Average Annual Wind Speed and Wind Energy

Here are some rules of thumb I came across from notes I made at a farm business conference energy workshop.

The amount of power harnessed from a wind turbine depends on the average annual wind speed - needing a relatively consistent wind flow. Wind systems require an average annual wind speed of 15 kilometers/hour to be viable. 25 km/hr is desireable and 29 km/hr is outstanding especially if you intend to sell the power.

The experts recommend that at least a year's weather data be collected before site selection. Have some wind experience to share - please comment.