Proposed new damp heat test standards for thin film PV modules

Transcription

1 Proposed new damp heat test standards for thin film PV modules K. Sakurai, K. Ogawa, H. Shibata, A. Masuda AIST A. Takano FWAVE H.Tomita, D.Schmitz, S.Tokuda Solar Frontier K.K. Presented at SAYURI PV, 2016 Oct 4 5 AIST, Tsukuba, Japan p Current n

2 Backgrounds Major international PV standards are now being created/revised under IEC TC82 WG2 a major overhaul of the whole set of test standards wider, stricter coverage of degradation modes includes the IEC61215, Design qualification and type approval of PV modules

3 10 Modules MQT 01 Visual inspection old IEC61215 s test procedure revised IEC61215 (draft) MQT 19.1 Initial Stabilization (Note 4) MQT 06.1 Performance at STC MQT 03 Insulation test MQT 15 Wet leakage current test 3 Modules Sequence A 1 Module Sequence B 2 Modules Sequence C 2 Modules Sequence D 2 Modules Sequence E MQT 06.2 Performance at NMOT (see Note 1) MQT 07 Performance at low irradiance (see Note 1) MQT 04 Measurement of temperature coefficients (see Note 1) MQT 05 & MQT 08 Measurement of NMOT & Outdoor Exposure Test 60 kwh/m 2 (see note 2) MQT 18 Bypass diode thermal test (see Note 2) MQT 19.2 Final Stabilization MQT 10 UV precondition test 15 kwh/m 2 MQT 11 Thermal cycling test 50 cycles 40 C to 85 C MQT 12 Humidity freeze test 10 cycles 40 C to 85 C 85 % RH MQT 11 Thermal cycling test 200 cycles 40 C to 85 C 1 Module MQT 16.1 Static mechanical load test (design load) MQT 13 Damp heat test h 85 C / 85 % RH 1 Module MQT 17 Hail test MQT 06.1 Performance at STC 1 Module 1 Module MQT 09 Hot-spot endurance test (see Note 3) MQT 14.1 Retention of junction box test wider/stricter coverage of degradation modes for improved reliability 1 Module measured together with modules from sequences C-E as control 2 Modules MQT 14.2 Test of cord anchorage MQT 19.2 Final Stabilization MQT 06.1 Performance at STC MQT 03 Insulation test MQT 16.2 Static mechanical load test (Test load, γ m >1) MQT 15 Wet leakage current test

4 Question... Among the test procedures, "heating in dark" is often applied. Damp heat Thermal cycling PID etc. However, in REAL conditions, how often does "heat + dark" happen? Is it always the best test method?

5 When hot in field, there's always light(voltage) Module temperature ( C) Module temperature (Middle east) Module temperature (Japan) Suns V oc result Normalized V oc (V = 100 %) Irradiation (Sun) In the real field, module temperature seldom exceeds 50 C without > 0.2 Sun irradiation. "High temperature + dark" condition is rare. At high temperatures, module is soaked in light and generating bias voltage.

6 Outline of this talk Two examples of when conventional "damp heat" tests are NOT the optimum test procedure for PV modules. Example 1: A flexible thin film Si module (prototype) Example 2: Some CIGS products in the market

7 Example 1 On damp heat testing of a prototype flexible thin film Si module

8 Unique degradation mode observed in a prototype Thin film Silicon flexible module(1) Power Generation (kwh/kwp day) Amount of Solar Radiation (kwh/day) Power Generation Radiation Relocation Efficiency Year (A.Takano et al, EU PVSEC 2013, 3BO.5.4) Efficiency (arb. units)

9 Reproducing the degradation by applying forward bias during damp heat test Series-Connect ion Holes Current-Collection Holes EL image Transparent Electrode (+) a-si Layer Metal Electrode (-) Backside Electrode Laser-Scribed Lines for Unit-Cell Separation Plastic-Film Subs trate (Leak points) Output Power (arb. units) Damp Heat Test Damp Heat & Current InjectionTest Test Time (h) Degradation reproduced by forward bias during damp heat testing made it possible to fix the problem before mass production (A.Takano et al, EU PVSEC 2013, 3BO.5.4)

10 Example 2 On damp heat testing of the some CIGS products in the market

11 The IEC draft, which defines the new damp heat test standard for CIGS modules, requires a light soaking (LS) process before and after the damp heat test. Pass/Fail criteria are also changed from the current standard. Then...

