Bifacial n- type crystalline silicon solar cells Bifacial n- type - - PowerPoint PPT Presentation

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Bifacial n- type crystalline silicon solar cells Bifacial n- type - - PowerPoint PPT Presentation

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Bifacial n- type crystalline silicon solar cells Bifacial n- type crystalline silicon solar cells Valentin D. Mihailetchi, A. Halm, A. Edler, G. Galbiati, L. J. Koduvelikulathu, R. Valentin D. Mihailetchi, A. Halm, A. Edler, G. Galbiati, L. J.

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SLIDE 1

Bifacial n-type crystalline silicon solar cells Bifacial n-type crystalline silicon solar cells

bifiPV workshop, Konstanz, April 2012

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Valentin D. Mihailetchi, A. Halm, A. Edler, G. Galbiati, L. J. Koduvelikulathu, R. Roescu, C. Comparotto, R. Kopecek, K. Peter, International Solar energy research Center (ISC), Konstanz (Germany) Valentin D. Mihailetchi, A. Halm, A. Edler, G. Galbiati, L. J. Koduvelikulathu, R. Roescu, C. Comparotto, R. Kopecek, K. Peter, International Solar energy research Center (ISC), Konstanz (Germany)

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SLIDE 2

Outline Outline

Motivation

  • why bifacial cells/modules?
  • installation possibilities of bifacial modules
  • n-type solar cell concepts

Fabrication of bifacial n-type solar cells

  • front and back contacted cells
  • all back contacted cells (IBC)

bifiPV workshop, Konstanz, April 2012

2

Summary

  • all back contacted cells (IBC)
  • our best cell results (monofacial measurement)

Preliminary tests of several small modules

  • standard cell versus back contact cell
  • indoor and outdoor tests
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SLIDE 3

Motivation Motivation

Why bifacial cells & modules?

Advantages:

  • increase power generation per m2
  • enables owners to generate more kWh per KWp

A bifacial panel generates electricity from ambient light reflected off surrounding surfaces, and combines with power from the front face of the panel.

bifiPV workshop, Konstanz, April 2012

  • enables owners to generate more kWh per KWp
  • …

3

Disadvantages:

  • more expensive fabrication !?
  • power output depends on installation site and conditions
  • difficult to quantify and predict the gain due to bifacial contribution
  • …

with bifacial (€/kWh) < without bifacial (€/kWh) ???

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SLIDE 4

Installation possibilities of bifacial modules

Reflected sunlight Direct sunlight

Slanted

Direct sunlight

Horizontal

Direct sunlight Direct sunlight

Vertical

Motivation Motivation

bifiPV workshop, Konstanz, April 2012

4 Reflected sunlight Reflected sunlight Reflected sunlight Reflected sunlight Balconies, Bus Shelters, Walkway Covers, Deck & Porch Coverings, Canopies, Carports, Fences, Facades, Siding, Trellises, Tracking Systems, BIPV, Ground Mount, Roof Mount, and more…!

Few application possibilities:

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SLIDE 5

Cell fabrication and module installation

Reflected sunlight Direct sunlight

Slanted

Direct sunlight

Horizontal Direct light Reflected light

>

Motivation Motivation

bifiPV workshop, Konstanz, April 2012

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Cells (or modules) fabrication:

  • can have asymmetric front/rear performance
  • should be optimized based on front side performance

Reflected sunlight Reflected sunlight

Direct light Reflected light Preferred orientation:

  • South (North) for slanted
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SLIDE 6

Direct sunlight Direct sunlight

Vertical

Cell fabrication and module installation

Front sunlight Rear sunlight

= if

Motivation Motivation

bifiPV workshop, Konstanz, April 2012

6 Reflected sunlight Reflected sunlight

Cells (or modules) fabrication:

  • could have symmetric front/rear performance

Preferred orientation:

  • East – West
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SLIDE 7

HIT solar cells

  • front, emitter: a-Si (p)
  • back, BSF: a-Si (n)
  • bifacial (Sanyo’s HIT double)
  • h

≤ 23% (Sanyo)

IBC solar cells

  • FSF/BSF: n+/n++ diffusion

h

N-type solar cell concepts N-type solar cell concepts

bifiPV workshop, Konstanz, April 2012

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Standard solar cells

  • front, emitter: p+ diffusion
  • back, BSF: n+ diffusion
  • bifacial
  • h

≤ 19.6% (Yingli)

