in

How to evaluate a vertical axis wind turbine?
A good vertical axis wind turbine shall have the following three features: a. high efficiency;
b. over-speed control function; and c. automatic brake(s).

How to assess the efficiency of a vertical axis wind turbine?
It can be easily determined from the appearance of a vertical axis wind turbine. Drag-type
vertical axis wind turbines typically have lower efficiency, while lift-type turbines have higher
efficiency. Even lift-type vertical axis wind turbines vary greatly in efficiency. A well-designed
lift-type vertical axis wind turbine should consider both the aerodynamic design and its
structure. Wind turbines are driven by the wind, therefore even slight changes to the turbine
structure will affect turbine efficiency greatly. Take aircrafts for example. Aircrafts with the
same size but different designs will result in different speeds, load capacity and performances.
to assess the efficiency of a lift-type wind turbine.

What is over-speed control?
Over-speed control functions when the wind speed exceeds the rated wind speed, so the
turbine won’t increase its RPM and output power too much. Turbines may disintegrate in
strong winds, since the RPM is proportional to the wind speed, while the centrifugal force
is proportional to the square of the RPM. The horizontal axis wind turbine can yaw to
reduce the windward area, but the vertical axis wind turbine can not. Therefore the
vertical axis wind turbine must have an over-speed control device.

How many over-speed control methods are available?
There are many kinds of over-speed control methods, such as pitch angle control, reducing
the windward area, dump load etc. However, if dump load is used for over-speed control,
the effective dump load power is related to the cut-out wind speed and rated wind speed
of the vertical axis wind turbine. The formula is:
Effective dump load power ≥ rated power * {(cut-out speed/rated speed)3-1}times
For example: a 3 kW turbine has its rated wind speed at 12 m/s, and cut-out wind
speed 26 m/s, the dump load power ≥ (26/12) 3-1 = 9.2 times, so the dump load
power shall be at least 3 *9.2 = 27.6 kilowatts.

Can over-speed control replace the brake?
No. The over-speed control is not a brake. Over-speed control only ensures the RPM and
output power will not increase too much. Therefore over-speed control can not replace the brake.

What are the types of brakes for vertical axis wind turbines?
Brakes for vertical axis wind turbines come in various types. There are disc brakes and
drum brakes; magnet valve brakes and hydraulic brakes.

How to determine the effectiveness of the brake?
Vertical axis wind turbines have lower rotation speed and higher torque, and the ratio
of the torque at survival wind speed and at the rated wind speed is the square of the
ratio of the respective wind speeds: Torque(survival wind speed) / Torque(rated wind
speed) = (survival wind speed/ rated wind speed)2 The braking torque of magnet valve
brake is restricted by the size of the magnet valve, so it does not have enough braking
torque to stop the wind mill at survival wind speed. Therefore, magnet valve brake
systems need two-stage brakes. The first stage brake works when the wind speed
reaches cut-out speed or slightly higher than cut-out speed, and the second stage is used
to lock the turbine when the survival wind speed is reached. For hydraulic brakes, the braking
torque is large enough for small vertical axis wind turbines, so one-stage brake is enough.

Is short-cut of the generator able to replace the brake of vertical axis wind turbines?
No. Short-cut of the generator can only be used in comparatively low wind speeds for a short
period (a few minutes). It can not be used in very high wind speeds for long time. So it can
not replace the brake. The reasons are: First, the generator does not allow for long time
operation under short cut condition. But usually the typhoon lasts for hours or even longer.
Long time short-cut will cause demagnetization of the generator. Demagnetized generators
can not generate any electricity, and short-cut of demagnetized generator can produce hardly
any reverse braking torque, so the turbine may disintegrate in strong winds. Second, using
short-cut of the generator as a brake is based on the principle that permanent magnet
generators could produce reverse braking torque in short cut condition. Usually a well-designed
permanent magnet generator short-cut current is 5-6 times of its rated current, and the ratio
of the torque at survival wind speed and the rated wind speed is the square of the ratio of
the respective wind speeds:
Torque(survival wind speed) / torque(rated wind speed) = (survival wind speed / rated wind speed)2
It means that the torque from wind mill in high winds is far bigger than the reverse braking torque of a
short-cut generator. For example, a wind turbine with rated wind speed at 12 m/s, survival wind speed
at 60 m/s, in the survival wind speed, the torque from the wind mill is (60/12) 2 = 25 times, so short-cut
of the generator can not replace brakes in vertical axis wind turbines.

How to choose a good location for installation?
A good installation location should be spacious, with no trees, buildings or other obstacles around.
If there are obstacles, the wind direction should be considered. If the environment is complicated,

How to choose the location and tower height for roof top installation?

What is Vertical Axis Wind Turbine compared with traditional horizontal axis wind turbine?
If the pivot of the turbine is vertical to the ground, then it is a vertical axis wind turbine, vice
versa. Most of the wind turbines, the ones with three blades that we see frequently today are
horizontal axis wind turbines.

Why vertical axis wind turbines make much less noise than horizontal axis wind turbines?
The cause of noise is mainly because of blades cutting through air flow. However, air flow
through vertical axis wind turbine is different and the rotation speed is much lower. As a
result, it produces much less noise, almost no noise at all.

Why are our products most advanced?
The design and development of the products followed a strict process. Firstly, we verified
our ideas by relevant theories, and then conducted computer facilitated simulation (CFD).
When choosing materials, we calculated, compared and adjusted intensity of various types of
materials. Before finalizing the design, each new product has to go through countless
experiments in wind tunnel to further prove its functions. We already have 9 international
invention patents resulted from the research. So Aeolus is the leader in the vertical axis wind
turbine section of the industry with cutting edge products and it is the only one who has
successfully transferred the technology to manufacturing.

Who are the potential users of vertical axis wind turbine?
As it has advantages such as lower noise, it can be used in both rural and urban areas given
the local wind and site conditions fit. Public lighting, monitor controlling system, oil fields
and other city facilities and commercial purposes could use our products as well. Because
wind directions don’t affect the function of the equipment, so it works even better on
yachts, islands, offshore oil fields where wind is more turbulent.

How to choose the capacity of the wind turbine group?
Generally speaking, capacity = rating load power X (1.3 -1.5),  depends on the  local wind
resources.

How to choose the capacity of the accumulator?
This formula could help to calculate: =daily usage x number of days without wind power /
number of accumulators / voltage of the accumulator

What are the Dos and Don’ts in installation?
1. Don’t incur any scratches on the surface of the equipment to prevent rust.
2. Keep blades parallel to the vertical axis when installing.
3. Screws should be reinforced with fixing glues after being screwed tightly
4. The main axis should be vertical to the ground.
Please refer to the Installation Manuel for detailed instructions.

How to get Aeolus products?
Please email to sales@sawt.com.cn or call 86 21 57246161 for product inquiries.

Copyrights 2006 Shanghai Aeolus Windpower Technology Co. Ltd.