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Bifacial PV modules: measurement

challengesM. Joanny, G. Razongles, L. Sicot, E. Gerritsen, H. Robin, A. Bettinelli,

P. Lefillastre and the CEA team

S. Schroder, P. Lay and the ECM Greentech team

- maryline.joanny@cea.fr

Division of Technological Research

Solar Technologies Department

Laboratory of PhotoVoltaic Modules

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1) Indoor one face

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• OUTLINE - Different measurements possible:

3) Outdoor bifacial2) Indoor bifacial

1) Introduction2) Indoor bifacial method3) Outdoor bifacial method4) Conclusion

Series resistance + on-site parameters

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Indoor STC

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1) Introduction

• First consideration: STC measurement

2) Indoor bifacial method3) Outdoor bifacial method4) Conclusion

Front side measurement1

Back side measurement2

�

�

Iscfront , Pmaxfront , Vocfront…

Iscback , Pmaxback , Vocback, bifacialityIsc…

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Indoor STC

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Gback

1000 W/m²PmaxSTC linear = Pmaxfront + Pmaxback x

monofacial

1) Introduction2) Indoor bifacial method3) Outdoor bifacial method4) Conclusion

Nota : Gback = irradiance on back side (W/m²)

• First consideration: STC measurement

1) the impact of the series resistance on Wp evaluation

2) the impact of the on-site parameters on Wp evaluation

Let’s draw a linear ideal Pmax with the front and back irradiance

It is a preliminary approach that does not consider:

Front side measurement1

Back side measurement2

�

�

Iscfront , Pmaxfront , Vocfront…

Iscback , Pmaxback , Vocback, bifacialityIsc…

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3) Outdoor bifacial2) Indoor bifacial

1) Introduction2) Indoor bifacial method3) Outdoor bifacial method4) Conclusion

Series resistance + on-site parameters

• OUTLINE

1) Indoor one face

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• CEA INES bifacial indoor characterisation set up

Mask

self-monitoring of

irradiance with Isc

Aluminium mirror

Mesh filters gives:

Gback = 230 W/m² or

Gback = 470W/m² or

Gback = 1000 W/m²

Mesh filter

4 cells module

1) Introduction2) Indoor bifacial method3) Outdoor bifacial method4) Conclusion

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monofacial

PmaxSTC linear for 16,7Wp STC 3BB module 88% bifacial (Pmax)

1) Introduction2) Indoor bifacial method3) Outdoor bifacial method4) Conclusion

• Performance evaluation

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Bifacial measurement and STC linear calculation give different values for Pmax�

monofacial

PmaxSTC linear for 16,7Wp STC 3BB module 88% bifacial (Pmax)

Pmaxbifacial measurement

1) Introduction2) Indoor bifacial method3) Outdoor bifacial method4) Conclusion

• Performance evaluation

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• Performance evaluation

monofacial

PmaxSTC linear - Pmaxbifacial meas.

Pmaxbifacial meas.

∆Pmax =

PmaxSTC linear for 16,7Wp STC 3BB module 88% bifacial (Pmax)

Pmaxbifacial measurement

Calculation of :�

1) Introduction2) Indoor bifacial method3) Outdoor bifacial method4) Conclusion

for 3 module architectures 3 bus ½ cells, 4 bus and 3 bus:

∆Pmax = 2,5%

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Highest ∆Pmax is obtained for highest Gback�

Lowest ∆Pmax is for 3 bus ½ cells and is < 1% for Gback < 500 W/m², but is higher for the others modules�

PmaxSTC linear - Pmaxbifacial meas.

Pmaxbifacial meas.

