Data-logging anemometer
In the fall of 2010, I and my students spent several weeks discussing how to measure wind power, and we built a data-logging anemometer.
Anemometer
We used Inspeed's vortex anemometers, which feature three cups on a very smooth rotor, and a reed switch activated by a magnet on the rotor.
Data-logger
Originally, we hoped to use PICAXE micro-controllers, but I was having trouble programming them from Mac OS X, so for the sake of expediency we switched to Arduino, with a very smooth process for programming and feedback.
We discussed two ways of taking data.
- The traditional way is to count rotations in 10 minutes. This yields an average wind speed. Optionally, we could have added a determination of the highest gust speed. With the Arduino, this option would be easy. In PICAXE, it would be tempting to use the "count" command to count the pulses in 10 minutes, but then we wouldn't get the gust speed. To solve this, we could compromise and use the count command every 5 or 10 seconds and treat the maximum count as representative of the highest gust speed; shorter times might limit the precision of the measurement.
- Another way is to measure the time of each rotation, yielding a speed. This might be useful if we wanted to create precise histograms of wind speeds.
Data analysis
While we didn't build the anemometer in time to set it up in the field to collect our own data, we looked at data from other sources. We saw from concurrent metrics at Alfred State that wind generally blows faster at 60m than at 40m or 50m above the ground. We learned from WeatherScope that there are many hours in the year when the wind doesn't blow significantly. We also noticed that the wind at 10m usually doesn't blow fast enough for wind turbines to produce any power; i.e., the wind at 10m above ground is usually below most turbines' cut-in speed. 7 meters per second can seem like a strong breeze to us non-avian creatures, but it won't do much for a wind turbine. No wonder we put them on tall towers.
Resources
- The PICAXE micro-controller
- http://www.rev-ed.co.uk/picaxe/
- The Arduino micro-controller
- http://arduino.cc/
- Inspeed wind sensors
- http://inspeed.com/
- Alfred State (State University of New York) wind data
- http://www.alfredstate.edu/about-us/going-green
- WeatherScope is a weather-data visualization tool from the Oklahoma Climatological Survey
- http://climate.ok.gov/software/ or http://www.mesonet.org/index.php/weather/weatherscope/
