INDUSTRY ARTICLE
Figure 2a and 2b: The wind profile maps wind velocity (x-axis in m/sec) at various heights (y-axis in metres). At a height of roughly 100 metres, the measured data (black line) show a visible blip, with wind speeds increasing drastically from that height. The zone below is marked by high turbulence intensity caused by the trees in the forest. Turbulence intensity is considerably weaker in the zone above, where the air flow is largely uninfluenced by trees and topography.
Mean turbulence intensity at a height of 140 m is 10.4 per cent. This relatively low turbulence intensity is important for the design and construction and thus the structural stability of the wind turbines. However, at lower levels, the complex topography and particularly the trees, cause a drastic increase in turbulence intensity.
TREES CAUSE TURBULENCE
Turbulence is a typical feature of forest areas, as wind that passes over trees in its path will swirl violently near ground level. The wind profile reflects this phenomenon, showing a visible blip at a measurement height of around 100 metres.
This height is an important design criterion for the projected wind turbines, which must be designed to harness the wind above the zone of wind turbulence and withstand the turbulence intensity prevailing at the site. Based on the measured data, the experts further determined the preliminary reference yield – an important tool for estimating the possible future energy output. The reference yield is calculated in comparison to a reference site with a reference yield of 100 %, i.e. an average site with favourable wind conditions on the coast of northern Germany.
The measurements in the Upper Palatinate region, carried out after one year of operation, revealed a reference yield of around 94 per cent. The site’s viability is thus comparable to that of a high-wind site near the coast in northern Germany. In the second year of operation this result is to be verified and statistically validated.
The measurements also showed major variance over the course of the year.
www.windenergynetwork.co.uk
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