WP9 Presentation

8/12/2019 WP9 Presentation

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Quality assurance of PV plants

connected to the grid


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Today widely extended technical quality assurance practises

STEP PROCEDURE OBJECTION

Design:

Energy yield forecast

Commercial software Based on non-guaranteed

information


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..for definitive simulations, the user is advised to carefully verify the library data

with the last manufacturers specificationsWe drop out any responsibility about

the integrity and the exactness of the data and performance including in the

library..

Disclaimer at PVSYS Users Guide

The PVsyst is based on the full I-V curve one-diode model. Required information

(series and shunt resistance, photo current, saturation current and diode quality

factor) is mainly obtained from I-V curves database from TISO (Centrale di prova

peer componente PV, Ticino, Switzarland) and Photon (German PV journal)

..These data are key parameters of the model, and should be part of the modules

specifications in the future..

A. Mermoud el al, 25thEuropean PVSEC (2010)

The database was compiled to the best of our knowledge and with the greatest

possible accuracy. At the same time, PHOTON cannot be held responsible from

any damage that results from the use of this database.

Disclaimer at Photon database


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Risk of relying on default settings that prescribe irradiance behaviour in PV*SOL

and Pvsyst module models

K. Sauer et al, from Yingly

PV Performance Modelling Workshop, Sandia Labs (2013)


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Design:



informationProcurement:

PV module sample

peak power testing

Prior to the

installation, at

qualified laboratories

Neither Light Induced

Degradation nor

Irradiance and temperature

behaviour are addressed


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Design:




PV module sample

testing

Prior to the

installation, al


Light Induced Degradation

not addressed

Commissioning:

PV plant production

testing

PRduring a week

(Often pass criteriaPR 80%)

-Time-dependence disturbs

technical qualityqualification


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Weekly PR evolution along the year

0,850

0,900

0,950

1,000

1,050

1,100

1,150

0 10 20 30 40 50 60

PRDC

PR

The weekly PR varies up to 10% along the year, and up to 5 % along a

same month.

c-Si PV array, Navarra (Spain), 2011


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Design:




PV module sample

testing

Prior to the

installation, al



not addressed

Commissioning:

PV plant production

testing

PRduring a week -Time-dependence disturb


- Detailed characterization of

real PV plant behaviour not

addressed

Infrared inspection Hot-spot detection - Acceptance criteria scarcely

addressed

Operation

PV plant production

PRduring full years - Ageing measurement not

addressed


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IEC 62446:

Grid connected PV systemsMinimum requirements for system

documentation, commissioning tests and inspection

7.2.2.2 IR test resultsModule hot spots

Module temperature should be relatively uniform, with non areas of significant

temperature difference. However, it is to be expected than the module will be hotter

around the junction box compared to the rest as the heat is not conducted as well tothe surrounding environment. It is also normal for the PV modules to see a

temperature gradient at the edges and supports.

A hot spot elsewhere in a module usually indicates an electric problem, possibly series

resistance, shunt resistance or cell mismatch. In any case investigate the performance

of all modules that show significant hot spot(s). Visual inspection may show signs ofoverheating, for example a brown or discoloured area.


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Design:




PV module sample

testing

Prior to the

installation, al



not addressed

Commissioning:

PV plant production

testing

PRduring a week -Time-dependence disturb


- Detailed characterization of

real PV plant behaviour not

addressed

Infrared inspection Hot-spot detection - Acceptance criteria scarcely

addressed

Operation

PV plant production

PRduring full years - Ageing measurement not

addressed


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SUMMARY:

Energy production of current large PV plants seems to satisfy investors

expectation

Nevertheless, Technical Quality Assurance procedures can be improved in

order to:

Clarify the rules for endorsement of responsibilities in the event of

problems (real production below expectation, hot-spots appearance, etc.)

Improve the technical soundness and the usefulness of in-field

commissioning testing


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QA Objective: Tightening real and predicted productions

Expectation in terms of , both, yearly energy production and degradation rate

Assumptions:

Phenomena Procedure Responsible

Weather evolution (G(0) and TA) Solar database Nobody

Operation conditions (G(in-plane)

and TC) evolution

Transposition models Nobody

PV plant response P*, INV, loses

PR, PRSTC

EPC; PV modules and

inverter manufacturers

Commissioning:

Testing the PV plant response during a few weeks period

Operation:

Monthly and yearly verification of PV plant response and

maintenance procedures


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Modelling the PV plant response

*

GPACP

G

TC

=

, , . .