∆Pmax =

1) Introduction2) Indoor bifacial method3) Outdoor bifacial method4) Conclusion

Need to integrate FF consideration�

• Performance evaluation

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→ Decrease of module FF with increase of irradiance

→ FF slopes depends on cell and module series resistance (3 bus ½ cells performs the best)

→ Same FF slope for STC measurement and bifacial measurement

→ Indoor measurement at 3 values of Gfront (700, 1000 and 1200 W/m²) gives confident FF slope

FFmodule

FFcell @ 1000 W/m²

• Evolution of FF with total irradiance

Total

1) Introduction2) Indoor bifacial method3) Outdoor bifacial method4) Conclusion

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• Extrapolation from indoor one face measurementsat 700, 1000 and 1200 W/m²

1) Introduction2) Indoor bifacial method3) Outdoor bifacial method4) Conclusion

� Integration of FF and Voc consideration gives better

Wp evaluation

Gback

1000 W/m²Pmaxextrap. from 700/1000/1200 = Pmaxfront x (1 + bifacialityIsc x ) x x

Voc extrap. from 700/1000/1200

Vocfront

FF extrap. from 700/1000/1200

FFfront

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3) Outdoor bifacial2) Indoor bifacial

1) Introduction2) Indoor bifacial method3) Outdoor bifacial method4) Conclusion

Series resistance + on-site parameters

• OUTLINE

1) Indoor one face

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Bifacial optimized mounting

structure → no shadowing

RENOLIT ALKORBRIGHT

synthetic roofing membrane

CEA bifacial modules: n-type, glass-glass, TPO Apolhya Solar from

CEA INES, Chambéry, France

• CEA INES bifacial outdoor characterisation set up

2 bifacial modules

working with high

albedo

2 bifacial modules

with black screen

for reference use

1) Introduction2) Indoor bifacial method3) Outdoor bifacial method4) Conclusion

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1) Introduction2) Indoor bifacial method3) Outdoor bifacial method4) Conclusion

• Bifacial outdoor measurement

Outdoor monitoring over 13 days (J1 to J13, on April 2015)

Energy Yield

(kWh/kWc)

GFront (W/m²)

GFront (W/m²)

Energy yield bifacial modules /

reference modules

Reference modules

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1) Introduction2) Indoor bifacial method3) Outdoor bifacial method4) Conclusion

• Bifacial outdoor measurement

Reference modules

Monitoring April 21st 2015

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1) Introduction2) Indoor bifacial method3) Outdoor bifacial method4) Conclusion

• Bifacial outdoor measurement

� On-site parameters to be considered:

Reference modules

Need to be linked also

to on-site parameters

• Temperature

Monitoring April 21st 2015

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1) Introduction2) Indoor bifacial method3) Outdoor bifacial method4) Conclusion

• Bifacial outdoor measurement

Reference module

Monitoring April 21st 2015� On-site parameters to be considered:

• Weather (diffuse or reflective) and Gfront - assessed by energy yield results

• Albedo

• Temperature

@25°C (with Tre correction)

Need to be linked also

to on-site parameters

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1) Introduction2) Indoor bifacial method3) Outdoor bifacial method4) Conclusion

• Bifacial outdoor measurement

Assymetry on back side contribution

Reference modules

Monitoring April 21st 2015 � On-site parameters to be considered:

• Weather (diffuse or reflective) and Gfront - assessed by energy yield results

• Albedo

• Temperature

• Geometrical parameters

South

North

EstWest

θ = 17°

4 modules

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1) Introduction2) Indoor bifacial method3) Outdoor bifacial method4) Conclusion

• Summary and conclusion

Wp

Ease of implementation

Series resistance considered

On-site parameters considered

If series resistance are considered

Albedo considered

Geometry/weather not considered

If flash test at 700 for instance +

1200 W/m² are added to 1000 W/m²

Depends on the equation used

The different approaches are complementary and will help building the equation, which is under STC

international discussion, for calculating the expected Pmax of bifacial modules, taking into account the

series resistance and the on-site parameters.

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Alternative Energies and Atomic Energy Commission

INES RDI | Savoie Technolac – BP332 – 50 avenue du Lac Léman

F-73377 Le Bourget-du-Lac - FRANCE

T. +33 (0)4 79 79 23 17

Email : maryline.joanny@cea.fr

Public establishment with commercial and industrial character | RCS Paris B 775 685 019

Thank you for your

attention

Technological Research Division

Department of Solar Technologies

Photovoltaïc Modules Division

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References:

M.Joanny, B.Soria et al., 2nd BifiPV Workshop, Chambéry (France, 2014)