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1. Solar Power Satellites and
Microwave Power Transmission
GOURAV KUMAR PRADHAN
DR.MGR UNIVERSITY
CHENNAI
EEE DEPARTMENT

2. Outline
 Background
 Solar Power Satellite
 Microwave Power Transmission
 Current Designs
 Legal Issues
 Conclusion

3. Background
1899-1990

4. Nikola Tesla
 1856-1943
 Innovations:
– Alternating current
– Wireless power
transmission
experiments at
Wardenclyffe

5. Wardenclyffe
 1899
– Able to light lamps
over 25 miles away
without using wires
– High frequency
current, of a Tesla
coil, could light lamps
filled with gas (like
neon)

6. 1940’s to Present
 World War II developed ability to convert
energy to microwaves using a magnetron, no
method for converting microwaves back to
electricity
 1964 William C. Brown demonstrated a
rectenna which could convert microwave
power to electricity

7. Brief History of Solar Power
 1940-50’s Development of the Photovoltaic cell
 1958 First US Satellite that used Solar Power
 1970’s Oil embargo brought increased interest
and study

8. Solar Power from Satellites
 1968’s idea for Solar Power Satellites
proposed by Peter Glaser
– Would use microwaves to transmit power to Earth
from Solar Powered Satellites
 Idea gained momentum during the Oil Crises of
1970’s, but after prices stabilized idea was
dropped
– US Department of Energy research program 1978-
1981

9. Details of the DOE Study
 Construct the satellites in space
– Each SPS would have 400 million solar cells
 Use the Space Shuttle to get pieces to a low
orbit station
 Tow pieces to the assembly point using a
purpose built space tug (similar to space
shuttle)

10. Advantages over Earth based solar
power
 More intense sunlight
 In geosynchronous orbit, 36,000 km (22,369
miles) an SPS would be illuminated over 99%
of the time
 No need for costly storage devices for when
the sun is not in view
– Only a few days at spring and fall equinox would the
satellite be in shadow

11. Continued
 Waste heat is radiated back into space
 Power can be beamed to the location where it
is needed, don’t have to invest in as large a
grid
 No air or water pollution is created during
generation

12. Problems
 Issues identified during the DOE study
– Complexity—30 years to complete
– Size—6.5 miles long by 3.3 miles wide
Transmitting antenna ½ mile in
diameter(1 km)

13. Continued
 Cost—prototype would have cost $74 billion
 Microwave transmission
– Interference with other electronic devices
– Health and environmental effects

14. 1980’s to Present
 Japanese continued to study the idea of SPS
throughout the 1980’s
 In 1995 NASA began a Fresh Look Study
– Set up a research, technology, and investment
schedule

15. NASA Fresh Look Report
 SPS could be competitive with other energy
sources and deserves further study
 Research aimed at an SPS system of 250 MW
 Would cost around $10 billion and take 20
years
 National Research Council found the research
worthwhile but under funded to achieve its
goals

16. Specifications
 Collector area must be between 50 (19 sq
miles) and 150 square kilometers (57 sq miles)
 50 Tons of material
– Current rates on the Space Shuttle run
between $3500 and $5000 per pound
– 50 tons (112,000lbs)=$392,000,000

17. Continued
 There are advantages
 Possible power generation of 5 to 10 gigawatts
– “If the largest conceivable space power
station were built and operated 24 hours a
day all year round, it could produce the
equivalent output of ten 1 million kilowatt-
class nuclear power stations.”

18. Possible Designs

21. Deployment Issues
 Cost of transporting materials into space
 Construction of satellite
– Space Walks
 Maintenance
– Routine
– Meteor impacts

22. Possible Solutions
 International Space
Station
 President’s plan for a
return to the moon
 Either could be used as
a base for construction
activities

23. Microwave Power Transmission
How the power gets
to Earth

24. From the Satellite
Solar power from the satellite is sent to
Earth using a microwave transmitter
Received at a “rectenna” located on
Earth
Recent developments suggest that
power could be sent to Earth using a
laser

25. Microwaves
Frequency 2.45 GHz microwave beam
Retro directive beam control capability
Power level is well below international
safety standard

26. Microwave vs. Laser Transmission
 Microwave
– More developed
– High efficiency up to 85%
– Beams is far below the
lethal levels of
concentration even for a
prolonged exposure
– Cause interference with
satellite communication
industry
 Laser
– Recently developed solid
state lasers allow efficient
transfer of power
– Range of 10% to 20%
efficiency within a few
years
– Conform to limits on eye
and skin damage

27. Rectenna
“An antenna comprising a mesh of dipoles
and diodes for absorbing microwave energy
from a transmitter and converting it into
electric power.”
Microwaves are received with about 85%
efficiency
Around 5km across (3.1 miles)
95% of the beam will fall on the rectenna

28. Rectenna Design
 Currently there are two different design types
being looked at
– Wire mesh reflector
Built on a rigid frame above the ground
Visually transparent so that it would not
interfere with plant life
– Magic carpet
Material pegged to the ground

29. 5,000 MW Receiving Station
(Rectenna). This station is about a
mile and a half long.

30. Rectenna Issues
 Size
– Miles across
 Location
– Aesthetic
– Near population center
 Health and environmental side effects
– Although claim that microwaves or lasers
would be safe, how do you convince people

31. Current Developments

32. SPS 2000

33. Details
 Project in Development
in Japan
 Goal is to build a low
cost demonstration
model by 2025
 8 Countries along the
equator have agreed to
be the site of a rectenna

34. Continued
 10 MW satellite delivering microwave power
– Will not be in geosynchronous orbit, instead
low orbit 1100 km (683 miles)
– Much cheaper to put a satellite in low orbit
– 200 seconds of power on each pass over
rectenna

35. Power to Mobile Devices
 If microwave beams carrying power could be
beamed uniformly over the earth they could
power cell phones
 Biggest problem is that the antenna would
have to be 25-30 cm square

37. Low Orbit
 Communications industry proposing to have
hundreds of satellites in low earth orbit
 These satellites will use microwaves to beam
communications to the ground
 Could also be used to beam power

38. Continued
 Since a low orbit microwave beam would
spread less, the ground based rectenna could
be smaller
 Would allow collectors on the ground of a few
hundred meters across instead of 10
kilometers
 In low orbit they circle the Earth in about every
90 minutes

39. Issues
 Would require a network of hundreds of
satellites
– Air Force currently track 8500 man made objects in
space, 7% satellites
 Would make telecommunications companies
into power companies

40. Reliability
 Ground based solar only
works during clear days,
and must have storage
for night
 Power can be beamed to
the location where it is
needed, don’t have to
invest in as large a grid
 A network of low orbit
satellites could provide
power to almost any
point on Earth
continuously because
one satellite would
always be in range

41. Legal Issues
 Who will oversee?
 Environmental Concerns
 International

42. NASA
 Funding the research
 In charge of space flight for the United States
 Would be launching the satellites and doing
maintenance

43. FCC
 Federal Communications Commission
– The FCC was established by the
Communications Act of 1934 and is charged
with regulating interstate and international
communications by radio, television, wire,
satellite and cable.

44. Environmental
 Possible health hazards
– Effects of long term exposure
– Exposure is equal to the amount that people receive
from cell phones and microwaves
 Location
– The size of construction for the rectennas is
massive

45. International
 Geosynchronous satellites would take up large
sections of space
 Interference with communication satellites
 Low orbit satellites would require agreements
about rectenna locations and flight paths

46. Conclusions
 More reliable than ground based solar power
 In order for SPS to become a reality it several
things have to happen:
– Government support
– Cheaper launch prices
– Involvement of the private sector