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.

Presentation Outline

1.The Cell

2.The Module

3.To Market

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

THE bSolar PERT CELL

INTRINSIC FACTORS INFLUENCING THE FRONT EFFICIENCY OF

MONO AND BIFACIAL CELLS

FRONT EFFICIENCY OF PRESENT bSolar INDUSTRIAL CELL

101

102

103

104

15

16

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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

JERUSALEM TEST SITE

BIFACIAL bSOLAR VS. MONOFACIAL MODULE

Geilenkirchen test field monitored by Fraunhofer ISE

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

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60

0

50

100

150

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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.