Tower height is very critical. A tall tower will get your turbine up and and out of turbulence. you did read about why turbulence is so bad, right? If not, that's ok, you can still read about how the landscape plays an important part in the performance of your turbine. The objective here is to get the wind turbine high enough off the ground so it can operate properly.
A good rule of thumb is for the bottom of the rotor to be a minimum of 30 feet above the tallest objects within a 500 foot radius. Just be sure to use it as a minimum, not a low goal to shoot for. Trying to save some money by going with a shorter tower is really not economical. The turbine will perform poorly and be subjected to the destructive forces caused by turbulence that could possibly lead to early failure. generally, the extra money spent on a taller tower is well justified!
The wind blows faster at higher altitudes because of the viscosity of air and the drag from the land and sea. The variation in velocity with altitude, called wind shear, is most dramatic near the surface.
Typically, during the day the variation follows the 1/7th power law, which concludes that wind speed rises proportionally to the seventh root of altitude. Doubling the height of the tower increases the wind speed by 10% and the expected power by 34%. Increasing tower height five times increases the wind speed by about 25% and almost doubles the power available.