OSA WATER WORKS

WIND POWER

Introduction

The first recorded use of wind power was for water pumping for irrigation to support Mesopotamian agriculture more than six thousand years ago.  And for those that have wind-surfed, hang-glided, flown jet aircraft, sailed, the notion of harnessing the wind for energy production will not seem at all foreign.  Arguably the most infallible analogy is a fan.  By applying electricity it causes wind.  Reverse that process, and by causing a fan's blades to turn an alternator, we can send electricity back into the outlet.  That is wind power.

At this writing Osa Water Works has not installed a wind power system and is only in the process of sourcing its own anemometer, so the discussion that follows is a literature review.  Soon this paragraph will be removed from the web site.  If you think you would like to be the first OWW wind power clients in Costa Rica, then you should send me an email.

 Theory

Like most forms of AC-power generation, wind energy consists of harnessing wind using aerodynamic rotary wings to turn a shaft inside an alternator.  At a baseline threshold wind velocity governed by technology and economics, wind generation is a viable alternative resource.  In all cases above the basic threshold, output varies as a direct function of the length of the blades.  Also, since wind velocities are higher above the Earth's surface and some height is needed to remove the turbulence in airflow caused by objects on the ground, the efficiency of wind power is much greater at greater heights.  Both turbine span and height above ground surface strongly govern capital costs, so in practice, the use of windmills to generate power in an area with acceptable wind is limited mostly by capital.

Wind is caused by differential heating of the Earth's surface and is strongly impacted by variations in the Earth's surface, such as where oceans contact land masses, or where great relief causes great variations in vertical temperature gradients.  While wind maps exist for many parts of the planet that provide some idea, albeit rough in many cases, of wind potential, it is important to gather as much information as possible on wind speeds to ensure that the final result reflects design anticipations.

Power production varies dramatically over very small differences in wind velocity.  In general, average wind velocities of 10 miles per hour and above are usually economic to develop as alternative resources for a private home.  Power production varies as a complex function of wind velocity.  The equation that governs this relationship is a deterministic one, shown below, which is the basis for the rule-of-thumb windpower cliche of the rule of threes because each increase in wind speed boosts overall power output by that windspeed increase raised to the third power.

                                                                                                                          (1)

where P = Power in watts, α is an efficiency coefficient, ρ  is the density of the air in kilograms per cubic meter, r = radius of the area swept by wind turbine in meters, and v = velocity of the air in meters per second.  Betz's law states that the maximum theoretical value for α is 0.59, though turbine manufacturers report the value which below the Betz Law limits varies as a function of turbine configuration. 

Application

As in the case of hydroelectric, wind power can be either introduced directly into a local or regional power grid or consumed by a private consumer, or it must be transformed to direct current and stored in batteries for use at a later time.  The design analysis for wind power usage on a residential or small commercial scale is very similar to the design analysis of distinguishing between mini- and micro-hydroelectric as the most appropriate mechanism of harvesting the power.

The design process for further consideration of the harvesting of wind power is given here (Wind Power Design Analysis).

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