Reactive Self-Tracking Solar Concentration Katherine Baker, Jason Karp, Justin Hallas, and Joseph Ford University of California San Diego Jacobs School of Engineering Photonic Systems Integration Lab November 3, 2011 OSA Optics for Solar Energy (SOLAR) Photo: Kevin Walsh, OLR
Concentrator Tracking - Motivation 2D Mechanical Tracking Calculations are for a flat collector in San Diego, CA, tilted at latitude. Calculations based on A. Rabl. Active Solar Collectors and Their Applications.(Oxford University Press, New York, 1985)
Concentrator Tracking - Motivation 2D Mechanical Tracking 1D Mechanical Tracking Static Collector 12/21 3/20 6/21 12/21 3/20 6/21 Goal: Use a material with a nonlinear response to light to minimize mechanical tracking needs. Calculations are for a flat collector in San Diego, CA, tilted at latitude. Calculations based on A. Rabl. Active Solar Collectors and Their Applications.(Oxford University Press, New York, 1985)
1.0mm Concentrated Output 4mm Planar Micro-Optic Solar Concentration 1mm 120 Reflective Prisms Couplers Injection Features Thousands of individual apertures couple to a common waveguide Fabrication Results Coupled light striking another prism will decouple dominant loss Concentrated Output 1.7mm Thickness J. H. Karp et al, Planar micro-optic solar concentrator, Optics Express, 18(2) (2010). J. H. Karp et al, Radial coupling method for orthogonal concentration within planar micro-optic solar collectors, OSA Optics for Solar Energy (2010) 41μm
Photovoltaic Passive Prototype Performance Xe arc lamp solar simulator Concentrated Output Lens Array Optimized Current 91.0% 76.2% 52.3% (measured) Optimized Current 37.5x concentration (2 edges)
Mechanical Tracking Aligned Misaligned - Loss Large Scale Mechanical Tracking Typical for CPV systems High accuracy requirements Wind-Loading problems Mechanical Micro-Tracking Moving one optical element relative to the other allows tracking of large angle with small motions J. Hallas et al, Lateral translation micro-tracking of planar micro-optic solar concentrator, Proc. SPIE 7769, 776904 (2010).
New approach: Reactive Tracking Create nonlinear response to focused sunlight Continuous Coupling Facets Incoming Sunlight Tilted Incoming Sunlight Coupled Light High Index Region Shifted High Index Region Coupled Light Reactive Tracking Coupler relocates in response to sunlight Cladding index material response Spot moves less than 60 um/minute for a 4mm lenslet/slab distance
Angle-range Optimized Lens Design Acrylic asphere lens F2 Glass Waveguide Off-Axis performance falls off Easy to fabricate Acrylic and polycarbonate aspehere lenses F2 Glass Waveguide Improved off-axis performance; smaller spot sizes overall More difficult to fabricate Vignetting at Extreme Angles 0 10 20 30 35 0 10 20 30 35
Optical Efficiency Optical Efficiency Simulated Results On-Axis Singlet Lenses Doublet Lenses 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 Doublet Singlet 0 100 200 300 Geometric Concentration At 128x geometric concentration Singlet: 65% On-Axis Efficiency 83x effective concentration Doublet: 86% On-Axis Efficiency 110x effective concentration 1 0.8 0.6 0.4 0.2 Bulk Fluid Index = 1.20 1.25 1.30 1.35 0 1.2 1.4 1.6 1.8 Index of Refraction of High Index Spot
Simulated Results Off-Axis 1D Polar Tracking Static Panel Passive Design Reactive Singlet Reactive Doublet 25% - Static Panel 60% - 1D Polar Tracking Accepted Annual Energy: 28% - Static Panel 83% - 1D Polar Tracking
Nanofluidic design concepts Index response can be achieved through localized trapping of high index particles in a low index suspension Optical Tweezers Focused Sunlight Low-Index Suspension Optical Gradient: High Particle Concentration K.C. Neuman and S.M. Block, Optical trapping., The Review of scientific instruments, vol. 75, Sep. 2004, pp. 2787-809. As light refracts through a sphere, it changes angle. Through conservation of momentum, the particle will move in the opposite direction Direct Trapping Design Optical trapping of particles Particles large enough for the needed index change would cause scattering and fail to stay in suspension Ideal solution since no extra components are needed
Nanofluidic design concepts Index response can be achieved through localized trapping of high index particles in a low index suspension Focused Sunlight Optically-induced dielectrophoresis Same trapping force with 100,000 times less optical intensity compared to optical trapping Organic Photovoltaic Low-Index Suspension Optical Gradient: High Particle Concentration Direct Trapping Design Photovoltaic Design Photoconductor Design Optical trapping of particles Ideal solution since no extra components are needed Won t work Electro-optical trapping of particles Requires photovoltaic layer and additional processing, but no external power Electro-optical trapping of particles Requires photoconductor layer and external power P.Y. Chiou et al Massively parallel manipulation of single cells and microparticles using optical images., Nature, vol. 436, Jul. 2005, pp. 370-2.
Reactive Materials Testing Patterned Indium Tin Oxide Electrodes (a Transparent Conducting Oxide) Patterned ITO Slide Colloid Under Test Solid ITO Slide 80 μm Induced Non-Uniform Electric Field attracts high index particles ITO Coated Slides ~30 Ω/ sheet resistance Mach-Zehnder Interferometer
1 Results Signal Applied Signal Removed 60 nm Polystyrene Spheres in Water (10% by volume) 2 Volts rms 60 Hz Square Wave Applied for 60 seconds Fast, Reversible Index Change Demonstrated
Delta n 1 Measured number of fringe shifts Results 0.05 0.045 0.04 0.035 0.03 0.025 0.02 0.015 0.01 0.005 0 2 1.5 1 0.5 0 0 0.5 1 1.5 2 2.5 Voltage (rms); 60 Hz Square Wave Average change in index =.033 2.3x increase in concentration (10% to 23%) Equivalent increase for titanium dioxide in perfluorotriamylamine (FC-70 from 3M) would result in a.141 change
Conclusions Self-tracking reactive concentration could enable a wide acceptance angle for concentrator systems without precision tracking requirements. Wide-angle lenslet design works, given sufficient change in index of refraction While direct optical trapping won t work, DEP trapping can Initial experiments with aqueous polystyrene demonstrate DEP-induced change in index of refraction Additional materials work must be done in collaboration with industry and/or academic partners to produce the necessary change in index of refraction This research is supported by National Science Foundation under SGER award #0844274 California Energy Commission as part of the California Solar Energy Collaborative Special thanks to Robert Norwood and Palash Gangopadhyay of the University of Arizona for materials information and preparation and to Eric Tremblay for assistance with optical design
Thank you, kabaker@ucsd.edu psilab.ucsd.edu