- Dealing with the PV plant response requires modelling of= , ,

- Because associated responsibilities, involved specifications (P*, thermal

response, etc.) must be agreed with PV manufactures.

- Current specification practises:

- Guaranteed: P*, degradation rate in %/year

- Standard information: NOCT, Thermal coefficients

- Additional information: I-V graphics


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= , , modelling alternatives

1- Considering just the MPP

=

1

+ .

+ .

standard data sheet information (IEC 61215 and IEC 61646)

(a, b,c) a=1, b=0, c=0

200

/1000

(IEC 61215 and IEC 61646)

granting generality to published values (1)

Commissioning tests

2- Considering the full I-V curve

Adjusting 5 parameters (ISC, VOC, RS, RP and m) to a given I-V curve is not straightforward

Module to module parameters variation is typically larger than MPP variation

3Specific energy rating attempts

Kings model from Sandia Lab

Power matrix as defined at IEC 618532

(1) R. Kenny et al, Prog. Photovolt: Rs.Appl. (DOI: 10,1002/pip.2365 (2013)


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Available literature warns about scarce benefits from complexity

Surprisingly, there doesnt seem to be a need for overly complicated modelling to

achieve this accuracy for most technologies

PERFORMANCE final brochure (EPIA, 2009)

A simplified version of the Kings model, using a single expression for the maximum,

power point and requiring just 6 empirical coefficients performs as well as the original

(Huld, T. 2011)

The authors feeling is that the complexity of the standard [ IEC 618532] is actually not

beneficial for an accurate energy prediction, as it requires data which is actually

normally not know and the generation of this.. seems to affect the overall agreement

more than it would be without this complicated step

(Jyotirmoy Roy, 2008)


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Experimental comparison of different practical possibilities

- 6 PV arrays of different technologies (1.9 < P*(kW)


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Weekly energy errors [(ModelledExperimental)/Experimental ], for the c-Si

PV array, weighted by the daily irradiation and expressed in %.

DATA SHEET ADDITIONAL EXPERIMENTS

Full I-V MPP

MPP

, 200

Full I-V MPP

, ref (1)

MPP

, meas.

W1 0.4 1.85 2.67 -0.08 2.15 1.41W2 -1.69 0.84 1.81 -0.79 1.12 0.28

W3 -1.78 0.97 2.03 -0.8 1.26 0.32

W4 3.95 1.89 3.79 -0.64 2.93 1.17

Year 2.11 1.50 2.64 -0,83 1.86 0.85

1.42 1.27 1.29 1.07 0.9 0.97

- PREAL* 1% larger than PNOMINAL*

- Selected weeks are centred on the equinox (W1 and W3), on the summer solstice

(W2) and on the winter solstice (W4)

An MPP model considering just the power temperature coefficient given at

the data sheet explains up to 97% of the observed variability.

Considering also the efficiency variation with irradiance reduces uncertainty

by about 1%


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Yearly energy errors at 12 different commercial Spanish PV plants

- G and TC given by reference PV modules, MPP model with and 200/1000

- P* and INVERTERvalues obtained at Commissioning tests

Nominal power(MW)

Real yearly Yield(kWh/kW)

Modelled yearlyyield (kWh/kW)

Error (%)

2 2038 2067 1.4

2.16 2056 2095 1.9

2.95 2050 2096 2.2

2 2194 2163 -1.4

1.5 2074 2032 -2.1

1.4 1561 1597 2.3

2.03 2142 2140 -0.1

11.2 2016 2038 1.1

2.1 2204 2198 -0.3

1.9 2320 2279 -1.8

9.7 2108 2111 0.1

25.3 1594 1616 1.4


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Daily energy errors at 45.6 kW Amaraleja PV plant

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8-5

0

5

10

15

20

KTd

heoretical-

easured(

-6 -4.5 -3 -1.5 0 1.5 3 4.5 6 7.5 90

5

10

15

20

25

Theoretical-Measured (%)

requency

Mean: 1.3 %

STD: 1.9 %

- G and TC given by 9 reference PV modules, MPP model with

- P* and INVERTERvalues first obtained at Commissioning tests andperiodically reviewed


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Commissioning testing: Current state of art - 1

- The simplest possibility rely on the Performance Ratio concept

- Acceptation , .

