08 lossen bosch solar energy
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Increased Energy Yield for Bosch´s n-Type Solar Cells in Bifacial ApplicationSolar Cells in Bifacial ApplicationJan Lossen, Tim Böscke, Hans-Joachim Krokoszinski
bifi PV workshop Konstanz 24 04 2012bifi PV workshop, Konstanz, 24.04.2012
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Increased Energy Yield of Bifacial n-Type Solar Cells
OutlineOutline
Bosch’s n-Type solar cells Bosch s n Type solar cells
Challenges of correct power rating
Outdoor Evaluation
Set-up of outdoor-measurement
Bifacial performance under different mounting conditions
Bifacial performance for different weather conditions
Conclusions
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Increased Energy Yield of Bifacial n-Type Solar Cells
Bosch´s n-Type Solar Cells: Bifacial PERT (J-H)Bosch s n Type Solar Cells: Bifacial PERT (J H)
ARC/Passivation LayerAg Front Grid
n-Type Base (CZ-Wafer)Boron Emitter
n
Passivation LayerTextured Rear Side
Ag Rear GridPhosphorous Back Surface Field
The solar cell is optimized for high front side efficiency at low production costs
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Increased Energy Yield of Bifacial n-Type Solar Cells
Bifacial properties of the cellBifacial properties of the cellJsc
[mA/cm2]Uoc[mV]
FF [%]
Eta[%]
Pmpp[Wp]
F t id 38 94 647 5 79 4 20 0 4 82
(Bosch in-house measurement)
Front side 38.94 647.5 79.4 20.0 4.82
Rear side 34.65 644.4 79.6 17.8 4.29
bifacial ratio 0.89 ~1 ~1 0.89 0.89(Bosch in house measurement)
Reduced Jsc from rear side:
Rear side • higher metallisation fraction• dielectric layer thickness
Front side Rear side
thickness• poorer passivation
Figures : EQE Reflection and IQE measured form front and rear side: All data are measured in an area
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Figures.: EQE, Reflection and IQE measured form front and rear side: All data are measured in an area including fingers, IQE is calculated as EQE/(1-R) without further corrections
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Increased Energy Yield of Bifacial n-Type Solar Cells
Unbiased IV-measurement of bifacial cells?Unbiased IV measurement of bifacial cells?Measurement on golden chuck Chuck Jsc
[mA]Voc[mV]
FF [%]
eta[%]
G ld *
- reflection from the chuck
Golden* 39.12 647.5 79.47 20.13Black* 38.69 647.1 79.35 19.86Combined 39.12 647.5 79.35 20.10
- reflection from the chuck- reduced series resistance
Measurement on black non
∆ 1.1% <0.1% 0.2% 1.3%
A black non conductive chuck yields
(*ISE CalLab measurements)
Measurement on black non-conductive chuck with contact on bus bars
A black non conductive chuck yields correct front side efficiency, but does not reflect operating conditions.
Bosch would favour industry standard a white non-conductive chuck (or a combined measurement)
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Increased Energy Yield of Bifacial n-Type Solar Cells
Set up of outdoor measurement Set up of outdoor measurement Location: Erfurt, CiS Test SiteAngle: 40°
A bifacial module (early stage) and a reference module are mounted next to each other in short circuit condition
Serial number Pmpp[ ]
Isc[ ]
Uoc[ ]
FF [ ][W] [A] [V] [%]
110512_Ref 234.4 8.40 36.69 76.08
110512_BiFa_cov 233.7 8.27 37.88 74.61
Photo of modules on test site
Sequential tracking of the short circuit currents (Isc) every 30 sec Additionally the irradiance, temperature and wind are logged.
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Additionally the irradiance, temperature and wind are logged.
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Increased Energy Yield of Bifacial n-Type Solar Cells
Variation of mounting conditions
The albedo is varied bymanipulation of mounting:The albedo is varied bymanipulation of mounting:The albedo is varied bymanipulation of mounting:
Variation of mounting conditions
RefThe albedo is varied bymanipulation of mounting:manipulation of mounting:1. covered rear side, upper rowmanipulation of mounting:1. covered rear side, upper row2. open rear side above grass
manipulation of mounting:1. covered rear side, upper row2. open rear side above grass3 open rear side above foil
Bifacial
Ref
manipulation of mounting:1. covered rear side, upper row2. open rear side above grass3 open rear side above foil3. open rear side above foil Ref
Bifacial
3. open rear side above foil
4. covered rear side, lower row5 open rear side above grass5. open rear side above grass6. open rear side above foil
E h i ti i k t f Each variation is kept for some days, containing at least one (almost) sunny day
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Increased Energy Yield of Bifacial n-Type Solar Cells
Results for the different mounting configurations Results for the different mounting configurations
80
Yield [A*h] on a sunny day Bifa
Ref
Yield/STC normalized to reference
40
50
60
70
80
ld [A
*h]
1.12
1.24
1.06
1.19
1.1
1.2
1.3
1.4
_nor
mal
ized
0
10
20
30
18.05. cov rear
25.05. open
30.05. white gr up
28.06. cov rear
02.08. open
12.07. white gr down
Yie 1.00 0.98
0.8
0.9
1
18.05.
25.05. open, 30.05. white
28.06.
