Windenergie 2 - Site Assessment

15 October 2025, Po Wen Cheng

Exam

Date not known yet
No tools in Questionaire, Two sheets of A4 handwritten or printed, Calculator in rest of exam
Exam very simmilar to Excercises - so do them
Verständnisfragen 30 min
Rechenteil 60 min

Misc

Windenergielabor tomorrow 2pm in Allmandring 5b in 0.42
Wind Energy Project student group meeting wednesday, 9:45 in Allmandring 5b in 0.42, more information on Ilias

Literature

Bailey, Bruce H.; McDonald, Scott L.; Bernadett, Daniel W.; Markus, Michael J.; Elsholz, Kurt V.: „Wind Resource Assessment Handbook“, Subcontract No. TAT-5-15283-01, National Renewable

Erich Hau: „Windkraftanlagen – Grundlagen, Technik, Einsatz, Wirtschaftlichkeit“, Kapitel 13, 4. Auflage, 2008, Springer

Site characterization

Identify potentially windy areas which also possess all the necessary requirements for the errection of wind turbines

Identification of potential wind development areas
Inspection and ranking of the candidate site and
Selection of actual tower location(s) within the candidate site

Standard measurements for site assessment are wind speed, wind direction, atmospheric pressure, air temperature, relative air humidity.
wind atlas website is not sufficient, because it is too uncertain

Data has to be collected over at least a year, usually by Met Mast with sensors on several heights
The highest measured height should be at least 2/3 of the intended hub height. Sensors include:

Cup anemometer
Wind vane
Sonic anemometer
Temperature sensor
Pressure Sensor

Sometimes, remote measurements are used (Lidar and Sodar)

Wind flow models

Two approaches to model the velocity profile of the atmospheric boundary layer

Using logarithmic approximation
Using the power law approximation

Atmospheric stability

Usually unstable during summer: air close to the ground is warmer and wants to rise up, forming large convection cells, little wind shear
Usually stable during winter: cold, heavy air on the ground, turbulence dominated by the friction with the ground, large wind shear

Low turbulence intensity if function of surface roughness, atmospheric stability, distance above ground, wakes from the turbines
High tubulences can reduce the turbines expected lifetime, e.g. because turbine has to keep power constant by pitching constantly
IEC turbulence classes to classify wind turbines into wind speed and turbulence categories I, II, III

IEC turbulence classes

Modeling used to extrapolate measurements to other locations, possible methods are:

Conceptual models
- Based on practical experience and boundary layer meterology
Experimental models
- Older
- Terrain model in wind tunnel for testing
Statistical models
- More modern
- Based entirely on measurements
Numerical Wind Flow Models
- Uses physics, not statistics
- Mass consistent models
- computational fluid dynamics
- Jackson-Hunt models
- Standard today: WAsP model by Risø, Denmark, still not good enough with very complex terrain, then you need CFD

Measure correlate predict (MCP)

No time, will be done next lecture