1 4th PV Performance Modeling Collaborative Workshop

Modelling of bifacial PV modules

Gianluca Corbellini

Vasco Medici

2 4th PV Performance Modeling Collaborative Workshop

• Located in Lugano (Ticino)

• 4500 students

• 30y+ experience in PV

• Outdoor test stand

• Swiss PV Module Test Center

• Swiss BIPV Competence Centre

3 4th PV Performance Modeling Collaborative Workshop

Agenda

• Outdoor measurement

• Modelling

• Indoor measurement

• Fit of parameters

• Results of modelling

• Conclusions and next steps

4 4th PV Performance Modeling Collaborative Workshop

Outdoor measurement Testing of outdoor performance for 12 PV modules between June 2014 and June 2015

Orientation: 45° tilt at 3°E azimuth

Location: Lugano (south Switzerland)

Sensors: GHI, DHI, front GPOA , back GPOA , TBOM monofacial

All modules operating at MPP, I-V curve measurement every 5 minutes

Technology ɳ @STC γ (%/°C) ɳ @200W/m2

HJT BIFAC 1 18.6% -0.33% 3.1%

HJT BIFAC 2 17.7% -0.26% 3.1%

HJT BIFAC 3 17.6% -0.28% 2.3%

C-Si 1 16% -0.41% 5.1%

C-Si 2 15.9% -0.41% 5.1%

HJT MONO 1 19.4% -0.26% 4.9%

HJT MONO 2 19.4% -0.26% 4.9%

CIS 1 13.8% -0.34% 5.4%

CIS 2 13.7% -0.34% 5.4%

C-Si 3 13.4% -0.43% 2.4%

CdTe 1 10.9% -0.25% 0.5%

CdTe 2 10.6% -0.25% 0.5%

5 4th PV Performance Modeling Collaborative Workshop

Outdoor bifacial vs monofacial

All day types Overcast

PR ΔkWh/kWp PR ΔkWh/kWp

HJT BIFAC 3 101% 13.7% 106% 15.4%

HJT BIFAC 2 100% 12.5% 105% 13.9%

HJT BIFAC 1 99% 11.8% 104% 13.7%

CIS 1 97% 9.0% 95% 3.8%

CIS 2 96% 7.7% 97% 5.4%

CdTe 2 95% 7.0% 98% 6.5%

CdTe 1 94% 5.6% 94% 1.9%

c-Si 3 92% 3.4% 98% 6.4%

HJT MONO1 92% 2.9% 92% 0.2%

HJT MONO2 91% 2.2% 91% 0.1%

c-Si 1 90% 0.7% 93% 0.9%

c-Si 2 89% Ref. 92% Ref.

Bifacial modules show and additional 10 to 13% energy yield with respect to

monofacial HJT

Strong dependence on sky conditions (diffuse/direct ratio) and position of the sun

HJT Bifacial 2 vs HJT Mono 1 in clear sky days

6 4th PV Performance Modeling Collaborative Workshop

Modelling of Irradiation

SKY DIFFUSE RADIATION

DIRECT RADIATION

GROUND REFLECTED GROUND REFLECTED

COMPARISON OF 5 MODELS

7 4th PV Performance Modeling Collaborative Workshop

Modelling of Performance

LOW IRRADIANCE TERM CORRECTED FLASH TEST TEMPERATURE TERM

Tbom estimated from VOC and ISC

8 4th PV Performance Modeling Collaborative Workshop

Indoor Measurement Some parameters have been estimated with indoor testing:

- Low irradiance coefficients

- Temperature coefficients

- Power @STC front

- Power @STC back

Are these measures

correct for bifacials?

How do we estimate the

bifaciality factor?

PBPF

9 4th PV Performance Modeling Collaborative Workshop

Indoor Measurement

Comparison of front reference cell and a cell on the backside at

different position

1.09 0.44 0.48 1.12

1.1 0.58 0.48 0.82

1.11 0.56 0.52 0.51 0.93

5%

φ ≈ 0.0044

PF = PF +φPBPB = PB + φPF

PF = 291.74 W PF = 𝟐𝟗𝟎. 𝟓𝟕 W

PB = 261.61 W PB = 𝟐𝟔𝟎. 𝟑𝟎 W

Measure of reflections on the backside in the dark room [%]:

Bifaciality factor = 0.896 Corrected for JB = 0.948

10 4th PV Performance Modeling Collaborative Workshop

Modelling of TCELL

Cell temperature estimated from a one-diode model tuned using indoor data

Validation on 1 year outdoor data of a standard module (framed poly-Si 260W)

IPH

IS RS

RSH

ISH

V

+

-

ISC VOC

TCELL

α

β

Rsh (G)

TMODEL = 0.982 TMEAS + 0.748

RMSE = 0.4535

11 4th PV Performance Modeling Collaborative Workshop

Modelling of TCELL

Validation on a standard module

(framed poly-Si 260W)

TCELL modelled RMSE = 0.4535

IPH

IS RS

RSH

ISH

V

+

-

ISC VOC

TCELL

α

β

Rsh (G)

13 4th PV Performance Modeling Collaborative Workshop

Modelling of Performance

4 Variables

• GHI • TBOM (VOC ,ISC) • DHI • (Geff)

6 Parameters • PSTC • δ • ai

• Albedo • K0

• K1

Accounting as portion of effective ground reflected irradiance

Accounting as portion from diffuse irradiance Measured but can

be modelled

Estimated at 0.23 (gravel)

14 4th PV Performance Modeling Collaborative Workshop

Results of modelling

RMSE = 8.34W bias = -7.519W std = 3.607W

k1 = 0.193 [0.191 0.194] RMSE = 4.163W bias = -1.745W std = 3.780W

k0 = 0.437 [0.434 0.441] RMSE = 4.197W bias = -1.392W std = 3.959W

k0 = 0.115 [0.113 0.116] k1 = 0.131 [0.129 0.132] RMSE = 2.933W, bias = -0.445W, std = 2.899W

k0 = 0.207 [0.205 0.209] RMSE = 4.836W bias = -1.812W std = 4.484W

15 4th PV Performance Modeling Collaborative Workshop

Conclusions

Two parameters model covers very well the backside

contribution to module’s power, both terms are significant

Reflections in dark room need to be taken in account

TCELL(VOC, ISC) is very accurate on monofacials and

promising for bifacials

16 4th PV Performance Modeling Collaborative Workshop

Next Step

Improve TCELL(GBF, TAMB) modelling, only from environmental

variables

Testing of different tilt/azimuth – optimization for climates

New standard procedure for nameplate power definition and

indoor testing

Modelling of LCOE as the key factor for bifacial success

17 4th PV Performance Modeling Collaborative Workshop

Thank you for your kind attention

Thank you for your kind attention

Gianluca Corbellini - SUPSI

gianluca.corbellini@supsi.ch