System and method for monitoring wind characteristics

A system for investigating the variation of one or more wind characteristics within a volume over a given area comprises a plurality of detectors which output a data signal which is indicative of the value of a wind characteristic, the outputs of all the detectors deployed in the area are relayed to a central receiving unit which may include a recorder for recording the relayed data and may additionally provide a computer and a VDU for providing a real-time display of the data. Preferably each detector comprises a balloon or kite-like device each of which is tethered to one of a plurality of anchor points distributed around the area.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a method and apparatus for monitoring wind 
characteristic, such as wind speed, wind direction and air pressure within 
a volume above an area of land. 
The invention is primarily aimed at but not limited to providing services 
for manufacturers, operators and investigators in wind plant, to monitor 
existing wind farm sites and also to establish the suitability of proposed 
sites. The invention may allow the modelling of wind flow and equipment 
turbulence. 
Another field in which the present invention may have utility is the 
detection of micro bursts and critical wind shears at airports. 
2. Description of the Related Art 
The siting of wind energy conversion plant has a direct impact on its 
operating efficiency and profitability. However, current practice in the 
industry for siting, often relies upon intuitive judgement based upon 
relatively sparse wind speed measurements and extrapolation along 
topographical features such as hill crests, valleys and the like. Trial 
and error methods based on actual performance are also used. 
More dense ground coverage by conventional anemometers and the like is 
often considered too expensive and impractical for site evaluation. 
Current practices at established wind farm sites may limit the locations 
of anemometers to the wind plant sites only. 
A further problem with wind farms is the effect that the wind plant has on 
the wind field itself. The extraction of wind energy, coupled with the 
turbulence caused by supporting towers, nacelles etc., changes the actual 
wind field characteristics relative to that estimated prior to the 
existence of the plant. 
It is an object of the present invention to alleviate some or all of the 
above-mentioned problems so that siting of wind energy conversion plants 
can be optimized for any given topography, wind regime and wind energy 
conversion equipment. 
It is another object of the present invention to enable data indicative of 
the magnitude of wind characteristics within a volume to be collected at 
frequent and regular intervals with respect to easting, northing, 
elevation and time. 
It is another object of the present invention to permit accurate imaging of 
what are termed "wind pressure waves". These waves can be imagined when 
thought of as waves blowing across a wheat field. These waves are 
important to wind farm operators as they are the manifestation of the wind 
irregularity that reduces the quality of electrical power sold by wind 
farms. The form of these "wind waves" has a very strong linkage to the 
ground topography, wind direction and speed. Consequently, they are very 
hard to predict and model. The present invention enables measurement of 
these wind waves directly and therefore allows appropriate siting of 
plants so as to minimize the effects of machine induced turbulence, 
thereby improving the overall efficiency of the wind farm. 
It is another object of the present invention to optimize the siting of 
wind plant in both existing wind farms and proposed wind farms. 
It is yet another object of the present invention to permit the detection 
of desirable wind energy "hot spots" and unwanted turbulence zones or 
areas of low wind speed. 
It is still another object of the present invention to provide the means 
for recording a large body of wind characteristic data, thereby allowing 
large scale academic and scientific research to be carried out using the 
recorded data. 
It is still another object of the present invention to provide a data 
acquisition method, digital electronic data recording and storage means, 
high speed data processing and computer aided visualization means. 
It is another object of the present invention to monitor the magnitude of 
at least one wind characteristic over a large area without requiring a 
proportionally large number of wind characteristic measuring means. 
It is another object of the present invention to provide an array of wind 
characteristic measuring means in which the measurement provided by each 
measuring means is not perturbed by the presence of the other wind 
characteristic measuring means within the array. 
It is another object of the present invention to allow for much denser and 
more regular coverage and much more frequent time sampling than has 
hitherto been possible. 
It is still another object of the present invention to allow the deployment 
of large numbers of simple and low cost detectors. This deployment can be 
at any elevation above ground, dependent upon the scope of the survey 
objectives. 
It is another object of the present invention to permit deployment of 
detectors at regular intervals in orthogonal directions such that .delta.X 
and .delta.Y can each be held constant. This will ease the task of any 
consequent numerical modelling or analysis. As the ground area is 
adequately covered by a uniform lattice, the gradient, divergence or curl 
of the characteristic field can be calculated. For example, if the 
characteristic is pressure, then the gradient is the wind velocity field 
(i.e. speed and direction) Similarly, if wind speed is being measured, 
then the gradient of the speed surface may be thought of as the direction. 
SUMMARY OF THE INVENTION 
The invention herein described may be utilized, in particular, in two 
preferred modes of operation. 
