windgen.org vawt discussion

                                       Plastic                           Paper

5.0 mph                       3.0 Hz  .8 TSR              7.8 Hz   2.0 TSR

11.8 mph                     7.0 Hz   .8 TSR             20.0 Hz  2.2 TSR

NGR  #40 C anemometers      .757 m/s/Hz

The 3 cone (cup) maintained its RPS much better when tilting into the wind or away from the wind.

Maybe the way to go when controlling a turbine with an anemometer would be to use an anemometer with the same style rotor as turbine so it will react to the same type of wind as the turbine.

I do log ambient air temperature but not atmospheric pressure.  In this third year of logging with the buck controller I have noticed that air temperature does have an impact on power output.

The max and min temperature extremes occur in August and February here.  The turbines generate about 10% more power in February than in August for the same wind speed.  Because the controller is using the table look-up method instead of trying to find max power point I can't really tell if TSR is different at the max power point for different air temperatures.  But that would be a good test to run for this summer and next winter.

I've built a few different anemometers for the buck controller but haven't come to a conclusion yet as to which is better.  There are pros and cons to each type.

I do find the low inertia type have a faster response to quickly changing winds which is what I needed since I was dealing with very small turbines that responded very quickly to the changing wind.

Here is one that uses a single magnet and coil so it generates a pulse each revolution.

I also have a few built from pc muffin fans which provides two pulses per revolution:

The cups are ping pong balls cut in half.  The two units pictured are about four years old.

  The pulses from the anemometer trigger an interrupt routine that increments a counter.  The wind measurement routine runs every 250msecs.  If the counter is greater than 1 or time since last calc is greater than 4 secs then wind speed is calculated, the counter is reset, and the time since last calc is updated to current time.

Its a fairly easy calc for doing TSR in real time with the controller so I have that displayed in the wind column on the local display of the controller along with wind speed and direction.

I did try one algorithm that just looked at the current TSR.  If actual TSR was greater than design TSR then increase load.  If actual TSR was less than design TSR then decrease load.  It works but does not always give maximum power but is close.  I found out that my blades TSR and maximum power point changes with wind speed,  the TSR at maximum power point does not stay constant for all wind speeds.

BTW I'm not sure how we got on the subject of how to digitize the anemometer input.  When I said my anemometer just averages the quickly changing wind, I meant because of it's inertia, not because my firmware averages some period of time.

If I give the anemometer a good spin with my hand, it spins for quite a while, even though there is no wind.  So even if the wind were to drop from 15mph to 0 instantly, the anemometer would take at least 30 seconds to reach zero.