A Review of Sandwich Conversion Modules for Space Solar Power Dr. Paul Jaffe, U.S. Naval Research Laboratory Paul.Jaffe@nrl.navy.mil
Overview Space Solar Power What is a Sandwich Module? Why Sandwich Modules? Origins and History Sandwich Module Development and Tes>ng at the U.S. Naval Research Lab Future Direc>ons
SPECTRUM ALLOCATION IS A CRITICAL PREREQUISITE FOR WIRELESS POWER TRANSMISSION & SPACE SOLAR POWER
Space Solar 1. Sunlight collected in space Power 2. Energy sent wirelessly to Earth 4. Energy consumed 3. Energy received at ground receiver
What is a Sandwich Module?
In geosynchronous orbit, the sunlight collec>on surface and power transmission surface of a solar power satellite must point in different direc>ons and move with respect to each other Why Sandwich Modules? The Reference Design of the DOE/NASA studies of the 70 s proposed using a massive rota>ng joint to carry the energy across the junc>on of these surfaces SpacecraZ mechanisms engineers generally try to avoid such joints because they can be expensive, unreliable, and failure-prone NASA/DOE SPS Reference System, circa 1978
Merging the collec>on and transmission surfaces in a sandwich allows dispensing with the rota>ng joint and allows for sunlight concentra>on, but requires a way to redirec>on either the incoming sunlight or outgoing microwaves Why Sandwich Modules? Sandwich modules lend themselves well to massproduc>on and modular spacecraz construc>on techniques widely viewed as required for SSP realiza>on Thousands of adjacent sandwich modules form this surface Modular Symmetrical Concentrator, circa 2007
Some SSP Sandwich Conceptual Designs NASA/DOE Microwave sandwich concept, circa 1980 Modular Symmetrical Concentrator, circa 2007 SPS-ALPHA, circa 2013
An Early SSP Sandwich Concept From Maynard, Owen, E., "Solid State SPS Microwave Genera>on and Transmission Study," NASA Contractor Report 3339, Contract NAS8-33157, November 1980.
Sandwich Module Hardware Hiroshi Matsumoto, Kyoto University, with SPRITZ Solar Power Radio Integrated Transmifer, 2001 Nobuyuki Kaya s Kobe University Sandwich Module, 2003 Texas A&M U. concept, 2009
Naval Research Laboratory Sandwich Modules Completed and tested in space-like condi>ons the most efficient, highest specific power sandwich conversion modules to date, >le & step 8% & 7%, ~4x previous record 4.5 W/kg & 5.8 W/kg Tile Module, 2013 Step Module, 2013 Selected thermal analysis models Demonstrated and tested a novel new step sandwich module design that addresses thermal concerns Provided a meaningful empirical basis for space solar power economic studies
12 Future OpportuniGes for Sandwich Module Technology Advancement Specialized Test Facility Development Antenna Element & Array Characteriza>on Mass Reduc>on: Materials, Integra>on Thermal Management Improvements Thermal Instrumenta>on Improvements Layer Efficiency Enhancements Addi>onal Module Func>onality: Filtering, Retodirec>ve Control Alterna>ve Sandwich Module Approaches Caltech/Northrop Grumman Sandwich Module mockup, 2015
Conclusion The sandwich approach has been inves>gated in various capaci>es over the past 35 years It offers a number of poten>ally compelling advantages for space solar power satellite implementa>ons Many opportuni>es exist to further technologies associated with the sandwich approach
Thank You Dr. Paul Jaffe, U.S. Naval Research Laboratory Paul.Jaffe@nrl.navy.mil
Backup Charts 15
Sandwich Module Performance Comparison (To be supplied)
NRL Sandwich Module Areas of Future Work Specialized Test Facility Development Antenna Characteriza>on Mass Reduc>on Thermal Management Improvements Thermal Instrumenta>on Improvements Efficiency Enhancement Addi>onal Module Func>onality Add retrodirec>ve control Output Filtering Alterna>ve Sandwich Module Approaches Detailed discussions of each area can be found in A SUNLIGHT TO MICROWAVE POWER TRANSMISSION MODULE PROTOTYPE FOR SPACE SOLAR POWER" hfp://drum.lib.umd.edu/bitstream/1903/14811/1/jaffe_umd_0117e_14747.pdf
