fk concentrator outdoor measurements
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1
FK concentrator outdoor measurements
San Diego, August 2013
Maikel Hernández1, Juan Vilaplana1, Pablo Benítez1,2,
Rubén Mohedano1, Pablo Zamora2, Juan C. Miñano1,2, João Mendes-Lopes2
1LPI, USA and Spain 2Universidad Politécnica de Madrid (UPM), Spain
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FK concentrator overview
Optimal spectral design
Latest measurement results
Conclusions
Outline
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FK overview – Spectral design – Measurements - Conclusions
Köhler integration• Two-stages design where input/output stage forms image of a preferred object
point onto a point of the output/input stage• Canonical example: two identical lenses imaging a point source at infinite (plane
wavefronts) onto each other
in out
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Köhler integration in the FK• Advanced concentrator using LPI-proprietary 4-channel Köhler homogenization• POE folds image the sun onto SOE folds, which in turn image the POE folds
onto the square solar cell
FK overview – Spectral design – Measurements - Conclusions
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Köhler integration in the FK• Advanced concentrator using LPI-proprietary 4-channel Köhler homogenization• POE folds image the sun onto SOE folds, which in turn image the POE folds
onto the square solar cell
FK overview – Spectral design – Measurements - Conclusions
6
Köhler integration in the FK• Advanced concentrator using LPI-proprietary 4-channel Köhler homogenization• POE folds image the sun onto SOE folds, which in turn image the POE folds
onto the square solar cell
FK overview – Spectral design – Measurements - Conclusions
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FK compared to other Fresnel concentrators•Higher Concentration-acceptance product (CAP): for a fixed minimum acceptance angle, the FK can concentrate more
Concentration Cg
0
200
400
600
800
1000
1200
0.25 0.5 0.75 1 1.25 1.5
Effective* acceptance angle (deg)
*includes sun finite size, optical losses, and MJ cell photocurrent
FK overview – Spectral design – Measurements - Conclusions
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FK features• Optical depth reduced with respect to other Fresnel systems (0.85<f#<1.2)
Freeform secondary lens (SOE)Fresnel lens (POE)
FK overview – Spectral design – Measurements - Conclusions
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FK features• High concentration • High optical efficiency• High spatial and spectral irradiance uniformity on the cell (high cell
efficiency and long-term reliability)• High acceptance angle (preserves high efficiency at array level)• Low cost optics
P. Zamora, et. al. “Experimental characterization of Fresnel-Köhler concentrators,” J. Photon. Energy. 2(1), 021806 (Oct 16, 2012).
Measured CAP = 0.56
FK overview – Spectral design – Measurements - Conclusions
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FK overview – Spectral design – Measurements - Conclusions
VentanaTM Optical Train:A complete off-the-shelf optics solution by Evonik and LPIusing acrylic POE
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FK concentrator overview
Optimal spectral design
Latest measurement results
Conclusions
Outline
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Spectral transmission issue• Solar cell junctions are series-connected, the goal is keeping balanced
photocurrents for bottom, middle and top sub-cells
FK overview – Spectral design – Measurements - Conclusions
Source: www.emcore.com
+
_
V
I
IL,top
IL, middle
IL, bottom
RS
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Spectral transmission issue• Solar cell junctions are series-connected, the goal is keeping balanced
photocurrents for bottom, middle and top sub-cells
• Best performance is achieved when the concentrator considers spectral characteristics of both sunlight and solar cell
0.000
0.200
0.400
0.600
0.800
1.000
1.200
1.400
1.600
350 550 750 950 1150 1350 1550 1750
dI/d
l (W
*m
-2*n
m-1
)
Wavelength (nm)
AM 1.5 spectrum containing a power density of 900W/m2 3J solar cell EQEs (Source: www.emcore.com)
FK overview – Spectral design – Measurements - Conclusions
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300 500 700 900 1100 1300 1500 1700
wavelength (nm)
300 500 700 900 1100 1300 1500 1700wavelength (nm)
Jsc,k = ∫S(λ)T(λ)EQEk (λ)dλ
Jsc ,top
Jsc ,mid
Jsc ,bot300 500 700 900 1100 1300 1500 1700wavelength (nm)
Concentrator optical transmission T(λ)
EQEtop(λ)
EQEmid(λ)
EQEbot(λ)
300 500 700 900 1100 1300 1500 1700wavelength (nm)
Solar spectrum S(λ)
×
Isc = min{Isc,top , Isc,mid , Isc,bot}
Spectral transmission issue• A careful optical design and good choice of optical materials maximize
energy production throughout the year
FK overview – Spectral design – Measurements - Conclusions
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Tracker angle = 0º
FK
RTP
P. Espinet-González et al., “Triple-junction solar cell performance under Fresnel-based concentrators taking into account chromatic aberration and off-axis operation”, CPV-8 Proceeding, Toledo, Spain (2012).
Spectral irradiance issue modelled
FK overview – Spectral design – Measurements - Conclusions
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Tracker angle = 0.6º
FK
RTP
Spectral irradiance issue modelled
FK overview – Spectral design – Measurements - Conclusions
P. Espinet-González et al., “Triple-junction solar cell performance under Fresnel-based concentrators taking into account chromatic aberration and off-axis operation”, CPV-8 Proceeding, Toledo, Spain (2012).
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Silo
(º)
100
75
50
25
0.4 0.8 1.2
Optical efficiency (%)
Electrical power (%)
FK
(º)
100
75
50
25
0.4 0.8 1.2
Optical efficiency (%)
Electrical power (%)
Spectral irradiance issue modelled
FK overview – Spectral design – Measurements - Conclusions
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FK concentrator overview
Optimal spectral design
Latest measurement results
Conclusions
Outline
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0,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
4,0
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
‐1,6 ‐1,2 ‐0,8 ‐0,4 0 0,4 0,8 1,2 1,6
Power (W
)
Isc (A)
Sun tracking error (degs)
Electrical power (%)
Optical efficiency (%)
P. Zamora, et. al. “Experimental characterization of Fresnel-Köhler concentrators,” J. Photon. Energy. 2(1), 021806 (Oct 16, 2012)
Spectral irradiance issue measured• Measurements confirm the models
FK overview – Spectral design – Measurements - Conclusions
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