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Durability of Thin Film Solar Cells
04.04.2012 Empa, Dübendorf
Hans-Dieter Mohring
Zentrum für Sonnenenergie- und Wasserstoff-Forschung (ZSW)Baden-Württemberg
Outdoor measurements and comparisonof thin film solar cell technologies
- 2 -
• Motivation
• Methods for field data evaluation
- STC power and temperature coefficients
- Self referencing
- Dependence on irradiance level
- Long term stability
• Summary
Content
- 3 -
Motivation
Higher uncertainties of module parameters for thin film technologies(CIGS, CdTe, a-Si/µ-Si) compared to c-Si.
Operational parameters, energy yield and long term stability can bedetermined from outdoor measurements.
- 4 -
More energy from thin film PV –Marketing or reality?
Quelle: Broschüre Q-Cells
Quelle: Schott Solar Thin Film, EUPVSEC 2010
Quelle: http://www.nexpw.com/techology_tfa.html
More energy from thin film PV in principlepossible by:
• lower temperature coefficient• good performance under low/diffuse light• annealing or light-soaking effects
- 5 -
Information from data sheet
• STC power/tolerance
• Temperature coeff.
• Dependence on irradiance
Source: http://www.avancis.de/fileadmin/media/portal/produkt/Datenblatt_PowerMax-STRONG.pdf
- 6 -
Information from simulation programs
Source: PVSYST
Data for
• STC power/efficiency
• Temperature coefficients
• Dependence on irradiance
Where are these data from??
- 7 -
Information from simulator measurements
Quelle: TÜV Rheinland
Measurement according to IEC 61853(PV Module Performance Testing and Energy Rating):
• Irradiance 100, 200, 400, 600, 800, 1000, 1100 W/m²• Temperature 15, 25, 50, 75 °C
Restrictions for thin film flasher measurements:
• Metastability effects• Crystalline Si reference cells• Current mismatch for tandem cells• Transient effects
- 8 -
Results from outdoor module characterization
• STC power:- data collection days to weeks- spectrum dependent on location and season- stability presupposed
• Energy generation, Performance Ratio (PR):- typically 1 year- comparison of different technologies (benchmark c-Si)- valid for selected site
• Parameter determination:- typically 1 year- power, Voc, Isc,.. under STC- temperature coefficients, operation temperature- dependence on irradiance, incidence angle, spectrum
• Long term stability- several years
- 9 -
Energy and Performance Ratio
• Energy Yield:
Y = Ecounter / Pnom (kWh/kWp)
• Performance Ratio (PR)
PR = Y / EPOA (%)
• Which Pnom ? Label? Flasher or outdoor measurement?
• Measured irradiation in module plane (EPOA) depends on sensor
- 10 -
Outdoor measurements at ZSW• Widderstall (since 1988)• Girona/Spain (since 2011)
• Module measurements- module kept at MPP- I-V characteristics (1 per minute)- Tmod- Pyranometer and c-Si ref. cell- Ta, GHI, DHI, DNI, TNI, vwind
• Generator measurements- 1kW, identical inverters- DC, AC voltage and current- Tmod, POA irradiance
• PID-test stand
- 11 -
Outdoor measurements at ZSW
0.0
0.5
1.0
1.5
2.0
2.5
0 10 20 30 40 50
Spannung (V)
Stro
m (A
)
Module I-V characteristics
- 12 -
Power and temperature coefficient:(1) Selection of irradiance interval
