Andrey Sitnikov

Multi Bifacial Solar Cells Multi Bifacial Solar Cells Multi Bifacial Solar Cells Multi Bifacial Solar Cells in comparison with Bifacial in comparison with Bifacial

mono cells and modulesmono cells and modules3D Solar AG 3D Solar AG Solar Wind LtdSolar Wind Ltd

Solar Wind Ltd experience (Since 1997): If Bifacial solar modules are used as standard modules,it provides power gain of 7-9%

There are systems, emphasizing the advantages of double-sided modules

The gain is up to 30%

Solar Wind Ltd experience (Since 1997): If Bifacial solar modules are used with special tracking system, it provides power gain of up to 30%

The test results of bifacial modules on «TRAXEL», show a significant advantage in compare with standard modules of similar capacity

to 30%

Bifacial modules advantages realization Czech Republic, Crumlov SOLAR PARK 0.43 MWtTRAXEL system with the trackers

Standard bifacial modules parametersProducing power is up to 178 & 250 W/м2

MSW Side Standard AM1,5

conditions – 178 W/ м2 Cells,

125x125 mm LWT, mm

Weight, kg

Additional 70% rear illumination – 250 W/ м2

Isc, A Uoc, V Pmax, W Umpp, V Impp , A Isc, A Uoc, V Pmax, W Umpp , V Impp , A

85/50 Front 5,41 22,25 85 17,07 4,98

multi

9 x 4

1186

x 55

0 x 46

7,18

7,57 23,14 119 17,41 6,83

Rear 3,49 21,78 50 16,95 3,12

90/60 Front 5,51 22,39 90 18,00 5,01

mono

7,71 23,29 126 18,36 6,86

Rear 3,70 21,82 60 17,80 3,37

95/60 Front 5,69 22,50 95 18,20 5,22 7,97 23,40 133 18,56 7,16

1186

mono 95/60 Rear 3,80 21,96 60 17,80 3,37

100/70 Front 5,79 22,61 100 18,60 5,37 8,11 23,51 140 18,97 7,38

Rear 4,20 22,20 70 18,30 3,82

170/100 Front 5,41 44,51 170 34,14 4,98

multi

12 x 6

1575

x 8

07 x 4

6

14,05

7,57 46,29 238 34,82 6,83

Rear 3,49 43,56 100 33,90 3,12

190/120 Front 5,69 44,52 190 36,40 5,22

mono

7,97 46,30 266 37,13 7,16

Rear 3,80 43,92 120 36,00 3,37

195/130 Front 5,79 44,80 195 36,30 5,37 8,11 46,59 273 37,03 7,37

Rear 3,80 43,92 130 35,60 3,65

200/140 Front 5,79 45,22 200 37,20 5,37 8,11 47,03 280 37,94 7,38

Rear 4,20 44,40 140 35,60 3,82

Non-frame bifacial modules with the increased resource

Lisek & Solar Wind cooperationNon-frame bifacial module with the area 4,7 sq.m was made by LISEK (Austria) technology.

It contains 264 Solar Wind cells, laminated between two cells, laminated between two tempered glasses with thickness of 2.1 mm.

Such design, besides the increased resource has also other advantages to double-side application.

In particular, there is no shadowing by a frame.

Front power of the module – 711 W, rear – 433 W

Solar Wind standard bifacial mono crystalline solar cells

20%30%40%50%60%70%80%90%

100%ex

tern

al q

uant

um e

ffic

ienc

y [%

]

FaceRear

Mono Solar Wind SC №5

Calculated short circuit current, mA/cm 2

Face 38,6 Rear 25,99

Measured in PASAN with Fraunhofer Standard

0%10%20%

300 400 500 600 700 800 900 1000 1100 1200exte

rnal

qua

ntum

eff

icie

ncy

wavelength[nm] ОМЭ НИИЯФ МГУ 06.10.2011

Face 38,6 Rear 25,99

Voc Isc Pmax FF Vpm Ipm Eff

FaceAverage 0,626 5,761 2,879 79,821 0,537 5,365 18,621

± 0,003 0,021 0,019 0,515 0,004 0,037 0,123Best 0,629 5,766 2,910 80,38 0,540 5,398 18,82

RearAverage 0,619 4,002 1,989 80,36 0,536 3,714 12,87

± 0,001 0,092 0,047 0,68 0,004 0,093 0,30Best 0,621 4,126 2,070 80,950 0,544 3,813 13,39

Multi silicon as material for bifacial solar cells

It is believed that multi crystalline silicon is not entirely suitable for double-sided applications, entirely suitable for double-sided applications, due to the low minor carriers lifetime.

