Innovations Required for Retail Beamed Power
Transmission Over Short Range
Girish Chowdhary and Narayanan Komerath
Daniel Guggenheim School of Aerospace Engineering
Georgia Institute of Technology
Atlanta
IMETI 2010, Orlando, FL June 2010
Beamed Retail Power Transmission/ Distribution System
•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
Beam Formation
Transmission & Reception
DC to mm
wave
conversion
mm wave to
DC
conversion
Market Indicator For Micro-Scale Retail Power
“Malawian teenager .. transformed his village by building electric windmills
out of junk… Jude Sheerin, BBC News 1 October 2009
http://news.bbc.co.uk/2/hi/africa/8257153.stm
Notes:
1.Original motivation: power a radio to fance to music
2.Business plan: charging station for cellphones.
Lesson: Demand for cellphones and other electronic systems is far ahead of
national Power Grid expansion rate.
Introduction
Beaming power may be a viable alternative to constructing wire 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.
This paper looks at the rationale, applications, choices and tradeoffs.
Overview
•Long-term rationale: why we are interested
•Near-term applications
•Technical barriers
•Cost tradeoffs
•Possible innovations needed
Aerospace Interest: Stratospheric/ Space Power Grid
• Way to exchange power between day/night regions to boost solar
power baseload capability
• Minimize storage needed to capture wind power spikes
• Provide evolutionary path to space solar power
Retail power beaming is the end-user infrastructure for delivery of power
in a global exchange, including space solar power.
Why SSP? Why has it Remained a Dream?
Feature
SSP
Ground-based solar
power
Steady generation
24 hour, year-round.
~12,000KWh/m^2 per yr
Daily /seasonal/ weather
fluctuations. Average ~900 to
2,300 KWh/yr
Waste heat
Dissipated in Space
Released on Earth
Transmission efficiency
Low, weather-dependent
High, independent of weather
(see above)
Receiver/distributor
Infrastructure size
Massive for GEO sats due to
beam width, for any power
level
Massive for GEO sats.
Scalable from rooftop to
Sahara size
Very high due to GEO launch
cost
Moderate
Generator size
Installation cost per watt
Scalable
The Space Power Grid Approach
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 revenuegenerating infrastructure.
•Exploit large geographical,
daily and seasonal fluctuations
in power cost.
•Beam to other satellites.
•Retail delivery (SPS2000).
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
Near-term Rationale: Wired vs. Beamed Power Transfer
Wire Grid
Beamed Power
Excellent efficiency with high voltage
lines (~94%)
Low efficiency (~20 to 50%)
Requires large transmission
infrastructure.
Few transmission and reception points
Large amount of developed land, trees
cleared etc
Clear line of sight, can be above tree
level
Concentrated at points
Remote area maintenance
Radiation hazard along the beam
Power line hazards under and near
lines: high voltage, aircraft collision, ice
and wind storm issues
Vandalism and terror attacks
Less susceptible
High cost as number of receiving points
increases
Each device has to have a converter
Potential Near-Term Applications
•
•
•
•
•
•
•
•
Broad area low intensity power
distribution for emergencies
Areas with cellphones/ players
but no power grid
Rapid power delivery to remote
military or scientific outposts
High endurance miniature robots
Distributed micro power
generation
Remote area exploration
Increased range for electrically
powered vehicles
Rapid restructuring of grid
topology for damage mitigation
Technical Issues
•Antenna size vs. distance relationship means that space grid system is not
viable at any power cost, without going to millimeter wave regime, above
100 GHz
•Atmospheric transmission window at 220 GHz seems ideal
•Anything above 10 GHz is extremely sensitive to rain; finding alternative
routes is the answer.