Calculation of P1000 (linear scaling with reference irradiance)
1000 W/m² +/- 10%2854 Data points
1000 W/m² +/- 2%492 Data points
1000 W/m² +/- 0,2%74 Data points
70
80
90
100
110
120
10 20 30 40 50 60 70
Tmod [°C]
P10
00 [
W]
70
80
90
100
110
120
10 20 30 40 50 60 70
Tmod [°C]
P10
00 [
W]
70
80
90
100
110
120
10 20 30 40 50 60 70
Tmod [°C]
P10
00 [
W]
Data collection September, Widderstall, Si-TF module
Reasonable range:• Irradiance interval +/-1 to 2 %• some 100 to 1000 data points
- 13 -
y = -0.2793x + 85.416
y = -0.2756x + 85.491
66
68
70
72
74
76
78
80
82
20 25 30 35 40 45 50 55 60 65
Modultemperatur (°C)
Mod
ulle
istu
ng (W
) AprilJuliLi (A il)
Power and temperature coefficient:(2) Different measurement periods
Measurement months April and July, Widderstall, CIGS module
• Higher module temperature in July• No change of STC module power
- 14 -
P1000 vs. Tmod
• Determination of Tcoeff. fromslope (-0,21 %/K)
Moderate degree of correlation
Power and temperature coefficient: (3) Evaluation
y = -0,0006x + 99,172R2 = 2E-06
70
80
90
100
110
120
0 10 20 30 40 50 60 70
Tmod
P100
0 Tk
orrP1000 T-corr. vs. Tmod
• STC power 99,2 W
• Deviation by time constants of - pyranometer- module back temperature
y = -0,2085x + 104,36R2 = 0,2107
70
80
90
100
110
120
0 10 20 30 40 50 60 70
Tmod [°C]
P100
0 [W
]
- 15 -
Voc1000 vs. Tmod
• Determination of STC-Voc
• Determination Tcoeff Voc
• Correction of Tmod usingVoc1000 Teff
Power and temperature coefficient :(4) Improvement of accuracy
100
110
120
130
140
0 10 20 30 40 50 60 70
Tmod [°C]
Voc1
000
[V]
y = 0,003x + 1,386R2 = 0,161
1,1
1,2
1,3
1,4
1,5
1,6
1,7
1,8
0 10 20 30 40 50 60 70
Teff [°C]
Isc1
000
[A
]
Isc1000 vs. Teff
• Determination of Isc@STC
• Definition: Eeff = Isc/ Isc@STC
Module used as irradiance sensor
=> “Self referencing”
y = 0,003x + 1,386R2 = 0,161
1,1
1,2
1,3
1,4
1,5
1,6
1,7
1,8
0 10 20 30 40 50 60 70
Teff [°C]
Isc1
000
[A
]
- 16 -
020406080
100120140160180200
20 30 40 50 60 70Modultemperatur (°C)
Mod
ulle
istu
ng P
1000
(W)
c-Si
a-Siµc-Si
DSV
CdTea-Si/µc-Sic-Si
-0.29-0.2-0.42Tk Pmpp (%/K)
59.1122.4185.2Pmpp @ 25 °C (W)
Power and temperature coefficient :Example c-Si, a-Si/µc-Si, CdTe
- 17 -
Parameter determination under low irradianceJune 2011, irradiance interval (Pyranometer) (98…102) W/m²
Linear Correction of measured power to100 W/m²
Plot vs. back temperature
y = -0,097x + 17,764R2 = 0,166
1011121314151617181920
5 10 15 20 25Tback (°C)
P100
(W)
Spectral- and incidance angle influences
No accurate evaluation possible!
- 18 -
Parameter determination under low irradianceJune 2011, Self referencing Eeff = (0.098…0.102) suns
Linear Correction of measured power to 0.1 suns
Plot vs. back temperature
Accurate evaluation possible! low irradiance degradation
y = -0,066x + 16,226R2 = 0,992
1011121314151617181920
5 10 15 20 25Tback (°C)
P100
eff (
W)
- 19 -
Self referencing of irradiance
ZSW Testfeld WIdderstall
- 20 -
Reference cell or pyranometer?
0
0.2
0.4
0.6
0.8
1
1.2
06:00 08:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00
G R
efze
lle/G
Pyr
anom
eter
8.7.
22.7.
