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Flux Mapping of the Beam Down Solar Thermal Concentrator at Masdar City. Steven Meyers, Marwan Mokhtar, Peter Armstrong, Matteo Chiesa Laboratory of Energy and Nano -Science (LENS) Solar Energy Group . Outline. Flux Mapping Basics Beam Down Solar Thermal Concentrator Initial Results - PowerPoint PPT Presentation
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© November 2009 Masdar Institute of Science and Technology. All rights reserved.
Flux Mapping of the Beam Down Solar Thermal Concentrator at
Masdar City
Steven Meyers, Marwan Mokhtar, Peter Armstrong, Matteo ChiesaLaboratory of Energy and Nano-Science (LENS)
Solar Energy Group
Outline Flux Mapping Basics Beam Down Solar Thermal Concentrator Initial Results Forward Optical Model Bidirectional Reflectivity Distribution Function Convolution Model Results Discussion
Page 2
Flux Mapping Basics
SolarPACES 2011 Page 3
• Flux Mapping – A method to determine the distribution and quantity of concentrated solar radiation generated by a CSP facility
•Three Basic Tools• CCD Camera • Diffuse Reflector (Lambertian)• Heat Flux Sensor (HFS)
•CCD Camera –Luminance Map (cd/m2)• 300-750 nm
•HFS – Discrete flux measurement (kW/m2)• 300-3000 nm
•Conversion ratio (kW/cd)•Yields a continuous flux map of (kW/m2) Kaluza and Neumann, 1998
Diffuse Surface
Page 4
•Lambert’s Cosine Law (Lambertian surface)• The measured radiation intensity by an ideal diffusing surface is directly
proportional to the cosine of the angle between the observer’s line of sight and the surface normal (Photometria, 1760).
Source: www.odforce.net
•If the surface obeys Lambert’s Cosine Law, the radiation angle of incidence (AOI) and azimuth are inconsequential
•However, if the surface does not perfectly follow the Law, the reflected radiation to a stationary observer will change based on the radiation AOI and azimuth
SolarPACES 2011
The Beam Down Solar Thermal Concentrator (BDSTC)
Page 5
Central ReflectorStructure
CCD Camera Location
Heliostat Field
Target Receiver
100 200 300 400 500 600 700 800 900
100
200
300
400
500
600
700
800
900
15
HFS Location
N
•Designed by Tokyo Tech, constructed by MES•100 kW/m2 peak flux at a net incident energy of 100 kWt•Flux measurement instrumentation
• Thermally regulated CCD camera (Konika Minolta CS-2000)• Eight in-situ calibrated (Mokhtar et al. 2011) Head Flux Sensors (Medtherm - Gardon,
Schmidt-Boelter)• Diffuse Reflecting Target (sandblasted unglazed tile)
•Goal – Determine the conversion coefficient to generate a flux map (HFS/CCD)
37
WE
SolarPACES 2011
Initial Results
Page 6
AM (blue) PM (red)
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 1
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 2
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 3
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 4
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 5
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 6
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 7
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 8
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 1
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 2
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 3
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 4
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 5
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 6
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 7
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 8
• Increasing trend due to spectral sensitivity differences between CCD camera and HFS
• (Kaluza and Neumann. 1998, Ulmer et al. 2002)
SolarPACES 2011
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
0
5
10
15
20
25
Air Mass
Devi
atio
n (%
)
Spectral Influence on HFS/CCD Ratio
Kaluza and Nuemann - 1998Ulmer et al. - 2002
Beam Down Optics
Page 7
• The 360 degree field of heliostats contribute significantly different radiation quantities over the day
•Not observed in north field dominant towers and dishes due limited changes in cosine loss
•Needed to quantify the changing levels of radiation contribution from each heliostat over the day
SolarPACES 2011
Optical Model Combined heliostat efficiency
Radiation Angle of Incidence on the Receiver
Radiation Azimuth direction
Mean AOI and Azimuth
Assumed Gaussian flux profile (no astigmatism)
Page 8
CCD Camera
HFS
X HFS
Y HFS
Y CR
X CRZ CR
AOI recφrec
CRMirror
SolarPACES 2011
Optical Model
Page 9
