Abstract

Planar micro-optic concentrators are passive optical structures which combine a lens array with faceted microstructures to couple sunlight into a planar slab waveguide. Guided rays propagate within the slab to edge-mounted photovoltaic cells. This paper provides analysis and preliminary experiments describing modifications and additions to the geometry which increase concentration ratios along both the vertical and orthogonal waveguide axes. We present simulated results for a 900x concentrator with 85% optical efficiency, measured results for small-scale experimental systems and briefly discuss implementations using low-cost fabrication on continuous planar waveguides.

© 2011 OSA

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References

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  1. D. Feuermann and J. M. Gordon, “High-concentration photovoltaic designs based on miniature parabolic dishes,” Sol. Energy 70(5), 423–430 (2001).
    [CrossRef]

2001 (1)

D. Feuermann and J. M. Gordon, “High-concentration photovoltaic designs based on miniature parabolic dishes,” Sol. Energy 70(5), 423–430 (2001).
[CrossRef]

Sol. Energy (1)

D. Feuermann and J. M. Gordon, “High-concentration photovoltaic designs based on miniature parabolic dishes,” Sol. Energy 70(5), 423–430 (2001).
[CrossRef]

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Figures (13)

Fig. 1
Fig. 1

The micro-optic concentrator pairs a lens array with a planar slab waveguide (a). Localized 120° prisms placed on the waveguide surface couple light into guided modes without shadowing effects (b).

Fig. 2
Fig. 2

The lens array and coupling prisms create two bundles exiting the waveguide (a). Within the polar plot, output angles (green circles) fill only a portion of the total angular spectrum (b).

Fig. 3
Fig. 3

Orthogonal waveguides provides additional concentration along the slab width (a). Radial coupler orientation appears as a lens focusing into a v-trough (b).

Fig. 4
Fig. 4

Dimensions of the orthogonal waveguide layout.

Fig. 5
Fig. 5

Optical efficiency as a function of orthogonal concentration factor for various lens f-numbers. All systems incorporated 200mm of propagation in glass to the exit aperture.

Fig. 6
Fig. 6

Efficiency comparison between rectangular and orthogonal waveguide geometries. Both systems used an F/3 lens array and 1mm thick glass waveguides.

Fig. 7
Fig. 7

Optical layout showing 8x orthogonal concentration using F/3 lenses (note: system scale has been reduced for visualization purposes) (a). Sidewalls confine light along the slab width, increasing the angular spectrum in one dimension (b).

Fig. 8
Fig. 8

Optical layout of the prototype concentrator (a). SEM image of the waveguide surface showing coupler spacing and diameter (inset) (b). Image of the system under test (c).

Fig. 9
Fig. 9

Geometry of the experimental orthogonal concentrator (a). Image of the fabricated waveguide (b) and the concentrator under test (c).

Fig. 10
Fig. 10

Layout of the SOE positioned between two opposing waveguides.

Fig. 11
Fig. 11

Raytrace highlighting the odd and even reflection ray paths within the SOE (a) and the associated angular spectrum when capturing the output from F/3 focusing lenses (b).

Fig. 12
Fig. 12

Orthogonal waveguides can be combined with secondary optics to reach very high concentration levels (a). The associated angular spectrum increases in two dimensions (b).

Fig. 13
Fig. 13

Equivalent micro-optics increase concentration without sectioning the lens array or waveguide and enable continuous manufacturing approaches.

Equations (6)

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C 2 D = 1 sin θ i n , C 3 D = 1 sin 2 θ i n
C g e o = l ( w 1 + w 2 ) / 2 w 2 h
tan α = 1 2 F / # + tan θ
f w i = C + 1 2 C 2 ( 3 C 2 2 C 1 ) 1 / 2   where   C = w i w 2 = 1 sin ( α / n )
tan ψ = w 1 2 f
l = f ( 1 1 C )

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