Pyranometer
ISET Sensors
Ratio of c-Si sensor to pyranometersunny (8.7.) und cloudy (22.7.) day
• Moderate deviation under direct irradiation around noon time and under diffuse light • strong deviation under direct light morning/evening (incidence angle, spectrum)
Quelle: Kipp & Zonen
- 21 -
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
0 200 400 600 800 1000 1200
G Pyranometer (W/m²)
Wirk
ungs
grad
bedecktklar
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
0 200 400 600 800 1000 1200
G Pyranometer (W/m²)
Wirk
ungs
grad
bedecktklar
Efficiency vs. pyranometer irradiance
Data are as measured:
• Cloudy day: high efficiency
• Sunny day:strong influence of spectrumand incidence angle morning/eveningTemperature influence at noon
• NO UNIQUE FUNCTION!
a-Si/µc-Si: Efficiency vs. G
c-Si: Efficiency vs. G
- 22 -
c-Si type
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
1.05
1.1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2Eff. irradiance (suns)
norm
.effi
cien
cy
Tmod = 10 °C 25 °C 40 °C 55 °C
CIGS type
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
1.05
1.1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2Eff. irradiance (suns)
norm
.effi
cien
cy
Tmod = 10 °C 25 °C 40 °C 55 °C
0.5
0.6
0.7
0.8
0.9
1
1.1
4:00 8:00 12:00 16:00 20:00
Time (CET)
Nor
m. e
ffici
ency
cloudy clear
0.5
0.6
0.7
0.8
0.9
1
1.1
4:00 8:00 12:00 16:00 20:00Time (CET)
Nor
m. e
ffic
ienc
y
cloudy clear
Efficieny vs. effective irradiance (1)
c-Si CIGS
Normalized efficiency vs. effective irradiance with parameter Tmod (top) and daily profile cloudy/clear (bottom)
Similar to c-Si, different at low
light level
- 23 -
c-Si type
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
1.05
1.1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2Eff. irradiance (suns)
norm
.effi
cien
cy
Tmod = 10 °C 25 °C 40 °C 55 °C
0.5
0.6
0.7
0.8
0.9
1
1.1
4:00 8:00 12:00 16:00 20:00Time (CET)
Nor
m. e
ffic
ienc
y
cloudy clear
Efficieny vs. effective irradiance (2)
c-Si CdTe
Normalized efficiency vs. effective irradiance and daily profile cloudy/clear
CdTe type
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
1.05
1.1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2Eff. irradiance (suns)
norm
.effi
cien
cy
Tmod = 10 °C 25 °C 40 °C 55 °C
0.5
0.6
0.7
0.8
0.9
1
1.1
4:00 8:00 12:00 16:00 20:00Time (CET)
Nor
m. e
ffic
ienc
y
cloudy clear
smaller T-coeff.
- 24 -
c-Si type
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
1.05
1.1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2Eff. irradiance (suns)
norm
.effi
cien
cy
Tmod = 10 °C 25 °C 40 °C 55 °C
0.5
0.6
0.7
0.8
0.9
1
1.1
4:00 8:00 12:00 16:00 20:00Time (CET)
Nor
m. e
ffic
ienc
y
cloudy clear
Efficieny vs. effective irradiance (3)
c-Si a-Si/µc-Si
Normalized efficiency vs. effective irradiance and daily profile cloudy/clear
aSi-µcSi type
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
1.05
1.1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2Eff. irradiance (suns)
norm
.effi
cien
cy
Tmod = 10 °C 25 °C 40 °C 55 °C
0.5
0.6
0.7
0.8
0.9
1
1.1
4:00 8:00 12:00 16:00 20:00Time (CET)
Nor
m. e
ffic
ienc
y
cloudy clear
Smaller Tcoeff. different at low
light level
- 25 -
c-Si type
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
1.05
1.1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2Eff. irradiance (suns)
norm
.effi
cien
cy
Tmod = 10 °C 25 °C 40 °C 55 °C
0.5
0.6
0.7
0.8
0.9
1
1.1
4:00 8:00 12:00 16:00 20:00Time (CET)
Nor
m. e
ffic
ienc
y
cloudy clear
Efficieny v s. effective irradiance(4)
c-Si a-Si/a-Si
Normalized efficiency vs. effective irradiance and daily profile cloudy/clear
aSi-aSi type
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
1.05
1.1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2Eff. irradiance (suns)
norm
. effi
cien
cy
Tmod = 10 °C 25 °C 40 °C 55 °C
0.5
0.6
0.7
0.8
0.9
1
1.1
4:00 8:00 12:00 16:00 20:00Time (CET)
Nor
m. e
ffic
ienc
y
cloudy clear
Best Tcoeff., good at low light
level
- 26 -
Long term stability
ZSW Test Field WIdderstall
- 27 -
Initial Light-Soaking of CIGS Module
P: +10% in 6 Wochen
50
55
60
65
70
75
80
85
Jun. 03 Jul. 03 Aug. 03 Aug. 03 Okt. 03
P (W
), U
oc (V
)P@25°C Uoc@25°C
- 28 -
Initial degradation of a-Si/a-Si Modul
Source: Schott Solar, 21st EU PVSC
Staebler-Wronski-Effect, SWE
- 29 -
Long term stability of CIGS Module
Long term stability CIS @ 1000 W/m²
8.0
8.5
9.0
9.5
10.0
10.5
11.0
Jan. 03 Jan. 04 Jan. 05 Jan. 06 Jan. 07 Jan. 08
Tem
p. c
orr.
