Wind Power Fundamentals
The amount of wind power at your site will determine the amount of power you can expect from a wind turbine. How do you work you the power generated from a wind turbine? It is quite straightforward really! The amount of power (p) in the wind is a function of air density (p), the area of the turbine blades intercepting the wind (A), and the instantaneous wind velocity (V), or wind speed. An increase in any of these factors will increase the power available from the wind. Air density is affected by temperature and height. Warm air is less dense than cold air therefore a wind turbine will produce less power in the summer than winter, when it is colder, for winds of the same speed. Depending on location relative to standard conditions at sea level, power can reduce by up to twenty (20) percent, and maybe more. Power in the wind varies with the cube of the wind speed. Double the wind speed and you increase the power by eight (8) times. The SWEPT AREA of a wind turbine directly affects power output. If you double the area you effectively double the power available. Wind Turbine Height Wind speeds do typically increase with height. This is very important. If the turbine is mounted in an area of rough terrain then height is important and the higher the better. Height equals stronger winds and less turbulence. Estimating Performance So, how much power does a wind turbine generate? A good question? Simple, but deceptive. If you’re into number crunching then it shouldn’t be a problem. On the other hand, if your working out the detail for your battery charging system then results can be difficult. Since there is no international standard for agreement on performance we must feel our way along. Given that there are two different types of wind turbine uses: grid connected and off-grid (battery charging) systems we can work out what the norm should be for both types of wind power turbine system. With a battery charging wind turbine system, and when the batteries become fully charged, the wind turbine must be able to dump, excess energy available. Some manufacturers offer dump loads with others offering special controls and circuits to get rid of the excess energy generated. In truth most small wind turbines simply disperse the left over energy.
