A Gigawatt-Level Solar Power Satellite Using Intensified Efficient

Conversion ArchitectureBrendan Dessanti

Shaan ShahNarayanan Komerath

Experimental Aerodynamics and Concepts Group

School of Aerospace Engineering

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Conference Papers from Our Team

• B. Dessanti, R. Zappulla, N. Picon, N. Komerath, “Design of a Millimeter Waveguide Satellite for Space Power Grid”

• N. Komerath, B. Dessanti, S. Shah, “A Gigawatt-Level Solar Power Satellite Using Intensified Efficient Conversion Architecture”

• N. Komerath, B. Dessanti, S. Shah, R. Zappulla, N. Picon, “Millimeter Wave Space Power Grid Architecture 2011”

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Outline

• The Space Power Grid Architecture• Girasol Converter Satellite Conceptual Design• Gas Turbine Comparison with Broadband PV• Girasol Satellite Mass Summary and Design Conclusions• Mirasol Reflector Satellites • Girasol Effect on Architecture Analysis• Conclusions

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Space Power Grid Architecture

Phase I• Constellation of LEO/MEO Waveguide Relay Sats• Establish Space as a Dynamic Power Grid

Phase II• 1 GW Converter Satellites – “Girasols”• Gas Turbine Conversion at LEO/MEO

Phase III• High Altitude Ultra-light Solar Reflector Satellites – “Mirasols”• Direct unconverted sunlight to LEO/MEOfor conversion

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Space Power Grid ArchitectureDeviations from Traditional Approaches

• Use Primary Brayton Cycle Turbomachine Conversion of highly concentrated sunlight (InCA: Intensified Conversion) Specific Power, s

• Separate the collection of sunlight in high orbit from conversion in low orbit Antenna Diameter

• Millimeter Wave Beaming at 220GHz Antenna Diameter

• Use Tethered Aerostats Efficiency Through Atmosphere

• Power Exchange with terrestrial renewable energy Cost to First Power Barrier

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Girasol Converter Satellite Conceptual Design

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Gas Turbine vs. Broadband PV Conversion

Potential for Order of Magnitude Improvement Using Gas Turbine

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Gas Turbine vs. Broadband PV Conversion

• Broadband PV scales linearly• Specific Power of High Intensity PV arrays limited by heat

radiation problemWhy? Sun Intensity = Heat That Must Be Radiated = ATCS Mass

Fundamental Broadband PV issue:Broadband energy must penetrate a solid surface layer before photons can drive electrons through the semiconductor array

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IηCAIntensified Efficient Conversion Architecture

1. Primary Brayton Cycle Conversion2. Optional Narrowband PV Conversion

Attempt to achieve 50% efficiency at ground, thus each girasol collects 2GW directed sunlight

Given high Brayton Cycle efficiency and high specific mass of mechanical to electrical converter not cost effective to use narrowband PV conversion

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Girasols

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Closed Helium Brayton Cycle

Helium • High and Constant Specific Heat• High Thermal Conductivity• Low Mass Flow Rate Required

Closed Helium Brayton Cycle Operating In Space• Starting Point: Intercooled Helium Brayton Cycle Liquid

Fluoride Nuclear Power Plant Cycle (DOE - ORNL)• Eight 125MW Sections – Dimensions similar to jet engines• Alloys exist that can meet 3650K Operating Temperature• Advantages over terrestrial jet engines:

1. Predictability of orbit2. No atmosphere3. Temperature in space

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Girasol Turbomachinery

1) 300m Collector2) Intensified Feed3) Heater4) Compressor5) Turbine and Generator6) Radiator7) Phase Array Antenna

Components:

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Thermodynamic Cycle Analysis

Efficiencies Based on Jet Engine Efficiencies

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Girasol Satellite Mass Budget and Cycle Analysis

Element Mass, kg Percent

Collector 3,534 0.92Cooling Sys. 168,000 44.0

Brayton Cycle 20,000 3.91AC Generator 50,000 9.79Cryogenics 20,000 3.91

220 GHz Amp. 17,000 3.00Antennae 20,000 3.53

Propulsion 170,300 30.0Misc. 30,930 5.45

Structure 56,700 10.0Total Girasol 567,000

Total Mirasol 53,000

Total Mass 620,000

3650K He Gas Turbine Cycle Analysis

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Mirasols

High Altitude (GEO or Near GEO), Ultralight Reflector Satellites direct sunlight to girasols• Utilize technology similar to solar sails• Optical linking between mirasols/girasols• Sunlight wavelengths on order of μm

very little beam divergence, even over large distances

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Girasol Satellite Design Conclusions1. By separating solar spectrum, narrow band PV conversion can extract roughly 14% of

total solar power as DC2. Narrowband conversion of pre-separated spectrum minimizes active thermal control

requirement3. Closed Brayton Cycle can achieve over 80% conversion of remaining solar spectrum to

AC electrical power4. Given high Brayton Cycle efficiency and high specific mass of mechanical to electrical

converter, not cost effective to use narrowband PV conversion5. Superconducting generators needed to achieve high power per unit mass needed for

mechanical to electric power6. IηCA Architecture with Brayton Cycle converter and superconducting AC generator

offers specific power >1.6 kW/kg vs. <0.2 kW/kg for PV architectures7. Future Improvements and refinements could lead to >3.4 kW/kg

– A potentially revolutionary impact8. If roadblocks encountered with heat rejection systems, could use spectral separation

and narrowband conversion with PV to increase specific power

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Technical and Economic Results Analysis:Breakeven vs. Selling Price

Baseline: SPG Architecture presented at March 2011 IEEE Aero ConfIηCA: Current architecture including Iηca Concept

For Given Price of Power, Significant Improvement in Viability

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Technical and Economic Results Analysis:Girasol Effect on NPV Trough

Amount of Investment Required Reduced Significantly from Baseline

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Conclusions:Girasol Effect on Architecture Summary

1. Girasol Brayton Cycle IηCA offers far better efficiency and specific power, and shorter technology path, than previously considered direct conversion options

2. Girasol Brayton Cycle IηCA greatly improves SSP viablity

3. IηCA can achieve breakeven by Year 31, with NPV trough <$3T, at $0.11/kWh

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Questions?

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