  • FSF/BSF: n+/n++ diffusion
  • emitter: p+ diffusion
  • h

≤ 24.2% (Sunpower)

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SLIDE 8

Outline Outline

Motivation

  • why bifacial cells/modules?
  • installation possibilities of bifacial modules
  • n-type solar cell concepts

Fabrication of bifacial n-type solar cells

  • front and back contacted cells
  • all back contacted cells (IBC)

bifiPV workshop, Konstanz, April 2012

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Summary

  • all back contacted cells (IBC)
  • our best cell results (monofacial measurement)

Preliminary tests of several small modules

  • standard cell versus back contact cell
  • indoor and outdoor tests
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SLIDE 9

Fabrication of bifacial n-type solar cells Fabrication of bifacial n-type solar cells

N-type cell process development at ISC-Konstanz

Standard solar cells IBC solar cells (ZEBRA)

  • n-type Cz substrate
  • n-type Cz substrate

bifiPV workshop, Konstanz, April 2012

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  • n-type Cz substrate
  • 156×156 mm2 area
  • homogeneous diffusion
  • front side textured, rear side flat
  • industrial partner:
  • n-type Cz substrate
  • 156×156 mm2 area
  • homogeneous diffusion
  • front side textured, rear side flat or

textured

  • industrial partner:
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SLIDE 10

N-type cell process development at ISC-Konstanz

Standard solar cells IBC solar cells (ZEBRA)

BBr3 diffusion, p+ emitter BBr3 diffusion, p+ emitter

Fabrication of bifacial n-type solar cells Fabrication of bifacial n-type solar cells

bifiPV workshop, Konstanz, April 2012

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POCl3 diffusion, n+ BSF POCl3 diffusion, n+ BSF Saw damage etching, alkaline texturization, cleaning steps Saw damage etching, alkaline texturization, cleaning steps SiO2/SiNx passivation & ARC SiO2/SiNx passivation & ARC Screen printing and firing of p and n fingers, busbars Screen printing and firing of p and n fingers, busbars PECVD masking PECVD masking Laser ablation Laser ablation

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SLIDE 11

N-type cell process development at ISC-Konstanz

Standard solar cells IBC solar cells (ZEBRA)

Fabrication of bifacial n-type solar cells Fabrication of bifacial n-type solar cells

bifiPV workshop, Konstanz, April 2012

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Both cell concepts are bifacial !!!

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SLIDE 12

Best cell results (monofacial)

Cell type area [ cm2 ] JSC [ mA/cm2 ] VOC [ mV ] FF [ % ] h [ % ] Pmax [W] Standard (both sides contacted) 241 38.8 643 77.6 19.4 4.66 ZEBRA (back contacted) 238.9 41.2 646 79.1 21.0 5.03

Fabrication of bifacial n-type solar cells Fabrication of bifacial n-type solar cells

bifiPV workshop, Konstanz, April 2012

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Highlights:

  • 156×156 mm2 Cz substrates!
  • pseudo-FF ≥ 82% → no indication of shunts!
  • implied Voc ≥ 670 mV → good surface passivation!

What is the bifacial performance?

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SLIDE 13

Cell type

  • ptimized for best:

ηfront (%) ηrear / ηfront Standard monofacial 19.4 0.75-0.8 Standard bifacial* 18.0** 0.91***

* compared with monofacial cell, it has larger rear side metal finger pitch and higher BSF sheet resistance ** FF of ≤ 72% due to higer series resistance *** ratio different than 1 because of a flat rear side (different Jsc values)

Optimization route for best bifacial performance

100

Fabrication of bifacial n-type solar cells Fabrication of bifacial n-type solar cells

bifiPV workshop, Konstanz, April 2012

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0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 10 20 30 40 50 60 70 80 90 100

Monofacial optimized cell: front illumination rear illumination Bifacial optimized cell: front illumination rear illumination

IQE [%] Wavelength [µm] Cells with symmetric front & rear performance can be fabricated !!

