Mixing wind turbines with the tropics
Wind Storm – Disaster!
Less than a week after I left the island, I got an email saying that there had been an overnight wind storm with gusts about 35mph and that the wind turbine was destroyed (Figure 5).
Figure 5: The tropical wind was too much for the wind turbine assembly.
Although this turn of events was quite a disappointment, the box and the solar cells were unscathed. I had known all along that the wind turbine mechanical design was the weak link in the project, but I was still surprised it only survived a week.
What Happened
As you can see in Figure 5, the turbine has been shattered and the mounting pipe is out of the base. The week before I left I'd been sitting at coffee at a friend's house watching the turbine spin in the wind, and I noticed how the turbine mounting unit shook back and forth in the wind.
After the pictures came in of the destruction, I concluded that I suffered from a "Galloping Gertie" syndrome [3] in my mounting unit. The wind reached a certain speed (above 25mph?) and the whole mounting pipe whipped back and forth and popped the turbine out, and promptly destroyed itself. The middle of the solid block turbine mount was broken, and the unit was clearly out of the pipe.
In the absence of any hard measured data, I believe this was the problem for three reasons. First, I ran the wind turbine up to 50mph in a car with absolutely no problems (although I did notice how hard it was to hold the mounting pole), which indicates that the block probably didn't break because of the wind. Second, I saw the mounting poles sway back and forth in a 10mph wind from 200 feet away. Wind force goes up with the square of the wind, so it surely would sway much more at 30mph than at 10mph. Third, the mounting PVC pipes are completely intact with no damage.
Thus, I need to change the vibration mode of the mounting poles and make sure the turbine cannot pop out of the pipe.
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