02.08. open, d
12.07. white d
Yie
ld/S
TC_
The analyised days yield between 50 A*h an 70 A*h for all configurations Normalized (Yield [A*h]/STC normalised to the value of the reference
cov_rear, up
open, up
gr., up cov_rear, down
open, down
gr., down cov_rear, up
up gr., up cov_rear, down
down gr., down
( [ ]/module) shows clear advantage of bifacial configurations: White foil on ground and Installation on upper rack are advantures
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Installation on upper rack are advantures
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Increased Energy Yield of Bifacial n-Type Solar Cells
... So far, only sunny days were analysed
Bifacial Performance for different weather conditions
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Increased Energy Yield of Bifacial n-Type Solar Cells
Bifacial gain on a sunny day (30.05.)Bifacial gain on a sunny day (30.05.)
2.29 Bifacial
Configuration: Open rear side, white ground, upper rack
1 41.61.82
5678
A]
Reference
ratio
1.182
0 811.21.4
2345
Isc
[A
0.40.60.8
012
06:00 09:00 12:00 15:00 18:00
Good signal, plain curves Slightly higher gain in the afternoon Additional gain for very low irradiation angles due to free standing rack
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Additional gain for very low irradiation angles, due to free standing rack
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Increased Energy Yield of Bifacial n-Type Solar Cells
Bifacial gain on a day with white clouds (28.05.)Bifacial gain on a day with white clouds (28.05.)
2.29Bifacial
Configuration: Open rear side, white ground, upper rack
1 41.61.82
5678
A]
Bifacial
Reference
ratio
0.811.21.4
2345
Isc
[A
0.40.60.8
012
06:00 09:00 12:00 15:00 18:00
Noisy signal, due to slight time difference between measurments Very high absolute values for both modules Increased bifacial gain due to increased albedo
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Increased bifacial gain, due to increased albedo
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Increased Energy Yield of Bifacial n-Type Solar Cells
Bifacial gain on a cloudy day (31.05.)Bifacial gain on a cloudy day (31.05.)
2.29Bifacial
Configuration: Open rear side, white ground, upper rack
1.41.61.82
5678
A]
BifacialReferenceratio
0 60.811.2
12345
Isc
[A
0.40.6
01
06:00 09:00 12:00 15:00 18:00
Low absolute values Increased bifacial gain, due to increased albedo
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Increased Energy Yield of Bifacial n-Type Solar Cells
Bifacial gain for different weather conditionsBifacial gain for different weather conditions
Yield/STC normalized to reference
Yield [A*h] on days withdifferent weather
1.24 1.261.31
1.25
1 1
1.2
1.3
1.4
norm
aliz
ed
150
200
250
[A*h
]
0.8
0.9
1
1.1
Yie
ld/S
TC_n
0
50
100
30 05 sunny 28 05 white 31 05 Sum 27 5 -
Yie
ld
Cloudy days yield higher relative gains for the bifacial module, but th d t t ib t t h i t t l b
30.05. sunny day
28.05. white clouds
31.05. cloudy day
Sum 27.5.-31.5.
30.05. sunny day
28.05. white clouds
31.05. cloudy day
Sum 27.5.-31.5.
they do not contribute to much in total numbers The dataset of this experiment is not sufficient for a comprehensive
study
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Increased Energy Yield of Bifacial n-Type Solar Cells
Conclusions from the outdoor evaluationConclusions from the outdoor evaluationDoes it make sense to use Bosch cells in bifacial modules?
Technical:Technical: Module integration with transparent back sheet causes 3-5% additional
embedding losses In appropriated systems this loss can by far be compensated by a higher In appropriated systems, this loss can by far be compensated by a higher
energy yield due to bifacial gain. Above grass +10%, above bright surfaces >20% seem realistic.
CommerciallyCommercially: Today´s PV market prices products only on Wp, but not on energy yield
Proposal to solve the dilemma: p If the community could agree on Standard Bifacial Test Condition (SBTC),
including certain amount of albedo (e.g. 10%), modules might be sold with higher power rating, reflecting better their real value.
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higher power rating, reflecting better their real value.
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Increased Energy Yield of Bifacial n-Type Solar Cells
Acknowledgments:Acknowledgments:Matthias Kugler and Philipp Schinköthe of
CiS Forschungsinstitut für Mikrosensorik und Photovoltaik GmbHfor operating the test site
Bosch´s R&D Team for excellent work, especially:Daniel Kania, Anke Helbig, Thomas Roth, Claus Schöllhorn, Martin Dupke, Patrick Sadler, Matthias Braun, Daniel Stichtenoth, Tobias Wütherich, Reik Jesswein, Dennis Fiedler, Robert Carl, Karsten Meyer
ISC Konstanz for fruitful cooperation on n-Type solar cells in the p ypprojects enSol and hoch-n-Solar
BMU for funding of hoch-n-Solar under the contract FK 0325369B
SE/ECC | 24/04/2012 | © Bosch Solar Energy AG 2012. All rights reserved, also regarding any disposal, exploitation, reproduction, editing, distribution, as well as in the event of applications for industrial property rights.
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BMU for funding of hoch n Solar under the contract FK 0325369B
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Increased Energy Yield of Bifacial n-Type Solar Cells
Thank you for your attention!
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