Exploring Wind Power by Countrylife Archives
Wind is tricky. It comes from different directions at different times with different speeds. Still, with proper design, a wind power system can be reliable and efficient. Unfortunately for home users, although recent advances have been made in siting and efficiency, a major trend in recent years has been the increase in the size of the wind turbines for improved performance. These improvements make the systems less applicable for the home.
The power that can be collected by a wind device is given by
P = (1/2) rho A V^3 E
where P is the power, rho is the density of air, A is the area of your device, V is the velocity of the wind, ^3 means cubed (or to the power of 3), and E is the efficiency of you generating system. For P in watts, A in square feet, and V in mile per hour, and rho evaluated at sea level, the equation is
P = 0.003065 A V^3 E
Using this equation, it is simple to get approximations for the power your system will deliver.
Wind itself can be broken up into two major components, the prevalent winds and the energy winds. The prevalent winds are low velocity winds, generally 5 to 15 m.p.h.. They blow consistently, 5 days per week or so, in a relatively constant direction. The energy winds are higher velocity winds, 10 m.p.h. and up, that blow less frequently in gusts in randomly varying directions. Although less frequent, these winds provide considerable energy due to their high velocity and the cubic dependence of power on velocity.
To maximize the output power of your system, there are a number of things to consider. Looking at the equation for power, your room for improvement is in the area of the device, the velocity of the wind, and the efficiency of your system.
Increasing the area of your device is simple conceptually, but can be impractical to implement. Power is linearly dependent on area, so doubling the area of your device will double your output power. Doubling the area, however, may more than double the cost of your device and the difficulty of its design and construction.
Increasing the velocity of wind may sound impossible, but actually it is achieveable and provides a cubic improvement to the power. The first consideration in the design is to maximize the useable velocity. There are two basic designs categories for wind turbines. The more familiar is the orizontal axis wind turbine. Their rotor has an axs of rotation which is parallel to the ground and in the direction of the wind stream. These system only utilize wind in the direction they are pointing. Vertical axis windturbines have an axis perpendicular to the gound and the wind stream. These systems utilize wind omnidirectionally. Besides increasing the useable velocity, you can also increase the actual velocity of the wind hitting the rotor. This is accomplished by using an airfoil, similar to in concept to an airplane wing.
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