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FK concentrator outdoor measurements

San Diego, August 2013

Maikel Hernández1, Juan Vilaplana1, Pablo Benítez1,2,

Rubén Mohedano1, Pablo Zamora2, Juan C. Miñano1,2, João Mendes-Lopes2

1LPI, USA and Spain 2Universidad Politécnica de Madrid (UPM), Spain

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FK concentrator overview

Optimal spectral design

Latest measurement results

Conclusions

Outline

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FK overview – Spectral design – Measurements - Conclusions

Köhler integration• Two-stages design where input/output stage forms image of a preferred object

point onto a point of the output/input stage• Canonical example: two identical lenses imaging a point source at infinite (plane

wavefronts) onto each other

in out

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Köhler integration in the FK• Advanced concentrator using LPI-proprietary 4-channel Köhler homogenization• POE folds image the sun onto SOE folds, which in turn image the POE folds

onto the square solar cell

FK overview – Spectral design – Measurements - Conclusions

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Köhler integration in the FK• Advanced concentrator using LPI-proprietary 4-channel Köhler homogenization• POE folds image the sun onto SOE folds, which in turn image the POE folds

onto the square solar cell

FK overview – Spectral design – Measurements - Conclusions

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Köhler integration in the FK• Advanced concentrator using LPI-proprietary 4-channel Köhler homogenization• POE folds image the sun onto SOE folds, which in turn image the POE folds

onto the square solar cell

FK overview – Spectral design – Measurements - Conclusions

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FK compared to other Fresnel concentrators•Higher Concentration-acceptance product (CAP): for a fixed minimum acceptance angle, the FK can concentrate more

Concentration Cg

0

200

400

600

800

1000

1200

0.25 0.5 0.75 1 1.25 1.5

Effective* acceptance angle (deg)

*includes sun finite size, optical losses, and MJ cell photocurrent

FK overview – Spectral design – Measurements - Conclusions

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FK features• Optical depth reduced with respect to other Fresnel systems (0.85<f#<1.2)

Freeform secondary lens (SOE)Fresnel lens (POE)

FK overview – Spectral design – Measurements - Conclusions

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FK features• High concentration • High optical efficiency• High spatial and spectral irradiance uniformity on the cell (high cell

efficiency and long-term reliability)• High acceptance angle (preserves high efficiency at array level)• Low cost optics

P. Zamora, et. al. “Experimental characterization of Fresnel-Köhler concentrators,” J. Photon. Energy. 2(1), 021806 (Oct 16, 2012).

Measured CAP = 0.56

FK overview – Spectral design – Measurements - Conclusions

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FK overview – Spectral design – Measurements - Conclusions

VentanaTM Optical Train:A complete off-the-shelf optics solution by Evonik and LPIusing acrylic POE

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FK concentrator overview

Optimal spectral design

Latest measurement results

Conclusions

Outline

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Spectral transmission issue• Solar cell junctions are series-connected, the goal is keeping balanced

photocurrents for bottom, middle and top sub-cells

FK overview – Spectral design – Measurements - Conclusions

Source: www.emcore.com

+

_

V

I

IL,top

IL, middle

IL, bottom

RS

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Spectral transmission issue• Solar cell junctions are series-connected, the goal is keeping balanced

photocurrents for bottom, middle and top sub-cells

• Best performance is achieved when the concentrator considers spectral characteristics of both sunlight and solar cell

0.000

0.200

0.400

0.600

0.800

1.000

1.200

1.400

1.600

350 550 750 950 1150 1350 1550 1750

dI/d

l (W

*m

-2*n

m-1

)

Wavelength (nm)

AM 1.5 spectrum containing a power density of 900W/m2 3J solar cell EQEs (Source: www.emcore.com)

FK overview – Spectral design – Measurements - Conclusions

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300 500 700 900 1100 1300 1500 1700

wavelength (nm)

300 500 700 900 1100 1300 1500 1700wavelength (nm)

Jsc,k = ∫S(λ)T(λ)EQEk (λ)dλ

Jsc ,top

Jsc ,mid

Jsc ,bot300 500 700 900 1100 1300 1500 1700wavelength (nm)

Concentrator optical transmission T(λ)

EQEtop(λ)

EQEmid(λ)

EQEbot(λ)

300 500 700 900 1100 1300 1500 1700wavelength (nm)

Solar spectrum S(λ)

×

Isc = min{Isc,top , Isc,mid , Isc,bot}

Spectral transmission issue• A careful optical design and good choice of optical materials maximize

energy production throughout the year

FK overview – Spectral design – Measurements - Conclusions

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Tracker angle = 0º

FK

RTP

P. Espinet-González et al., “Triple-junction solar cell performance under Fresnel-based concentrators taking into account chromatic aberration and off-axis operation”, CPV-8 Proceeding, Toledo, Spain (2012).

Spectral irradiance issue modelled

FK overview – Spectral design – Measurements - Conclusions

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Tracker angle = 0.6º

FK

RTP

Spectral irradiance issue modelled

FK overview – Spectral design – Measurements - Conclusions

P. Espinet-González et al., “Triple-junction solar cell performance under Fresnel-based concentrators taking into account chromatic aberration and off-axis operation”, CPV-8 Proceeding, Toledo, Spain (2012).

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Silo

(º)

100

75

50

25

0.4 0.8 1.2

Optical efficiency (%)

Electrical power (%)

FK

(º)

100

75

50

25

0.4 0.8 1.2

Optical efficiency (%)

Electrical power (%)

Spectral irradiance issue modelled

FK overview – Spectral design – Measurements - Conclusions

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FK concentrator overview

Optimal spectral design

Latest measurement results

Conclusions

Outline

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0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

‐1,6 ‐1,2 ‐0,8 ‐0,4 0 0,4 0,8 1,2 1,6

Power (W

)

Isc (A)

Sun tracking error (degs)

Electrical power (%)

Optical efficiency (%)

P. Zamora, et. al. “Experimental characterization of Fresnel-Köhler concentrators,” J. Photon. Energy. 2(1), 021806 (Oct 16, 2012)

Spectral irradiance issue measured• Measurements confirm the models

FK overview – Spectral design – Measurements - Conclusions