Wind Design
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Transcript of Wind Design
1/17/2014
1
Wind Design Example
Location of the site
Project Location
Wind Resorce
AssesmentAssesment
Wind Speed Probability Distribution (Approximately Weibull)
Wind speed distribution• Measurements of wind speed distribution or frequency distribution is an essential
ingredient in calculating the output of the wind energy at a particular site. The wind speed distribution can be mathematically represented by several analytical functions.
• One of the mathematical functions that have been successfully applied to fit wind speed distributions is the Weibull distribution function. The general form of the Weibull distribution function, which is a two‐parameter function, for wind speed is given by,
(Reference: “Modeling Wind Speed Distributions in Selected Weather Stations”: Proceedings of the Technical Sessions, 23 (2007) 1‐6 Institute of Physics – Sri Lanka)
Where f (v) is the probability of observing wind speed v, k is dimensionless Weibullshape parameter and c is a scale parameter having units of wind speed
1/17/2014
2
Cumulative Distribution Function
• Scale parameter, c, indicates ‘windiness’ of a location under consideration, whereas the shape parameter, k, indicates ‘sharpness’ of the wind speed distribution (i.e. if measured wind speeds are very close to a certain value, the distribution will have a high k value and be narrow)
• The cumulative distribution function is given as,
• Fitting the above equation to a set of wind speed data determines the parameters of the Weibull distribution function. Taking the natural logarithms of both sides of the above equation twice, gives, ln{‐ln[1‐F(v)] = k ln(v) – k ln( c )
• Thus a plot of ln{‐ln[1‐F(v)] Vs ln(v) represents a straight line of which the gradient is k and the intercept is kln( c).
Cumulative Wind Speed Distribution
Shape Parameter
• The higher the value of Shape (from 1 to 3) the higher the median wind speed.
• Locations with lots of low wind speeds as well as some pvery strong winds would have a value of shape of below 2.
• Locations with fairly consistent wind speeds around the median would have a shape value of 3.
Plot of ln{‐ln[1‐F(v)] Vs ln(v
Shape Parameter and Scale Parameter
• From the graph k and c are estimated.
– Shape Parameter (k) = 1.42
– Scale Parameter ( c ) = 5.82
• Shape parameter of 1.42 and scalar parameter of 5.82 represent good power in the wind.
Energy Calculation