By James R. Stalker

I just returned from a two-day workshop on wind resource assessment. The global wind energy community does not seem to be ready to face the difficult challenges posed by wind. In this context, the wind energy community should go beyond the current practices of just wanting to measure wind. Afterall, wind is the net effect and the wind forces are the underlying causes. Should one just ingore all the causes and expect to do well by focusing on the effect alone? Unfortunately, that is exactly what the wind industry has been doing, i.e., focusing on the effect, so far.

This discussion elaborates on what is beyond our current horizon (wind forces) and why these forces are paramount to the global wind energy community’s successful deployment of wind projects.

Wind resource assessment is just one of many pieces of the wind project development puzzle. However, it is understandably one of the most important aspects of wind project development.

As mentioned above, the global wind energy community has focused on measuring wind at potential wind sites. It is from this type of wind information, other energy and financial analyses are made to ascertain wind project viability.

Unless one is developing a single-turbine wind project with the measurement height matching the hub height, has enough time to measure (a year or longer), and has the appetite to assume significant risk involved in long-term energy projections, wind measurements made at a location for a year are limiting.

The above limitations do not result from any inaccuracies of the measurements themselves. Such measurements are demonstrated to be incredibly accurate these days and should be utilized as much as the project time line, budget, etc. allow.

So where do these limitations come from? These limitations result when one uses the location, height, and time-specific wind measurements to estimate wind information at other locations, heights, and for other time periods. These limitations occur due to the fact that there is no information about the (atmospheric) wind forces (e.g., pressure gradient force, gravitational force, etc.) that shape the wind behavior at the site being considered in the first place. In other words, unless one has a quantitative understanding of the underlying wind forces, the above limitations will not be properly identified and overcome.

If we consider a measured wind speed value of 5 m/s at a location, as an example, that wind speed was essentially forced by a specific combination of wind forces. This specific combination of forces that caused the wind speed to be 5 m/s, could have been one of numerous other possible combinations of wind forces. In other words, any other combination of forces could have caused the wind speed to be 5 m/s. However, using this specific measured wind speed (5 m/s) to estimate wind speed at other locations or heights or time periods, without the knowledge of the exact combination of the wind forces, will result in an inherent and unknown error. This is the reason why one needs to worry about the wind forces.

So, in summary, this specific measured wind speed does not contain a clue to point us to that exact combination of wind forces that produced that wind speed. One might argue that he/she has measured the wind speed they need and they really don’t need to know the combination of wind forces. One can live without knowing the exact combination of the wind forces that caused the 5 m/s wind speed, as long as the use of that wind information is just for that location, height, and time. The moment one moves away from the measurement location, however, these wind forces must be taken into account.

If this discussion is of interest to you, try to join the LinkedIn group (Wind Forces at Work!).

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