1

Outdoor Module Characterization Methods:

Power Matrix, Angle of Incidence and

Spectral Mismatch Correction

M a n i G . T a m i z h M a n i

T U V R h e i n l a n d P T L

A r i z o n a S t a t e U n i v e r s i t y P R L

Presented at the 2014 Sandia PV Performance Modeling Workshop, Santa Clara, CA. May 5, 2014 Published by Sandia National Laboratories with the Permission of the Author.

gtamizhmani@us.tuv.com

Motivation

Qualification PLUS A New ANSI/TUV-R Standard

• As the PV Industry matures, PV Reliability is becoming more important

o Project developers want to make bankable investments

• PV customers are asking for tests that “go beyond” the standard qualification test (IEC 61215).

Note: “Qualification PLUS” testing is expected to be adopted by the California Energy Commission in the near future.

TÜV Rheinland PTL, a Standards Developing Organization (SDO) for the

American National Standards Institute (ANSI), has now initiated the development

of two new American National Standards:

• ANSI / TUV-R 71732-01:201X: Qualification PLUS (Q+) Testing for PV

Modules - Test and Sampling Requirements

• ANSI / TUV-R 71733-01:201X: Quality Management System (QMS)

Requirements for PV Manufacturing

TUV Rheinland is now seeking industry participation in the respective

standards’ working groups. Stakeholders include manufacturers of PV Modules,

Project Investors and Developers, Utility Companies, PV Consumers, Incentive

Programs as well as Engineering and Insurance Companies. To get involved,

please click here.

http://education.tuv.com/join-ansi-working-groups/

Seeking Members for the ANSI Working Group (WG)

4

Outline

P m a x m a t r i x g e n e r a t i o n s t a n d a r d s

O u t d o o r m e t h o d s t o g e n e r a t e P m a x m a t r i x

M e t h o d 1 : S a n d i a m e t h o d b a s e d o n a n a u t o m a t e d 2 - a x i s t r a c k e r ( u s e d a t T U V R h e i n l a n d P T L )

M e t h o d 2 : M e s h s c r e e n m e t h o d b a s e d o n a m a n u a l 2 - a x i s t r a c k e r ( u s e d a t T U V R h e i n l a n d P T L )

M e t h o d 3 : M P P T m e t h o d b a s e d o n a f i x e d t i l t a r r a y m e t h o d

A n g l e o f i n c i d e n c e e f f e c t

C l e a n a n d s o i l e d m o d u l e s u s i n g o u t d o o r m e t h o d

S p e c t r a l m i s m a t c h e r r o r

S p e c t r a l m i s m a t c h e r r o r c a l c u l a t i o n f o r o u t d o o r m e t h o d

C o n c l u s i o n s

5

Pmax Matrix Generation Standards:

UL 4730 and IEC 61853

Key to improve accuracy:

• Avoid/minimize extrapolation

• Avoid/minimize long range translat ion

UL 4730: 5 Test Conditions

www.solarABCs.org

UL 4730 standard is based on the

following Solar ABCs report

7

www.solarABCs.org

IEC 61853-1: 23 Test Conditions

IEC 61730-1 standard is validated in the

following Solar ABCs report

8

Pmax Matrix Generation:

Method 1

9

Pmax Matrix Generation: Sandia method – Automated 2 -axis tracker based

I-V

curve

tracer

Pyranometer

Reference Cell

Module

Thermocouple 2

Thermocouple 1

Automatic

2-axis tracker

Automated 2-axis tracking

(take I-Vs daylong)

J. Granata et al., IEEE PVSC 2011

Irradiance

W/m2 15 C 25 C 50 C 75C

1200 358.1 341.7 301.0 260.6

1100 328.6 313.6 276.1 239.0

1000 299.0 285.3 251.2 217.4

800 239.5 228.5 201.1 173.9

600 179.6 171.3 150.6 130.0

400 119.3 113.7 99.7 86.0

300 89.1 84.9 74.3 63.9

200 58.9 56.0 48.9 42.0

100 28.9 27.4 23.7 20.2

Module Cell Temperature

10

Pmax Matrix Generation: Using Sandia model and results (example)

Eff

icie

ncy d

oes n

ot

rem

ain

th

e s

am

e!

Sh

ort

ra

ng

e t

ran

sla

tio

n f

or

ac

cu

rate

ma

trix

gen

era

tio

n is

re

qu

ire

d!

11

Pmax Matrix Generation:

Method 2

12

Manual 2-Axis Tracking

(Cool the module; Take I-V as it warms up)

Mesh screens to change irradiance

Pmax Matrix Generation: M esh screen method – M anual 2 -axis tracker based

Karen Paghasian et al., IEEE PVSC 2011

Two reference cells

13

1, 2 & 3 = IEC 60891 procedures; 4 = NREL procedure

Pmax Matrix Generation: Using IEC 60891 models and results (example)

Efficiency does not remain the same!

Short range translation for accurate matrix generation is required!