Firstly, the invention may be deployed over an area of land, such that a 
model can be built to show wind flow over a given area of land for a 
number of wind speeds and directions. Interpolation and extrapolation can 
be used to model all eventualities. 
Secondly, the invention can be deployed around a specific piece of wind 
energy conversion equipment. The purpose of this is to determine the exact 
shape of the effective turbulence zone, emanating from the equipment for 
all wind speeds. This will provide certifiable data, specific to any piece 
of equipment. 
In preferred embodiments of the present invention, the plurality of wind 
detectors in the apparatus are arranged into one of a number of preferred 
configurations. Some embodiments of the invention involve locating the 
array of wind characteristic measurement means at a first location, 
gathering wind characteristic data at that location and then subsequently 
redeploying the array at another location. By redeploying the array in 
several locations within a particular area, and subsequently collating the 
data from each of those locations, wind characteristic data throughout the 
area to be investigated can be obtained. 
In a preferred embodiment, data from the area is logged over a period of 
time on a recording means, and that recorded data may be subsequently 
analyzed. The recorded data may be down-loaded to another recording means 
so that it can be down-loaded to a different location for analysis. 
Alternatively, the recording means itself may be transported to a 
different location for analysis. 
The electrical output of the detectors may be calibrated by the use of more 
sophisticated and accurate devices placed at strategic locations within 
the survey area. This calibration may be performed by Fourier analysis and 
decomposition of the time series signals produced by the simple detectors 
with respect to the calibration signals. This calibration can take place 
any time after the signals are recorded. Preferably, the plurality of wind 
characteristic measuring means are arranged into one or more lines. The 
height of the detectors in one line may differ from the height of the 
detectors in another line. For example, if two lines of detectors are 
deployed with the detectors at two different respective heights and the 
two lines are arranged to coincide on the ground, then the detectors will 
be arranged into a wall configuration. This configuration may be 
particularly useful for investigating the turbulence caused by a 
particular piece of wind energy conversion equipment. 
Alternatively, the two lines of detectors may be spaced parallel to one 
another, thereby being arranged into a ramp configuration. 
In either of the above cases, the presence of one line of detectors does 
not effect the measurements of the other line of detectors. 
Advantageously, the apparatus of the present invention may be deployed as a 
line, a wall or a ramp. Any of these modes can be utilized such that when 
there are sufficient data collected at any given position, the whole array 
can be moved incrementally to cover a different area of ground. In this 
way, much larger areas can be covered than would otherwise be permitted by 
a given number of detector devices.

A DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
Referring to the drawings, FIG. 1 shows an array of detectors 1 deployed in 
a spatially regular manner over an area of land. The detectors are 
supported and held in a generally vertical position by a support means 2. 
The height of the detectors 1 above the ground can be adjusted by 
adjusting the height of the support means 2. The electrical output from 
the detectors is transmitted via telemetry or wires 3 to a local line 
control unit 4. The line control units incorporate internal data storage 
means in addition to process control means and are connected via telemetry 
or wires to a central recording and control unit (RCU) 5. The RCU 5 has 
data links to various recording means 6 and an additional computer 7. 
Attached to the computer 7 are a further recording means 8, computer screen 
video display unit 9, keyboard and mouse 10 and paper printing means 11. 
The line control units 4 and the recording and control unit 5 may have 
means to multiplex and demultiplex the electrical signals from analog to 
digital format and from digital format to analog. Similarly, the computer 
7 may also have means to multiplex and demultiplex from analog to digital 
format and vice-versa. In addition, the computer 7 will possess means to 
record data onto various storage means 8, reproduce data from recording 
media 8, process data using computer programs and record the results on 
storage means 8, display the results on video screen 9 or paper printing 
means 11. 
The components numbered 1 through to 6 may be capable of operating in 
isolation from the components numbered 7 through to 11. This allows the 
computer to be used either for the processing of previously recorded data 
or for the real-time monitoring of data which is currently being recorded. 
The processing equipment receives data from the detectors 1 and processes 
this data to enable an operator to identify an optimum position or 
positions for a wind farm. 
An alternative wind characteristic measuring means is shown in FIG. 2. The 
measuring means comprises an anchor module 51 which is arranged to be 
secured to the ground. An umbilical tethering device 52 of variable and 
controllable length rises upwards from the anchor module 51. This tether 
52 consists of a shielded electrical conductor 53 encased in a tube 54. A 
balloon 55 filled with lighter-than-air gas is attached to the uppermost 
end of the tube 54. The tube 54 is arranged to be capable of transporting 
the lighter-than-air gas to the balloon 55. 
