Planar micro-optic solar concentration using multiple UCSD Photonics - - PowerPoint PPT Presentation

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Planar micro-optic solar concentration using multiple UCSD Photonics - - PowerPoint PPT Presentation

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Planar micro-optic solar concentration using multiple UCSD Photonics imaging lenses into a common slab waveguide Jason H. Karp, Eric J. Tremblay and Joseph E. Ford Photonics Systems Integration Lab University of California San Diego Jacobs

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UCSD Photonics

8/5/2009

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

Photo: Kevin Walsh, OLR

Planar micro-optic solar concentration using multiple imaging lenses into a common slab waveguide

Jason H. Karp, Eric J. Tremblay and Joseph E. Ford

Photonics Systems Integration Lab University of California San Diego Jacobs School of Engineering

August 4, 2009

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UCSD Photonics

Concentrator Photovoltaics (CPV)

  • 1. Primary Focusing Optic

– Performs light concentration – Large collecting lens or mirror – Trend towards multiple apertures

Energy Innovations

Solar Systems

SolFocus

  • 3. Mechanical Tracking

– Alignment for direct insolation – Angular acceptance defines tracking accuracy – Wind loading and environmental stability

Flatcon System Tracking

Concentrix Solar

  • 2. Secondary Homogenization Optic

– Mounted between primary and PV cell – Uniform illumination for high efficiency – Non-imaging optical design

Xiaohui Ning, Appl. Opt. 26, 1987

Light Prescriptions Innovators

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UCSD Photonics

Continuous Roll-to-Roll Fabrication

  • Continuous roll-to-roll processing

– Rigid or flexible substrates – Emboss, coat and bond layers

  • Inexpensive mass-fabrication
  • Constraints: Uniform thickness

Limited complexity

8/5/2009

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

Goal: Design a uniform thickness, high-flux solar concentrator compatible with continuous roll-to-roll manufacture Roll-to-Roll for CPV?

Konarka Global Solar

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UCSD Photonics

Micro-optic Slab Concentrator

8/5/2009

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

Advantages:

– Sub-apertures couple light to single output – Homogeneous output intensity – Uniform thickness (roll-to-roll fabrication) Direct Incidence Sunlight

Concentrated Output Coupling facets Lens Array Slab Waveguide

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UCSD Photonics

Waveguide Coupling Facets

8/5/2009

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

  • Reflective facets tilt light to satisfy TIR
  • Couplers are localized at each lens focus (<1% surface area)

Reflective facet Other coupling points Focused rays from lens Slab waveguide

Guided Rays TIR

TIR TIR

Waveguide Decoupling (Primary Loss)

Symmetric coupling

120º Symmetric Prism:

Repeatable structure No blocking

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UCSD Photonics

Lens Array Slab Waveguide Waveguide Cladding

Geometric Concentration Ratio

geo

Slab Length C Slab Thickness

System Layout

Slab Thickness

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UCSD Photonics

Coupling Facet Alignment

  • Align lens focus to each coupling facet
  • Large area concentrators (~1 meter)
  • >100,000 points of alignment

8/5/2009

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

Lateral Alignment Rotational Alignment

VERY CRITICAL

Solution: Self-Alignment

  • Mold prism structure within photopolymer
  • Crosslink using UV exposure
  • Cures only at each lens focus
  • Guarantees alignment

UV Exposure

  • <50μm lateral alignment accuracy
  • <0.01° (0.2mrad) rotational alignment

– Difficult over large area

Crosslinked regions remain part of the final concentrator

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UCSD Photonics

Roll Processing Flowchart

Acrylic Superstrate and Waveguide Emboss from Coupler Master Self-Alignment UV Exposure Development Removes Uncured Polymer UV-Curable Polymer (cont.) Lens Array Embossing

8/5/2009

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

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UCSD Photonics θ

Design Tradeoffs

8/5/2009

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

f·tanθ f d f f·tanθ θ d

Field Displacement: Sun subtends ±0.25°

Short focal length → small coupling area Long focal length → easier TIR condition

Waveguide Thickness:

Length Slab Thickness

Thick waveguide → increased efficiency

Length Slab Thickness

Thin waveguide → high concentration

Cflux = Slab Length Slab Thickness x Efficiency

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UCSD Photonics

Optical Model

8/5/2009

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING Richard R. King et al., “Advances in High-Efficiency III-V Multijunction Solar Cells,” Advances in OptoElectronics, vol. 2007 (2007).

