This article is the fourth 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 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.
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.
Johannes Juul is very famous for having designed, engineered and operated three wind turbine prototypes, the Vester Egesborg- (1950), Bogø- (1952), and Gedser turbines (1957). The Gedser turbine, a three-bladed upwind turbine, was consequently refurbished at the RISØ test site during the 1970’s and, in parallel to that, Juul’s work formed the basis of the design of Danish wind turbines. Some aspects of this fascinating story can be found in English on a couple of websites and in many books, yet most of the details I could find are from documents in Danish, see for instance what I could receive from the Energy Museum in Bjerringbro: “Johannes Juul and his wind turbines” and “A Danish electrician“. Juul, born in 1887, was one the younger students of Poul LaCour, with whom he worked on the first electrified windmill at the turn of the 20th century. He then pursued a carrier as an electrician, and only went on designing wind turbines after the second world war (note that in 1949, he was then 62 years old). For writing this article, I have used the following references:
- [Juul1949] Investigation of the Possibilities of Utilisation of Wind Power” (1949). |Link|.
- [Juul1952a] “Report on the Results Achieved with SEAS experimental Mill” (1952).|Link|.
- [Juul1952b] “Supplement to the Report on the Results Achieved with SEAS’s experimental Mill” (1952). |Link|.
- [Juul1953] “SEAS’s Examination of Windpower in 1952: Change of a Wind Power Mill from Direct Current to Alternating Current Production” (1953). |Link|.
- [Juul1956] “Wind Machines” (1956), “Arid Zone Research – VII. Wind and Solar Energy. Proceedings of the New Dehli Symposium” (1956) by the
United Nations Educational, Scientific and Cultural Organization (UNESCO). |Link|. - [Juul1961] “Design of Wind Power Plants in Denmark“, in “Proceedings of the United Nations Conference on the New Sources of Energy. Solar Energy, Wind Power and Geothermal Energy. Rome, 21-31 August 1961. Volume 7, Wind Power” by United Nations (1964). |Link|.
- [Juul1962] “Development, Testing and Operation of a 200 kW Wind Power Station in Denmark” (1962). Report of the Windpower Comittee of the Association of Danish Electricity Undertakings (DEF). Copenhagen 1962. |Link|.
In addition, from “Technical papers presented to the Wind Power Working Party” (minutes from a meeting held 1952, but published only in 1954) by the Committe for Productivity and Applied Research, Working Party no.2 (Wind Power) of the Organisation for European Economic Co-operation|Link|, I have used:
- [Juul1954a] “Measuring Wind Velocities at Varying Heights above Ground“.
- [Juul1954b] “Results Obtained with the Experimental Windmill of Sydøstsjællands Elektricitats Aktieselskab-Seas“.
- [Juul1954c] “Conversion of Wind Power Plant from Direct Current to Alternating Current Output“.
- [Juul1954d] “Wind-Power Plants in Denmark“.
See below a map places where Juul carried out his tests and experiments. As you can see most of them are in Southern Zeeland (Sydsjælland), where the Sydsjællands Elektricitets Aktieselskab (SEAS, the utility who supported the work of Juul) was active. Juul himself had his workshop in Køge. He died in Haslev in 1969.
Below are best estimates of the locations of the turbine prototypes, from the information I could find (either from Juul’s articles directly, or from the Internet). I have used the background map “Lavkantkort 1900-1945” from HistoriskAtlas.dk. The Vester Egesborg turbine was located at the South of the city, on a 20m hill next to the fjord (see it spinning here).
The Bogø turbine was located on top of a hill, close to the city.
The Gedser turbine was located at the tip of the Gedser peninsula, close to the coast.
The bibliography listed above includes an english translation of the 1962 report from the Danish Windpower Comittee [Juul1962] who concluded that “steam power provides electricity more cheaply than wind power when the cost of the fuel is less than 17-19 kr/Gcal. The price of fuel at present is 8-9 kr/Gcal and during the last 10 years or so, the average price has been about 13.50 kr/Gcal”. Yet:
J. Juul has declared himself to be in disagreement with the other Committe members regarding the conditions and evaluations contained in Section (4): “Cost of Electricity from Wind Power and from Steam Power” […]. He has therefore been unable to subscribe to the above conclusions.
This episode is discussed in a number of publications, for instance see “The Valuation History of Danish Wind Power” by Henrik Bach Mortensen (Mortensen, 2018), and is not discussed further in this post.
First trials, 1947-1950
The work of Johannes Juul consisted from the start by investigating experimentatly both wind- and turbine-related topics, and included a great deal of testing in wind tunnels and in open field. For instance, [Juul1949] makes a concise overview of the wind conditions over Denmark, as well as the energy sources in Europe, and goes on with some detailed description of the variation of the mean wind speed with height at different mast locations. For each of these, montlhly means are provided as well.
Wind measurement campaigns were carried out at several locations (at the Dalby and Menstrup hills, as well as close to the coast in Masnedsund , Gedser, and Blåvanduk), see the overview on the map above, and the data below.