Supported by the balloon 55 is an antenna 56, electrically connected to the 
conductor 53. The antenna 56 is specifically dimensioned so as to act as 
the antenna of a rover component of a differential Global Positioning 
System (GPS). The electronics associated with the rover are housed in the 
anchor 51. 
In use, a number of detectors (FIG. 2) are deployed in an array. One or 
more base stations 57 are then deployed at known geographical positions 
close to the array. Both the base stations 57 and the rovers receive radio 
transmissions from satellites orbiting the earth. This is conventional GPS 
methodology. 
A second preferred embodiment of the present invention is shown in FIG. 3. 
In this embodiment, three lines of detectors (FIG. 2) are deployed on the 
leeward side of the wind turbine 61. Each line (58,59,60) of detectors 
comprises three detectors. Each of the detectors in the first line 58 has 
its tether 54 set to a length which results in the height of the balloon 
55 being in the lowermost region of the height range being investigated. 
Each of the detectors in the second line 59 has its tether 54 set to a 
length which results in the balloon 55 of those detectors being disposed 
at a height approximately in the middle of the height range being 
investigated. Finally, each of the detectors in the third line 60 has the 
length of its tether 54 set to a height in the uppermost region of the 
height range being investigated. The three lines 58,59,60 are arranged to 
coincide, that is to say that the anchor modules of the detectors of the 
lines 58,59,60 are disposed along a straight line. The detectors are 
thereby arranged in a wall configuration, whereby the measurement provided 
by any one detector is not affected by the presence of the other 
detectors. 
The base station 57 comprises a signal receiving means (not shown) and a 
signal data recording means (also not shown). 
The base station 57 and rovers incorporate an electronic multiplexing 
system, such that each rover is interrogated at fixed time intervals. 
The maximum value of the sample time interval is determined by the minimum 
turbulence wave length to be detected. For example, commercial wind 
turbine equipment has a diameter of 10 meter:i, and is unlikely to be 
effected by turbulence wavelengths of less than a few meters. 
If V is the wind speed at which measurements are to be made and L is the 
minimum desired turbulence wavelength to be measured, then the minimum 
sampled time interval for each rover station is given by: 
##EQU1## 
The minimum measurable turbulence wavelength is also determined by the 
physical dimensions of the balloon 55. For example, a balloon 55 of 
diameter 1 meter is unlikely to be effected by turbulence cells of 10 
centimeter wavelength or less and wind turbine of 40 meter diameter is 
unlikely to be effected by a turbulence wavelength of 1 meter or less. 
For example, given the extreme requirements of L=2 meters and V 20 meters 
per second, then all rover stations must be sampled within a time of 25 
milliseconds. This is termed the "Half Nyquist" sample interval and 
represents the largest sampling interval permitted to completely define 
the wavelength in question. The above described embodiment is arranged to 
operate in a "Recording Only" mode. 
In this mode, raw satellite data received by the antenna 56 of the rovers 
is transmitted to the base station 57 where it is recorded for future 
analysis. 
Once data representative of the turbulence created by the wind turbine has 
been recorded, the array can be moved to successively spaced positions 
behind the wind turbine 61, The data obtained from each of these positions 
can be collated to build up data representative of the turbulence zone 
around the wind turbine. This method of utilizing the detectors enables a 
small number of detectors to be used to provide data representative of 
wind Characteristics over an area larger than the area that can be covered 
at any one time by that number of detectors. 
Alternatively, the system can be operated in "Real-Time" mode. In the 
Real-Time mode, the base station 57 additionally comprises the components 
7 though to 11 already described in relation to the first embodiment. 
On deploying such a system, the positions of the anchors 51 are determined 
precisely and this information is entered into the computer 7 via the 
keyboard 10. Additionally, for each anchor 51, the length of deployed 
umbilical 52 is also determined precisely and made available via the 
keyboard 10 to the computer 7. Computer programs in the computer then 
operate on the keyed-in data and the data relayed by the rover components 
to establish, for each detector, the horizontal/vertical deviation of the 
balloon 55 relative to the anchor module 51. Subsequently, the computer 
program compares this deviation with the wind-speed-versus-deviation 
characteristics for the geometry of the detector to infer instantaneous 
wind speeds and other turbulence characteristics. 
This data may thereafter be used to provide a Real-Time (less than a few 
milliseconds delay) three-dimensional displays of the response of the 
detectors. For example, the data may be processed to provide a screen 
image of the VDU 9 such that the horizontal axis represents the easting 
coordinate of the detector locations, the vertical axis represents the 
northern coordinates of the detector locations, the individual screen 
pixels being coloured according to the values output by the deployed 
detectors. 
