Planar micro-optic solar concentration Jason H. Karp Eric J. Tremblay, Katherine A. Baker and Joseph E. Ford Photonics Systems Integration Lab University of California San Diego Jacobs School of Engineering November 10, 2009 PHOTONIC SYSTEMS INTEGRATION LABORATORY UCSD JACOBS SCHOOL OF ENGINEERING Photo: Kevin Walsh, OLR
Photonic Systems Integration Lab (PSI) Dr. Joseph E. Ford Principle Investigator Photonic Systems Integration Lab Concentric Multi-reflection Lenses (aka Origami Optics) 8-fold telephoto lens, 40mm focal length, 5mm thick 5.7 full angle field of view E. Tremblay, R. Stack, R. Morrison, J. Karp, and J. Ford, "Ultrathin four-reflection imager," Appl. Opt. 48, 343-354 (2009) Group Members: Stephen Olivas Eric Tremblay Brett Nadler Jason Karp Justin Hallas Kate Baker Pavel Shekhtmeyster
Concentrator Photovoltaics (CPV) Silicon Solar Cells Single material bandgap 12-18% efficiency Multijunction Solar Cells 2 or more material bandgaps >40% efficiency GaInP GaInAs Solar Concentration 100x 500x increase in flux Ge Goal: Design and fabricate a highflux concentrator compatible with inexpensive manufacturing
Concentrator Components Solar Systems 1. Primary Focusing Optic Performs light concentration Large collecting lens or mirror Trend towards multiple apertures Energy Innovations SolFocus 2. Secondary Homogenization Optic Mounted between primary and PV cell Uniform illumination for high efficiency Non-imaging optical design Light Prescriptions Innovators Xiaohui Ning, Appl. Opt. 26, 1987 3. Mechanical Tracking Alignment for direct insolation Angular acceptance defines tracking accuracy Wind loading and environmental stability Flatcon System Tracking Concentrix Solar
Optical design & modeling Multiple apertures couple to single output Homogeneous output intensity Uniform thickness (roll-to-roll fabrication) Focused Sunlight Decoupling Loss Slab waveguide 120 120 symmetric prism coupling J. H. Karp, E. J. Tremblay and J. E. Ford, Planar micro-optic solar concentrator, Optics Express, Submitted for publication, October 12, 2009. Reflective prisms tilt light to TIR Couplers occupy <0.1% of waveguide surface Subsequent interaction decouples as loss
System Layout Lens Array Cladding Layer Slab Waveguide Slab Thickness Geometric Concentration Ratio Slab Length Cgeo 2x Slab Thickness
Fabrication process: Self-alignment Critical Alignment Tolerance Lens focus must overlap with each coupling location <50μm lateral alignment tolerance <0.01 (0.2mrad) rotational alignment UV Exposure Solution: Self-alignment Mold prism structure in UV-curable photopolymer Expose through lens array to define coupling regions Cured regions remain part of the final device Coupling features made by exposure through lenses Low-cost manufacturing process Continuous roll processing (same used for holographic packaging) on flexible or rigid substrates
Design Tradeoffs Field Displacement: Sun subtends ±0.25 θ θ d f tanθ d f tanθ f f Short focal length small coupling area Long focal length easier TIR condition Waveguide Thickness: C flux = Slab Length Slab Thickness x Efficiency Length Slab Thickness Length Slab Thickness Thin waveguide high concentration Thick waveguide increased efficiency
Zemax Raytracing Model Zemax Non-Sequential Model Lens aberrations Polychromatic illumination Material dispersion Coatings and surface reflections Air Cladding Design 100μm air spacing Supports steep ray angles All glass construction 1mm thick waveguide F/2.45 lenses Fluoropolymer Cladding Low index cladding (n=1.33) Solid profile Polymer lens, glass waveguide 1mm thick waveguide F/4.11 lenses J. H. Karp, E. J. Tremblay and J. E. Ford, Planar micro-optic solar concentrator, Optics Express, Submitted for publication, October 12, 2009.
Broad Spectrum Performance Optimized for 400-1600nm sunlight Accurate range of material models Minimum bandwidth for multi-junction PV cells
Fabrication Process 1. Spin SU-8 and Softbake 5. UV Exposure UV Exposure Source 2. Apply Mold and Pull Vacuum Hg arc aspheric collector collimating mirror beam expansion and iris T T 3. Bake Under Weight 6. Deposit Reflective Coating 6 diameter beam 1kg 4. Separate Mold and Invert 7. Heat Above T g and Develop Uniform, collimated UV illumination Hg arc lamp Waveguide Un-crosslinked SU-8 Prism Mold Crosslinked SU-8 Lens Array PHOTONIC SYSTEMS INTEGRATION LABORATORY UCSD JACOBS SCHOOL OF ENGINEERING Adjust beam divergence using the iris
Fabricated Couplers Al-coated prism facet 75mm Transparent glass slab 50μm 50mm 200μm 20µm Depth
Prototype Testing Alignment stage Calibrated detector Illuminated prototype Lens Array ±0.25 Illumination Waveguide 44.8% simulated efficiency 32.4% measured efficiency ±1.0 angular acceptance Non-ideal lens array Very short focal length Aberrations Large spots Low fill-factor (72.5%) 27.5% loss 72.5% fill
Solar Illumination Testing Aligned Misaligned
Future Directions 2 nd Prototype concentrator Replace existing lens array >65% predicted efficiency Integrate with PV cell Orthogonal focusing Additional concentration Secondary extraction Orthogonal focusing Spectral band splitting Dichroic output edges Tilt/roll tracking platform PV Cell Tracking System Design
This research is supported by: National Science Foundation (NSF), Small Grants for Exploratory Research (SGER) program California Energy Commission (CEC), Energy Innovations Small Grant (EISG) program Thank You Email: jkarp@ucsd.edu Website: http://psilab.ucsd.edu