3 yusufoglu ok

Yusufoglu, Institute of Semiconductor Electronics

Modeling and simulation of annual

energy yields of bifacial modules at

different climate zones

U. Yusufoglu, T. Lee, T. Pletzer, H. Kurz

Institute of Semiconductor Electronics, RWTH Aachen University, Germany

A. Halm, L. J. Koduvelikulathu, C. Comparotto, R. Kopecek

International Solar Energy Research Center (ISC), Konstanz, Germany

bifiPV Workshop 2014, 27.05.2014


Albedo

moduleelevationVertical

Outline

Annual energy yield simulation based on individual characteristics of solar cells

27.05.2014Modeling and simulation of annual energy yields of bifacial modules at different climate zones2

Optimization of tilt angle

Location

South facing

S i m u l a t i o n r e s u l t s

Gain with respect to standard module

Annual E

nergy Yield

Measured I-Vof solar cells

Cell/Module Temperature

M o d e l i n g s t e p s

Two-Diode-Model

Irradiance reaching both cell surfaces

Direct Diffuse Albedo (effect of shadow for rear)

AOI losses & spectral mismatch


Measurement of I-V characteristics

27.05.2014

Modeling and simulation of annual energy yields of bifacial modules at different climate zones3

Six-inch mono-Si n-type bifacial solar cells [1] Separately available I-V characterics of front and rear Bifaciality of cells on average 80 %

Front

Rear

Rear

FrontBlack chuck

Front illumination Rear illumination

Black chuck

[1] Mihailetchi et al., bifiPV2012

Black chuckBlack chuck

Simulations with 60-cell modules using their two-diode model representation


Irradiance at both planes

GHI, DNI, DHI data acquired from GeoModel Solarwith a time resolution of 15 minutes

Three irradiance types separately determined for front/rear

Direct irradiance– Angle of incidence using azimuth and elevation– For rear planes of south facing modules mainly insignificant

Diffuse irradiance– Perez model [1]

Encapsulation losses resolved over angle of incidence via raytracing [2]

Spectral mismatch with King‘s model [3]

[1] Perez et al., Solar Energy 1990; 44(5); 271-289[2] Tracey, PVLighthouse, http://www.pvlighthouse.com.au/simulation/hosted/tracey/tracey.aspx[3] King et al., SAND2004-3535



Albedo


)cos1(5.0, TiltAngleGHIE frontAlbedo

odulemRodulemRrearAlbedoPOM VFDHIVFGHIE 21,,

R1

R2

METHOD 1

Calculation of view factor from center of shadow to module surface

Low computational load Homogeneous irradiance at rear plane

METHOD 2

Twice numerical double integration over shadow and each cell surface

Large computational load Inhomogeneous irradiance at rear plane

2

2221

21coscos

AAdA dA

SVF

2 1212

21

121

coscos1A A

AA dAdASA

VF


Cell temperature

Time resolved ambient temperature data available

Cell temperature calculation with NOCT formula

𝑇𝑐𝑒𝑙𝑙 = 𝑇𝑎𝑚𝑏𝑖𝑒𝑛𝑡 +𝐼𝑟𝑟𝑎𝑑𝑖𝑎𝑛𝑐𝑒 [𝑊/𝑚2]

800 𝑊/𝑚2(𝑇𝑁𝑂𝐶𝑇 − 20 °𝐶)

Standard modules TNOCT = 45 °C

Bifacial modules TNOCT = 47 °C



Locations studied

Two locations with highly different climates

Oslo, Norway: predominantly diffuse lighthigher percentage of low-light

Cairo, Egypt: predominantly direct lightlong time intervals with high insolation


0 200 400 600 800 10000

200

400

600

800

1000

Freq

uenc

y [h

ours

/yea

r]

Global horizontal irradiance [W/m2]

Oslo

Cairo

Constraints in simulations: Single module operation

smaller shadows than in field no additional reflection from next row

No soiling/snow

Constant albedo throughout the year


South facing modules: Tilt angle optimization


1397

1402

1208

1213

1088

1093

44 46 48 50 52 54 56 58 60 621045

1050

Ann

ual e

nerg

y yi

eld

[kW

h/kW

p]

2323

2331

1988

19961777

1785

22 24 26 28 30 32 34 36 38 401746

1756

α= 0.5

α= 0.2

Oslo Cairo

STD STD

STDSTD

BIF

BIF

BIF

BIF

Tilt angle [°]