Recommended Next Step: Add FuncGonality PrioriJzing This Specialized Test Facility Development Antenna Characteriza>on Mass Reduc>on Thermal Management Improvements Thermal Instrumenta>on Improvements Efficiency Enhancement AddiJonal Module FuncJonality Add retrodirecjve control Output Filtering Alterna>ve Sandwich Module Approaches
PrioriJzing This will also likely yield benefits in These AddiGonal Benefits Specialized Test Facility Development Antenna Characteriza>on Mass Reduc>on Thermal Management Improvements Thermal Instrumenta>on Improvements Efficiency Enhancement AddiJonal Module FuncJonality Add retrodirecjve control Output Filtering Alterna>ve Sandwich Module Approaches
PrioriJzing This will also likely yield benefits in These and will make work done Here more meaningful Clarified ImplementaGon Specialized Test Facility Development Antenna Characteriza>on Mass Reduc>on Thermal Management Improvements Thermal Instrumenta>on Improvements Efficiency Enhancement AddiJonal Module FuncJonality Add retrodirecjve control Output Filtering Alterna>ve Sandwich Module Approaches
NRL Space Background NRL s Long and Diverse History in Space Over 100 Satellites more than 40 Launches for Na>onal, DoD, and Civil Sponsors on a Variety of Vehicles 3 Major Space Systems Transi>oned to Industry Extensive Experience With Leader/Follower Acquisition and Industry Transition Approaches
WITHIN TEN YEARS Satellite cost ($/kg) 20x Reduc>on Power/mass (W/kg) >50x Increase Less than 10 /kwh, assuming no reducjons in launch cost
Photovoltaic RF Converter Antenna Element Module Research ObjecJve: Resolve trades and execute proof of principle development of an integrated module for converjng received light energy into transmi[ed microwave energy to support terrestrial, marine, and space-borne wireless power transfer applicajons, with a focus on the space case. Approach: ² Performed cri>cal trades of photovoltaic, DC-to-RF conversion, and antenna element candidates ² Analyzed thermal challenges and integra>on schemes ² Developed and integrated a proof of principle Photovoltaic RF-DC converter Antenna element Module (PRAM) unit ² Conducted lab tes>ng and performance characteriza>on ² Executed environmental tes>ng of units Prospec>ve users of systems employing such modules: ² Forward based troops and other remote energy consumers that require baseload power ² Power companies and coopera>ves PRAMs, a.k.a. sandwich modules form a large microwave transmivng aperture
Photovoltaic RF Converter Antenna Element Module Research Rela>onship to Other Projects / Organiza>ons ² Our team is a top group na>onally and interna>onally inves>ga>ng the thermal limita>ons of sandwich modules, integra>on challenges, and was the first to target and demonstrate prototype environmental tes>ng. Other groups working with sandwich module development (Kobe University, Kyoto University, Texas A&M University, Caltech/Northrop Grumman, others) are now seeking to improve upon our results. ² Collabora>ons currently being inves>gated for possible formaliza>on through MOUs, MOAs, CRADAs: ² ARTEMIS Innova>on, LLC ² Follow-on hardware development via NASA NIAC or ARPA-E ² Solaren Corpora>on ² Solaren is currently under contract to provide clean power to PG&E in 2019 ² NRL s Tech Transfer office has drazed an NDA for Solaren, our discussions with them are ongoing Kobe U. prototype and concept Kyoto U. prototype Texas A&M U. concept
