Collecting windspeed data for site selection




Be sure you have a site with enough average daily windspeed to charge your system. About half the people I talk to overestimate their sites potential; it's worth it to take some samples. But If you know there's enough wind, like the trees are twisted and hedged down to look like bushes with the branches leaning to the downwind side, no topsoil, etc., just check for turbulence and skip the windspeed estimation unless there's a lush undergrowth of annuals and fleshy weeds, which may indicate any strong winds are seasonal. If you want to be technically accurate, buy or make a recording anemometer, they cost between $120 and $500. The following procedure requires keeping track but doesn't cost anything, so read it and then decide how accurate you want to be.

Get a kite and fly it around in a likely looking spot. If the kite dips and flops around, it's a sign of turbulence and should be avoided. If turbulence is all you have though, Dragonflies will handle it, it's just not ideal. Find a spot with nice steady pull so the kite's flying quietly at the same height you'd put the wind generator. The higher the better, but towers cost money and tall trees for a masthead mount will have to be available nearby because they don't transport easily. See that it has a clean shot and smooth terrain from whatever direction the storms come from, no cliffs or trees and ideally 30 feet above and / or 300 feet downwind from any obstacles. But use the kite and get a feel for what the wind does. Then put up some poles (bamboo, Eucalyptus, 2x4's, or plastic pipe) with one-inch-wide plastic streamers three feet long, cut from a plastic garbage sack and tied to the pole about every four feet. Stick the poles up in the general vicinity, say thirty or 60 feet apart, and guy them with plastic bailing twine or something cost effective.

During storms (which is where the real amp. hrs. lurk), watch the streamers for the same behavior and find a nice, even breeze. Because of the way the jet stream works, some approximation of a "storm" comes along on the average of once every 2 weeks. Put up a cotton flag in the best spot, about two feet by three feet, like a post office flag or dish towel or flour sack cut open and trimmed to that size. Commercial flags sometimes use lightweight materials so they fly in lower winds, so stick with cotton, getting wet doesn't really affect it much. Watch the top edge of the flag and when it's straight out, the wind speed is 15 mph+. When it's down about 30 degrees from level, that's about 10 mph, and that is minimum charging speed. 30 deg. flag Leave some slack in the rope that holds up the flag so it will stand out from the pole far enough to clear the pole's turbulence for better accuracy. There is also a windspeed scale developed by the English Navy called the Force Beaufort Scale which will work for us too.

Then get a calendar that has boxes for every day and mark on it an estimated number of hours per day that the wind was blowing at 10 mph or more. Care and perseverance here will help for accuracy. Mark the days when you forgot too, so they don't figure in the tally. Do this for week or so for every season (monsoon, surasco, false spring, indian summer, etc.) Get samples of unique weather that you can use to extrapolate as outlined below. What you'll have is a list of estimations between 10 and 15 MPH, (using the flag method) most useable daily wind falls in this range, That is, if it's less, we can't use it. More is rare, mark those days too.

To confirm your figures, get a record of what the wind was doing at the nearest weather station during this time and a years average for daily wind. Then extrapolate your site's wind energy potential for the year like this: The wind speed at the station and the wind speed at your site are connected like a ratio. So whatever you got on that day will be in proportion to what wind was blowing at the station, so long as they've got the same terrain and are within a "reasonable" distance. Figure up how many hours it was blowing say 12 MPH, check the Windspeed-Power Chart (below right) and expect a charge of about 5 amps for as many hours as you added up on your calendar. Mountains in hot areas tend to create thermal updrafts which may be usable, but will not show up on Coast Guard records and they indicate a different wind pattern for cold weather. Here are some sources:

Once you know how much wind energy is available at your site, there are two ways to calculate how much it will run. We got the adding-on way and we got the chopping-off way.

The chopping-off way is hardest because you have to be cold-hearted and mathematically precise. I only include it so nobody's temperament gets slighted (heh). Make a list of your appliances' watt-hour ratings, then multiply by the number of hours each one is to be used. To this total, add estimated line losses, (you want it to be 10% or less depending on the size of wire you buy.

Amps

American Wire Gauge sizes 12 Volt. 2 wire, 10% Volt drop
12
10
8
6
4
2
0

2
85
130
220
360
560
900
1500
5
35
56
90
144
225
362
600
10
18
29
45
77
112
181
300
15
11
18
40
45
75
120
200
20
8.5
13
22
36
56
90
150
25
6
11
17
29
45
72
120
30
5
8
15
25
37
60
100
50
3
5
8
15
22
36
60

Wire length in feet

Heavy wire costs more but it might save money in the long run by reducing the size of the battery bank which will wear out before the wires do. Storage retrieval losses (about 30% loss from lead acid batteries) are also added to the list of watt hours. This is the demand figure you start with in estimating what size wind generator you need. If a system with this capacity costs more than you can afford, go back and start chopping off toasters, electric element heaters of all kinds, compressor refrigerators, Jacuzzis and well pump motors. (Direct water pump windmills do a better job than electric ones with all the power conversion losses.) When supply and demand are in balance, you puts your money down and takes your chances.

Naturally, The adding-on way is best for people who aren't possessed by a lot of appliances in the first place. First, put up as big a wind generator as you can either afford or stand to have around (They make about as much noise as an exposed tree in the same wind, except they have a rhythmical sound, or a car (non-streamlined) traveling at 30-40 mph., minus noise of engine & tires). Get one or two used car batteries and start adding on utilities. Start with florescent lights and stereo which are all the same voltage as the wind generator system, for example 12 volt DC. If there's enough capacity for this, add on a washing machine and an inverter to run the 110 VAC washing machine motor. Match the inverter for output because the bigger the inverters are, the more juice they use, so don't get one bigger than you need. Still have more juice than you can use? Put on a vacuum cleaner, electric toothbrush, electric fish comb, etc.

Design your storage system around the longest stretch of calm days that your site survey turned up. I used one 100 Amp hour battery in my first system, but there were voltage spikes when the wind gusted, bigger banks or line volt regulators will prevent that. If batteries charge fast and run down fast, add more batteries. If they charge fast and run down slow, add more appliances, (or sell some batteries). If they charge slow and run down fast, dump some appliances. If they charge slow and run down slow, that's about right.


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