Two hypotheses on wind energy

New Development of Wind Energy: Windmills on a Larger Scale
In the summer of 2000, Tvindkraft celebrated its 25th anniversary for cutting the first sod. This first cut was performed by everyone present at Tvind: The Mill Team, teachers and students from the schools; about 300 people digging with whatever was available, from spades to teaspoons. And the construction was thus off the ground.

In the spring of 1978, Tvindkraft took its first turns of honor with the newly mounted wings - while 360,000 visitors that same year leaned their heads back and enjoyed the whizzing of the wings. It was the first of its kind, it was the world's largest - right here in Denmark. It was a striking argument against nuclear power, and for the use of the renewable energy forms.

At that time no other windmills were to be seen, but today - from the cap of Tvindkraft - it is possible to spot the first 100 windmills with the naked eye, merrily converting the energy of the westerly wind to environmentally friendly and green electricity.

The quarter century was marked with a gathering of the old mill builders. There was strong agreement within this assembly that it would be good to make more strong moves for wind energy. They spoke of building for example 50 really big windmills in Denmark.

Only 13% of the electricity in Denmark comes from wind energy, and there are many examples of how wind energy can be produced on a grand scale. One of the outcomes of these joyful hours was the idea for a research project, which could blaze the trail for the production and the erection of big windmills, by formulating some central questions, investigating these and then finding the solutions.

The Application for "The two Hypotheses"
In June 2000, Estate applied to the Foundation for a research project for the development of wind energy. The board of Estate had had two models for big windmill parks elaborated, consisting of 2 MW and 10 MW windmills, with defined specifications for the mills and their conditions for production. The board wished to have it proved or disproved whether these two windmill types could be produced at the stated prices.

Only then would it be possible to plan concretely: Windmill parks - how many, where, and when, who should implement it, who should pay? etc.

The board of the Foundation decided on June 30, 2000, to grant the requested amount for this investigation as a research project of relevance for a renewed development of wind power in Denmark, and thereby also of a development of power plants based on renewable energy, but this time of a magnitude comparable to the traditional power plants run on fossil fuels.

The board of the Foundation emphasized the general interest which the final report of such a project would have, for example within windmill circles.

Hypothesis 1
The hypothesis is that it is possible to produce 2 MW windmills for ½ million US$ each. A number of preconditions form the basis of this hypothesis. Namely:

• that the windmills are erected in windmill parks
• that they are 70 m tall; with a tower consisting of easily transportable units
• that there are three wings, with a wing diameter of 60 m; the pitch of the wings are to be regulated electrically; each wing with its own separate security system; the wings are produced of plywood or another composite material
• that the generator is a synchronous generator with permanent magnets, producing current at 5 to 25 revolutions per minute, and mounted directly on the tower; the wings mounted directly on the generator
• that each of the main components has its own computer for measurements
• that each of the windmills has its own frequency converter and its own computer; here all the measurements are collected; from here the windmill is controlled
• that a sales and management company organizes everything concerning the construction of the power plants
• that all the main components are subcontracted by inviting tenders, are produced at the tender's location, and then transported to the windmill park where they are mounted.

Technical life expectancy for the mills: 50 years.
Yearly output in zone 2: 3,5 GW/year.

Hypothesis 2
The hypothesis is that it is possible to produce 10 MW windmills for 2½ million US$ each.

The following preconditions apply for this hypothesis:

• that the windmills are set up in windmill parks
• that they are 120 m tall; with a tower of reinforced concrete or steel tubes
• that there are three wings, with a wing diameter of 110 m; the pitch of the wings are to be regulated electrically; each wing with its own separate security system; the wings produced of plywood or another composite material
• that the generator is a synchronous generator with permanent magnets, producing current at 5 to 20 revolutions per minute, and mounted directly on the tower; the wings directly mounted on the generator
• that each of the main components has its own computer for measurements.
• that each of the windmills has its own frequency converter and its own computer; here all the measurement are collected; from here the windmill is controlled
• that a sales and management company organizes everything concerning the construction of the power plants
• that the company itself produces the major parts of the windmill. The production should take place where the windmill park will be placed. Smaller items are contracted to the ones with the best tenders.

Technical life expectancy for the mills: 50 years.

Yearly output in zone 2: 15 GW/year.

The Investigations Performed
The investigations have taken place by visiting:

• Anders Grauers, Chalmer's College, Göteborg, Sweden: Generators and frequency converters.
• Martin Winther-Jensen, Risø, Denmark: Wings, mounting, generator, production management.
• Semikron, Nürnberg, Germany: IGBT-controlled frequency converters.
• Preben Maegaard, Nordvestjysk Folkecenter for Vedvarende Energi (North West Jutland People's Center for Renewable Energy), Denmark: Wing construction, generator.
• Yukihiro Kurokawa, Fuji Electric, Frankfurt, Germany: IGBT and control systems.
• Peter Jaimeson, Garrad Hassan, Scotland: Tower construction, wing building, wing mounting, calculus.
• John Armstrong, JA Consult, London, England: Wing construction, production procedures, tower construction.
• Jim Platts, Cambridge University, England: Wing construction, tower construction, development procedures, production procedure, financing, organizing.
• E. Lucetta, Glacier, Shoredam-by-Sea, Brighton: Magnetic bearings and generators.
• Allan Lund Jensen, Tvindkraft, Denmark: Windmill construction, control, electric flow organizing.
• Troels Thomsen, LM Fiberglass, Beijing, China: Wings, prices and production in China and India.
• NEG Micon, Randers, Denmark: Prices and production.
• Vestas, Lem, Denmark: Prices and production.
• Bonus Energy, Brande, Denmark: Prices and production.
• Per Steen Jensen, Viking Management, Denmark: Financing.
• Mike Davis, MeesPierson NV Energy Finance Group, London, England: Financing.
• Miss Gaodan, Dalian Municipal Commission for Foreign Economic Relations, China: Chinese administration assistance.
• Lucy Craig, Garran Hassan Midlands, England: Tower construction.
• Zhang Dehua, Vice Director, Dalian Development Zone, China: Establishment of windmill production.
• Hou Qing Qiang, Dalian New Shipbuilding Heavy Industry, China: Tower and nacelle-production.
• Daosteel, Dalian, China: Production of towers of stainless steel.
• Chi Bing, Foreign Investment Bureau, Dalien, China: Financing of mill production.
• Li Dong, China Construction 8th Div.: Concrete foundations and tower construction.