14

Pmax Matrix Generation:

Method 3

Outdoor Method 4: Matrix Generation Using Fixed Tilt Modules (or

Grid Tied Arrays)

15

• Monitor (6 minutes): MPPT, POA irradiance and Module temperature

• If one module used: Many days of monitoring required

• If two or more identical modules used: Only few days of monitoring required

• A combination of back-insulated, mesh screen-filtered modules can also be

used to reduce the number of monitoring days

Source: K. Koka et al., IEEE Photovoltaic Specialists Conference, June 2011

16

Angle of Incidence (AOI) Effect

AOI Setup: Five Module Technologies

( Superstrate : Glass; Interface: air/glass)

AOI Effect on Cleaned Modules:

Practical ly no AOI dif ference between technologies as the interface (air/glass) is the same for al l

Soiling level: A – Heavy, B – Medium-Heavy, C – Medium, D –Light, E – Cleaned

Sample Name (Soiling Level) Critical Angle (3% and above loss)

Sample E (Cleaned) 57o

Sample D (Light; 1.7 g/m2) 42

o

Sample C (Medium; 2.7 g/m2) 38

o

Sample B (Medium Heavy; 4.9 g/m2) 37

o

Sample A (Heavy; 11.8 g/m2) 20

o

Source: J.J. Joseph et al. SPIE,

San Diego, August 2014 (accepted)

AOI Effect on Soiled Modules:

AOI loss increases as the soi l ing density increases

20

Spectral Mismatch Error

21

Source: Sandia

Reference spectrum ~ Outdoor Test Spectrum

Test spectra (AMa=2.46 and Ama=4.70) are ONLY SLIGHTLY DIFFERENT from the reference spectrum (Ama=1.5)

Reference spectrum # Test Spectrum

Test spectrum is VERY DIFFERENT from the reference spectrum

Red line = Reference spectrum

Black line = Xe-arc lamp spectrum

If matched reference technology is NOT used to measure the irradiance level, the performance

measurement error (spectral mismatch error) will be very HIGH (see later).

23

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Janu

ary

Feb

ruar

y

Mar

ch

Apr

il

May

June

July

Aug

ust

Sep

tem

ber

Oct

ober

Nov

embe

r

Dec

embe

r

Ref

eren

ce

Mea

sure

d S

pec

tral

-Ban

d I

rrad

ian

ce (

%)

Month

Analysis of Full Year Spectrum

900-1100nm

800-900nm

700-800nm

600-700nm

500-600nm

400-500nm

Source: ASU-PRL

On clear sunny days during solar window (9am-3pm):

Less than 5% deviation from reference spectrum (Mesa, Arizona)

Even if matched reference technology is NOT used to measure the irradiance level, the

performance measurement error (spectral mismatch error) will be very SMALL (see later).

Reference spectrum ~ Outdoor Test Spectrum

24

where:

M = spectral mismatch parameter;

E(λ) = spectral irradiance (Wm-2/nm);

E0(λ) = reference spectral irradiance (Wm-2/nm);

Rr(λ) = spectral response of reference cell (A/W);

Rt(λ) = spectral response of photovoltaic device (A/W).

Spectral mismatch factor (M) = Current correction factor

M= E λ R λ dλ

b

a

E λ Rr λ dλd

c

× E0 λ Rr λ dλ

d

c

E0 λ Rt λ dλb

a

M = 1 if the reference device is matched with the test device

M = 1 if test spectrum is matched with the reference spectrum

Spectral Response Depends on the Technology

If the reference cell technology (e.g. c-Si) is not matched with the test technology (e.g. CdTe),

then it is imperative either to experimentally match the test spectrum or to mathematically correct

for the spectral mismatch error.

26

Source: Newport Corporation, Application Note 51

Spectral Mismatch Factor for Simulated Light (Xe-arc lamp)

If the reference cell technology (e.g. c-Si) is not matched with the test

technology (e.g. CdTe), the spectral mismatch error can NOT be ignored.

27

0.940

0.960

0.980

1.000

1.020

1.040

1.060

7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00

Sp

ec

tra

l Mis

ma

tch

Fa

cto

r

Time (hh:mm )

Spectral Mismatch Factor for May 25, '09A191 (Mono-Si) is the reference device

A191 (Mono-Si)

A209 (CdTe)

A187 (Mono-Si)

A203 (Poly-Si)

A210 (GaAs)

-5% Limit

+5% Limit

Spectral Mismatch Factor for Natural Sunlight (Daily)

Even if the reference cell technology (e.g. c-Si) is not matched with the test

technology (e.g. CdTe), the spectral mismatch error will be very small because

the test spectrum is practically matched with the reference spectrum!

• Pmax Matrix Generation Three outdoor methods presented First two methods are used by TUV Rheinland PTL

• Angle of Incidence Effect Practically identical for all technologies if clean-glass

superstrate is used AOI loss increases as the soiling density increases

• Spectral Mismatch Error Negligibly small if natural sunlight is used with the

matched reference cell technology

Conclusions

Thanks for your attention!

Mani G. TamizhMani

gtamizhmani@us.tuv.com