Multi bifacial solar cells in comparison with bifacial mono cells and modules

1. Andrey Sitnikov
Multi Bifacial Solar CellsMulti Bifacial Solar CellsMulti Bifacial Solar CellsMulti Bifacial Solar Cells
in comparison with Bifacialin comparison with Bifacial
mono cells and modulesmono cells and modules
3D Solar AG3D Solar AG
Solar Wind LtdSolar Wind Ltd

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

3. 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%

4. Bifacial modules advantages realization
Czech Republic, Crumlov SOLAR PARK 0.43 MWt
TRAXEL system with the trackers

5. Standard bifacial modules parameters
Producing power is up to 178 & 250 W/м2
MSW Side
Standard AM1,5
conditions – 178 W/м2 Cells,
125x
125 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
1186x
550x
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
mono95/60
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
1575x
807x
46
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

6. Non-frame bifacial modules
with the increased resource
Lisek & Solar Wind cooperation
Non-frame bifacial module
with the area 4,7 sq.m was
made by LISEK (Austria)
technology.
It contains 264 Solar Wind
cells, laminated between twocells, 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

7. Solar Wind standard bifacial mono crystalline
solar cells
20%
30%
40%
50%
60%
70%
80%
90%
100%
externalquantumefficiency[%]
Face
Rear
Mono Solar Wind SC №5
Calculated short circuit current, mA/cm2
Face 38,6 Rear 25,99
Measured in
PASAN with
Fraunhofer
Standard
0%
10%
20%
300 400 500 600 700 800 900 1000 1100 1200
externalquantumefficiency
wavelength[nm] ОМЭ НИИЯФ МГУ 06.10.2011
Face 38,6 Rear 25,99
Voc Isc Pmax FF Vpm Ipm Eff
Face
Average 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 0,123
Best 0,629 5,766 2,910 80,38 0,540 5,398 18,82
Rear
Average 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 0,30
Best 0,621 4,126 2,070 80,950 0,544 3,813 13,39

8. 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

9. 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
bifacialitycoeff
0,60
0,70
0,80
0,90
bifacialitycoeff
32
28
24
40
idealAM1,5rearcurrent,mA/cm2for180mcm
0,00
0,10
0,20
0,30
0,40
200 400 600 800 1000 1200
bifacialitycoeff
wavelength, nm
100 mcm 200 mcm 300 mcm
400 mcm 600 mcm 800 mcm
1000 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
idealAM1,5rearcurrent,mA/cm

10. 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
diffusionlength,mcm
bifacialutycoeff
0,5
0,6
0,7
diffusionlength,mcm
bifacialutycoeff
320
480
240

11. Test Series1: Multi crystalline solar cell
20%
30%
40%
50%
60%
70%
80%
90%
100%
externalquantumefficiency[%]
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
externalquantumefficiency
wavelength [nm] ОМЭ НИИЯФ МГУ 06.10.2011
Face 34,29 Rear 24,3
Measured in
PASAN with
Fraunhofer
Standard

12. MONO = MULTI ?
The diffusion length in multi silicon is quite suitable for
manufacturing of bifacial solar cells. The overwhelming part of it
has diffusion length more than 300 microns that considerably
exceeds 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 and
mono makes 93 %, for obverse currents this relation decreases
to 89 %.
Except insufficient antireflection properties of an acid textured
structure there is one more mechanism, able to make essential
impact on an obverse current of short circuit. It is the mechanism
known as «light trapping» it is connected with design features of
cells and it is shown in a long-wave part of radiation.

13. Refraction and reflection in different cells design

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

15. 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
Iscspectraldensity,mA/nmcm2
AM1,5
Pyr. EVA Ref
Pyr. EVA no Ref
Pyr. Air Ref
Pyr. Air no Ref
Smooth Ref
Smooth no Ref
0,00
300 400 500 600 700 800 900 1000 1100 1200
Iscspectraldensity,mA/nmcm
wavelength, nm
0,00
0,10
0,20
0,30
0,40
0,50
0,60
900 950 1000 1050 1100 1150 1200
Iscspectraldensity,mA/nm
cm2
wavelength, nm
AM1,5
Pyr. EVA Ref
Pyr. EVA no Ref
Pyr. Air Ref
Pyr. Air no Ref
Smooth Ref
Smooth no Ref

16. Thank you for your
attention!