•Poor conversion efficiency from DC to mm wave
Feasibility of low range low efficiency BPTS
BPTS Range (km) vs System frequency (GHz)
400
Modified Friis
equation
calculation
shows that
antenna
combination of
(20m; 5m)
is adequate for
100km range at
200 GHz.
(20m;1m) is
good for 10 km
375
350
Antenna diameter=
Antenna diameter=
Antenna diameter=
Antenna diameter=
325
300
275
20m,
20m,
20m,
30m,
20m
5m
1m
5m
Range in km
250
225
200
175
150
125
100
75
50
25
0
20
40
60
80
100
120
140
frequency in GHz
160
180
200
BPTS-offer
Power efficiency
System frequency efficiency
MM waves
high vsfree-space
0.8
range =
range =
range =
range =
0.7
50 km
75 km
100 km
150 km
0.6
0.5
Power Efficiency
Power Efficiency, Pr/Pt
20m transmitter diameter, 5m receiver diameter
0.4
0.3
0.2
0.1
0
0
20
40
60
80
100
120
140
System
Frequency
in
GHz
Frequency in GHz
160
180
200
Cost Model, Wired vs. Retail Beamed Power Infrastructure
Wired installation: Effective cost per km (~ US$1M / km) linear with distance above a threshold
level, steep cost for last few kms of retail distribution.
BPTS: power loss proportional to square of (distance/frequency). Effective cost ~ US$100K/km (1
transmitter/ relay per km)
Cost-effectiveness of BPTS vs. Wired Grid Installation
60
bpts  = 8GHz
bpts  = 10GHz
bpts  = 20GHz
effective cost of power transmission in thousands
Effective Installation Cost in $K
wired
50
40
Even at 20 GHz, BPTS is more cost effective
than wired installation for distance less than 6 km
30
20
10
0
0
1
2
3
4
Range in km
Range
in km
5
6
7
8
Required Technological Innovations
•Efficient mm Wave Generation
Thyratrons and Gyratrons replaceable by massive arrays of microchips with digital synthesis
and phase-locked loops. Use in communications and radar are routine; power transfer needs
development. Translate optical rectenna R&D to mm waves
•Advancements in Antennas: Antenna directionality/gain in 220 GHz regime using DSP.
•Circuits and Switching in the 200-250 GHz regime
•Advancement in Thermal management systems: Efficient use of waste heat from
conversion/ transmission at high power levels.
•Decentralized grid management through networked control
•200GHz radiation monitoring: Health and safety issues need investigation
•Compact converters from DC/AC to mmwave and back, for micro power systems.
•Smart Grid devices for micro-scale power capture and grid input measurements.
Conclusions
•
BPTS offers a way for technology market and convenience to leap-frog the conventional
wired grid expansion to unconnected areas.
•
BPTS using mm waves offers compact size and high free-space efficiency. 220 GHz is
desirable for compatibility with Space Power Grid.
•
Several applications including connectivity for micro-renewable power systems.
•
Basically cost-effective compared to wired grid installation, when renewable, fluctuating
power sources are used.
•
DPS / PLL approaches appear to offer more efficient and cost-effective conversion to and
from mm wave regime.
•
Technological innovations needed include improved antenna design, efficient frequency
conversion, radiation monitoring, and antenna design.
ACKNOWLEDGEMENTS
The work reported in this paper was made possible by resources being
developed for the “EXTROVERT” cross-disciplinary learning project
under NASA Grant NNX09AF67G S01. Mr. Anthony Springer is the
Technical Monitor.
Antenna Diameter (m) vs System frequency (GHz)
600
range =
range =
range =
range =
range =
500
1 km
5 km
30 km
50 km
100 km
Antenna Diameter, m
400
300
200
100
0
0
20
40
60
80
100
120
System frequency in GHz
140
160
180
200
The Space Power Grid: Synergy Between Space, Energy and
Security Policies
Narayanan Komerath
Daniel Guggenheim School of Aerospace Engineering
Georgia Institute of Technology
Atlanta, GA 30332-0150 USA
komerath@gatech.edu
Space Power Grid: Redistributing Energy
Update on Space Solar Power from New Scientist Magazine: Dec.22. 2008
http://www.newscientist.com/data/images/archive/2631/26311601.jpg
Long Term Goal
Constant, “24-365” solar power available from Space. Concepts to build solar power satellites are
unable to get past the “cost to first power” barrier.
Problem specification:
•How to develop an evolutionary approach where revenue generation starts early with small
investment, and ultimately scales up to full-scale Space Solar Power (SSP) in 25-30 years.
•Viable business plan and minimal costs to taxpayers.
Approach:
•Build, market and infrastructure for SSP by facilitating terrestrial renewable power.
•Articulate the policy needs and show examples of successful practice.
This paper: Interplay of technology, economics, global relations and national public policy
involved in making this concept come to fruition.
