For those considering investing in a residential wind power system, one of the most important factors is the wind velocity of the area. Information about wind speed, strength, and frequency can vary, as the methods for measuring wind data are still controversial. One of the methods recommended is to measure the wind data on your property for a year, using a "wind resource evaluation system".

Using this system, you'll measure wind speed over time with an anemometer mounted on a pole outside. The machine collects wind data and sends it to the computer, where annual wind velocity can then be determined. The anemometer and accompanying equipment costs between $500-$5,000, depending on the quality and sophistication of the kit.

Many homeowners may not wish to spend thousands of dollars and a year of their time meticulously measuring wind speeds on their property. However, a wind turbine only generates electricity efficiently at wind speeds higher than 10 mph, and energy savings can only be realized when the system is working efficiently. As wind energy systems cost $6,000-$45,000, a homeowner should be sure they'll realize energy savings before making such a large initial investment.

Residential wind turbines need back-up power for those times when the wind isn't blowing, and most systems use the utility grid as their back-up. Because homeowners will still be drawing electricity from the grid and paying electric bills, they should look at how much energy savings they are willing to accept for their investment.

-A tower turbine can reduce household utilities by 50 – 90%. Is 50% enough savings for the initial cost of the wind system? Or will the savings have to be closer to 90% in order to make the upfront investment?

-Utility electricity can sometimes be cheaper than wind energy. If electricity costs less than $.10/kWh, there's no way a turbine can compete. While in many areas of the nation, electricity costs much more than $.10/kWh, there may be areas where low electricity costs prevent wind systems from creating energy savings.

-If the wind velocity on your property is lower than 10 mph, a tower turbine isn't efficient enough to create much energy savings. A roof mounted turbine can create energy savings of 10%. Would this be enough savings?

There are other factors that affect the efficiency of a wind turbine. A property of at least one acre, with exposed high ground unobstructed by buildings or trees is best for you, and installing the turbine at least 250 feet of space is best for your neighbors. Your property will need sufficient space to accommodate an 85-150 foot tower surrounded by guide wires.

Wind generally blows in a pattern, which can be affected by the location, surrounding obstacles, and seasons. Learning the wind signature of your turbine site will provide queues as to when to expect heavy winds. Winter and spring are generally good times of year for high wind velocity, while summer is a time of low wind velocity. Afternoons are usually peak times for wind speeds.

Wind velocity can be calculated using wind maps and climate data from local weather agencies. However, these calculations are only estimates. For more precise information, a wind assessor, either hired by you or provided by a wind turbine company, should come out to the property for an inspection.

Due to the many factors which form a wind signature, like obstacles and elevation, the homeowner should have wind data assessed on the exact spot where the turbine will be built. This is the area which matters most to the efficiency of a wind energy system.

A wind assessor should take measurements on a "normal" day, not a day when a storm is approaching. Storms or unusually high winds could skew the wind data higher than normal. The assessor will measure wind speed from the ground first, and then from various heights up to the height of the tower. Distance from the ground can affect wind speed a lot, so a variety of readings is helpful for accuracy.

There is nothing more important to a residential wind system than a good wind assessment. Securing an accurate wind velocity is a crucial step for anyone interested in making an investment in a wind turbine.