[Juul1949] contains a detailed description of the measurement devices, which were home-made anemometers (there were no affordable devices commercially-available). I have reproduced the text of the article below, as it worth a read:
The beginning of the investigations was handicapped by the fact that not a single type of anemometer was commercially available and long delivery times were quoted, in addition to very high prices. No other alternative was therefore left than to construct the instruments ourselves. As direct-reading instruments a small alternator with revolving permanent magnet of the type used for cycle lighting was chosen.
[…] The [….] instrument could produce a constant deflection of a voltmeter depending on the speed of the generator. This was then coupled to a small windmill of about 30 cm diameter and it was thus possible to obtain a voltmeter reading proportional to the wind speed driving the mill.
It only remained to carry out the adjustment of the appartus. The only wind tunnel in the country, at the Polytechnic Institute, was found to be small to allow of the adjustment. Another way had therefore to be found. The mill with the generator was mounted at 2 m height on a pole above the radiator of a car with an accurately working speedometer. On a even asphalted road running for a distance of about 2 km through forest, the adjustement was carried out in a perfect calm by driving the car at various speed according to the speedometer, exactly corresponding to the desired wind speeds. By this method, five different anemometers were adjusted and it wad found that those, when placed side by side in natural winds, all registered practically the same wind speed.
Follows a long discussion about experimental aerodynamics and turbine design, where tests at the SEAS wind tunnel (also home-made) are described in details. See a summary below.
Around the Vester Egesborg turbine
Using the results from his first trials, Juul went on and carried out further tests and measurements, at and around the Vester Egesborg turbine (a downwind 2-bladed turbine set up by SEAS) and the Bogø turbine (a three-bladed turbine originally set up by FL Smith, which was redesigned as a upwind tubrine by Juul when SEAS acquired the Bogø power plant); but he carried out experiments elsewhere, see the example of the Masnedsund mast below (see [Juul1954a]). The aim of this experiment was to better characterise the variation of the wind speed with height. The mast was in reality a wind-instrumented pole supporting a powerline crossing the Masned Sound (Sund in Danish).
Anemometers were placed on both sides of the mast (to avoid mast effects), at 5, 15, 35 and 55 m. The measurements were read 25 times at 30 seconds intervals and averaged. This procedure was repeated 50 times, leading to 50 12.5-minutes wind profiles. From these, some are have been plotted in the Figure below. The small wind shear from the offshore directions is clearly noticeable, for instance.
The Vester Egesborg turbine, and what seems like a met mast next to it, is shown in the Figure below (from [Juul1954b]). It was built on top of a small hill, South og the city of Egesborg.
[Juul1954b] highlights the difference in temporal variability betwen the wind- and power production time series when the wind comes from land, and when it comes from the sea, see below.
As always, Juul nicely combined the wind- and power measurements to make sense of the computed vs realised production. He made use of power coefficient curves measured by means of the type of anemometer manufacturered by EDF (see this article), which measured the power of the wind over a given period. Following discussions which took place during the Wind Power Working Group meeting, he suggests that the unsteadyness of the onshore winds leads to a bias in the power curve leading to an understimation of the wind power production for the summer months.
Furthermore, Juul also investigated loads on the turbine, see for instance the thrust below (apologies the Figure is not of very good quality): again, the unsteadyness of the onshore wind conditions are reflected on the loads.
The Gedser and Bogø turbines
From the papers above-mentioned, I could not find further details about Juul’s wind & site studies. Building up on experience on wind turbine design-, construction- and operation, he provides wonderful details about the turbines, yet the wind & sites aspects stay limited to the estimation of the power curve and the comparison of the turbine performances. An interesting Figure from [Juul1961] (the U.N. conference) is provided below, showing a wind map of Western Europe.
Juul’s legacy, and the refurbished Gedser turbine
After the negative outcome of the 1962 Wind Power Comittee, the Gedser continued operating until 1967. Juul passed away in 1969, sadly without ever knowing that his turbine prototype would form the basis of modern wind turbines. As mentioned earlier, the decision was taken in 1974 to refurbished the Gedser turbine and perform a series of tests. These were carried out by people at RISØ, originally a nuclear test facility near Roskilde, which later became the Danish Wind Energy laboratory. The report “Analysis of data from the Gedser wind turbine 1977-1979” by
Per Lundsage, Sten Frandsen and Carl Jørgen Christensen stands is available on the Internet, see a copy on the Aeolians.net library. I intend to dig a bit deeper into this report, when time allows, so as to compare the results herein and the ones from the 1962 report and earlier works from Juul !
Summary
We went through Juul’s early wind & site works, spanning high-level meteorology, measurement technology, analysis of wind profiles and wind turbine testing. Most of the details about these wind & site activities are found in his first papers, up to- and including the testing period at Vester Egesborg. Having gained confidence with his methods, Juul repeated its testing procedures with the Bogø and Gedser turbines. It could be that writings about some these Bogø and Gedser wind & site works are available somewhere, for instance among the few archives papers available at the Energy Museum in Bjerringbro, where I am planning a visit. I’ll try to keep you posted if I find anything !
I hope to have highlighted that the very ingenious and comprehensive work carried out by Juul has in some way or another helped him understand better the design-driving environmental conditions (turbulence for blade loads for instance). Of course, it takes more (much more) than wind & site studies to design good turbines; but it is difficult to do without.
Comments, questions, are welcome.