GEO: Geo-Stationary Earth Orbit
Satellite “stationary” 36,000 km above equator.
1960s concepts: Very large solar-cell arrays in GEO, beaming electric power
down as microwaves to large receivers on Earth. Frequencies << 10 billion
cycles per second (10GHz) are generally not absorbed by the atmosphere selected for power transmission.
NASA etc. focused on GEO-based collector/converter/beaming. Consequences:
1.Frequency must be very good for atmospheric transmission: <10GHz.
2.Minimum beam diameter is several kilometers for this frequency range and
distance, regardless of power transmitted.  large stations.
2. Assembly at GEO.
3. Enormous ground infrastructure.
4. Only massive government spending as possible funding source.
5. Published estimate of “$300B to first power” is based on 1960s estimate of
$100 per pound to low earth orbit via Space Shuttle. Actual cost today is ~
$14000/lb to LEO via SPS
Real issue is lack of an evolutionary path to get the SSP system through
initial infrastructure development, to a self-sustaining size.
New Window Of Opportunity: Renewable Power & Climate Control
•“Baseload Power” criterion forces renewable plants to install fossil-burning auxiliary generation
•Best locations for wind and solar extraction are high deserts, plateau edges, mountain slopes,
glacier bases and coastlines.
•Insufficient, non-existent or inefficient distribution grids over most of the planet.
•Huge temporal fluctuations in power prices especially in urban areas.
10-fold fluctuation in power cost:Real-time retail beaming
opportunity
From Landis, G., “ Reinventing the Solar Power Satellite”
http://gltrs.grc.nasa.gov/reports/2004/TM-2004-212743.pdf
3-Step Evolutionary Approach to Space Solar Power
Years 6-23: L/MEO constellation enables global reach for renewable plants in ideal locations.
Revenue from baseload supply and price differentials.
Year 23+: Replacement sats augmented with power converters.
Year 23+ High MEO/ GEO reflectors concentrate sunlight on L/MEO converters to feed grid
System expands.
Method of Analysis
Frequency and orbit height  antenna sizes, efficiency
+ Power level per satellite  satellite mass  revenue, # of satellites and ground stations
 System costs from NASA/USAF & FUTRON cost models.
NPV analysis with target cost /KWH, IRR, growth model
System size for breakeven in 17 years.
Minimum power transaction level per satellite  satellite size
Effect of public funding on cost per KWH.
Results
•Frequency 200 GHz or greater.
•60MW handling capacity per satellite
•Startup with 20 satellites and 12 plants
•Phase 1 breakeven in 17 years, grows to 100 satellites and 100 plants.
Technology Challenges
• Conversion efficiency to & from 200-220 GHz
• Satellite waveguides
• Thermal management
• Atmospheric transmission schemes
• Direct conversion technology for Phase 2
• Ultralight conformable reflectors for Phase 3 high orbit.
Economics Of The Space Power Grid SSP
Business case is based on 5 features:
1) Allow solar and wind power plants to
• achieve baseload provider status,
• compete for premium prices by exchanging power with plants anywhere.
• locate at prime, remote sites including islands,
• reduce need for backup power generation.
• receive carbon credits, qualify for larger public investment.
2) Eliminate need for major assembly in orbit, minimizes development and launch costs.
3) Match constellation size to growth of participating plants and revenue.
4) Use of a constellation as a power grid minimizes the impact of weather by providing transmission
alternatives.
5) Early revenue growth with a few satellites and participating plants, eliminating cost-to-first-power
barrier of GEO-based concepts.
Feature
SPG
Steady generation
Constellation ensures that some face the Sun at all times, without GEO.
Transmission efficiency
Weather dependence alleviated by choice of atmospheric transmission paths.
Infrastructure size
Small due to lower orbit (2000km) and high frequency (200 GHz)
Generator
Scalable
Installed cost per watt
Moderate.
Infrastructure investment Pays for itself on terrestrial power generation. Expands to capture space solar
power after break-even. 17 years to improve conversion technology before
Phase 2 launch. Phase 3 (high orbit, large area) system is independent of
conversion technology on mid-orbit system.
•Breakeven power cost of 30 cents /KWh with IRR of 8% within 23 years from project start, given the
first satellite launch in Year 6, with zero government funding.
