took this yesterday in Oklahoma.finally seen one parked.I was across a 4 lane expressway plus a ditch can you imagine how high these things would be in a set of three? thanks for viewing and any comments Efficiency is important for windmills, because the entire cost is in the technology, not the source of energy, which is wind. The most significant factor determining the efficiency of windmills is the number of blades. This is because more blades capture more energy. But large windmills must use few blades due to stress on the metal. When the diameter of rotation is 300 ft (100 m), two blade systems must be used. When the diameter is 150 ft, three blade systems can be used. Yet windmills are unnecessarily large or too few in blades. Over sea coasts, they must be large; but most places, they could be smaller and use more blades. For homeowners, they are small, yet they are not using the large number of blades which would create high efficiency. The overall efficiency of a windmill has to be directly measured, it cannot be calculated, because there are too many interacting factors. A good guess at design efficiency can be made by direct observation. Only measurements under operating conditions can improve upon direct observation. . Three blade systems are used on wind farms. Overall efficiency means the amount of electricity that can be generated over time on a cost basis. In other words, will a kilowatt hour cost ten cents, twenty cents, or what? Two factors are important in determining overall efficiency of a windmill. One is its ability to use low velocity wind, and the other is its conversion efficiency. The ability to use low velocity wind determines whether the windmill is working or doing nothing while wind velocities are low, which is a large part of the time. For example, an locale might have wind of 15 miles per hour (mph) or greater 20% of the time, and 10 mph or greater 40% of the time. A windmill that can use 10 mph wind is operating 40% of the time, while one requiring 15 mph wind is only operating 20% of the time. To utilize low velocity wind effectively, there has to be more blades. The researchers studied two blade systems. They never even made comparisons to systems with more blades. Conversion efficiency also requires more than two blades. More blades allows lower rpms, which results in less turbulence, so conversion is more efficient. A quagmire of technicalities does not change these overall facts. Arguers will talk about torque and velocity trying to prove something, but it proves nothing, because there are infinite options in integrating all of those factors. For example, they repeatedly say high rpm rotors are needed for generating electricity. That's mindlessness, because the rpms (revolutions per minute) are determined by diameter—the larger the slower. The tip speed of the blade increases as the circular diameter of motion increases. In the government experiments, two blade systems were used, with rotors up to 300 ft long. Tip speeds were in excess of 200 mph, which created problems with noise and vibrations. Normal rotation was 18 rpm. This means more than 3 seconds per revolution. Notice that the rpms have to decrease as the diameter of motion increases. Otherwise tip speeds would be excessive. So the rpms are determined by the diameter of motion, not the number of blades.