-60 -40 -20 0 20 40 60
-150
-100
-50
0
50
100
150
Hour Angle
Dire
ctio
n (D
egre
es) f
rom
Nor
th
Change of Mean Radiation Azimuth
HFS1HFS2HFS3HFS4HFS5HFS6HFS7HFS8
-60 -40 -20 0 20 40 600
0.5
1
1.5
2
2.5
3
3.5
Hour Angle
AO
I fro
m N
orm
al
Change of Mean Radiation AOI
HFS1HFS2HFS3HFS4HFS5HFS6HFS7HFS8
SolarPACES 2011
BRDF• Lambertian assumption?• A Bidirectional Reflectance
Distribution Function (BRDF) was constructed
Page 10
Source: NIST
( ) ( , )[ ( , )]( ) cos( ) ( )cos( )
r r r r ri r
i i i i i i i i
dL dLBRDF fL d L d
SolarPACES 2011
BRDF Results indicated a significant backscatter reflectance,
consistent with a rough diffuse surface (Oren-Nayar model)
Page 11
-30 -20 -10 0 10 20 300.7
0.8
0.9
1
1.1
Theta - Detector
Nor
mal
ized
Ref
lect
ivity
10 AOI Lambertian Test
Measured DataCosine Law
-40 -20 0 20 400.7
0.8
0.9
1
1.1
Theta - Detector
Nor
mal
ized
Ref
lect
ivity
15 AOI Lambertian Test
-40 -20 0 20 400.7
0.8
0.9
1
1.1
Theta - Detector
Nor
mal
ized
Ref
lect
ivity
20 AOI Lambertian Test
-50 0 500.7
0.8
0.9
1
1.1
Theta - Detector
Nor
mal
ized
Ref
lect
ivity
25 AOI Lambertian Test
-60 -40 -20 0 20 40 600.7
0.8
0.9
1
1.1
Theta - Detector
Nor
mal
ized
Ref
lect
ivity
45 AOI Lambertian Test
0 20 40 60 800
0.2
0.4
0.6
0.8
1
1.2
Theta - Detector
Nor
mal
ized
Ref
lect
ivity
Normal AOI Lambertian Test
SolarPACES 2011
BRDF
Page 12
Sun – AfternoonCCD Camera
θ θ
Peak Reflection
Reflected Ray Measured by CCD Camera
South East North West
L L
SolarPACES 2011
Convolution By convoluting the optical
forward model with the BRDF, we can estimate the quantity of light which is measured by the CCD camera (Fmodel )and compare that to predicted light assuming a true Lambertian surface (Flambertian)
Page 13SolarPACES 2011
Results
Page 14
1 2 3 412
14
16
18
Air Mass
HFS/
CCD
HFS1
1 2 3 48
10
12
14
Air Mass
HFS/
CCD
HFS3
1 2 3 410
15
20
Air Mass
HFS/
CCD
HFS5
1 2 3 46
8
10
12
14
Air Mass
HFS/
CCD
HFS7
1 2 3 40.948
0.95
0.952
0.954
0.956
Air Mass
Fm/F
l
HFS1
1 2 3 40.95
0.952
0.954
0.956
0.958
Air Mass
Fm/F
l
HFS3
1 2 3 40.955
0.956
0.957
0.958
Air Mass
Fm/F
l
HFS5
1 2 3 40.95
0.955
0.96
0.965
Air Mass
Fm/F
l
HFS7
Fmodel / (Flambertian) Original Data
West WestEast East
AM (blue) PM (red)
SolarPACES 2011
Discussion The AM/PM trend correlates to the HFS located on the East or
West side of the Diffuse Surface
By applying this methodology to many points across receiver (x,y), compensation for any non-Lambertian reflections allows for proper extraction of the flux levels on the surface and not the light levels reflected to and measured by the CCD camera
A homogeneous Diffuse Surface BRDF is critical to the success of this method
Page 15SolarPACES 2011
𝑘𝑊𝐶𝑑 𝑥 , 𝑦 ,𝜔𝑠
=(𝐻𝐹𝑆𝐶𝐶𝐷 )𝜔 𝑠
∗𝐹𝑚𝑜𝑑𝑒𝑙 (𝑥 , 𝑦 ,𝜔𝑠 )
𝐹𝑙𝑎𝑚𝑏𝑒𝑟𝑡𝑖𝑎𝑛 (𝑥 , 𝑦 ,𝜔𝑠 )
Limitations Assumed Gaussian flux distribution
and no astigmatism Modeled BRDF function valid for
only one location, not entire surface Inconsistent inter-HFS/CCD ratios
due to non-uniform tile surface (poor conditioning) HFS 2 had minimal AM/PM
difference – Measured BRDF was very
Lambertian HFS 5 had significant AM/PM
difference – Measured BRDF showed large back
scattering reflection
Due to non-uniform tile surface, we were unable to generate an accurate flux map
Page 16
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 1
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 2
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 3
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 4
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 5
1 2 3 4
10
15
20
Air MassH
FS/C
CD
(W/C
d)
HFS 6
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 7
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 8
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 1
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 2
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 3
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 4
1 2 3 4
10
15
20
Air MassH
FS/C
CD
(W/C
d)
HFS 5
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 6
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 7
1 2 3 4
10
15
20
Air Mass
HFS
/CC
D(W
/Cd)
HFS 8
SolarPACES 2011
Conclusion Method can be used to
minimize errors caused by non-ideal Lambertian surfaces
Simple forward optical model and BRDF can provide significant insight into the changing radiation measured by the CCD camera
Allows for less precise (cheaper, more rugged) surfaces to be used for flux analysis, as long as they are homogeneous
Page 17SolarPACES 2011
Thank you
Page 18
Questions?