•With $6B govt. investment in development, achievable without large increase in system efficiency.
•Carbon Credits, savings in transmission infrastructure, improve the economics.
Results: Phase 1 SPG, 200GHz, 2000km Constellation
Parameter
Value
Satellite Power Level:
60MW
Satellite mass:
4510 kg
Launch cost to 2000 km high circular orbit:
$ 19.8M
Development cost for system:
$ 330M
Production cost for 1st 36 satellites:
$1370M
Ground facilities development cost:
$1000M
Per satellite annual mission operations and data analysis cost:
$2.75M
Ground station power level
$55MW
Cost of production of power
4 cents / KWH
End-to-end efficiency of beaming power grid
0.3
Sales price at delivery point
30 cents / KWH
Gross margin
5 cents / KWH
SPG share of gross margin:
4.5 cents / KWH
Water Absorption Loss vs. Frequency
October
http://www.islandone.org/LEOBiblio/microwave_transm.gif
Atmospheric Transmission in the
200-250 GHz regime
Special Policy Needs / Opportunities of the Space Power Grid
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Global real-time energy trading (expanded from US model)
Distributed terrestrial transmission infrastructure (Smarter Grid, DG)
Public acceptance of beamed power from Space (“IPOD” model? )
Global technology sharing on Space systems (ITAR vs. ESA model)
Global Infrastructure Collaboration Model (ESA model; IATA model)
Integration with Utility-Scale Terrestrial Power (EU- TRANS-CP)
Retail Beamed Power Transmission Systems (BPTS paper)
Integration with micro renewable power systems (MRES paper)
Global model for carbon credits (Copenhagen?)
Global model for renewables portfolio (EU example?)
Global model for Infrastructure Avoidance Credit? (ESA argument)
EU TRANS-CP
European Union’s Trans-Mediterranean Connection for Concentrated
Solar Power (TRANS-CP) proposes to set up a high-voltage DC grid
connecting solar plants in the Sahara desert across the Mediterranean
and English Channel to North Atlantic / North Sea British/German /
Dutch wind generators.
EU TRANS-CP Recommendations
Policy Issues
Financial Benefits
•Discrepancy of Awareness and Action
•Grants to producers and consumers
•Feed-in Tariffs to foster innovation.
•Low-interest loans
•Renewable Portfolio Standards (RPS)
•Tax exemptions, rebates
•Competitive Bidding for RPS capacity
allotments
•Depreciation
•Demand guarantees, price controls
•Net metering.
•Market access
•Renewable Energy Certificates
•Land access
•Green Power Purchasing
•Environmental licenses
Security Concerns, Space Law and a Global Infrastructure
Consortium
1.
2.
3.
4.
5.
6.
Concern about militarization
Access to national space facilities
Dual-use technologies
Competitive issues mixed with security laws
Risk of terrorist attack
Fear of being excluded from space resources
Opportunity in Crisis & Common Imperative
•Shift in security concerns from international rivalry to terrorism concerns.
•Thick layer of security at individual level added to national criteria.
•New technology and laws provide opportunity to rethink space security.
•May render fragmented national rules irrelevant and superfluous.
Global Govt – Commercial Consortium overall framework for private
entrepreneurship:
- long-term government-backed financing available
– directly provided by participating nations, or
- underwritten by Consortium through private and public funds.
Presence of the Consortium and infrastructure cuts lending risk
- cuts loan costs.
-Consortium model provides a consistent economic and policy solution.
Consortium Answer to Resource Exploitation / Property Rights Issue
All resource exploitation ventures must be multinational public ventures,
- open to investors from all member nations,
- limits on maximum stock ownership to avoid single-nation dominance
- long-term leases awarded
CONCLUSIONS
•Obstacles and issues in bringing space solar power to earth are discussed.
•Congruence of international interest in renewable energy sources and in reducing greenhouse gas
emissions, provide a window of opportunity to bring about Space Solar Power in synergy with the
development of clean renewable power on earth.
•Policy initiatives advanced in Europe for comparable solar power grid project are discussed.
•The special features of the space power grid are presented, and shown to provide an excellent
vehicle for global collaboration. While substantial technical challenges remain, there are viable paths
for these challenges, as well as for the economics and public/ international collaboration needed to
make Space Solar Power available to humanity.
