How solar power can be harvested in space and beamed to earth.A seminar for elecrical engg. students.

1. Jane Doe
7th
semester
Electrical Engineering
Regd.no.xxxxxxxxxx
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OUTLINE
 Introduction
 Solar Power Satellite
 Microwave Power Transmission
 Issues
 Conclusion

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INTRODUCTION
A great concern has been voiced in recent years
over the extensive use of energy, the limited supply
of resources, and pollution of the environment from
the use of present energy conversion systems.
Thus the search for alternative sources of energy is
being encouraged. The solar power satellite
(SPS) concepts envisions using the constant
availability of light in space to generate
baseload electricity on Earth.

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The SPS is a gigantic satellite designed as an
electric power plant orbiting in the Geostationary
Earth Orbit (GEO). It consists of mainly three
segments; solar energy collector to convert the
solar energy into DC (direct current) electricity,
DC-to-microwave convert-er, and large antenna
array to beam down the microwave power to the
ground.

6. More intense sunlight.
SPS would be illuminated over 99% of the time.
No need for costly storage devices.
Power can be beamed to the location where it is
needed.
No air or water pollution is created in the
process.
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POSSIBLE DESIGNS
www.spacedaily.com/images/solar
-sps-satellite-bg.jpg

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www.ssi.org/assets/images/slide02.jpg

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PROBLEMS AND POSSIBLE SOLUTIONS
Cost of transporting materials to space can be
minimized by using materials from moon or
asteroids .
Difficulty in construction can be overcome by
using International space station or moon as
construction base.
Routine maintenance can be carried out using
robots.

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How to transmit power to earth?

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The beamed microwave power transmission system
can be used to transmit power to earth. Its major
advantage is its ability to transfer energy across
large distances.
Basic Parts of beamed microwave power
transmission system are:-
1.DC to microwave conversion
2.A beam forming antenna.
3.Free space transmission
4.Reception and reconversion to DC

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Beamed microwave power transmission system
DC to
microwave
conversion
Beam
forming
antenna
Free
space
transmis
sion
Reception
Conversion
to DC
70-90% 70-97% 5-95% 85-92%
Maximum possible DC-DC efficiency --- 76%
Experimental DC-DC efficiency ---54%

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The solar energy collected is converted into electrical
energy by the solar PV cells. To transmit the power to
earth the SPS converts the DC electricity into
microwaves using an onboard cavity magnetron which
is same as an microwave oven magnetron except
being modified so as to provide directional beam with
less noise.

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Now the microwave produced needs to be transmitted
so as to be received on earth. The efficiency of
transmission, wavelength used and the distance
depends upon the transmitter and receiver aperture.
The relationship between
aperture to aperture
efficiency and character ‫ר‬

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The microwaves are transmitted using phased array antenna
as we have to control the microwave beam direction
accurately and speedily. The phased array is a directive
antenna which generate a beam form whose shape and
direction by the relative phases and amplitudes of the waves
at the individual antenna elements. It has low efficiency but it
steers electrically and thus has no moving parts

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For accurate target detection and high efficient beam
forming retro-directive system is used. Usually they
have phase conjugate circuits in transmitter or receiver
antenna. A pilot signal transmitted by the target is
received and re-radiated from the phase conjugate
circuit. If the pilot signal is received back by the target
then it is set and power is transmitted.

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RECTENNA
It is an unique device which spreads over receiv- ing
area and combines the function of antenna and
rectifier. A simple rectenna element consists of a
dipole antenna with an RF diode connected across the
dipole elements. The diode rectifies the AC current
induced in the microwave to produce DC power. The
rectenna will be used as an array for high power MPT
because one rectenna element rectifies a few W only.
The SPS requires a rectenna array whose diameter is
over km. It has an overall efficiency of about 85%. It
has low specific mass of 1-2 kg for each KW of DC
power.

19. www.powersat.com/image_library.html

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ENVIRONMENTAL ISSUES
A suggested microwave beam would have a
maximum intensity at its center of 23 mW/cm^2,
which is comparable to the OSHA safety limit of
10 mW/cm^2.
Over 95% of the beam energy will fall on the
rectenna. The remaining microwave energy will
be absorbed and dispersed well within standards
currently imposed upon microwave emissions
around the world.
Rectennae are supposed to be located at remote
areas.

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LEGAL ISSUES
SPS needs to be allocated a slot in the
geosynchronous orbit which has limited capacity.
LEO(Low Earth Orbit) can come as a possible
solution.
Another legal concern of using SPS is whether the
satellites that beam energy to Earth are allowed
under international treaties that prohibit military uses
of outer space.
Microwaves may interfere with the communication
signals.
Handling space debris related to SPS may cause
legal concerns.

23. Too little is currently known about the technical,
economic and environmental aspects of SPS to
make a decision about it’s deployment. An SPS
research program could ultimately assure an
adequate information base for these decisions. If
future demand growth is expected to be high,
SPS might be needed early in the 21st
century,
and an increase in research effort would be
justified.
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24. www.bu.edu/law/central/jd/organizations
www.bvucoepune.edu.in/pdf's
www.sspi.gatech.edu/wptshinohara.pdf
Office of Technology Assessment (OTA),
Princeton, workshop on solar power satellite
www.spacedaily.com
www.ssi.org
www.wikipedia .com
IEEE transactions on microwave theory and
techniques, vol. 40, no. 6, june 1992
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