Let us consider in more detail the work of bi-facial solar cells and its dependence on the diffusion length

Dependence of the bifacial coeff. from the wavelength for monochromatic illumination and from the minor carriers diffusion length

0,50

0,60

0,70

0,80

0,90

1,00

bifa

cial

ity c

oeff

0,60

0,70

0,80

0,90

bifa

cial

ity c

oeff

32

28

24

40

idea

l AM

1,5

rear

cur

rent

, mA

/cm

2 fo

r 18

0 m

cm

0,00

0,10

0,20

0,30

0,40

200 400 600 800 1000 1200

bifa

cial

ity c

oeff

wavelength, nm100 mcm 200 mcm 300 mcm400 mcm 600 mcm 800 mcm1000 mcm

0,10

0,20

0,30

0,40

0,50

100 200 300 400 500 600 700 800 900 1000

Ln, mcm

160 mcm 180 mcm 200 mcm

21

17

12

7

idea

l AM

1,5

rear

cur

rent

, mA

/cm

Measurement of diffusion length on the real bifacial multi crystalline solar cells

0,3

0,35

0,4

0,45

0,5

0,55

0,6

0,65

0,7

0,75

0 10 20 30 40 50 60 70 80

Distance, mm

200 250 300 350 400 450 500 550 600

Ln, mcm

diffu

sion

leng

th, m

cm

bifa

cial

uty

coef

f

0,5

0,6

0,7

diffu

sion

leng

th, m

cm

bifa

cial

uty

coef

f

320

480

240

Test Series1: Multi crystalline solar cell

20%30%40%50%60%70%80%90%

100%ex

tern

al q

uant

um e

ffic

ienc

y[%

]

Face

Rear

Multy Solar Wind SC №2

Calculated short circuit current, mA/cm2

Face 34,29 Rear 24,3

Voc Isc Pmax FF Vpm Ipm Eff

F a c e Average 0,618 5,288 2,557 78,217 0,525 4,867 16,363

± 0,001 0,015 0,027 0,562 0,006 0,007 0,171 Best 0,621 5,295 2,610 79,34 0,537 4,855 16,70

R e a r Average 0,611 3,933 1,893 78,800 0,521 3,636 12,247

± 0,001 0,092 0,053 0,330 0,001 0,106 0,345 Best 0,611 4,116 2,00 79,46 0,520 3,847 12,937

0%10%20%

300 400 500 600 700 800 900 1000 1100 1200

exte

rnal

qua

ntum

eff

icie

ncy

wavelength [nm] ОМЭ НИИЯФ МГУ 06.10.2011

Face 34,29 Rear 24,3

Measured in PASAN with Fraunhofer Standard

MONO = MULTI ?

The diffusion length in multi silicon is quite suitable formanufacturing of bifacial solar cells. The overwhelming part of ithas diffusion length more than 300 microns that considerablyexceeds standard wafer thickness (180-200 microns).

Actually multi silicon diffusion length doesn't differ from the mono.

At the same time, if the relation of back currents for the multi andAt the same time, if the relation of back currents for the multi andmono makes 93 %, for obverse currents this relation decreasesto 89 %.

Except insufficient antireflection properties of an acid texturedstructure there is one more mechanism, able to make essentialimpact on an obverse current of short circuit. It is the mechanismknown as «light trapping» it is connected with design features ofcells and it is shown in a long-wave part of radiation.

Refraction and reflection in different cells design

“Light trapping” effect manifestation on the transmission of various structures

The result of “light trapping” action in various structures

Calculated Isc without optical losses

for 180 mcm thickness wafer with Ln 500 mcm, mA/cm2

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,70

0,80

Isc

spect

ral d

ensi

ty,

mA

/nm

cm

2

AM1,5

Pyr. EVA Ref

Pyr. EVA no Ref

Pyr. Air Ref

Pyr. Air no Ref

Smooth Ref

Smooth no Ref

0,00300 400 500 600 700 800 900 1000 1100 1200Is

c sp

ect

ral d

ensi

ty,

mA

/nm

cm

wavelength, nm

0,00

0,10

0,20

0,30

0,40

0,50

0,60

900 950 1000 1050 1100 1150 1200

Isc

spe

ctra

l de

nsi

ty, m

A/n

m

cm2

wavelength, nm

AM1,5

Pyr. EVA Ref

Pyr. EVA no Ref

Pyr. Air Ref

Pyr. Air no Ref

Smooth Ref

Smooth no Ref

Thank you for your attention!