MicroSiting
(Part I)
UNESCO Desire – Net Project
Roma, 21/02/2007
Roberto Nardi
Wind Research Engineer, Siting & Performance Department
Siting & Wind Analysis
What is micro siting and why do it?
What kind of data do you need for micro
siting?
What are the results coming from the micro
siting activities?
2
What is micro siting?
“Micro siting” is a way to optimize the
park layout in any given site to obtain the
highest production on site.
• Calculate the production
• Calculate the wake losses due to other turbines
• Calculate sound emission from the turbines to the nearest neighbor
• Create a visualization of the park
• Ensure a 20 year design lifetime
All this is something that is done before the
park is erected so you can calculate the
feasibility of the project.
3
Why do it?
This can be said with a few words:
To optimize production and reduce loads
4
Where does Wind Energy come From?
All renewable energy (except tidal and geothermal
power), and even the energy in fossil fuels,
ultimately comes from the sun. The sun radiates
100,000,000,000,000 kilowatt hours of energy to
the earth per hour. In other words, the earth
receives 10 to the 18th power of watts of power.
About 1 to 2 per cent of the energy coming from the
sun is converted into wind energy. That is about 50
to 100 times more than the energy converted into
biomass by all plants on earth.
5
Wind resources 50 metres above ground level
Sheltered terrain
m s¯ ¹
W m¯ ²
Open plain
m s¯ ¹
W m¯ ²
At a sea coast
m s¯ ¹
W m¯ ²
Open sea
m s¯ ¹
W m¯ ²
Hills and ridges
m s¯ ¹
W m¯ ²
> 6.0
> 250
> 7.5
> 500
> 8.5
> 700
> 9.0
> 800
> 11.5
> 1800
5.0 - 6.0
150 - 250
6.5 - 7.5
300 - 500
7.0 - 8.5
400 - 700
8.0 - 9.0
600 - 800
10.0 - 11.5
1200 - 1800
4.5 - 5.0
100 - 150
5.5 - 6.5
200 - 300
6.0 - 7.0
250 - 400
7.0 - 8.0
400 - 600
8.5 - 10.0
700 - 1200
3.5 - 4.5
50 - 100
4.5 - 5.5
100 - 200
5.0 - 6.0
150 - 250
5.5 - 7.0
200 - 400
7.0 - 8.5
400 - 700
< 3.5
< 50
< 4.5
< 100
< 5.0
< 150
< 5.5
< 200
< 7.0
< 400
European Wind Atlas - (c) 1989 Risø National Laboratory, Denmark
6
Wind resources over open sea
Wind resources over open sea (more than 10 km offshore) for five standard heights.
10 m
ms -1
> 8.0
7.0-8.0
6.0-7.0
4.5-6.0
< 4.5
Wm-2
> 600
350-600
250-300
100-250
< 100
25 m
ms -1
> 8.5
7.5-8.5
6.5-7.5
5.0-6.5
< 5.0
Wm-2
> 700
450-700
300-450
150-300
< 150
50 m
ms -1
> 9.0
8.0-9.0
7.0-8.0
5.5-7.0
< 5.5
Wm-2
> 800
600-800
400-600
200-400
< 200
100 m
ms -1
Wm-2
> 10.0
> 1100
8.5-10.0
650-1100
7.5-8.5
450-650
6.0-7.5
250-450
< 6.0
< 250
200 m
ms -1
Wm-2
> 11.0
> 1500
9.5-11.0
900-1500
8.0-9.5
600-900
6.5-8.0
300-600
< 6.5
< 300
(c) 1997 Risø National Laboratory, Denmark
7
For a good micrositing is needed:
•
Min. 1 year of wind data measured
on site
•
Wind direction measurements
•
The wind speed measurements
must be conducted for at least 2
heights → wind shear
•
The measuring height should be
as close to hub height as possible
•
Standard deviation measurements
→ turbulence
•
If possible temperature
measurements → air density
•
A digital 3-D contour map
covering an area of a radius of 5 –
10 km from the site centre
8
In order to do a proper wind assessment
on-site wind measurements are necessary!
•
One full year of measurements
are needed in order to take all
seasonal variations into account.
•
If more than one year of raw data
are used the year to year
uncertainty is taken into account.
•
If the temperature is measured
simultaneity with the wind speed,
it is possible to estimate weather
or not, a high/low temperature
turbine is needed.
•
Wind rose
On site measurements are needed
in order to investigate the wind
regime on site. Wind shear,
turbulence, wind rose, and wind
speed are factors that can easily
change with the complexity of the
landscape.
9
Anemometer mast
The measurement of wind speeds is usually done using a cup
anemometer, such as the one in the picture to the right. The
cup anemometer has a vertical axis and three cups which
