bReeze (version 0.2-2)

energy: Calculation of total wind energy content

Description

Calculates the total wind energy content per direction sector from Weibull data.

Usage

energy(wb, rho=1.225, bins=c(5, 10, 15, 20),
  digits=0, print=TRUE)
en(wb, rho=1.225, bins=c(5, 10, 15, 20),
  digits=0, print=TRUE)

Arguments

wb

Weibull object created by weibull.

rho

Air density as numeric value. Default is 1.225 kg/m3 according to the International Standard Atmosphere (ISA) at sea level and 15°C.

bins

Wind speed bins as numeric vector or NULL if no classification is desired.

digits

Number of decimal places to be used for results as numeric value. Default is 0.

print

If TRUE, results are printed directly.

Value

• Returns a data frame containing:
• total
  Total wind energy content per direction sector.
• ...
  Wind energy content per direction sector for each given wind speed bin.

encoding

UTF-8

Details

The total wind energy content can be perceived as the theoretic energy potential of a particular site. Therefore it is usefull for a resource assessment, independent of the wind turbine.

The power density function $$E(v) = \frac{1}{2} \, \rho \, v^3 \, f(v)$$ where $\rho$ is the air density, $v$ is the wind speed and $f(v)$ is its probability density function, leads to an analytical solution using wind speed bins as: $$E(v) = \frac{1}{2} \, \rho \, H \, \sum_{b=1}^{n} \! v_b^3 \, W(v_b)$$ where $H$ is the number of hours of the desired period, $v_b$ is the wind speed bin and $W(v_b)$ is the probability of that bin estimated by the Weibull distribution. The result for $H=8760$ is the available wind energy per square meter and year.

References

Fördergesellschaft Windenergie e.V. (2007) Technical Guidelines for Wind Turbines, Part 6: Determination of Wind Potential and Energy Yields, Revision 7

International Organisation for Standardization (1975) ISO 2533:1975 Standard Atmosphere. ISO Standard

Troen, I., Petersen, E.L. (1989) European Wind Atlas. Tønder: Laursen

See Also

weibull, plotEnergy, printObject

Examples

# load and prepare data
data(winddata)
set1 <- createSet(height=40, v.avg=winddata[,2], v.std=winddata[,5],
  dir.avg=winddata[,14])
set2 <- createSet(height=30, v.avg=winddata[,6], v.std=winddata[,9],
  dir.avg=winddata[,16])
set3 <- createSet(height=20, v.avg=winddata[,10], v.std=winddata[,13])
ts <- formatTS(time.stamp=winddata[,1])
neubuerg <- createMast(time.stamp=ts, set1, set2, set3)
neubuerg <- clean(mast=neubuerg)

# calculate Weibull object
neubuerg.wb <- weibull(mast=neubuerg, v.set=1, print=FALSE)

# calculate energy
energy(wb=neubuerg.wb)

# calculate energy for 1 m/s speed bins and without binning
energy(wb=neubuerg.wb, bins=0:25)
energy(wb=neubuerg.wb, bins=NULL)

# calculate energy with site specific air density
energy(wb=neubuerg.wb, rho=1.115, bins=NULL)

# change number of digits and hide results
energy(wb=neubuerg.wb, digits=2)
energy(wb=neubuerg.wb, print=FALSE)