•Public policy initiatives needed for renewable energy, are already acceptable in many nations.
•Security concerns that appear to pose formidable obstacles are cited as also posing
unprecedented opportunities for wel-controlled collaboration between nations, through the
participation of personnel who are cleared at the individual level, and through sequestering of
technologies particular to the project as done in the European Space Agency’s projects.
•The European TRANS-CP project is cited as a relevant current initiative to develop suitable policy.
Business Case
The business case is based on 4 features:
1) Enabling development of new solar and wind power plants by boosting their competiveness
Qualify these plants for larger public investment.
2) Early revenue growth with a few satellites and participating plants
Minimizes cost-to-first-power obstacle of GEO-based concepts.
Constellation growth is matched to commissioning of renewable power plants
Reduced lag between investment and revenue generation
3) L/MEO satellites: small antenna size and beam width compared to GEO
Global reach
Eliminates need for major assembly in orbit,
Minimizes development and launch investment.
4) Minimizing the impact of weather by providing different alternatives for power transmission to the
ground-based grid.
Previous Work
Boechler STAIF 2006:
•Achievable end-to-end efficiency
•Near-term no better than 50% of present terrestrial urban grid
•Long term (direct conversion from broadband solar to beamed narrowband) match or
exceed that of the terrestrial grid.
Komerath , IAC 2006:
•System based on 140 GHz regime and a constellation of 36 sun-synchronous satellites
at 800km altitude.
•Efficiencies not at the levels achieved in the 2.4 GHz regime.
Komerath,AIAA Space 2008:
•Compared the economics of using different frequencies and choices of orbits.
Frequency < 100 GHz not viable.
•Combination of near-equatorial, polar and elliptic orbits can offer the necessary
features of long transmission times from power plants, and retail worldwide power
delivery.
Orbits and Transmission Scenarios
Scenario 1: Near-equator plants and receivers:
•2000 km orbit height
•Access time within 45-degree cone, of 7 to 10 minutes at ground stations.
•For stations near the equator, the first several satellites are placed in orbits near the
equator.
•Thus a system start-up with as few as 6 satellites and 12 plants can be considered.
Scenario 3 is High Latitude, Burst-Mode Transmission
Burst-mode transmission for a few seconds (up to 2 minutes at 60 degree latitude, more
at higher latitudes) may be repeated at regular intervals essentially through each day
and night, with only a few satellites.
Scenario 4 is the Steady State Phase 1 SPG
As the number of satellites rises, sun-synchronous orbits become viable for continuous
transmission. For the 1900km sun-synchronous orbit, 72 satellites are needed, which is well
below the expected number of satellites in an established SPG system.
CONCLUSION
Opportunity
How can we achieve self-sustaining growth toward space solar power with reasonable
investment level?
1. GEO SSP:Immense receivers, sats and cost-to-first power.
2. SPS2000: LEO sats beaming over wide areas
3. Temporal and geographic price differential compensates for losses in beamed transmission
(Landis, Bekey et al).
4. Renewable-energy plants need large backup fossil generators or storage for baseload status.
5. Ideal solar and wind plants sites are deserts, high plateaux and mountain ridges: remote but
low atmospheric losses.
6. Near millimeter wave regime: compact antenna/receivers
7. Window of support for synergistic development of power plants and SPS distribution
infrastructure.
8. Solutions on the horizon for AC- near mm beam conversion efficiency problem,
direct solar conversion to mm wave, and spacecraft high-power thermal management?
October
SPG Status Summary
1. Synergy with terrestrial renewable power economics brings large policy advantages.
2. 220 GHz and laser advantages in sizing, orbit selection and ground facility
design, outweigh additional losses in atmospheric propagation.
2. System calculation sized for 220 GHz may work much better with lasers depending on conversion
and beaming.
2. Lower limit of power per spacecraft for breakeven ~ 60 MW.
3. Initial power plant output levels just below capacity of spacecraft.
4. Orbit height at 2000 km above Earth enables system startup with
6 satellites and 6 power plants. Initial launch in Year 6.
5. Expand to steady state size of 102 sats and 101 power stations for 30-year break-even. Replace
sats with augmented ones after 17 years of operation.
