Experimental Aerodynamics and Concepts Group Retail Beamed Power for a Micro Renewable Energy Architecture: Survey Narayanan Menon Komerath Professor, Daniel Guggenheim School of Aerospace Engineering Georgia Institute of Technology Atlanta, Georgia USA

Experimental Aerodynamics and Concepts Group India: 638,000 villages, 80 percent have at least one electric line. 415 million people have no access to electricity Over 450 million mobile phone accounts (Multiple accounts per user). Retail Power Beaming is a viable alternative to constructing wired grids for several future applications, despite low efficiency. Route for the small electronic devices market to leapfrog the centralized power grid, in many parts of the world. Demand for mobile connectivity and other electric devices far outpaces power grid expansion.

Experimental Aerodynamics and Concepts Group Aerospace Interest: 3-stage Approach to Power Delivery 1. Tower to village (KW-1MW per tower ) 2. Regional plant or Space – stratospheric platform – customer (10-100MW per platform) 3. Space Power Grid – national /global needs (100MW per satellite) Beamed delivery to remote sites and islands is possible from Space / Stratospheric Platforms/ UAVs Retail beaming can close the business case for beamed power, while enabling many communities to leap ahead of terrestrial power grid expansion Relay height AGL, km Regional global Surface range to visible horizon, km Local

Experimental Aerodynamics and Concepts Group Antenna Size Dictates Millimeter Wave Regime (GEO receiver size is off the chart) Frequency, GHz Receiver Diameter, m Frequencies below 100GHz are not viable for delivery from Space, due to costs of space and ground infrastructure. Hence interest in millimeter waves. Mmwave infrastructure is suitable for retail family / village sized receivers

Experimental Aerodynamics and Concepts Group hero/6358_ jp g 01/ENG/FAQ/FAQ-E1.htm hero/6358_ jp g Regional power plant to stratospheric platform (Stratoform) to customer site Range to 600 km Power level ~10 to 100 MW Multiple receivers “Burnthrough” beam to handle bad weather

Experimental Aerodynamics and Concepts Group 1. Expense of solid state arrays vs. PV arrays Issues and solutions IssueSolution/Argument Low efficiency of generation and transmission. Compare value of 1 st watt-hour Opportunity cost of waiting for grid Expense of solid state arrays vs. PV arrays Design for synergy. PV panels as mm wave antennae at night. Integrated PV/mmwave chips toreceive, convert and transmit power Atmospheric Propagation LossesMinimize horizontal path at low altitude. Use burn-through or Evaporation Ducts High Beam IntensityAutomatic cutoff unless link is functioning Health Effects of Millimeter WavesUnknown – needs research Generation of Millimeter WavesMass-produced solid-state arrays; Photonic approaches InfrastructureMobile Telephone Infrastructure as convenient “last kilometer” transmitters

Experimental Aerodynamics and Concepts Group Dealing With Low Efficiency Value of first watt-hour Opportunity cost of waiting for wired grid

Experimental Aerodynamics and Concepts Group Many needs are met by a few watt-hours

Experimental Aerodynamics and Concepts Group Baseline economic model for rural BPTS Wired or Stat-form power delivery to rural station Beamed “last kilometer” to customer antenna Synergy with mobile phone and railway infrastructure where possible Local industry/major users must subsidize costs of reaching small users

Experimental Aerodynamics and Concepts Group Potential Near-Term Applications Broad area low intensity power distribution for emergencies Deliver to local village grid Remote military or scientific outposts High endurance miniature robots Distributed micro power generation Remote area exploration Increased range for electric vehicles Rapid restructuring of grid topology for damage mitigation

Experimental Aerodynamics and Concepts Group Dry Atmospheric Absorption for Vertical Transit Good windows at ~100, 140, 220GHz Need: Narrow-band data to identify best windows near 100 GHz and 220GHz

Experimental Aerodynamics and Concepts Group Line A: Average absorption at sea level, 20C, 1atm, H2O vapor 7.5 g/m3) Line B: Altitude 4 kilometers pressure altitude, (0C, Water Vapor Density= 1 g/m3) Atmospheric Absorption for Horizontal Propagation (Why go up instead)

Experimental Aerodynamics and Concepts Group Impact of rain and fog: Need “burn-through”. 220GHz 94GHz DSP/solid state generation permits use of an initial burn-through frequency followed by main power beam

Experimental Aerodynamics and Concepts Group Technology Opportunities Integrate mm-wave receivers with solar panels Narrow-band phase-array receivers for laser and mm-waves, integrated with PV panels Nanotube broadband direct solar conversion antenna Burn-through rain, clouds and fog using mmwave and other wavelengths Lightning analogy: Create conductive path for mm-wave beam using “seed” beam Use waste heat on relay platforms to generate burn-through beam Co-use communications and power transfer control equipment Improve conversion efficiency to & from GHz Satellite waveguides Thermal management Effects of scattered 220Ghz radiation on humans/animals

Experimental Aerodynamics and Concepts Group 1.Rising demand for connectivity and personal electronics, creates an opportunity to leap-frog grid expansion using retail power beaming. 2.Millimeter wave beaming brings antenna sizes practical for retail installation. 3.Enables retail power distribution to off-grid locations and islands. 4.Closes the business case for distribution through Space and statospheric platforms. 5.Enables synergy with distributed micro renewable power architectures. 6.Value of first few watts and watt-hours >> marginal cost of utility power. 7.Synergy with photovoltaic arrays multiplies cost-effectiveness of micro power architectures 8.Optimal frequencies for moist atmospheres differ from those for long-distance dry air and vacuum beaming. 9.Solid-state arrays enable several beam frequencies from the same arrays in order to serve multiple purposes. 10. Indian village electrification offers an opportunity to establish a retail beaming infrastructure. Rural economics model works best with stratospheric platforms, local beamed delivery and subsidized cost to small users. 11. High-resolution data needed for 100GHz and 220GHz bands 12.Low efficiency and weather issues are not show-stoppers for retail millimeter wave power beaming. Conclusions

Experimental Aerodynamics and Concepts Group Acknowledgement Support from NASA under the “EXTROVERT” cross-disciplinary learning initiative is gratefully acknowledged.

