Agenda - Planning Commission - 08/07/2008

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costs and potentiaUand-use impacts. Because WECs can be controversial, it is reasonable to ask if they are effective. The answer depends partly on planners and local officials. A small WEC can produce impressive amounts of power, but only with access to good wind, which is largely a function of proper siting and adequate height-factors that zoning regula- tions impact mightily. UNDERSTANDING LOCAL WIND RESOURCES The U.S. Department of Energy (DOE) and National Renewable Energy Laboratory (NREL) provide state-level wind resource maps for nearly every state in the U.S., and some state governments provide more detailed maps. Wind resource maps show the average strength of the wind at 50 meters, with a ranking between 1 (weakest) and 7 (strongest). Most utility wind develop- ers today Ipok for areas with steady Class 4 or 5 winds, but Class 2 or 3 winds, which are found in much of the U.S., can power small WECs. Large-scale wind maps are a free resource that can help a community under- stand generally if wind energy potential is . . likely to exist. To determine the actual wind power generation potential ora given site, a site-specific wind resource assessment by a qualified professional is needed. Site-specific assessments are typically the responsibility of the property owner. FACTORS THAT INFLUENCE ENERGY PRODUCTION How much energy a WEC will produce depends primarily on three factors: (1) The engineered design of the turbine, which determines efficiency of power transfer. Modern WECs are highly engineered and most are very efficient. (2) The size of the rotor. Capacity increases with "swept area," meaning the total area of the spinning rotor blades. Area, and thus capacity, increases geometrically with blade length. C3) The speed and consistency of the wind. Power output increases exponentially with wind speed, but gusty or turbulent winds can damage turbili.es. Variations in topogra- phy and obstructions such as buildings and trees slow the wind and add turbulence near the ground. Therefore, adequate height is a critical factor in WEC effectiveness. In order to function well, the lowest part ofthe Totor blades must be a minimum of 25 to 35 feet higher.than surrounding obstructions. Height regulations that do not achieve such separation eliminate the benefits of invest- ing in a WEe. The National Renewable Energy Labo- ratory provides estimates ofyeariy energy gen- eration potential for small wind turbines. Using these figures, it is possible to estimate the power generation potential for various tur- bine sizes and wind classes and to gauge the number of average U.S. homes that can be powered. The table below illustrates the varia- tion by wind speed and rotor size (assuming good wind access). Depending on such fac- tors, a residential turbine can oftensupp,ly about one-third to one-half of an average u.s. home's energy demand and a substantially greater percentage if the home is energy effi- cient. Larger "small" WECs can supply con- sumers with higher energy demand, such as commercial or public facilities. CARBON El'JilSSION REDUCTIONS FROM WiND-GENERATED ENERGY Using 100 percent wind-generated energy ver- sus typical utility energy can reduc,e annual car- bon emissions by eight tons for a U.s. home with typical energy demand. This is equivalent to the carbon emissions produced annually by 1.4 typical U.S. passenger cars. Thus, for an average two-car household, converting the MEDlAN i'lUMBER Of HO!'J1ES POWERED BY SHECTED WECS SiZES AND WjND CLii,SS!FlCATiONS \Mind Strength Rotor Diameter Class 2 Class 3 (lESS -4 Ct~SS 5 Class 6 Class 7 3m 0.3 0.3 0.3 0-4 0.4 0.5 5m 0.7 1.0 1.2 1.3 1.5 1.9 7m 1.4 2.0 2.3 2.6 3.0 3.7 10 m 2.9 4.1 4.8 5.4 6.1 7.5 - 12 m 4.1 5.9 6.9 7-7 8.8 10.8 Estimated NREL median yearly energy production figures, expressed as kWh per square meter of swept area, are multiplied by swept area, then divided by U.s. national average annual home energy usage to estimate the number of average homes powered ZONING PRACTICE 7.08 AMERICAN PLANNING ASSOCIATION I P'6'3