6. Phase 1 system in isolation breaks even with no public up-front grants, and a 6 percent ROI over 30
years.
7. Public funding <$3B in first 10 years brings delivered price of power from 30 cents to 24 cents per
KWH.
8. Phases 2 and 3 can be started at Year 23 with replacement satellites, on a profitable Phase 1
market and infrastructure.
October
Once Phase 1 is shown to be self-sustaining, Phases 2 and 3 become much easier
1. Replacement or additional satellites in Years 23 onwards, incorporate receiver/converters
sized for ~ 160MWe each. High-intensity design to capture 100 suns or more in intensity. (~ 80m dia))
Brayton cycle thermal management with auxiliary power generation at other frequencies.
Dual frequency system would enable use of 200GHz for space-to-space beaming and low frequencies
for atmospheric propagation.
2. Constellation of ultralight collectors in high orbits (to minimize drag) to focus broadband
sunlight to the receivers. Launch cost to high orbits minimized.
200-satellite constellation would generate 32GWe. Equivalent to 320 new nuclear reactors.
As high-intensity converter technology advances, 200 satellites may handle upto 320GWe.
Limited by acceptable size of L/MEO constellation.
October
Long-Term Technical Issues
1.
Present show-stopper: Conversion efficiency to and from 220GHz (or lasers) for Phase 1.
1.
Finding ways around the atmospheric propagation loss
- using terrestrial grid to avoid places of bad weather
- tuning to narrow bands & power levels for optimal transmission
- Different systems for space-space transmission and atmospheric.
Backup Option:
- In phase 3, LEO-LEO transmission may not be needed, so we can use lower frequencies,
suited to larger power levels and spacecraft sizes.
3. Spacecraft thermal management with multistage power generation.
Concepts for upto 10MW being studied.
4. Direct conversion from broad-band solar for Phases 2& 3. Efficiency and mass per unit
power.
- High intensity solar cells
- Broadband/ multiband stacked cells
- Optical rectennae
5. Breakthrough in efficiency and mass per unit power of converting between
200GHz and 5.8GHz regimes.
October
Summary of Recommended Approach
Long-term solution:
Years 6-23: Space Power Grid transacting power between renewable plants
Years 20 - 30 Full scale SSP growth.
Forward Base Retail Delivery:
Year 1? Ship to base using UAV / LTA reflector. Need to ensure air dominance.
Use either radar frequencies or lasers. (no need for solar power here)
Year 6: Regional power plant to base with LEO satellites (6 needed for continuous
transmission. Cheaper power generation - renewable or not).
Year 6: CONUS plant with L/MEO satellites (SPG phase 1: Renewable power plants)
Year 15? SSP collectors in high orbits, L/MEO converter/retail beaming satellites. (SPG
Phase 3; Use space solar power)
Research priorities:
1. Conversion efficiency to and from beamed energy
2. Direct conversion from broadband to beamed energy: efficiency and mass per unit
power.
- optical rectennae
- lasers?
October
ARCHITECTURE
Independent Variables
Parameter
Baseline
Why
Orbit height above surface
880 – 1200 km
Launch cost, antenna size,
sun-sync orbits, retail
beaming
Atmospheric transmission
frequency
200-245 GHz
Reduce antenna sizes, avoid
water bands
Internal Rate of Return
8%
Infrastructure Consortium
Phase Array transmission
45 deg. half-angle
Cover 90 degree azimuth of
sky
Initial number of ground stations
100
Revenue generation rate
Initial number of satellites
36
Near-continuous beaming
October
SPG Satellite System Characteristics
Power transmitted (design, MW)
Average beam intensity, uniform, at ground, w/m^2
Average beam intensity, uniform, at satellite, w/m^2
Antenna mass, kg
Mass for space-space antennae, kg
Cooling system mass: 2000kg/2.5MW
Mass of fluid, for 400K heating in 60 seconds at
2.5MW, kg
Other systems
With margin of 1000 kg, total satellite mass, kg
October
250
1273
127323
38.9
546
2000
400
1000
5000
Business Case:Parameters for Phase 1: Space Power Grid
Launch cost at $6K/kg to 880km, $M
