Monday, May 2, 2011

Understanding Site Assessment for Residential Wind Turbines

Assessing the suitability of a site for a residential wind turbine isn't as simple as stepping outside and seeing if the trees are moving. At an opening purchase and installation price of approximately $20,106 USD, consumers need to know, before they proceed, that a viable amount of energy will be generated at the proposed turbine location.

What goal do you have in mind for the system? If you are planning a complete off-grid installation with no power coming from an electric utility, you'll need to consider a set-up that also includes back-up batteries and possibly a fuel-powered generator. Most homeowners are interested in a hybrid system that allows the home to draw partial power from the renewable energy source and the remainder from the electrical utility. Often, any excess electricity generated is sold back to the utility, furthering lowering the home's energy bill.

You will need approximately an acre of land, with the ability to position the turbine about 76.2 meters (250 feet) from the nearest adjacent structure. Optimal locations are on hills and lake or sea shores, but any area free of nearby obstacles, like buildings or trees can be considered. (These elements block the natural flow of the wind, causing turbulence, which degrades the turbine's ability to operate efficiently.)

There is no single kind of wind. Our planet has a general circulation of wind that moves over the entire earth, but synoptic-scale circulations are responsible for smaller, day-to-day changes by region. There are also local winds that are unique to one given place. If you listen to a wind assessor talk, you'll hear them discuss prevailing winds, storm winds, thermal lows, and even "puffs."

It is safe to assume that in most locales the wind begins to increase in frequency and duration in the fall, continues to blow throughout the winter and into spring, with the lowest occurrence in summer. Most places, however, exhibit daily wind peaks each afternoon. Certainly an examination of regional wind maps and annual climate data is integral to a complete wind analysis, but average wind speed data is too limited to completely evaluate a specific turbine site.

This is not to say that a professional wind assessor will not choose a clear, "normal" day with no impending weather events to come out and stand exactly where the turbine will be placed. This will allow for an evaluation of potential sources of turbulence. An anemometer (an extendable pole with rotating cups attached) will be used to take a base, ground-speed reading as well as wind speeds from increasing heights. Ideal conditions to move forward with a turbine project are steady wind speeds of 16-24 kph (10-15 mph).

The site may be completely unsuitable or the wind may be good, but lack constancy, which would indicate the need for more batteries at an off-grid site or a reevaluation of expectations from a hybrid system. In some cases, newer low-speed turbines with low cut-in speeds might be recommended. Lucky homeowners get the go-head. Regardless, there are too many relevant factors for wind site evaluation to be a do-it-yourself project. Consult professional wind turbine companies with qualified assessors to get the best value for your investment in both the short and long term.

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