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And the wind rages on

To the editor: Courtney Manors letter (Clinton Free Trader, 10/6/07) said "Technology is (developing) much smaller, ... wind turbines" producing energy levels equal to "the over 400 foot towers", which she expects 13 of near her on southern Rand Hill. Can smaller wind turbines be developed which will produce as much energy as todays larger ones? Intercepted air moving at any given velocity has only the energy it has. Intercepting less encounters less available energy regardless how much wed want. Smaller rotors intercept less. That said, wind turbines can only work under an ideal, but never reached, theoretical maximum percentage of moving airs (winds) total kinetic energy (energy of motion). Actual success has always been below that, but technology always tries to get closer. So, some small rotor size reductions may become possible, with no power loss, but dramatic reductions, such as dropping it from 77-meter (about 253- foot) rotor diameters to six meters (about 20 feet) are unlikely. With height: wind velocities near ground, especially in summer below treetops, are much lower than at higher altitudes, due to surface roughness (i.e. ground-level friction from unevenness and projections such as vegetation). Since kinetic energy equals one-half mass times its velocity squared, velocity affects its energy content exponentially: energy increases with the square of any velocity increase. For example, multiplying velocity by 2 multiplies energy by 4 (i.e. 2 times itself or 22). We neednt expect dramatic decreases in hub height either, such as from 262 feet to 100. Technology has come a long way in decreasing wind turbines rotor size and height without power loss. Some further size decreases toward this might someday be possible, but would probably not be extreme. Turbine design is quite mature. As technology advances over the 20 years or so that todays turbines are in service, replacements might become a little more compact, that being a general trend in most industries. Under climate emergencys rapid approach though, regardless whether efficiency improvements might ever significantly reduce size, waiting for better technology before deployment seems imprudent. David E. Manwell
Beekmantown

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