.PRGUARANTEED. (or PR PRGUARANTEED)

Given by the energy meter Specified at the contract (80%)

Nominal power Given by the in-plane solar radiation meter

- PRcalculation requires only Grecords

- Because it includes time-dependent unavoidable losses, the mere PRis generally

not adequate for sub-year periods (days, weeks, months ).


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Weekly PR evolution along the year

0,850

0,900

0,950

1,000

1,050

1,100

1,150

0 10 20 30 40 50 60

PRDC

PR

The weekly PR varies up to 10% along the year, and up to 5 % along a

same month.

c-Si PV array, Navarra (Spain), 2011


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Commissioning testing: Current state of art - 2

- Time-dependent unavoidable energy loses are removed at the Performance Ratio at

Standard Test Conditions concept:

=

(1)

- E means energy loses and I extends to all unavoidable phenomena:

- Thermal (due to TC TC* )- Efficiency variation with irradiance

- Anomalies: Shading, inverter saturation, PV plant disconnections, etc.

- PRSTCcalculation requires (additional to G) TC records .and modelling.

- PV reference modules are recommended to minimize uncertainty

- Acceptation PRSTC along T PRSTC, GUARANTEED


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Weekly PR and PRSTCevolution along the year - 1

0,850

0,900

0,950

1,000

1,050

1,100

1,150

0 10 20 30 40 50 60

PR

PRSTC

PR

PRSTC


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Commissioning testing: Advances procedures

- Not only energy production but also PV plant characterization is addressed

G

TCPDC PAC

PREAL* =PNOMINAL* . (1-FG); INV, REAL= INV, NOMINAL.(1-FINV

- Highly desirable for further careful operation surveillance

- PV plant in-field characterization requires G, TC, PDCand PACrecordsand modelling

- PV reference modules and accurate wattmeters are recommended to minimizeuncertainty


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PV reference modules and accurate wattmeters

I fi ld t ti AC


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In-field testing: AC power response

21

PAC,EXPPDC,EXPG, TC

I fi ld t ti STC f th PV t


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0

20

40

60

80

100

120

140

0 200 400 600 800 1.000 1.200

Gef(W/m2

)

PDC

Gef,

25C

W

PDC= 0,1087 Gef

R2= 1

In-field testing: STC power of the PV generator

*

CC

DCefDC

1

C25,

TT

PGP

PAC,EXPPDC,EXPG, TC

,EXP


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Mean

ISC*[A] 1240.0 6.4

VOC*[V] 862.3 5.1

IM*

[A] 1114.6 4.2VM

*[V] 703.4 10.6

PM, IEC-60891*[W] 784044 11067

FF* 0.733 0.003

PM,*[W] 742728 4894


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In-field testing: efficiency of inverters

0

10

20

30

40

50

60

70

80

90

100

0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0

pac

(%)

Inversor A

Inversor B

Inversor C

Modelo

Fabricante

h

P

PAC,EXPPDC,EXPG, TC


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Dealing with hot-spots - 1

Hot-spots threaten PV module lifetime and reduce operation voltage

THS 5oC

VOP= 29.5 V

THS 17.4oC

VOP= 26.3 V THS 14.3oC; THS 11.8

oC

VOP= 22.6 V


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Dealing with hot-spots - 2

Proposal for contracts:

- THS 20oC PV module rejection

- 10oC THS< 20oC and V > 20%


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CONCLUSIONS

- c-SI PV array response is properly described by a simple model considering

just the maximum power point and the power temperature coefficient

- The power temperature coefficient must be included at the guarantees

provided by the PV module manufacturers

- In-field commissioning testing must preferably deal with PRSTC(over the

mere PR). That requires measuring Gand TC and modelling unavoidable

loses

- Commissioning testing can also include the characterization of the

effective behaviour of the PV plant. That requires measuring G,TC , PDCand

PAC.

- Reference PV modules are preferred for measuring, both, Gand TC

- Proposed rejection criteria for PV module with hot-spots:

- Temperature differences larger than 20oC

- Temperature differences between 10oC and 20oC, and voltage

operation loses larger than 20%


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