Photovoltaic RF Converter Antenna Element Module Research Documenta>on ² Summary of presenta>ons and outreach ² 2014 Interna>onal Astronau>cal Congress ² MSNBC Interview, March 2014 ² IEEE Wireless Power Conference keynote, 2015 ² Summary of publica>ons ² Dozens of popular media pickups of NRL press release, Wired, Der Spiegel, etc. ² Energy Conversion and Transmission Modules for Space Solar Power, Proc. of the IEEE, Jun 2013 ² A Sunlight to Microwave Power Transmission Module Prototype for Space Solar Power, Doctoral Disserta>on, 2013 ² Sandwich Module Prototype Progress for Space Solar Power, Acta Astronau:ca, Feb 2014 ² Pat. Pending: US 2013/0099599 Thermally Efficient Power Conversion Module for Space Solar Power ² Awards: Alan Berman Publica>on Award, 2012 & 2015; IEST Publica>on Award 2015
Photovoltaic RF Converter Antenna Element Module Research Space solar power has been studied for many years in the absence of realis>cally prototyped components. This research effort cri>cally scru>nized the key challenges and produced, tested, and characterized a proof of principle unit like that employed in several popular concepts. ² Why NRL? ² NRL hosts staff with the unique blend of exper>se and knowledge needed to produce meaningful module prototypes ² Why Navy? ² The Navy and DoD s energy needs, par>cularly for disadvantaged forward opera>ng bases and combat outposts, demand cri>cal inves>ga>on of novel alterna>ves ² Why now? ² With global warming and energy security as looming threats, the inves>ga>on of alterna>ve energy sources is an impera>ve Tile Module in Vacuum Chamber for Tes>ng
Modular Architectures Modular Symmetrical Concentrator, circa 2007 (NSSO) Each PV/Microwave architecture has: Solar panel area Affects power collected Antenna transmission area With frequency, affects power beam direc>vity Some architectures match these two areas and increase power collected using concentra>ng reflectors Reduces wiring mass and avoids slip rings Thousands of adjacent sandwich modules form this surface Thousands of adjacent sandwich modules form this surface SPS-ALPHA, circa 2012 (Artemis Innova>ons)
Solar ConcentraGon Concentra>on advantages: Improves solar cell efficiency Reduces the required panel area Has the poten>al to reduce launch mass for given power, since reflectors tend to be lighter than solar cells per unit area Reflectors used for concentra>on may also be used to redirect energy to simplify onboard power distribu>on Concentra>on disadvantages: Compounds thermal challenges because of the addi>onal heat needing to be dissipated Requires addi>onal structure to implement reflectors Requires higher poin>ng accuracy Integrated Symmetrical Concentrator, circa 1998 (NASA)
29 Summary of the Thermal Challenge Using Idealized Efficiency Figures Light (about 7% of incident light is reflected) Photovoltaics ~30% efficient DC to RF ~80% efficient Antenna ~95% efficient TOTAL MODULE EFFICIENCY: ~23% Heat μwaves For every 100W of incident sunlight, about 72W must be radiated as heat power Stefan-Boltzmann Law: P = εσat 4 P is the heat power radiated ε is the emissivity of the material σ is the Stefan-Boltzmann constant A is the radia>ng area T is the temperature
Temperature ConsideraGons Solar cell and solid state power amplifier efficiencies decrease with rising temperature Op>ons to maintain acceptable opera>ng temperatures: P = εσat 4 (constant) Increase total module efficiency to reduce heat power PV is limi>ng factor, efficiency increase beyond scope Reduce sun concentra>on Reduces poten>al system mass savings Use high emissivity materials ( 1) Limited by black body radiator Increase device opera>ng temperature Beyond project scope Increase radiator area Means a departure from the flat module approach
Radiator Area Required to Maintain Temperature Equilibrium for a Flat, 28 cm x 28 cm Square Module at 23% Efficiency 31
Temperature of Flat 28 cm x 28 cm Square Module with Both Sides as Black Body Radiators for Various Module Efficiencies 32
33 Using a Tile Sandwich Module The top and bofom sides of >le module are available to radiate heat, sides connect to adjacent iden>cal modules which also need to radiate heat.