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SLIDE 14

Outline Outline

Motivation

  • why bifacial cells/modules?
  • installation possibilities of bifacial modules
  • n-type solar cell concepts

Fabrication of bifacial n-type solar cells

  • front and back contacted cells
  • all back contacted cells (IBC)

bifiPV workshop, Konstanz, April 2012

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Summary

  • all back contacted cells (IBC)
  • our best cell results (monofacial measurement)

Preliminary tests of several small modules

  • standard cell versus back contact cell
  • indoor and outdoor tests
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SLIDE 15

Preliminary tests of several small modules Preliminary tests of several small modules

One cell module: for bifacial test

Back sheet variation: black, white, transparent Indoor measurements (as reference): @ 1 sun and 25°C

bifiPV workshop, Konstanz, April 2012

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module type back sheet ηrear / ηfront (module) ηrear / ηfront (cell) Standard transparent 0.85 0.79 ZEBRA transparent 0.75 not measured

  • front versus rear performance ratios
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SLIDE 16

One cell module: for bifacial test

Back sheet variation: black, white, transparent Indoor measurements (as reference): @ 1 sun and 25°C

Preliminary tests of several small modules Preliminary tests of several small modules

bifiPV workshop, Konstanz, April 2012

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  • black versus white back sheet

module type back sheet gain in Isc Standard white vs. black +0.80% ZEBRA white vs. black +0.81%

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SLIDE 17

One cell module: outdoor measurements

test condition and assumptions:

  • ground reflectivity → ≈ 70% (300-1200nm) (white back sheet)
  • orientation and inclination → South, 30°
  • measurement interval → every 5 min. (10 sec. module measure time)
  • all modules assumed to have the same temperature during an IV scan
  • front glass taped black outside cell area

Preliminary tests of several small modules Preliminary tests of several small modules

bifiPV workshop, Konstanz, April 2012

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  • front glass taped black outside cell area
  • one additional module was used to measured the back side light intensity

Photograph of the outdoor setup.

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SLIDE 18

One cell module: outdoor measurements

0.7 0.8 0.9 1.0 1.1 1.2 1.3

1sun, indoor) ZEBRA, transparent ZEBRA, black albedo module (Isc/Isc @1sun) Light intensity (suns)

bifacial versus monofacial module performance:

40 45 (%)

morning & afternoon

Preliminary tests of several small modules Preliminary tests of several small modules

bifiPV workshop, Konstanz, April 2012

18 07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Pmax/Pmax(1sun, i Time (HH:mm)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 5 10 15 20 25 30 35 40 albedo contribution (% Outdoor light intensity (suns)

noon

More sunlight is reflected to the back side in the morning and afternoon !

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SLIDE 19

One cell module: outdoor measurements

0.6 0.7 0.8 0.9 1.0 1.1 1.2

Zebra, transparent Zebra, black Linear fit

/Pmax(1sun)

bifacial versus monofacial module performance:

24 28 32

gain (%)

morning & afternoon noon

Preliminary tests of several small modules Preliminary tests of several small modules

bifiPV workshop, Konstanz, April 2012

19 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 0.0 0.1 0.2 0.3 0.4 0.5 0.6

Standard, transparent Standard, black Linear fit

Pmax/Pm Outdoor light intensity (suns)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 4 8 12 16 20 24

bifacial ZEBRA bifacial Standard albedo contribution (%)

net power gain Outdoor light intensity (suns)

Standard n-type bifacial module performed better due to higher rear/ front ratio!

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SLIDE 20

0.0 0.1 0.2 0.3 0.4 0.5

  • 5

5 10 15 20 25 30 35 40 45 50 Relative enhancement (%) Rear side light intensity (suns)

Single cell module: Power Voc Jsc FF

One cell module: bifacial performance

28 29 30 )

Preliminary tests of several small modules Preliminary tests of several small modules

bifiPV workshop, Konstanz, April 2012

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0.0 0.1 0.2 0.3 0.4 0.5

  • 5

5 10 15 20 25 30 35 40 45 50 Relative enhancement (%) Rear side light intensity (suns)

Single cell module: Power Voc Jsc FF

.8 η η

front rear

0.0 0.1 0.2 0.3 0.4 0.5 20 21 22 23 24 25 26 27 28 efficiency (%) Rear side light intensity (suns)

estimated best cell efficiency (combined front and rear)

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SLIDE 21
  • we achived 21% conversion efficiency on back-contacted (IBC)

cells and 19.4% on standard (both sided metalized) solar cells. Both solar cell concepts have a good bifacial characteristics.

Summary Summary

  • we developed processes to fabricated n-type solar cells on 156×156

mm2 (industry-standard) using exclusively process steps that are already used in mass production for conventional cells.

bifiPV workshop, Konstanz, April 2012

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  • Outdoor measurements on small bifacial modules demonstrate at least

12% gain in power (over a day) for a slanted installation for both cell

  • concepts. Cell efficiencies (combined front and back) over 23%abs can

be achieved on our IBC (ZEBRA) cells.

Thank you for your attention!