High efficiency industrial PERT p-type bifacial cell and field results
Prof. Naftali Eisenberg1,2
Dr. Lev Kreinin1,2
Dr. Nelly Bordin1,2
Dr. Yossi Kofman2
1: Jerusalem College of Technology 2: bSolar Ltd.
Bifacial Cell Status
• More companies (Yingli, Nexolon, PVG Solution, Hareon, LG, Eversol, etc..) are understanding the huge potential of bifacial modules; this is mainly due to the recent development of n type Si technology cell production (with inherent bifacial design).
• However p-type Si solar cell standard fabrication technology accounts for 85 % of world PV production without acceptable industrial solution for bifacial cell fabrication.
• bSolar proposed and realized an industrial cost effective solution for p-type Si bifacial cell fabrication.
REQUIREMENTS FOR n+-p-p+ BIFACIAL CELL
Electro-physical parameters• Large bulk diffusion length: L>>d• Low effective back surface recombination: Seff
• Higher potential of back high-low barrier
Optical parameters• Effective light trapping for the photoactive wavelength range• Rejection of the non photoactive light
POSSIBLE ACTIONS TO ACHIEVE THE OBJECTIVES
• Use Si with high starting lifetime t• Retain t during cell fabrication• High doping at high-low junction• Proper pyramid textured front with retained flat back• Minimal contact coverage
FRONT EFFICIENCY OF PRESENT bSolar INDUSTRIAL CELL
101
102
103
104
15
16
17
18
19
20
Bulk lifetime, t, s
Eff
icie
ncy,
, %
Industrially fabricated with 7.2 % contact coverage
Industrially fabricated with 5 % contact coverage
(To be done)
bSolar CELL PARAMETERS
Parameter Range Average Expected
Short circuit currentIsc,, mA/cm2 37.5 – 38.1 37.7 38.5
Open circuit voltageVoc, V
616 - 629 622 638Fill factor
FF, % 78 – 79 78.5 80Efficiency (front)
Eff., % 18.1 – 18.8 18.45 19.6Bifaciality factor
Isc b/Isc f, %74 -79 75 79
Next generation
Present Future
Heavily doped BSF Controlled B doping
No back passivation Back passivation
7.2 or 5% contact coverage 3% grid contact
Bifaciality factor < 80 % Bifaciality factor > 95 %
101
102
103
104
16
17
18
19
20
21
22
23
Bulk lifetime, t, s
Eff
icie
nc
y,
,
%Based on controlled B doping, back surface passivation and 3 % contacting surface
Based on existing industrialtechnology and 5 % contact coverage
FRONT EFFICIENCY OF NEXT GENERATION BIFACIAL CELL
THE BEAUTY OF BIFACIAL SOLAR MODULE IS IN THE COLLECTION OF ADDITIONAL ENERGY BY THE CELL BACK SIDE
THE BIFACIAL MODULE
THE BIFACIAL GAIN CONCEPT
ROOFTOP TEST FIELD IN JERUSALEM
BIFACIAL MODULE GAIN OVER MONOFACIAL:
ABSOLUTE: G = { kWh/ kWp, front} bif - { kWh/ kWp, front} mono
Geilenkirchen test field monitored by Fraunhofer ISE
Annual Gain for the period 3/11 – 2/12 : 22.4%
( Albedo from 78 to 67 %)
0
10
20
30
40
50
60
0
50
100
150
200
250
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
Gai
n %
Yie
ld k
wh
/kw
p
Bsolar Yield
Monofacial yield
Gain
2011 2012
STANDARD, CERTIFICATION, BANKABILITY ETC…
THREE MAJOR TASKS:
1. Bifacial Module Certification2. Field Measurements and Characterization3. Development of Simulation Tool
To Market ? …… With more R&D
Bifacial Cell Equivalent Efficiency = Efficiency of Monofacial Cell Generating the Same Energy
(So a bifacial cell with a 20% front efficiency and an annual gain of 23 % has an equivalent efficiency of 24.6%)
Bifacial Module Equivalent Power = Power of a Monofacial Module able to Generate the Same Energy as a Bifacial Module in the Same Conditions
(So a bifacial module with a 250 W front power and an annual gain of 23 % has an equivalent power of 307.5 W)
CELL EQUIVALENT EFFICIENCY AND MODULE EQUIVALENT POWER
EXAMPLE OF SIMULATION: Germany,Berlin, Tilt=30°, NS=2.32m
Annual Gain and Equivalent Cell Efficiency for various Designs
The potential
• This type of cell will use almost standard Si starting material, standard fabrication equipment and standard module fabrication.
• A bifacial cell with 22% front efficiency and a 30% added collected energy from the back will be equivalent to a monofacial cell with front efficiency of 28.6% i.e. close to the physical efficiency limit.
Top Related