34 Using a Step Sandwich Module Addi>onal area on the step module for radia>ng heat versus the >le module allows cooler opera>ng temperatures and/or higher sun concentra>on levels
SimulaGon Shows Step Module Max Temp Runs ~60 Cooler at 3 Suns vs. Tile Module 35 SOLAR ARRAY FACE SOLAR ARRAY FACE TRANSMIT ANTENNA FACE TRANSMIT ANTENNA FACE RF & power electronics go here to lower heat exposure; note electronics temp is ~20 cooler than >le
36 Tile Sandwich Module Layer ImplementaGons Photovoltaics DC to RF Electronics Antenna
Solar Array: 28 Cells in Two Strings Array has two 14 cell strings in parallel 28.3% efficient Spectrolab UTJ cells used, mounted on FR4 1.59mm aluminum support substrate Step module u>lizes a con>nuous piece of pyroly>c graphite shee>ng for heat spreading Nusil RTV for bonding AM0, 1 Sun, 70 C Voc (V) 33.8 Isc (A) 0.919 Vmp (V) 29.1 Imp (A) 0.870 Pmp (W) 25.3 Power @ 28V (W) 24.4 Tile Module: 0.30m x 0.29m (12.6 x 11.3 ) Step Module: 0.30m x 0.29m (12.6 x 11.3 ) with 0.29m (11.5 ) radiators Output current scales nearly linearly with sun concentra>on for a fixed temperature 37
Tile Module Solar Array I-V Curve TesGng 4000W Xenon light source with different combina>ons of light afenua>ng screens used for measuring power output of each panel string 38
Electronics: 2.45 GHz RF Amplifier Chain RF chain matched for solar array is about 47% efficient Tile module uses a single chain, Step module uses three chains in parallel that are power combined 39
40 Electronics: Power Conversion Power electronics was designed to support both >le and step modules Power electronics measured efficiency ~96% or befer
Power and RF Electronics on Tile Module Baseplate Prior to Thermal Feature InstallaGon 41 Power Electronics Board Voltage Controlled Oscillator Final Stage RF Amplifier Driver Stage RF Amplifier
42 Power and RF Electronics on Tile Module Baseplate Aeer Thermal Feature InstallaGon Black Kapton Tape Blanke>ng Covering Power Electronics Board Thermocouple Wire Bundle
43 Antenna: Short Backfire Design Flat reflector version used q Max published gain ~ 18.1 dbi q Quoted efficiency ~ 91-95% Dia: 292mm Hgt: 61.2mm Electronics module output connected to dipole feed port (linear-polarized) Gain Pafern 2.45 GHz 16.5 dbi peak To be Measured: VSWR Radia>on Paferns & Gain Efficiency (Wheeler Cap method) E-plane H-plane
Integrated Tile Module with Antenna Mockup 44
Tile Module Solar Array & Power and RF Electronics TesGng 45
46 Step Sandwich Module Layer ImplementaGons DC to RF Electronics Photovoltaics Antenna
Integrated Step Module with Antenna Mockup 47
Step Module Solar Array & Power and RF Electronics TesGng 48
49 TesGng Apparatus Tile Module ConfiguraGon Protec>ve Shroud Sun Simulator and Afenua>ng Screens Vacuum Chamber Test Worksta>on
50 Tile Module IlluminaGon TesGng Electronics Powered by Solar Array The gobo prevents excess light from entering and unnecessarily hea>ng the chamber itself, rather than the test ar>cle Illumina>on Tes>ng at Ambient Pressure on Lab Bench Illumina>on Tes>ng Under Vacuum in Thermal Vacuum Chamber
Tile Module RF Conversion Efficiency and Solar Array Temp at Ambient Pressure Under Various IlluminaGon CondiGons Screen A No Screen E D C B
Tile module RF Conversion Efficiency, Solar Array Power, and RF Output Power Under Various IlluminaGon CondiGons at Ambient Pressure
