Development of a large-scale wind turbine with a rated power of 4.5 MW
Autor: Aloys Wobben, Managing Director ENERCON GmbH
Abstract:
In the following, the development of the largest wind turbine worldwide with 4.5 MW will be outlined. This
pioneering project was very challenging and it produced outstanding insights and new results in the field of
large-scale wind turbines. The process from the concept of a wind energy converter to its implementation is
very complex and demands a very precise approach. The strategy, to rely on our longtime experience in
turbine building, has proved successful. In February this year, the third converter of this power class was
erected, three more are under construction, severel others have been planned. Series production is being
prepared.
In the course of the past years we
have come closer to the goal to
achieve a proportion of 25 % from
wind energy in Germany. Presently,
wind energy covers approx. 4 % of the
electricity demand. Particularly the
district of Papenburg (East Frisia) with
a share of 54.2 % of wind energy
shows the feasibility of a far higher
share.
By now, ENERCON has installed more
than 6 GW worldwide and more than
6.900 wind turbines respectively.
Beginning in 1984 with the first
generation of wind energy converters, ENERCON looks back to a longtime experience of nearly 20
years as a developer and manufacturer. The know-how that has grown with it helped to implement
larger and larger projects and finally encouraged to build a turbine of a new power class.
Foundation and Tower
In 2001 the first foundation was built in Egeln (near Magdeburg). Considering the soil conditions and
the loads, the flat foundation was constructed with a height of 5 metres and a diameter of 28 m and
consumed 1600 m³ concrete and 154 t steel. Furthermore, the tower was erected in a height of 124
m and a diameter from 12 m (at the bottom) to 4 m (at the top). 1000 m³ concrete and 235 t steel
were used to build it.
Cast Parts
Most of the major components, such as the hub, blade adaptors, axle pin and the main carrier, are
cast parts which are subject to highest qualitiy standards. Only very few foundries are able to meet
these requirements.
The material used for the cast parts is spheroidal graphite cast iron. Before it came to their
fabrication, the components had been precisely calculated and tested by means of simulation. The
production process itself had been very complex concerning its model construction, mould
construction, casting, removement from the mould, finishing and extensive quality control (structural
investigations, ultrasound and x-ray test).
The example of the main carrier gives an idea of the dimension of this complexity: with its height of
3.4 m, length of 5.5 m and width of 4.3 m it consumed 53 t of steel and 850 tons of sand (for the
mould).
Rotor Blades
Because of the hub height and future offshore applications the rotor blades had been designed for
wind class 1. The structure has been appropriately adapted to the size and intended use in order to
guarantee the stability necessary. All three blades, consisting of epoxy resin and glass fibre, were
put through the stress test, and the deformation, resonant frequency and elongation were
thoroughly analysed before they were finally assembled to the turbine. With a weight of 20 t, a
length of 52 m and a surface of 450 m², these rotor blades needed a purpose-built vehicle to be
transported to the construction site in Egeln (near Magdeburg).
Assembly
The assembly of the 4.5 MW turbine was a challenge on itself. The components of the nacelle were
first assembled on-site into modules, none of which weighed more than 110 t. These were then
lifted by two cranes, sometimes working in tandem, and were then mounted in position. Afterwards,
the generator consisting of the stator and the rotor, the hub, the nacelle cover and finally the three
rotor blades were lifted one by one to a height of 124 m where they were fitted together.
In Operation
By now, the power measurements of the E-112 are finished. Official sound measurements are
carried out when wind blows adequately. Internal measurements are already completed.
With this large-scale wind turbine,
a new dimension in the field of the
generation of electricity from wind
energy has been entered. Its
complexity becomes clear when
considering the monitoring system
which is comparable to a modern
power station. This complete
control of sensors as well as the
operating status is necessary to
guarantee an average technical
availability of at least 98 %.
All components have to be
controlled which means that, in
total, more than 2,700 status
messages can be generated with
respective control measures.
Examples are: oscillations, pitch, generator (e.g. temperature, air gap), azimuth components (e.g.
currents, voltages), the bearings, the main security circuit (e.g. fuses, electronics), the grid feeding
(e.g. phase currents, voltages), etc.
Outlook
The 4.5 MW turbine has set off a new power class. One E-112 is able to generate 15 mill kWh per
year. With this amount, more than 4,000 households (average consumption of 3,500 kWh) can be
supplied. This amount saves more than 97,500 tons of CO2 emissions annually.
The potential of the E-112 is an interesting example: A share of 25 % wind power in the electricity
supply in Germany could be covered by only 7,500 E-112. In other words: distributed to the existing
number of villages (approx. 13,200 à < 20,000 inhabitants), every two villages one E-112 would be
enough to achieve these 25 %. A fact that one should reconsider.