- 2.1 Slow-Rotating-Windmills
- 2.2 Fast-Rotating-Windmilss
- Actual Situation of the use of wind-electricity
- Problems with windenergy
common carrier - Netzbetreiber
stall - Strömungsabriss
This kind of windmill is used in the USA very often. The typical of this windmills are the rotors
which consists of many wings. This is nescessary to provide a high torque even with very slow wind
speed. So this windmills are used to do mechanical work for example to pump up water. But with the
slow rotating speed it is not possible to produce electricity with high efficiency. So the
electricity is generated with Fast-Rotating-Windmills.
Fast Rotating windmills are the most commen windmill in germany. They are build with 1 to 4 wings.
The most windmills in germany are build with 3 wings. But there are two different types of power
connexion, the direct and the indirect.
The direct power connexion means, that the produced power is directly fed in the electricity
network. Therefore the axle which powers the generator must have a certain rotation speed,
that the produced power have a frequency of 50Hz. That fact leads to a difficult transmission
to make sure that the axle has the right speed even there is high or low wind speed.
The indirect power connexion do not need difficult transmission systems, but it needs more
difficult electronic devices. The principle is to transform the generated alternating
current with any frequency into direct current and transform it back into alternating
current with a frequency of 50Hz.
Because of that the most windmills are connected by indirect power connexion, so a higher range of
windspeed can be used more efficiencly than with direct power connexion.
3. Actual Situation of the use of wind-electricity
From 1990 until 2000 the windenergy-production increased about 200 times in comparison to the
production of 1990. So in 2002 windenergy provided 3% of the whole energyconsumption in germany.
Two years later there were windenergymachines installed with a capacity of about 16.000 MW. This
is about 1/3 of the world wide windenergy-capacity. So in this year the provided windenergy
increases to 4% of the whole energyconsumption. This high increasing rates are caused by the
EEG (renewable-energy-law). The EEG consists of 3 important points concerning windenergy:
Renewable energy must be payed by the common carrier with 8,7 ct/kWh (onshore) or
9.1 ct/kWh (offshore) for at least 5 years. After the 5 years they must pay
5,5 ct/kWh (onshore) and 6,19 ct/kWh (offshore) until 20 years are over.
The common carriers must pay the extansion of the electricity network which are nescessary
to connect the wind farm.
The common carrier must have at least a certain amount of renewable energy in his whole
energy. (2204: 8,3%)
But the EEG is not only the important for the actual situation, but also for future development of
renewable and therefore of windenergy.
In the EEG it is planed to rase up the amount of renewable energie to 12,5% until 2010 and up to 20%
until 2020. That means an installed windenergy capacitiy of about 50.000MW. The most of that power
will be produced by offshore wind farms. So at the moment the companies try to develop big windmills
with about 5MW or more and optimize them to work in offshore wind farms. That means the machines
must be run long times without service under very hard conditions.
4. Problems with windenergy
With windenergy have many problems apppeared. First there are the generally problems of
the efficiency of producing electricity from wind.
The problem is, that windmills can use maximal 59,3% of the kinetical energy of the wind. But to
reach that efficienc the rotor speed must be controled, because the efficiency depends on the
windenergie and the frequency of the rotor.
The regulation is done by two mechanisms.
The wings are rotated a little bit out of the wind, so that the speed of the rotor goes
down or rotated a little bit into the wind, so that speed of the rotor increases.
The regulation is done by planed stalls, which is done by a special wing design.
An other problem is the naturally low energy density of only 300W/m² (300 J crossing 1 m²
Then there are the problems that common carriers have. Their main problem is that windenergy can
not be planed.
E.ON Net Windenergie Report 2005
E.ON Net Windenergie Report 2005
In such cases the common carrier must have normal power plants which can be started very fast to
produce that energy. That, so called energy reserve, is about 90% of the produced windenergy. This
problem leads to an restricted future of the windenergy, because the more is windenergy of the whole
energyproduction the less wind energy can substitute normal power plants. A study has found out,
that in 2020 only 2.000MW of the prognosed 50.000MW will be used to substitue thermal energy.
But there is not only a problem with the variation downwards. Also the variation upwards is a great
problem. The problem is, that the wind farms produces as much electricity with strong wind, that the
electricity network can be temporarly overloaded so the whole power supply may break down. To stop
this risk, the wind farms are not allowed to fed in all the produced power if there are high
windspeeds and the power is lost.
So all in all onshore windenergy in germany cannot be the preffered renewable energy because of
the bed forecasting of power production.
But wind farms which are build offshore may have a better future, because their are more constant
windspeeds and so the forecasting situation and the efficiency is much better.