12 Light soaking effect of CIGS Change of Pmax by light soaking (sometimes takes years until maximum) long term degradation Initial (Nameplate) Exposure time in field

13 Damp heat test defined by the old IEC61215 Damp heat test pass/fail decision pass criterion Initial (NamePlate) decreased output (loss of light soaking effect + real degradation) increased Pmax by light soaking in field Time

14 Original draft for IEC Use Pmax after light soaking for pass/fail decision (not the nameplate value) Damp heat test pass/fail decision pass criterion Pmax@STC (NamePlate) LS decreased output (loss of light soaking effect + real degradation) LS Time

15 What actually happens Damp heat test pass/fail pass criterion (NamePlate) LS Loss of LS effect + test specific degradation (not observed in field) LS does not fully recover by LS (though no problems are observed in real field) Time

16 Exploring the "right" test options for CIGS 5 types of tests below were performed with 170W-class CIGS modules. Test type Normal DH Irradiation ー Bias ー DH with irradiation Wet DH with forward bias Normal dry heat test Dry Dry heat test with forward bias Test sequence 0.1~0.65 Sun* ー ー ー * Performed at AIST. Others were performed at SF. **NMOT : Nominal Module Operating Temperature. ー V pm@nmot ** V pm@stc * ー V pm@nmot ** V pm@stc * 1 st Pre-LS 2 nd Pre-LS Test 1000hrs 1 st Post-LS 2 nd Post-LS Open-circuit state Each LS process: 1kW LS chamber for 21 hrs (SF) or Outdoor for one week (AIST) Open-circuit state Each LS process: 1kW LS chamber for 21 hrs (SF) or Outdoor for one week (AIST)

17 Test with light irradiation Experimental setup Test with forward bias Current p n (light) p n Current Module temperature: 85 Chamber humidity: 85 %r.h. Module current : ~ 0.2 A (with NMOT V pm, T mod 85 ) Module temperature: 85 Module humidity: 85 %r.h. (raised the chamber humidity depending on chamber temperature)

18 Effect of light illumination Initial (Light soaked) illuminated Normalized Pmax not illuminated Test specific degradation Compared to illuminated DH, DH in dark invokes a degradation not observed in field

19 Effect of light illumination + short circuiting (preliminary) Initial (Light soaked) illuminated Test specific degradation Normalized Pmax dark illuminated+short Time Short circuiting of modules test specific degradation not the light, but forward bias voltage?

20 Effect of forward bias + DampHeat(DH)/DryHeat(HT) tests Initial (Light soaked) with bias voltage Normalized Pmax without bias voltage Damp heat test 85 (module) Damp: 95% r.h., Dry: <10% r.h. (chamber) Bias voltage gives same results to light illumination Test specific degradation does not depend on humidity

21 Part 3. Experimental result Does the test specific degradation recover by loooong light soaking? DH with NMOT V pm (N =4) ~3 + % Normalized Pmax (%) DH without bias (N = 4) Test specific degradation Pre LS DH 1000 h Post LS OC LS OC LS Pmpp LS Total Post LS : OC LS 42hrs & Pmpp LS 126hrs No, it does not

22 Summary In the real field, high temperature is always accompanied with illumination&voltage. ("Hot+dark" does not happen it's the MOST unnatural test condition!) The examined CIGS modules after DH with light irradiation or forward bias showed similar behavior to real field. Meanwhile, conventional DH invoked Test specific degradation, which is not observed in field. Test specific degradation is irreversible by light soaking. Mysteries Homeworks "DH+forward bias" option added to IEC (draft). The cause of test specific degradation Some other products show same behaviors, while some others do not (private communications) Understanding of mechanism of test specific degradation. Wavelength dependency of light Work on other samples Destructive analysis etc.

23 Important message Over 50 IEC standards are being created or revised right now; Though people are working hard, mistakes can happen. Keep watch on the progress of IEC TC82 WG2! Next face to face meeting: October 2016, Colorado Thank you for your attention Contact : k sakurai@aist.go.jp

24 Backup: How to determine the chamber RH value The curve of chamber relative humidity as a function of chamber temperature can be plotted using Tetens formula: Chamber RH (%) RH MOD : Relative humidity of the module surface (= 85 %) e(85): Saturated vapor pressure at 85 C (= 581 hpa) RH CHM : Relative humidity inside the chamber T CHM : Temperature of the chamber Chamber temperature ( C) Chamber RH should be set to realize the module surface RH 85%. In case of our study, chamber temperature was set 84 C to realize the module temperature 85 C. Then, according to this graph, we set chamber RH 88 %.