Wind Speed – Mystery Or Not?
When considering wind power, most people ask what the average annual wind speed is and how to get that number. The usual response is that you must monitor the wind speed at your site for at least 12 months, preferably longer, to determine whether a wind generator will work for you.
Sounds too long? Well, yes and no…
For a home system, this isn’t necessary. The costs involved in collecting wind data may not be justified when compared to the total cost of a small wind machine.
There is no economic formula to determine this, but it doesn’t make much sense to spend $1,200 on instrumentation if your wind machine costs only $3,000. You can get close to the actual number by making an educated guess using the empirical methods.
Options For Monitoring The Wind Speed
If you decide to monitor wind speeds, you have several options.
1 The first is to buy a weather anemometer and record observations on a regular basis. This is the least expensive way to collect wind data, but it has disadvantages. For the data to be valid, you must be methodical in collecting it.
Recording one instantaneous wind speed per day won’t do.
2 A second option is to automate data collection by installing a data collection board in a personal computer. This method works, but the computer must stay on all the time, and there are additional costs.
Since these are not plug-and-play components, some computer hardware and software knowledge is necessary.
3 A third option is to invest in an anemometer system specifically designed for collecting wind data. The least expensive systems simply average the wind speed over time and cost $200 to $300. These systems usually are sold without towers.
While the average wind speed is a useful measurement, it also is important to know the wind speed distribution.
- A portable tower,
- Instrumentation and
- Data logger.
After collecting data, you have equipment that may or may not be useful to you. The secondary market for used towers and data loggers is limited.
If you buy a used system, consider new instrumentation. This will help ensure quality data.
Usually the system has an anemometer and a wind vane. The anemometer measures wind velocity, while the wind vane registers direction. Both instruments should be mounted on a wind pole or tower that is as close as possible to the height at which your wind machine will be mounted.
If your anemometer is mounted too low, it will underestimate the actual wind resource available.
It is generally recommended that the hub height for small machines between 60 feet and 120 feet. Your anemometer also should be within this range.
To generate data for all seasons, average wind speeds along with distribution and peak gust information should be recorded for a minimum of three months, but ideally for a full year. Wind speed data can then be used with performance data for various wind machines to determine the expected output for each machine at your site.
For example, assume you have collected average wind speeds of 12.8 mph, 10.8 mph and 10.4 mph for the last three months, and the published data from a nearby site for the same three months is 10.9, 10.2 and 9.5.
Dividing your data by the published data will give you the following deviation factors: 1.174, 1.059 and 1.095. Averaging these results in a correction factor of 1.109. You can multiply the remaining published data by this correction factor to estimate wind speeds at your site. This method involves a fair amount of interpretation, and some sites do not correlate well.
If you are considering a large project, on-site data is a necessity.
These systems require taller towers – 40 or 50 meters. They include multiple levels of instrumentation and data loggers that can be accessed remotely. Assessing a site’s potential for utilityscale wind development is an expensive undertaking that requires committing significant financial resources.
Wind Turbines – How does it actually work? Investment?
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America used 3,200 billion kilowatt-hours of electricity in 1998.
The Energy Information Agency predicts that consumption will increase to 4,400 billion kilowatt-hours in 2020. No single energy source can deliver all the electricity we need to fuel our economy.
Resource: Montana Wind Power – A Consumer’s Guide to Harnessing the Wind