Experimental Aerodynamics and Concepts Group Beamed Retail Power Transmission/ Distribution System mm wave to DC conversion mm wave to DC conversion DC to mm wave conversion DC to mm wave conversion Beam Formation Transmission & Reception Wireless transmission of power (not just signals with information) over relatively short distances to multiple end-user receivers. Usually implies focused point-to-point transmission with highly directional antennae, and provisions for energy storage at either end. Conventional solutions using <10GHz microwave, and some proposed solutions using lasers. Our interest is in the millimeter wave regime, specifically near 220 GHz

Experimental Aerodynamics and Concepts Group 140GHz Propellant Heating Beam Being Considered by NASA/USAF Space Power Grid Concept: 220 GHz

Experimental Aerodynamics and Concepts Group 3. Space Power Grid Use space-based infrastructure to boost terrestrial “green” energy production from land and sea: argument for public support. Full Space Solar Power (very large collectors in high orbit) will add gradually to revenue- generating infrastructure. Exploit large geographical, daily and seasonal fluctuations in power cost (Landis 2004, Bekey 1995). Beam to other satellites Retail delivery (SPS2000). Technical risks in dynamic beaming/reception/ transaction system. Inefficient conversion to and from microwave vs. terrestrial high-voltage transmission lines. FIGURE 1. Space Power Grid Satellite Receving And Redistributing Beamed Power. Team: Brendan Dessanti, Janek Witharana

Experimental Aerodynamics and Concepts Group Power delivery to points of local distribution Low-altitude horizontal beaming is inefficient unless burn-through techniques are perfected. Use vertical beaming to and from high-altitude platforms wherever possible.

Experimental Aerodynamics and Concepts Group The Dream of Energy Independence Terrestrial solar, wind and biomass power plants Space-delivered solar power Beamed power to complement local generation, in off-grid communities Hydrogen generation using excess / spike power Stored hydrogen and bio-gas for fuel cells and transportation

Experimental Aerodynamics and Concepts Group Burn-through rain, clouds and fog using mmwave and other wavelengths Options to investigate: 1.Find narrow lines in 220GHz window, where propagation efficiency is higher. 2.Saturate? No experiments found so far on the effect of sustained beam energy addition on wet air for durations of minutes 2. Deliberately heat using selected frequencies and create low-density path? 3.Lightning analogy? Create conductive path for mm-wave beam using “seed” beam Solid state arrays / DSP-PLL generation approach allows consideration of tuning to narrow bands, and shifting to a pilot beam for a short duration to prepare the path for the main beam

Experimental Aerodynamics and Concepts Group Summary Observations -2 Direct conversion from broad-band solar to beamed mmwave appears feasible. Integrated antenna / PV generators already in use Large-scale arrays of solid-state devices with DSP and PLL to generate mmwave Laser efficiencies may be on cusp of breakthrough but need changes in laws/treaties Most current “systems analyses” of SSP prospects appear to assume <$400/lb launch costs to LEO. This is not realistic. Must insist on disciplined costing to see the real technology opportunities.

Experimental Aerodynamics and Concepts Group The Space Power Grid Approach Exploit large geographical, daily and seasonal fluctuations in power cost. Beam to other satellites. Retail delivery (SPS2000). Use space-based infrastructure to boost terrestrial “green” energy production from land and sea: argument for public support. Full Space Solar Power (very large collectors in high orbit) will add gradually to revenue- generating infrastructure.

Experimental Aerodynamics and Concepts Group Space Solar Power the old way GEO: S=36000km LEO: ~400km MEO: ~10000km Earth Radius ~6370km

Experimental Aerodynamics and Concepts Group Afternoon Sun system. 80 minutes of access per 24 hours per location. This orbit performs 23 revolutions around the earth every 48 hours. Ground Tracks of 6 sun-synchronous satellites at 1900 km

Experimental Aerodynamics and Concepts Group Absorption vs. Spillover Most GEO/ 5.8GHz architectures assume receivers sized for 83% beam capture because of the large receiver size Example: 5.8GHz: 84% Beam capture, 95% Transmission through atmosphere Net capture = 0.95*0.84 = 80% 220GHz: 99% Beam capture, 90% transmission = 89% Benefits of compact antenna are far beyond this. Both laser and mmwave enable compact, 99% capture receivers.

Experimental Aerodynamics and Concepts Group “Shown: An array of aligned, but randomly placed, carbon nanotubes which can act like a radio antenna for detecting light at visible wavelengths. The scale bar is one micron in length. Wang et al., Applied Physics Letters, 27 September 2004.” Antenna for Visible Light Nanotube broadband direct solar conversion antenna, with narrow-band high-efficiency receivers for mm wave.