Friday, December 17, 2010

Wind speed increases with height, and turbulence decreases with height.

http://windsine.org/?act=spage&f=wind

The Fundamentals of Wind Energy

This is a simple, yet very complex subject.
Wind is actually a roundabout way to capture solar energy. As you may know, wind is the result of uneven heating of the earth's surface and air by the Sun. The result is an uneven distribution of air and ground temperatures, which, in turn, creates convection currents in the air. This means that the warmer, less dense air will begin to rise, and the colder, more dense air will rush in to fill its place (displacement). And BAM!!, we have wind!

In a typical functioning wind turbine, moving air causes a rotor (made up of blades) to spin. Energy in the wind is transferred to the spinning rotor and directed to an electrical generator or alternator, thereby producing electricity when the wind is blowing. Inverters accept the raw, direct current (DC) and change it into a more usable form, alternating current (AC).

Wind turbines are designed to capture kinetic energy that is available in clean, laterally flowing air. Therefore, it is crucial that turbines are erected in areas with abundant laterally flowing, non-turbulent air.

Air turbulence leads to severe under-performance of a wind turbine due to the fact that it robs your machine of fuel (clean wind, which is an even supply of energy). Secondly, turbulence roughs up wind turbines in the same way that it roughs up an airplane and its passengers: would you enjoy riding through turbulent wind? Consequently, early maintenance issues usually manifest themselves in premature bearing and slip ring failure. Because turbulence is a wind turbine's worst nightmare, problems are to be expected when a turbine is installed on a short tower (or a roof), particularly near trees or buildings, which are the ultimate source of air turbulence. There is simply not enough clean air this close to the Earth, regardless of the type of turbine, vertical axis (VAWT) or horizontal axis (HAWT). This is not to say, however, that short-towered turbines will entirely not work, only that energy productivity and return on investment will be compromised exponentially.

Since wind speed increases with height, and turbulence decreases with height, it's safe to say that installing a wind turbine on the tallest tower you can will increase overall system productivity and, therefore, decrease serious maintenance issues and payback period. Wind turbines and towers do require periodic inspections and preventative maintenance. This should not be perceived as negative, but simply should be factored into the overall cost of the system early on.

"There is no renewable energy system that does not require some form of maintenance. Even solar PV needs periodic inspections to make sure it continues to work as expected for many years."

Wind energy (just like PV) is an inconsistent power source, meaning that it is never available 100% of the time. Therefore, we must be able to accept or deal with the energy as soon as it is produced. This is why we must have the ability (just like PV) to send it to the grid (Read about Net Metering) or store it in batteries for later use. One alternative storage method is to produce Hydrogen using an electrolyzer. This is great if you happen to use a fuel cell for electricity (they are powered by Hydrogen and Oxygen and only produce electricity, water, and heat). Remember, energy can not be created nor destroyed, it can merely change forms, so the possibilities are really only limited by your imagination.

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