This article is the third one of a series of five posts dealing with wind & site studies carried out by some of the major wind energy post-war pionneers (Putnam in the US, Golding in the UK, Hütter in Germany and Juul in Denmark). The first four articles will provide highlights of their works. It is my impression (I may be wrong), that these studies are not known among the community of wind & site practitioners, and that they deserve more attention.
As you may already know, Aeolians.net does not deal specifically with wind turbine design (the topic is well covered in various books and essays), but instead focuses on historicising wind & site studies. Therefore, these will be at the core of the articles, and some wind turbine design issues will be left aside (external references will be provided for the curious reader).
The aim of these articles is first of all to provide references to the major wind & site works by these pionneers. This is done either by pointing directly to a scanned version of the document in Aeolians.net’s library, or by referring to the book on worldcat.org (unfortunately, for copyright reasons the books of Putnam and Golding are not freely available on the net).
This series of posts also aims at comparing these pioneer’s studies: what questions do they attempt to answer, and by what means ? how are they linked to wind turbine design ? what results have been obtained, and how are these relevant today ? The last article of the series will compile and combine the comments and reflections of the individual posts.
Ulrich Hütter is not particularly known for his wind & site studies. As opposed to the extensive wind & site work carried out by Putnam (USA) and Golding (UK), he did not (that I know) carry out vast investigations of the wind resource or the wind structure. In contrast, Hütter is very famous for having designed slender and fast rotating two-bladed downwind turbines, which were used as a basis for the MW-size prototype turbines in the USA and Germany in the 1970’s and 1980’s. You can find more about these programs in this post. There has been a great deal of publications on the pro- and cons of this turbine design, in particular when it is scaled up to MW size turbines, see for instance Chapter 3 of Paul Gipe’s “Wind Energy Comes of Age”.
For writing this article I have used the following documents:
- “The Development of Wind Power Installations for Electrical Power Generation in Germany” (1954). |Link|
- “Planning and Balancing of Energy of Small-Output Wind Power Plant” (1956). |Link|
- “The Aerodynamic Layout of Wing Blades of Wind-Turbines with High-Speed Ratio” (1961). |Link|
- “Operating Experience Obtained with a 100-kW Wind Power Plant” (1964). |Link|
- “Past Developments of Large Wind Generators in Europe” (1973). |Link|
- “Review of Past Developments in West Germany” (1974). |Link|
- “Optimum Design Concept For Wind-Electric Converters” (1974). |Link|
- “Moderne Windturbinen” (1979). |Link|
Hütter did his first research during the war, and published as early as 1948. Just, I could not find any of these on the Internet. On my to-do list, is to fetch this report, and – of course – Hütter’s 1942 report.
Surprisingly enough, Hütter does not have any paper in the OEEC report from 1952, where the only two Germans are E. Frankenberger (German Met Office) and Hans Christaller (Schwaben A-G). The latter mentions Hütter several times in his papers though.
Wind resource and wind climates
The description of wind resource and wind climates, in Hütter’s papers, is always concise and elegant, providing the right amount of information for the purpose of the article, and based on traceable references. That it to say that he has mainly relied on the work of others (in particular the German Met Office, and the work of Golding), to understand quantitatively the distribution of wind speeds at different sites, as well as the amplitude of gusts and extreme winds.
A good example is his 1956 paper at the UNESCO conference in New Dehli, see below.
Later on, in the 1970’s, Hütter gave some presentations in the series of workshop organised by the Americans. He kept referring to the material he had presented during his earlier works, see for instance here in Stockholm in 1974:
Again here in 1979, where he points to the latest research work in wind energy meteorology (among others by Ljungström in Sweden).
As I understand his approach, he needed key inputs from wind & site studies for his turbine design, in particular the shape of the wind speed distritbution, in order to choose the optimum tip speed ratio of the turbine (reminder: all of these prototypes were fixed speed turbines, see here for a simple explanation).
Another important input which Hütter considered, was the fluctuation of the wind speed, and the amplitude of gusts. In his 1964 paper, he refers for example to a 1919 study “Beitrage zur Kenntnis der Struktur des Bodenwindes”, for prescribing the input to a specific design load case, see below:
He also uses mesurements from a weather station, and not only from a loading perspective but also from a power production perspective (how to deal with intermittency).
Wind turbine testing
Hütter, like Juul, carried out extensive test campaigns of his turbine prototypes. See for instance the graph below. It is the 1973 version of a graph already present in the 1964 article mentioned above. I like this chart, it is actually one of the first one that caught my attention and led me on the tracks of these early wind energy papers about three years ago now. It shows the power curve of the 100kW (34 m diameter) turbine from Hütter, compared with the one from the Andreau Enfield turbine (famous pneumatic concept).
The measurement setup is described in the 1964 paper, see below. The mast was a about 1.2D, quite close then. As the same time, Hütter’s turbine was not heavily loaded (about half of that of the Gesder turbine), so induction may not have been that large.
The fixed quantities for output were measured by a kWh meter which had been modified for this purpose – with contact made after the production of a fixed quantity of energy. The wind pickup was a triple cup anemometer which tripped a contact after an adjustable wind path had been covered. The wind transmitter was located 41 m from the center of the tower, set up at a height of 18.2 m on a free-standing tower. In order to determine the relationship between wind velocity and power (wind path and kWh output), it was therefore necessary to convert all wind velocity data to the corresponding values for the height of the axis of the effective rotor area above the ground (24.2 m).
For the anectote Hütter makes actually several times (1956, 1964) this remark about the fact that it is not needed to reach the highest efficiency (which is for 3 blades) because wind comes for free, and that it is better to save the cost of a third blade and have a downwind turbine which orients itself. It is really different from Juul who went for 3 blades because there are more efficient rotors (see Juul’s article in the 1956 UNESCO conference), and Hütter’s argument are really the same as the ones brought up later on by General Electric in the US during their monster optimisation study of 1976.
Summary
We have seen that Hütter wrote elegantly and very relevantly about the wind & site studies of his time, and that he used the main results for designing his turbines. Yet, he did not seem to contribute direclty to the field, but showed interesting and convincing test results based on his prototype open air testing.
Comments/suggestions are welcome,
Rémi.