As an alternative, the wind speed and direction may be displayed on the 
screen as arrows or vectors. The blunt end of the arrows are positioned at 
a fixed location on the screen, corresponding to the coordinates of the 
detectors, the length of the arrows representing the magnitude of the wind 
speed, and the direction of the arrows representing the azimuth of the 
wind. 
FIG. 4 shows a third embodiment of the present invention. In this 
embodiment, twelve detectors 2 are positioned in a predetermined regular 
spatial array over an area of land. Each detector comprises a base from 
which a support mast extends upwardly, the support mast supporting an 
anemometer at its uppermost end. Each detector is provided with a means 
for converting the anemometer reading to an electrical signal. 
The twelve detectors are arranged so that their positions form a regular 
grid over the area of land being investigated comprising four spaced 
parallel lines of three detectors, where the spacing between the detectors 
in each line is the same as the spacing between the lines themselves. 
Each of the detectors 2 in the first leeward line of detectors 1D has its 
support mast extended to its full height. Each of the detectors in the 
adjacent line 1C of the windward side has its support mast extended to 
three-quarters of its full height. Each of the detectors in the next 
adjacent line 1B has its support mast raised to one half its full height. 
Each of the detectors in the windward line 1A has its support mast raised 
to one quarter of its full height. 
The anemometers of the array are arranged into a "ramp" configuration, in 
which the regular spatial array of detectors is arranged into a series of 
lines, the height of the detectors in each line being greater than the 
height of the corresponding detectors in an adjacent line on the leeward 
side. This configuration has the result that the measurements of the 
leeward detectors are not affected by the presence of the other detectors 
on the windward side. 
Wires lead from each of the detectors in the two leeward lines 1C, 1D to a 
local line control unit 4. A second set of wires lead from each of the 
detectors in the two windward lines 1A, 1B to another local line control 
unit 4. Both local line control units 4 are provided with radio 
transmitters and are arranged to transmit signals to a common receiving 
unit 5. The receiving unit 5 has connections to data storage means 6. 
In use, the common control unit 5 is arranged to receive signals from each 
detector in turn, the signals being indicative of the reading of each of 
the anemometers. The common receiving unit 5 subsequently relays the 
signals to the recording means 6. In addition, the predetermined positions 
of the detectors in the predetermined spatial array are recorded by a 
person operating the system. Once a set of data indicative of one or more 
wind characteristics within the volume V lying above the area of land X 
has been collected, the spatial array can be moved to the area Y and the 
above process repeated. Similarly, once data from the volume lying above 
that area has been collected, the array can be moved to the area Z and 
data collected for that area also. 
These three sets of data are then collated to form a single set of data 
representative of the magnitude of the wind characteristic over the larger 
area X+Y+Z. It will therefore be seen that a body of data similar to that 
gathered in the FIG. 1 embodiment may be obtained and that fewer wind 
detectors are required to achieve this. 
FIGS. 5A to 5C show preferred configurations of detectors to be employed in 
accordance with the present invention. 
In FIG. 5A the bases of two or more detectors (in this example the type of 
detector shown in FIG. 2) are arranged to lie along a single line, the 
wind responsive part of each detector (in this example the balloon 55) 
being positioned at the same height as the others. This configuration of 
the detectors is known as a "line" configuration. By moving the line of 
detectors to gather new sets of data and collating that data with sets of 
data already gathered, it will be seen that it is possible to gather wind 
characteristic data over a large area with a small number of detectors. 
In FIG. 5B, two or more lines of detectors are utilized. The wind 
responsive part of the detectors in a first line are positioned at a first 
predetermined height, whereas the wind responsive part 55 of each of a 
second line of detectors is positioned at a second predetermined height. 
In addition, the two lines of detectors are arranged to coincide, that is 
to say the anchor module 51 of every detector is disposed along a single 
line. This configuration of detectors is known as a "Wall" configuration. 
This configuration has the advantage that the readings of the detectors 
are not distorted by the presence of the other detectors. 
In FIG. 5C, two or more spaced parallel lines of detectors are provided. 
The wind responsive part 55 of the detectors in the most windward line is 
positioned at a first predetermined height above the ground, whereas the 
windward responsive part 55 of each detector in the line immediately 
leeward of the most windward line is positioned at a second predetermined 
height above the ground. The second predetermined height is greater than 
the first predetermined height, and subsequently windward lines of 
detectors have their wind responsive part set at successively greater 
heights above the ground. Such a configuration of detectors is known as a 
"ramp" configuration. This configuration also has the advantage that the 
readings of the detectors are not distorted by the presence of the other 
detectors.