α = 0.2 Larger optimal tilt angles for bifacial modules

α = 0.5 Similar optimal tilt angles for both module types

Larger tilt angles for higher reflective ground

[1] Yusufoglu et al., Energy Procedia, in press


South facing modules: Tilt angle optimization

Larger tilt angles for

– Higher reflective ground

– Lower installations

Changes smaller for Oslo

1.5% yield loss @Cairo α=0.5 h=2m when using θopt = 32° instead of 42°



Module

elevation

Oslo Cairo

α = 0.2 α = 0.5 α = 0.2 α = 0.5

2 m 54 56 31 32

0.5 m 54 57 32 34

0 m 55 58 35 42


Vertically installed modules

Vertically installed modules yield nearly same whether front facing East or West

Provided a high albedo vertical installations can yield more than standard modules

No change in yield with varying module elevation


0

300

600

900

1200

1500

Ann

ual e

nerg

y yi

eld

[kh/

kWp]

STD

sou

thB

IF s

outh

BIF

fron

t E

ast

BIF

fron

t W

est

STD

sou

thB

IF s

outh

BIF

fron

t E

ast

BIF

fron

t W

est

OSLO

α = 0.20

400

800

1200

1600

2000

2400CAIRO

α = 0.2

STD

sou

thB

IF s

outh

BIF

fron

t E

ast

BIF

fron

t W

est

STD

sou

thB

IF s

outh

BIF

fron

t E

ast

BIF

fron

t W

est

α = 0.5 α = 0.5


Module elevation & albedo on yield

Annual gain increases with increasing height– Effect of module elevation small in Oslo less prone to nonoptimal installation

Linear relationship between albedo coefficient and annual yield– Larger slope for higher installed modules



0,20 0,35 0,501900

2000

2100

2200

2300

2400

Ann

ual e

nerg

y yi

eld

[kW

h/kW

p]

Albedo coefficient

Distance of lowermodule edge from ground

2 m 0.5 m 0 m

@ Cairo

190020002100220023002400

0,0 0,5 1,0 1,5 2,01210

12141304

13081398

1404

Cairo

Albedo coefficient 0.5 0.35 0.2

Oslo

Ann

ual e

nerg

y yi

eld

[kW

h/kW

p]

Lower module edge from ground [m]


Comparison with standard modules

Increased yields with bifacial modules than standard ones with

– Higher reflective ground

– Higher installations

Yield gain with higher installations insignificant for Oslo



Module

elevation

Oslo Cairo

α = 0.2 α = 0.5 α = 0.2 α = 0.5

2 m 15.5 % 28.3 % 13.8 % 30.6 %

0.5 m 15.5 % 28.3 % 12.9 % 28.8 %

0 m 15.4 % 28.1 % 10.6 % 24.3 %

Bifaciality gain in yield with respect to standard modules


Inhomogenity at rear module plane


Module elevation: 2 mα = 0.5

Module elevation: 0.1 mα = 0.5

Irradiance at the module rear side [W/m2] on an examplary summer day in Cairo


Inhomogenity at rear module plane


Reduction of nonuniformity with higher module elevation

Module installation optimization more beneficial for direct light dominated regions

Module

elevation

Oslo Cairo

α = 0.2 α = 0.5 α = 0.2 α = 0.52 m 15.5 % 9.3 % 28.3 % 13.9 % 13.8 % 10.0 % 30.6 % 21.5 %0 m 15.4 % 9.3 % 28.1 % 13.3 % 10.6 % 8.3 % 24.3 % 16.5 %

Bifaciality gain in yield with respect to standard modules

Including the inhomogenity at the rear side


Conclusion

Optimal tilt angles of south facing bifacial modules is f(Location, α, h)

Generally larger than those of standard modules

Larger tilt angles required for higher reflective ground & lower installations

Locations under predominant diffuse light less sensitive to non-optimal installations

Vertical installations are favorable provided a high reflective ground

Larger annual yields with higher elevated modules Increased influence of module elevation at direct light dominated regions Linearity between α and annual energy yield

Annual yield gain through bifaciality– 30 % (upper limit) vs. 10 - 20 % (realistic) for single module case



Thank you for your attention!

This work is part of the project “Kompetenzzentrum für innovative Photovoltaik-Modultechnik NRW” and has been supported by the European Union – European Regional Development Fund and by the Ministry of

Economic Affairs and Energy of the State of North Rhine-Westphalia, Germany.

Thanks to the colleagues at ISC Konstanz for

the measurements.

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