08 lossen bosch solar energy

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

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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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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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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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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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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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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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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Results for the different mounting configurations Results for the different mounting configurations

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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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... So far, only sunny days were analysed

Bifacial Performance for different weather conditions


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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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Bifacial gain on a day with white clouds (28.05.)Bifacial gain on a day with white clouds (28.05.)

2.29Bifacial


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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Bifacial gain on a cloudy day (31.05.)Bifacial gain on a cloudy day (31.05.)

2.29Bifacial


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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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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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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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


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BMU for funding of hoch n Solar under the contract FK 0325369B

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Thank you for your attention!


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08 lossen bosch solar energy

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