Per satellite cost for one of the first 36, $M
Operations cost per satellite per year, $M
Satellite system development cost, $M
Ground facilities development cost for 1st 100
stations
Connection cost per additional station, $M
Cost of production of power, $/KWh
Fraction received as useful electric power
Sales price, $ per KWh
Gross profit per KWh
Beamed average MW per plant
MWh per year, for 1 plant at 50% duty cycle,
per satellite available (100%=36sats)
October
30
30
5
1000
1000
25
0.04
0.3
0.2
0.02
100
12175
Parameters for Phase 2: Augmented SPG
Collector/Converter Diameter, m
Area, sq.m
Satellite Mass: Add 2000kg
Per satellite cost, $M
Launch cost @$6000/kg, $M
Solar conversion efficiency
KWh per year per ASPG sat, at 50% duty cycle
End-to-end efficiency
Cost of production
Sales price, $per KWh, Phase 2
Gross profit per KWh
Gross profit per year per Augsat, $M
October
300
70686
7000
42
42
0.25
100,621,000
0.4
0
0.15
0.06
6.04
Phase 3: Full Space Solar Power Parameters
Collector Diameter
Satellite Mass: 0.015kg/m^2
3km
106029
Per satellite cost, $M
100
Launch cost @$10000/kg, $M
1060
Solar collector efficiency
0.995
KWh per year per SSP sat, at 100% duty cycle
80E+09
End-to-end efficiency
0.4
Cost of production
0
Sales price, $per KWh, Phase 2
0.15
Gross profit per KWh
0.06
Gross profit per year per Augsat, $M
4806
Total KWh per year added by 96 sats
7.69E+12
Note: MEO satellite costs still exceed $110B for 100 collectors
(300 sq km of solar collection), but at realistic launch cost,
and in a staged manner over 40 years, tied to revenue generation
October
Prior Work
Direct Approach:
100 megasatellites in GEO, large earth stations. 2.4GHz beams.
Step-by-step approaches:
• All involve satellites and beaming from GEO or beyond, or lunar power plants and
earth-based receivers. (Large beam spread, high cost of GEO access)
• Cost of earth-based receivers, and marginal cost per installed watt of power in space,
continue to be large.
• Bekey et al (IAC1995): Beam Canadian power through GEO reflectors to Japanese
ground station with reservoir. 35% Internal Rate of Return projected.
Recent concepts:
• SPS2000: Retail, wide-beam power beaming from LEO sat (Nagotomo, 1991).
• Modular GEO sat, each module self-contained (IAC2005)
• Laser beaming (IAC2005)
• Direct-conversion laser with 38% efficiency (Saiki, IAC2005)
October
End-to-End Efficiency Projections
Conventional terrestrial:
40%conversion from solar to DC (using best technology)
Near 100% conversion to hi-voltage AC.
94% delivered to end-user.
Total: 38% of original solar.
Short-term using SPG: 40%conversion from solar to DC
70% conversion DC to microwave
0.9x0.9 for atmospheric traverse
0.98 for in-space transmission
90% conversion from microwave to useful power
Total:
Short-term: 20% of original, delivered to end-user.
Short-term:
50% of
conventional
Long-term:
Slightly better than
conventional
Long-term: 50% direct conversion, solar to microwave
36% of original solar delivered to end-user
Full SPS: 99% capture from GEO; only one atmosphere pass.
39% of original solar delivered to end-user
October
Ground Component
•Ground stations located at ideal solar / wind collector locations.
•US Southwest, South Dakota, Hawaiian Islands, North African, Gobi,
Thar and Australian deserts and Greenland are examples envisaged.
•Retail receiving stations on the ground can be located almost anywhere much smaller than those for GEO-located SSP systems.
•No need to co-locate receiving stations with generator stations except for
power smoothing.
October
TECHNOLOGY ISSUES
•LEO sats alleviate launch cost.
•Serve sites at extreme latitudes with minimal atmospheric transmission penalties.
•Shorter transmission distance (1,200km to LEO vs. 36,000 km to GEO) - smaller receivers.
•The limiting transmission is between satellites (2,400 km) or less.
• Waveguides to distribute incoming power.
• Heat rejection issue: No more complex than for SSP; partial recovery using thermo-electric systems
Tradeoffs:
•10GHz range: Low absorption, but large receivers/ less efficient reception; Interference.
