Should trees be considered when placing a wind turbine?

Thursday 01 Feb 18


Ebba Dellwik
Senior Scientist
DTU Wind Energy
+45 46 77 50 32

In recent years, researchers among, DTU Wind Energy have looked into what trees in the landscape mean to the winds.

How does a single tree or a small cluster of trees affect the wind? That is what a selected group of researchers from DTU Wind Energy has joined the European Forest Institute from Finland and Western University from Canada to find the answer to in the research project ”The Single Tree Experiment,” which is financed by the Danish Research Council.

In 2017, the group made the first full-scale wind experiment on a single tree at Risø Campus, Further, small trees were investigated in the big WindEEE dome in Canada, where atmospheric conditions are recreated indoors. 

The project, that started last year, has a fundamental focus but various societal problems are also being investigated. For the very large modern wind turbines, a single tree has a very limited meaning. Nevertheless, the overall effect of many single trees, avenues and small forests can have a significant impact on the wind's average value taken over the entire landscape.

"Today, you use satellite imagery, when you model the landscape's effect in wind and meteorology models. The landscape will then be interpreted in the model. When you look at the landscape through satellite images, you do not see the small forests or the individual trees, that we now have an impact on the wind. The trees weaken the wind. This is why for example we will look at the meaning of trees for wind measurements," says project manager Ebba Dellwik from DTU Wind Energy.

For the smaller domestic wind turbines, it can be crucial for the calculated electricity production to understand, how nearby trees shade for the wind. Based on the first test carried out by the group there is a very clear picture:

"In winter, two thirds of the wind comes through a full-grown broad-leaved tree because of the lack of leaves on the trees. In the summer, on the other hand, it is a completely different picture. There it is about 10% of the wind coming through the trees, so there is significantly less wind to the wind turbines. So you can say, the leaves make the difference,” explains Ebba Dellwik.

An interdisciplinary project
The research team from DTU Wind Energy has focused most on what is happening in the wind, but the project is dealing with different research disciplines, and in particular, the collaboration with researchers investigating the importance of the wind for trees and forests has accelerated. The goal of researchers is to be better at understanding and predicting when trees fall over in a storm.

"It is incredibly rewarding to work with researchers who consider the same problem, but from a completely different point of view," Ebba Dellwik says.

The collaboration has resulted in a joint workshop at Risø Campus in April 2018, where researchers from all over the world will meet and discuss the pros and cons of the new experimental techniques used to understand the interaction of trees.

Cooperation across DTU
In order to interpret the wind measurements correctly and to make the results overall, it is very important to describe the studied trees with a high degree of detail.

The studied trees have therefore been scanned with a state-of-the-art laser scanner, and data from the scanner was examined in collaboration with DTU Compute.

The results showed that even the most advanced algorithms had difficulty describing the fine-scale structure of the tree (small branches and twigs) while retaining sufficient detail in the larger elements (stem and large branches).

The research project "The Single Tree Experiment" runs until July 2020. In 2018, experimental work continues, while focusing on developing the numerical models of the future where the interaction of the trees with the wind is better handled than today.