Your site location will play a large part in the success and cost of your wind generator. The cost of wiring from the turbine to the batteries can be significant if you must cover a great distance. Therefore, staying close to the batteries is a priority if practical. Obviously, if the batteries are located in a valley with no wind, there is no point in installing the turbine there. You will have to bear the expense of placing the turbine in a suitable location.
We will briefly discuss how various geographic features can affect wind flow patterns.
The first geographic feature we will look at is water. The earth heats up more quickly than a body of water and can be its own source of convective activity in a local area.
During the morning, the sun begins to warm the earth quicker than the surrounding water - this sets the stage for afternoon winds. As the warm air over the earth rises the cool air from the body of water rushes in to replace it. Thus the afternoon wind pattern will be from over the water flowing towards the shore. At night the earth cools quicker than the water. This results in the wind leaving the shore and flowing out over the body of water.
If you live near a large body of water this could provide you with a somewhat predictable wind pattern. One important fact to also note is the typically higher average wind speed along the shoreline. This is a result of the long unobstructed area the wind has as it blows across the water. There are no parasitic obstructions such as hills and trees to contend with.
On hills and plateaus you may also experience higher wind speeds than in surrounding areas. this is due to the fact that the wind becomes compressed or "heaped up" on the windy side of the hill, and once the air reaches the ridge it can expand again as its soars down into the low pressure area on the lee side of the hill.
Hills and plateaus can provide high ground on which to site your wind generator. Typically you'll find higher wind speeds there too. The air approaching a hill begins to compress or "heap up" and results in higher wind speed as it races down the other low pressure side of the summit.
This may sound good but there is a downside to this. Placing a wind generator on a steep hill or bluff may seem to be the perfect place to take full advantage of the wind but you'll encounter turbulent conditions at the edge of a bluff. The higher wind speeds found on the edge of a bluff is often outweighed by the damaging effect turbulence has on a wind generator. The wind climbing the face of the hill will mix with the wind traveling parallel to the earth and create turbulence. If you have enough flat land behind a bluff you could possibly be setup for a good wind site.
The most optimal site would be flat with few trees and obstacles. The wind will be more consistent and efficiently converted into usable power.
If you are located in a valley, do your research and carefully observed the wind patterns around you. If you live in a valley that is sheltered at both ends you would probably also have a sheltered winds site. However, your valley may also be a wind funnel especially if it runs parallel to the prevailing wind. I would suggest if you are planning to site your turbine in a valley area that you spend some time there for personal observations.
Turbulence (swirling, disturbed air flow) is caused by the wind passing over objects and uneven surfaces such as buildings and trees. Turbulence also decreases the output of the turbine. Forces hitting the blades from rapidly varying angles will cause inefficiencies as well as added wear and tear. If the turbine is rapidly turning to seek the prevailing wind, the full power production potential is not realized.
Trees and buildings are typically hard to avoid so you just need to understand and minimize their affect on your wind generator. Good, direct exposure to your strongest prevailing winds is critical. For most sites this will be the winter winds.