Spectrolab triple-junction cell

– 240x flux concentration – 40.7% efficiency

Provide 240x flux per edge System Simulation:

– Model overall efficiency – Optimize design tradeoffs – Cladding options

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UCSD Photonics

Analytic Model

Simple mathematical simulation

– Scattering loss – Material absorption – Mirror reflectivity

8/5/2009

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

Very promising, but incomplete…

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UCSD Photonics

Zemax Raytracing Model

Zemax Non-Sequential Model

– Lens aberrations – Polychromatic illumination – Material dispersion – Coatings and surface reflections

8/5/2009

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING Includes single layer MgF2 AR coating (@545nm) on lens array surface

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UCSD Photonics

Broad Spectrum Performance

Optimized using 0.425-1.3µm illumination

– Accurate range of material models – Minimum bandwidth for multi-junction PV cells

8/5/2009

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING Includes single layer MgF2 AR coating (@545nm) on lens array surface

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UCSD Photonics

Proof-of-Concept Fabrication

8/5/2009

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

Goal: Demonstrate self-aligned coupling facet fabrication

  • Use off-the shelf components
  • Waveguide: Fisher Scientific

– Microscope slide (75mm x 50mm) – BK7 float glass

  • Molding Polymer: MicroChem

– SU-8 Photoresist – Chemical and thermal resistances

  • Prism Mold: Wavefront Technology

– 120° symmetric prisms – 50μm period, 14.4μm deep

  • Lens Array: Fresnel Technologies

– F/1.1 hexagonal lens array – 200μm image of ±0.25° source – UVT acrylic

255 mm 203 mm

10μm field displacement

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UCSD Photonics

Fabrication Process

8/5/2009

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

Waveguide Un-crosslinked SU-8 Prism Mold Lens Array Crosslinked SU-8

  • 1. Spin SU-8 and Softbake
  • 3. Bake Under Weight

1kg

  • 2. Apply Mold and Pull Vacuum
  • 4. Separate Mold

and Invert

  • 5. UV Exposure
  • 6. Deposit Reflective Coating
  • 7. Heat Above Tg

and Develop

Hg arc lamp Uniform, collimated UV illumination

aspheric collector

T T

beam expansion and iris collimating mirror Hg arc 6” diameter beam

UV Exposure Source

Adjust beam divergence using the iris

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UCSD Photonics

Fabricated Couplers

Transparent glass slab Al-coated prism facet 200μm 50μm

75mm 50mm

20µm Depth

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UCSD Photonics

Prototype Alignment

  • White light illumination

– Calibrated to ±0.25°

  • Efficiency measurement

– Newport 818-ST wand detector

8/5/2009

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

±0.25° Illumination Calibrated detector Alignment stage Illuminated prototype

Lens Array Waveguide

  • 6-axis alignment

– Tolerance analysis SUCCESSFUL COUPLING

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UCSD Photonics

Prototype Performance

  • Zemax model of prototype concentrator

– Include actual lens performance and coupler size

  • Prototype uses off-the-shelf (non-ideal) components

8/5/2009

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

Prototype lens characteristics

37.5x : Fabricated Concentration Ratio

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UCSD Photonics

Prototype Loss Mechanisms

  • Lens F-Number

– 72.5% fill factor – Spherical aberration – Coupler annulus (50μm)

8/5/2009

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

Lens array Coupler annulus

  • Coupler Fabrication Yield

– Isolated instances – Trapped gas bubbles – SU-8 solvent removal

72.5% fill

Good prism molding Trapped gas bubbles

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UCSD Photonics

Uniformity and Alignment Tolerance

8/5/2009

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

Beam Uniformity

– Finite width contributes to non-uniformity – Uniformity increases with system size

Lateral Alignment Tolerance

– 90% collection with 37μm shift (±1°) – Alter UV source to add alignment tolerance

Lens Array Slab Waveguide

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UCSD Photonics

Misaligned Aligned

Solar Illumination Testing

8/5/2009

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

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UCSD Photonics

8/5/2009

PHOTONIC SYSTEMS INTEGRATION LABORATORY – UCSD JACOBS SCHOOL OF ENGINEERING

Thank You

Email: jkarp@ucsd.edu Website: psilab.ucsd.edu

This research is supported by the National Science Foundation Small Grants for Exploratory Research (SGER) program