PublicSecrets.Org
'Secrets' To Becoming More Independent
Google


Independent Power - Wind Turbines Primer

Wind Power Basics

Wind Power is a science, and there is a lot of great information available on the web. One of the best sites I know of is The Danish Wind Industry Association. This site has a lot of great information, but it can be intimidating. I think for most people it's first important to get an overview of wind power. An overview might not be technically rigorous, but it can be very helpful in understanding the basic principles of wind power. I see a lot of people buying wind generators that are more suitable as lawn ornaments than for serious energy production.

There are good books on wind power valuable, and a few of them are highlighted on this page. However, let's get on with the brief overview.

Wind Principles

There are a few pieces of information required in order to predict the suitability of your site for wind power. The most important pieces of information you need is the average wind speed at your location. Wind at low speeds has very little power, but as wind speed increases the energy in the wind increases exponentially.

Take a look at the following table:

Miles/Hour 
Watts/Feet2
 
Meters/Second 
Watts/Meter2
0
0
 
0
0
2.2
6.5
 
1
0.6
4.5
52.7
 
2
4.9
6.7
177.6
 
3
16.5
8.9
421.9
 
4
39.2
11.2
820.2
 
5
76.2
13.4
1424.1
 
6
132.3
15.7
2261.5
 
7
210.1
17.9
3375.6
 
8
313.6
20.1
4806.1
 
9
446.5
22.4
6592.9
 
10
612.5
24.6
8774.7
 
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 2mph 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 can be extracted from the wind.

Blade Area

You can see from this table that the area of the wind machine makes a huge difference in output power. When you think of a sail for a boat, you picture in your mind huge sail that captures a lot of wind. The swept area of the blades of a wind power generator also needs to capture large amounts of wind in order to capture large amounts of power.

The formula for area in pi * (radius^2). To see the significance of size, all you need to do is calculate the area on a few examples and look at the results.

Diameter in Feet Area in Square Ft
3
7.1
4
12.6
5
19.6
6
28.3
7
38.5
8
50.3
9
63.6
10
78.5
11
95.0
12
113.1
13
132.7
14
153.9
15
176.7
16
201.1

A 3,000 watt wind machine rated for a wind at about 23 mph will require about 15 feet of blade diameter. This means that if I reduced the diameter or swept area of the blades to 7.5 feet I would only get 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. Don't buy a little wind machine and expect too much. It might be enough to help keep your batteries topped off in a remote location, but itty bitty machines produce itty bitty power.

Tower Height

Air is invisible, so you normally never see air turbulence. Wind power systems perform better when the air flow through the blade system is smooth. Trees, buildings, hills, vehicles, or any other object within 300 feet of a wind power system will have an effect on airflow. This is why, when possible, the bottom of the blades of a wind power system should be 30 feet higher than any surrounding objects within 300 feet. The increase in power output with proper height is considerable!

A quality wind power system is a real investment, so if you're going to install such a system take care to do the whole job right. A great system poorly installed is not going to give you the benefits you deserve.

Tower Type

Murphy's Law dictates that more difficult it is to service a wind system the more likely it is that you'll need to service it. So do yourself a favor and make sure that the tower is designed in such a way that if you need to bring the system down for service that you can get it done easily. My system here has required 2 repairs over 7 years. My tower is a tilt-over and servicing has been pretty easy, but I look at some systems and wonder how the owner is ever going to make a repair if one becomes necessary.

Special Weather Considerations

Sometimes (as in my case) when trying to evaluate the available power at a proposed site, you may decide that wind power is worth it as a backup for solar panels in bad weather. We live in an area of the country where we get a lot of sunshine. Solar panels are usually the way to go, but when we have poor weather and the solar panels are not doing all that much, the wind is usually blowing. This offsets the lack of sun and has been really good for us here.

Site Specific Considerations

There are a lot of different wind power solutions on the market. The feature that caused me to buy my Whisper 3000 system was the HVLV option. Power is generated as a nominal 240v 3 phase AC, and the wire run for my system is a couple hundred feet. For this system the wire can be as small as 14 gauge, since the wire losses are very small due to the high operating voltages. If you have a DC system and have to have very large wire, installation costs (more than just the wire) can be high. I also wanted the HVLV system in case I move and have an even longer run of wire at the new location.

I've been very impressed by the performance of this system, and it delivers more than rated power to my battery system regularly. There are times when we get a big storm in the winter when the heat generated by the shunt load for the wind machine's voltage regulator provides considerable heat. The Whisper 3000 is no longer in production under that name, since Southwest Windpower purchased the company. Parts and similar systems are readily available through them or their dealer network.

Logging anemometers are available, which allow you to have a very clear idea how much wind you have to work with. Every year is different so far as the wind goes, and in many cases a site is marginal, so it takes 3 years or more to collect enough data to be very sure what to expect. In most cases though, you'll be able to see whether a site has potential very quickly.

There are wind maps available, but they paint wind potential with a large brush making the data shaky for any specific location even if they are accurate in general.

Wind Power is Great!

I really enjoy our system, and I think wind power is an essential ingredient to a successful solar powered home, if you have a location favorable for a wind power system.


Copyright © 2013 by PublicSecrets.Org