•95 - 140 GHz: small receivers, more efficient reception. Higher atmospheric absorption.
Forces ground stations to dry, high locations.
•Cloud cover problem alleviated by having LEO system. Multiple choices of beam path.
•Tradeoff between system mass costs, atmospheric absorption and unreliability due to weather
(alleviated by having multiple earth station choices separated by several kilometers) not properly
understood, since much of the high-frequency data comes from astronomical observatories until now.
October
Direct Conversion to Microwave
•1950s: Solar-Powered Masers with projected efficiency of 50%
•2005: Solar-Powered Laser with 38% efficiency demonstrated.
•Direct Solar Conversion to microwave beams with 50% efficiency and reduced mass by 2035.
•To replace current global production with solar energy at 50% efficiency, 5600 sq.km of solar
collector area in space (where solar intensity is 1GW/sq.km) is required.
•SPG satellites will then be replaced with Direct Conversion Augmented-SPG (DCA-SPG)
satellites, with a 1km diameter sun-tracking ultra light collector and converter on each adding 0.5
GW to the grid.
•Deploying large ultra-thin collectors with highintensity solar cell arrays is an alternative to any
Direct Conversion technology, alleviating
technological risk.
October
Full Space Solar Power Phase
•GEO sun-sats (2040s?) : 100 sq.km ultra light collector/ reflectors that
focus sunlight onto the 1sq.km collectors of the DCA-SPG.
•Each is expected to add 50GW to the grid at 50% efficiency.
•System of 72 LEO satellites and 72 GEO ultralight mirrors, with a 70%
transmission efficiency, will generate 90% of today’s global energy
production.
October
Cost
•
Baseline sizing to recover 50% of system deployment cost in 20 years from savings in
costs of ground transmission, based on current cost of long-term debt.
•
Satellite cost < cost of replacement GPS satellite.
•
Basic cost of delivered power from SPG is twice that of US domestic power cost
(efficiency is only half as much).
Advantages yet to be quantified:
•
•
•
•
•
Use excess power from spikes in generation at “green” plants (wind / solar).
Deliver to peak-demand locations (greater revenue)
Access markets with much higher present-day costs
Market for beamed power in Space
Industries enabled by point retail delivery anywhere on Earth
Disadvantages of The Competitors, Yet to Be Quantified:
•
•
Kyoto Protocol / equivalent CO2 penalties
Added costs to nuclear energy generation/ waste disposal costs
October
Comparison with Conventional SSP and Terrestrial Solar
SSP
SPG
Energy
Production
Primary solar
generation
Exchange; new terrestrial plants, Constrained by
Augmented SPG, then Full SSP duty cycle, &
location
Launch cost
>$13,200/kg to $6,600/kg to 1215km alt. orbit
GEO
N/A.
Space Mass
>1kg/kw
<0.01kg/kw for SPG phase;
0.1 kg/kw in DCA/SSP phases
N/A
Cost Items to
First Power
Sats + grnd
rec’ers
Space system + ground
x’mission & rec’ng + control.
Gnd system+ line
+ land costs.
Duty cycle
24hr w/
reflectors
24 hr – with multiple sources
6hr/day; weather
Assembly
LEO assembly, Pre-assembled – deploy in LEO. Earth
boost to GEO
construction
October
Terrestrial Solar
CONCLUSIONS
•
•
•
SSP can be made viable by integrating new realities of environmental and energy
policy issues.
“Space Power Grid” uses LEO to exchange power across the world - market
opportunity.
“End-to-end efficiency” shows beamed power transmission to be inferior to
transmission via high voltage lines if only US/European domestic markets are
considered.
Long-term end-to-end efficiency superior to present power grid.
However, a space-based power grid opens up various markets and opportunities that
are otherwise closed.
Present concept provides a revenue-generating evolutionary path towards SSP
Key breakthrough sought is in high-efficiency solar-powered Masers.
•
Current advances in solar-powered lasers offer hope.
•
•
•
•
October
Our Approach: 3-Stage Evolution
1.Microwave converters and beaming equipment installed.
2. Thirty-six 200-MW SPG satellites launched.
3. SPG in operation.
4. Direct converter-augmented satellites: DCA-SPG
5. SSP collector beams sunlight to SPG: Full Space Solar Power
October