9
63.6
 1081
10
78.5
 1335
11
95.0
 1615
12
113.1
 1923
13
132.7
 2256
14
153.9
 2616
15
176.7
3000
16
201.1
 3419

A 3,000 watt wind machine rated for a wind at about 23 mph will require about 15 feet of blade diameter. If the diameter or swept area of the blades is reduced to 7.5 feet, power output drops to 1/4 of that power or 750 watts! At 32 feet diameter I could expect 12KW of power. There is no substitute for size when it comes to wind power.

This table is based on real world output for a wind machine. Different configurations will change the results somewhat, but not by that much. It should serve as a good guide for what you can expect in the real world.

Calculating Daily Power
The first thing you need to know is the average wind speed at your site. By looking at the speed/power chart above, you can gauge how much power you'll get on average. Even small variations in wind speed make a big difference. Be sure you place your turbine at the best spot for wind. Extra thought here can make a big difference, so do this right. It might be more convenient to put it somewhere else, but it reduces the benefits considerably.

Other Installation Issues & Maintenance
If you want to avoid headaches, make sure that the generator (brushless) is the only part that is mounted on top of the tower. All other electronics, regulation, etc. should be in a charge control system in the building. Make sure there is a way to stop the generator in unusually high winds so a big storm doesn't destroy your system.

Never mount a wind turbine to the side of your home, the vibration is conducted into the building and can drive you crazy.

Mount your turbine 20' higher than any obstacles within 500'. Power output increases and the turbine will last longer if you can get it mounted up in less turbulent air. Wind turbulence has a big effect on the efficiency of the blades, and the wind machine does not change direction as much. This increases the life of the brushes that conduct power to the wires that bring power to the controller.

If you want to mount the wind machine a long way from your home, consider a HVLV (High Voltage Low Voltage) system which sends power as high voltage AC to the controller which reduces wire size, and reduces power lost dramatically.

Be sure you properly ground the system and tower to minimize the chance of attracting lightning. In the mounting instructions with your wind turbine they will cover these issues, so take the time to follow the provided guidelines.   

Always mount your system with the idea that you might want to pull it down for servicing.

We have really appreciated our Whisper 3000 which is not made anymore, and I'm really glad we got a larger machine. I hope if you decide to use wind power that you'll invest enough to really see the benefit. Wind power is a great addition to a PV solar power system.

Go solar!

ALEKO® 4.5KW 4500 Watt Residential Wind Turbine Wind Generator 4500W
Amazon Price: $5,000.00 Buy Now
(price as of Aug 14, 2016)
Sunforce 45444 600W Wind Turbine
Amazon Price: $0.00 Buy Now
(price as of Aug 14, 2016)
Advertisement
Advertisement

Comments

May 9, 2013 8:57pm
MrRooibos
It is ironic that your article combines an emphasis on the economies of scale that come into play with wind turbines with advertisements for residential wind turbines. Nonetheless informative.
May 12, 2013 4:18pm
lashworth
My focus is on residential wind turbines where it makes sense to install one. The economies of scale apply to home turbines as well as larger commercial installations. Most people buy a turbine that is too small so they don't see much benefit from wind power. Going large makes a big difference.

Thank-you for your comment.
May 15, 2013 8:47pm
MrRooibos
Thanks for the response
Add a new comment - No HTML
You must be logged in and verified to post a comment. Please log in or sign up to comment.

Explore InfoBarrel

Auto Business & Money Entertainment Environment Health History Home & Garden InfoBarrel University Lifestyle Sports Technology Travel & Places
© Copyright 2008 - 2016 by Hinzie Media Inc. Terms of Service Privacy Policy XML Sitemap

Follow IB Technology