capture the wind. The number of revolutions per minute is
registered electronically.
Normally, the anemometer is fitted with a wind vane to detect the
wind direction.
Other anemometer types include ultrasonic or laser anemometers,
hot wire anemometers.
The advantage of non-mechanical anemometers may be that they
are less sensitive to icing.
10
NRG Logger with GSM modem
• standalone wind logger
• automatic data transmission
• data on web
• data in database
• logger network
11
10min Wind data
Data measured every 10sec - but only a mean value for 10min is logged on data logger.
12
Typical Wind Data from a Meteorological Station
The wind data must
include:
1. Date, time, 10 min mean
wind speed and direction
2. 10 min mean standard
deviation
3. Temperature (if possible)
The following parameters
are important to check
the loads from the
turbines:
1. Weibull fit, turbulence
2. Air density
3. Inflow angles
FIELDS DESCRIPTION OF ASCII FILES FOR 10 METER MAST
00480105.N98
01:10 Metric
-------------------- Site Information -------------------Printed: 02-10-1998 14:10:05
- 48
Site Number
- ORSARA DI PUGLIA 1
Client Name
- NEW
Client Code
- ORSARA DI PUGLIA 1
Project
- ORSARA DI PUGLIA 1
Location
-0
Elevation
- 221
Serial Number
-1
Time Zone
Magnetic Declination - 0
- 10
Interval
Sensor Number 1
Sensor Number 2
Sensor Number 3
Sensor Number 4
Sensor Number 5
Sensor Number 6
Sensor Number 7
Sensor Number 8
Sensor Number 9
Sensor Number 10
Sensor Number 11
Sensor Number 12
COD
48
48
48
48
48
48
48
48
48
48
48
48
48
48
48
48
Type - #40 Anemometer
Type - No sensor installed
Type - No sensor installed
Type - No sensor installed
Type - No sensor installed
Type - No sensor installed
Type - NRG #200P Direction Vane
Sensor Type - No sensor installed
Sensor Type - No sensor installed
Sensor Type - No sensor installed
Sensor Type - No sensor installed
Sensor Type - No sensor installed
HH:MM:SS
YY-MM-DD
09:40:00
98-01-05
09:50:00
98-01-05
10:00:00
98-01-05
10:10:00
98-01-05
10:20:00
98-01-05
10:30:00
98-01-05
10:40:00
98-01-05
10:50:00
98-01-05
11:00:00
98-01-05
11:10:00
98-01-05
11:20:00
98-01-05
11:30:00
98-01-05
11:40:00
98-01-05
11:50:00
98-01-05
12:00:00
98-01-05
12:10:00
98-01-05
Offset - 0
Scale - .7636933
2
0
0
0
0
0
2
0
0
0
0
0
TEMP
9.6
10.0
10.0
10.0
10.4
10.4
10.9
10.9
11.3
11.3
11.3
11.3
11.3
11.3
11.3
11.3
VOL_BATT
9.0
9.0
9.0
9.0
9.0
9.0
9.0
9.0
9.0
9.0
9.0
9.0
9.0
9.0
9.0
9.0
Units - m/s
Offset - 0
Height - 0
Units - degrees
WS
WS_STD
1.74
1.53
1.60
1.67
2.16
1.98
1.90
1.74
1.90
2.07
1.82
1.74
1.74
1.98
1.74
1.67
17.90
15.09
14.85
17.09
18.54
20.89
19.47
20.72
19.10
20.89
21.34
20.06
19.95
19.52
19.89
20.16
WDIR
226
228
233
228
231
228
226
229
230
230
232
232
231
228
230
232
Height - 0
Descrp - #40 Anemometer
Descrp - #200P Wind Vane
WDIR_STD
6
8
8
7
6
6
7
6
7
6
5
6
6
7
5
5
13
Weibull fit
F(u) = exp.(-(u/A)k)
A = scale parameter
k = shape parameter
14
The wind rose
•
The wind rose is needed in order to
make the optimal layout.
•
The optimal layout is perpendicular to
the mean wind direction.
•
More than one wind vane should be
used, in order to check for errors in
the direction data.
•
An optimal layout has a closer
spacing perpendicular to the main
wind direction and bigger spacing
along the mean wind direction.
Example (Wind Rose):
Sector A-factor C-factor
1.94
10
1
1.19
5.2
2
1.12
2.7
3
2.19
12.6
4
2.19
13.1
5
1.63
7
6
1.72
4
7
1.96
6
8
1.79
7.2
9
1.38
5.5
10
1.89
7.2
11
2.25
6.8
12
1.48
8.7
Total
Freq.
9.61%
2.43%
1.25%
6.95%
29.47%
9.78%
3.78%
4.12%
7.68%
9.49%
8.20%
7.24%
100.00%
15
Wake Effect
Since a wind turbine generates electricity
from the energy in the wind, the wind
leaving the turbine must have a lower
energy content than the wind arriving in
front of the turbine.
This follows directly from the fact that
energy can neither be created nor
consumed.
A wind turbine will always cast a wind shade
in the downwind direction.
In fact, there will be a wake behind the
turbine, i.e. a long trail of wind which is