effic
ienc
y (%
)
Measurement close to AM1.5 and normal incidence, then temperature correction
- 30 -
Long term stability of CIGS Module @ 800 W/m²
Continuous evaluation possible
0.9
0.95
1
1.05
1.1
0 0.5 1 1.5 2 2.5 3Jahre
P_M
PP_
800(
t)/P
_MPP
_800
(0)
- 31 -
Which degradation rate can be detected?
Here assumed 0,3 % per year
0.9
0.95
1
1.05
1.1
0 0.5 1 1.5 2 2.5 3Jahre
P_M
PP_
800(
t)/P_
MPP
_800
(0)
- 32 -
Effective efficiency, corrected to reference temperatureand normalized to Pnom
0,00
0,20
0,40
0,60
0,80
1,00
1,20
0,0 0,2 0,4 0,6 0,8 1,0 1,2
effective Irradiance [suns]
norm
. Per
form
ance
Meas. Period 1
Meas. Period 2
- 33 -
Low light level degradation / STC-Degradation
Outdoor measurements
0.94
0.96
0.98
1
1.02
1.04
Time ------->
eta(
t)/et
a(0)
1000 W/m² 100 W/m²
Different kinetics
- 34 -
Potential Induced Degradation
(1) Leakage currentindoor
35....85 °C50…95 % -1000 Vsome hours
1,E-07
1,E-06
1,E-05
1,E-04
1,E-03
00:00 12:00 00:00 12:00 00:00 12:00 00:00 12:00 00:00
Time (h)
Leak
age
curr
ent d
ensi
ty (
A/m
²)
Reihe1Reihe2
(3) Leakage currentoutdoor
Module temperatureHumidityGenerator Voltagemonths to years
(2) Power degrad. indoor
85 °C85 % -1000 V1000 h
Teils sonniger, trocken-kalter Tag
1,0E-08
1,0E-07
1,0E-06
1,0E-05
03.01.201206:00
03.01.201208:00
03.01.201210:00
03.01.201212:00
03.01.201214:00
03.01.201216:00
03.01.201218:00
Leck
stro
m
[A] Si-TF 2
Si TF 3CIGS 3CIGS 4CIGS 5CdTe 2c-Si 2
Estimation of Time to PID Failure
- 35 -
Time to PID Failure
> 5*E21,4> 300Si-TF 6
2,63533 Si-TF 27,97,823CdTe 2
0,820,6c-Si 2
> 5*E20,5> 87CIGS 4> 5*E20,19> 37CIGS 3
2,51,61,4CIGS 1
Time* to P90 t [a]
Daily* Qdfrom Outdoor
[mC/m²]
Q _ HV-DH for P90[C/m²]
ModuleType
• Time to PID Failure depends on climate
* Average values fall/winter at Widderstall
„PID-Failure“90 % of initial power (P90)
- 36 -
Summary
• Methods for evaluation of characteristic module parameters from fielddata have been presented
• Self referencing uses the module itself as a best matched irradiancesensor
• Module power is a unique function of effective irradiance, transformation to laboratory measurements under reference conditions
• From long term measurements stability trends can be extracted withhigh accuracy
• Time to PID Failure can be estimated
- 37 -
Thank you for your attention!
ZSW Testfeld WIdderstall