The Results of the Investigations
The Foundation has not received the final report.

During the investigations, which have taken place in Europe as well as in China, the board has seen it as an obvious opportunity to suggest that the results of the investigations could be used by producers in China. The production of the windmills prove to be much cheaper in China, and regarding windmill production there is no technical limitation in letting the production take place there. Another perhaps more weighty argument is, that in countries like China there is especially a need to show new roads for the production of clean energy. There is a heavy pollution, for example from power plants, and China - a country in the midst of rapid changes - has an enormous and still growing demand for energy. Good, and at the same time big, examples are important here.

The investigation carried out demonstrates where some of the difficulties are to be found when one concretely starts designing mill projects of this magnitude. Some examples:

• There will be a task to secure funding for the very first mill of its kind. It is the very far-sighted venture capital, which has to be found. (Also Tvindkraft only came into being because the Teacher Group paid for everything and supplied manpower)
• It will not be possible to obtain the required type approvals of the mills (ISO 14006) without first producing a prototype - which makes it more difficult to find financing for the prototype. However, the interest surrounding type approvals for windmills is growing.
• The same difficulty concerning financing applies to the required approval of the production apparatus (ISO 9001).
• Many of the components for both types of mills are by no means to be found in production today. This means a new kind of production has to be arranged especially for these mills, and both products and standards have to be developed.
• A special challenge lies in developing a design, which is both possible to construct within the budgets (i.e. lighter and simpler than the designs we know today) and at the same time is new and beautiful. This is the minimum requirement before one can create such big new wind power plants, since they must be a delight to the eye as well as to the mind.

Examples of Possible Solutions of Construction Details
Some of the central decisions concerning the construction lie in the choice of generator, the choice of wing material and the choice of tower construction. The investigations seem to indicate that the most important construction detail is the generator. It must be a slowly revolving, many-poled synchronous generator with permanent magnets. It revolves so slowly that the wings can be mounted directly on the generator. No gear box is needed. This construction is not currently used by the Danish windmill producers. It is used by one German producer, Enercon.

The generator is constructed as two rings, with one revolving around the other. The inner ring is fixed. This is the stator with the coils, where the current is actually induced. The stator ring is mounted directly on the tower with a journal bearing for yawing. Outside the stator the rotor is turning with the permanent magnets. It has to be on the outside so the wings can be mounted directly onto it. Thus, the rotor and the hub in one piece. In this way no actual nacelle ("mill cap") is needed, as the only large component will be the generator. The bearings between the rotor and the stator can be common roller bearings, but possibly magnetic bearings should be used to reduce friction and wear. The magnetic bearings might be combined with the actual function of the generator itself.

The wings are proposed to be made of carbon fiber. This will reduce the weight of the wings to 20% of what they are today, and at the same time the price can be reduced to 80%. Normal wings are rigid so they do not bend uncontrollably in the wind. They are mounted on a wing bearing, enabling them to turn around their own axis. This is called pitch regulation. It will of course be simpler to mount the wings directly onto the hub (the generator rotor). The control can then take place using so-called Passive Pitch Control, where one actually utilizes the fact that the wings are flexible. The trick is then to get them to bend in the right way, so that they hold less pulling force as the wind speed and the number of revolutions increase. The only control of the wings will then be a small flap to stop the mill.

A Possible Future Procedure
A committee consisting of engineers and windmill enthusiasts in consultation with architects and designers is appointed. This group will decide on a feasible and good design.

First a prototype is built for the 2 MW windmill parks. It could possibly be built and tested in China, to keep the expenses for the prototype at a minimum. New ideas will be tested with regard to the construction of the mill, to the generator with a multi-polar system and to wings of carbon fiber. After one year the 2 MW prototype should be finished with its startup corrections and be running well.

Then one can start seeking the ISO 14006 type approval. At the same time the concrete financing of the production of the mill park can be finalized. The contractors can be found, and the production plans be elaborated. Based on this, one can apply for ISO 9001 type approval of the production apparatus. An actual serial production of the 2 MW mills could then be started about two years after the start of construction of the prototype.

The 10 MW windmill prototype is the next task. The financing may be solved by using part of the income from the produced 2 MW mills, and partly by using financing sources who can see that the 2 MW mills are succeeding and who therefore are willing to venture into the 10 MW mill project.

A final report is expected by the end of this year.

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