IEC : Measurement of current-voltage characteristics of bifacial photovoltaic devices

Transcription

1 IEC : Measurement of current-voltage characteristics of bifacial photovoltaic devices Energy Rating for Photovoltaics: evaluating real-world performance, NPL Teddington (UK) Nicolas Bassi and Vahid Fakhfouri (Pasan)

2 Outline Motivations and Challenges IEC project team s approach Equivalent Irradiance (G E ) method Method description In practice Project status and historical background Conclusions and Outlook 2

3 BiFi standardization Motivations and requirements Main need: assessment of the bifacial PV devices How to label bifacial devices? How to value the Bifacial gain? Comparability and measurement accuracy to be guaranteed Apple-to-Apple comparison Particularities: Different needs in laboratory and production environments Different possibilities in laboratory and production environments 3

4 Bifacial power generation Complexity Isc 1 = E λ R1 λ SR BS λ dλ Isc 2 = E λ SR FS λ dλ Isc T2 = E λ T DUT λ R2 λ SR BS λ dλ Isc 3 = E λ T Enc. λ R2 λ SR BS λ dλ Isc 4 = E λ R2 λ SR BS λ dλ Installation-specific conditions: Albedo Height Tilt Distance between modules Orientation There is no standard bifacial installation/use condition. 4 Isc = Isc 1 + Isc 2 + Isc T2 + Isc 3 + Isc 4 E λ : is the irradiance. SR xx λ : is the spectral response (BS: of the back side, FS: of the front side). T yyy λ : is the transmission (DUT: of the PV device under test, Enc.: of the encapsulant). R z λ : is the reflectivity of different objects The DUT s intrinsic properties are underlined.

5 IEC project Approach Focus on Power rating in the frame of this project (vs. Energy rating) Common playground for power assessment Reproducible measurement procedures and conditions In accordance with existing IEC standards Practical Value the bifacial gain Comparability vs. power plant simulation (power rating only) Transparent distinction of the Bifacial gain (additionnal key data) 5

6 Equivalent Irradiance (G E ) method Step 1: Bifaciality determination at STC Bifaciality coefficients: φ Isc = Isc r Isc f φ Voc = Voc r Voc f φ Pmax = Pmax r Pmax f 6

7 Equivalent Irradiance (G E ) method Step 2: Bifacial gain determination Outdoor: at 1kWm -2 or corrected to 1kWm -2 on the front side plus different backside irradiations G Ri (at least 3 levels) or Indoor: at Equivalent 1-side irradiance levels G Ei (at least 3): G Ei = 1000Wm 2 Currently under + φ Isc G Ri ; reflection: i = 1, 2, 3, φ Example: For φ Isc = 80%, G R1 = 200Wm 2 Pmax instead of φ Isc, G E1 = 1160Wm 2 Pmax reporting with 2 specific bifacial gains; interpolation of the data: Pmax BiFi10 with 1kWm -2 on the front and G R =100Wm -2 or at G E = 1kWm -2 + Isc. 100Wm -2 Pmax BiFi20 Alternative method, double-side illumination (for research purposes or in some laboratories) 7

8 8 Findings: Outdoor STC measurement Indoor 1-sided and outdoor 2-sided methods are consistent (within measurement uncertainty)

9 G E method Requirements <3Wm -2 of irradiance on the nonexposed side For Cells; extrapolation may be required to compensate. Non-uniformity < 5% outdoor and for double-side illumination; <2% for single-side* * To be consistent with Hohl-Ebinger et al.: Mounting chucks for bifacial solar cells 9

10 Power rating of Bifacial PV devices In practice PV Laboratories PV Production Modules STC measurement of both sides, without back reflection Bifacialities I V characterization vs. backside illumination STC (monofacial) reporting of the key data Reference module BiFi coefficients and I V characterization vs. backside illumination reporting Calibration using the Reference module; IV measurement at STC Bifacialities and I V characterization vs. backside illumination reporting in the datasheet Specific BiFi rating with clear denomination Pmax BiFi10 and Pmax BiFi20 Cells STC measurement of both sides without Back Reflection (BR-compensated) Bifaciality I V characterization vs. backside illumination STC (monofacial) reporting of the key data Reference cell BiFi coefficients and I V characterization vs. backside illumination reporting Calibration using the Reference cell; IV measurement at STC Bifacialities and I V characterization vs. backside illumination reporting in the datasheet Specific BiFi rating with clear denomination Pmax BiFi10 and Pmax BiFi20 10

11 BiFi standardization Short status Date Event Key information January 2016 March 4 th 2016 May 11 th 2016 NWIP circulation and voting 1 st Conference Call, 12/15 participants, 6 guests 2 nd Conference Call, 8/16 participants, 7 guests The NWIP was accepted. A group of 15 experts was nominated to write the IEC Pasan is managing the IEC project. Two approaches discussed; 1 st poll; Experimental validation of the G comp approach launched, theoretical study for AOSG initiated. Experimental validation results for G comp presented by NREL; Simulation partial results presented for AOSG. A major improvement to G comp suggested: G E June rd meeting G E approach presentation and acceptance October 2016 November 2016 Project team draft CD The draft A is now circulating for project team corrections until October 25 th. Committee draft in November 11

12 Conclusion A standard method for the power rating of bifacial devices is proposed: Applicable to cells and modules No major change in production environments Compatible with current STC measurements Outdoor 2-sided measurements are consistent with Indoor 1-sided measurements with proportional overexposure. Double-side illumination considered as alternative method There is a need for an Energy rating standard for bifacial devices. Next CD in November Energy rating standard 12

13 Thank you for your attention Pasan s new BiFicompatible module tester 13 Meyer Burger s HJT bifacial modules with busbarless cells on CSEM s facade