Tile Module Data Show Vacuum Correlates with Reduced Output Power Each cluster of 3 points represents (in order) the mean, min, and max Chamber window (not used for ambient) incurs ~5% power loss Ambient,P wr Sim Ambient,Li ght Vacuum,Li ght Vacuum,Li ght+ Vacuum,Li ght++ Light, Light+, & Light ++ correspond increased light intensity & degraded field uniformity Data was collected over a 30 minute equilibrium period for each condi>on (σ<0.4 C for every temperature point)
Tile Module Data Show Vacuum Correlates with Higher Module Temperatures Ambient,P wr Sim Ambient,Li ght Vacuum,Li ght Vacuum,Li ght+ Vacuum,Li ght++ Each cluster of 3 points represents the mean, min, and max Data was collected over a 30 minute equilibrium period for each condi>on (σ<0.4 C for every temperature point)
Tile & Step Module Figures of Merit Mass per unit area (Lower is be[er) Antenna mockup rather than antenna used Tile Module: 21.9 kg/m 2 1.91kg/(0.286m * 0.305m = 0.0872m 2 ) Step Module: 36.5 kg/m 2 3.33kg/(0.286m * 0.319m = 0.0913m 2 ) Results fall within 4 kg/m 2 to 40 kg/m 2 predicted range found in the literature Specific power (Higher is be[er) Antenna and miscellaneous small parts masses are esjmated Tile Module: 4.5 W/kg measured @ minimum 1.0 sun illuminajon in vacuum Solar array temps 122-150 C, 9W RF output / 1.91kg module mass Step Module: 5.8 W/kg measured @ minimum 2.2 sun illuminajon in vacuum Solar array temps > 103-130 C, 19W RF output / 3.33kg module mass
56 Tile Module Efficiency in Vacuum Module conversion efficiency with minimum one sun incident on module (>117 W over 0.0872 m 2 ) Element Goal Achieved Power Out (W) Solar Panel 24% 19% 22 Power Electronics 95% 97% 22 RF Chain 50% 44% 9 Antenna 95% 95%* 9 COMBINED MODULE 11% 8%** 9 Solar Panel: power measured during integrated module under vacuum and solar illumina>on, solar array temps in range 122-150 C as seen in plot for case Light++. Note cell voltage at peak power drops ~6.5mV/ C. Power Electronics: power measured during electronics board standalone test under loading condi>ons similar to integrated module test RF Chain: power measured during integrated module test under vacuum and solar illumina>on, driver stage amp @ 80 C, final stage amp @ 83 C (Combined efficiency and power out at ambient under Antenna: *efficiency calculated from simula>on illumina>on with no chamber window were 11% and **Combined figure use simulated antenna efficiency value. 14W)
57 Step Module Efficiency in Vacuum Module conversion efficiency with minimum 2.2 suns incident on module (>275 W over 0.0913 m 2 ) Element Goal Achieved Power Out (W) Solar Panel 20% 17% 46 Power Electronics 95% 97% 44 RF Chains 50% 44% 19 Antenna 95% 95%* 18 COMBINED MODULE 9% 7%** 18 Solar Panel: power measured during integrated module under vacuum and solar illumina>on, solar array temps in range >103-130 C. Note cell voltage at peak power drops ~6.5mV/ C. Power Electronics: power measured during electronics board standalone test under loading condi>ons similar to integrated module test RF Chains: power measured during integrated module test under vacuum and solar illumina>on, driver stage amps in range 105-107 C, final stage amps 95-101 C Antenna: *efficiency calculated from simula>on **Combined figure use simulated antenna efficiency value.
58 Summary Trade studies, analyses, and simula>ons were performed in the design and produc>on of sandwich module prototypes for space solar power A novel approach for increasing thermal dissipa>on capabili>es in modular SSP architectures was explored The first-ever sandwich module tes>ng under space-like condi>ons was conducted This work provides an empirical basis for informing technical and economic analyses for a prominent class of SSP systems