quite turbulent and slowed down, when
compared to the wind arriving in front of
the turbine. You can actually see the
wake trailing behind a wind turbine, if
you add smoke to the air passing
through the turbine, as was done in the
picture on the right.
Wind turbines in parks are usually spaced at
least three rotor diameters from one
another in order to avoid too much
turbulence
around
the
turbines
downstream. In the prevailing wind
direction turbines are usually spaced
even farther apart, as explained on the
next page.
16
Park Layout
Ideally, it is suggested to space turbines as far apart as possible in the prevailing wind
direction. On the other hand, land use and the cost of connecting wind turbines to the
electrical grid would tell us to space them closer together. At last the layout will be a
balance between technical and commercial issues.
As a rule of thumb, turbines in wind parks are usually
spaced somewhere between 5 and 9 rotor diameters
apart in the prevailing wind direction, and between 3 and
5 diameters apart in the direction perpendicular to the
prevailing winds.
In this picture have been placed three rows of five
turbines each in a fairly typical pattern.
The turbines (the white dots) are placed 7 diameters
apart in the prevailing wind direction, and 4 diameters
apart in the direction perpendicular to the prevailing
winds.
17
Speed Up Effects (1)
If you take a walk in a narrow mountain pass, you will notice that the air becomes
compressed on the windy side of the mountains, and its speed increases considerably
between the obstacles to the wind. This is known as a "tunnel effect".
So, even if the general wind speed in open terrain may be, say, 6 meters per second, it
can easily reach 9 meters per second in a natural "tunnel".
Placing a wind turbine in such a tunnel should be one clever way of obtaining higher wind
speeds than in the surrounding areas.
To obtain a good tunnel effect the tunnel should be "softly" embedded in the landscape. In
case the hills are very rough and uneven, there may be lots of turbulence in the area,
i.e. the wind will be whirling in a lot of different (and rapidly changing) directions.
If there is much turbulence it may negate the wind speed advantage completely, and the
changing winds may inflict a lot of useless tear and wear on the wind turbine.
18
Speed Up Effects (2)
A common way of siting wind turbines is to place them on hills or ridges overlooking the
surrounding landscape. In particular, it should be always an advantage to have as wide a
view as possible in the prevailing wind direction in the area.
On hills, normally the wind speeds are higher than in the surrounding area. Once again, this
is due to the fact that the wind becomes compressed on the windy side of the hill, and
once the air reaches the ridge it can expand again as its soars down into the low
pressure area on the lee side of the hill.
You may notice that the wind in the picture on the right
starts bending some time before it reaches the hill,
because the high pressure area actually extends
quite some distance out in front of the hill.
Also, you may notice that the wind becomes very
irregular, once it passes through the wind turbine
rotor.
As before, if the hill is steep or has an uneven surface,
it will appears a significant amounts of turbulence,
which may negate the advantage of higher wind
speeds.
19
Turbulence
•
•
•
•
Back ground turbulence;
Wake turbulence, turbulence made
by other turbines.
Close spacing among turbines
gives high wake turbulence hence
high turbulence.
High turbulence reduces the
turbine life time dramatically.
The principle of wake effects in wind farms:
2

D  

V  U 1  1  1  Ct 
 

 
D

2
kX




k = Wake decay constant
Wake loss should be less then 4-5%
U
Slope =
k
V
D
Dw=D + 2kX
Turbine rotor
Wind farm turbulence consists of 2
elements:
Turbine rotor
•
X
•Mean goal of micrositing is to reduce loads and optimise production!
20
Questions
21