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SOLAR POWER SATELLITE(SPS)
SUBMITTED BY:-LIBIMOL.V.A
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CONTENTS PAGE NUMBER
1. INTRODUCTION 32. THE RENEWABLE ENERGY-SOLAR POWER 43. SPACE BASED SOLAR POWER 54. DESIGN OF SPACE BASED SOLAR POWER 7
a)SOLAR ENERGY CONVERSION 8
b)WIRELESS POWER TRANSMISSION TO EARTH 9
y MAGNETRON 11y RETRODIRECTIVE ANTENNA ARRAY 13
c)RECTENNA 14
5.LOCATION OF SATELLITE 15
a)GEO
b)LEO
6.LAUNCHING SATELLITE IN SPACE 16
7.MICROWAVE-ENVIRONMENTAL ISSUES 17
8.ADVANTAGES AND DISADVANTAGES 18
9.REFERENCES 19
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1.INTRODUCTION:-
The global demand for energy is increasing due to population growth at the same time that
growingenergy use is driven by the equally strong economic growth in many developing nations.
Electricitycontinues to be the most rapidly growing form of energy consumptionand it will be raised
to almost 22 billion kilowatthours in 2020. To supply this need, 403 gigawatts of new generating
capacity will be required by 2020 to meet growing demand.
world wide demand for electrical enerrgy
Fossil fuels are non renewable source because they take millions of years to form, and reserves are
being depleted much faster than new ones are being made. The production and use of fossil fuels
raise environmental concerns. A global movement toward the generation of renewable energy is
therefore under way to help meet increased energy needs. Renewable energy is energy which comes
from natural resource such as sunlight, wind, rain, tides, and geothermal heat. Renewable energy is
derived from natural processes that are replenished constantly.There are different forms of renewable
energy available-nuclear ,hydroelectric,wind,solar etc..
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2.T E E E BLE E E L E
The t t l energy out ut ofthe Sun each second is 3.861026 J. The Earth recei es
174 petawatts (PW) ofincoming solar radiation) atthe upper atmosphere. Approximately 30% is
reflected backto space while the restis absorbed by clouds, oceans and land masses.
. Fig-solar energy upon erath
Solar panels use this light energy (photons) to generate electricity through the photovoltaic
effect. Once these photons from the sunlight strike the solar cells, they allow some extra electrons to
be knocked offtheir orbits. This, in turn, emits electric fields within the solar cells and itlures the
free electrons into a current. Ifthere are more solar cells, then more electricity would be produced.
fig-solar cells
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3.SPACE-BASED SOLAR POWER(SBSP):-
Space-based solar power (SBSP), or space solar power (SSP) is a system for the
collection of solar power in space.In this the solar panels used to collect the energy would reside on a
satellite in orbit, often referred to as a solar power satellite (SPS), rather than on Earth's surface.Producing electricity from sunlight in space is not new. It has already been done by hundreds of
operating satellites. The major difference would be that SSP would capture much more energy and
beam it down to earth for our use.
A major interest in SBSP stems from the length of time the solar collection panels can be
exposed to a consistently high amount of solar radiation. For most of the year, a satellite-based solar
panel can collect power 24 hours per day, whereas a terrestrial station can collect for at most 12
hours per day, unless at the poles, but then only for 6 months of the year, if weather permits, and
only during peak hoursirradiance under the best of conditions is quite reduced near sunset andsunrise. Capturing the sun's rays in space has distinct advantages since there is no loss of microwave
energy passing through the Earths atmosphere and there is no contribution to the global warming
problem by the addition of CO2 during the production stage. In addition, the orbit of rotation can be
selected such that sunlight is received by the satellite ~96% of the time.
HISTORY:-
y 1968: Dr.Peter glaser introduced the idea of a large solar power satellite system with squaremiles of solar collectors in high geosyncronous orbit (GEO is an orbit 36,000 km above the
equator), for collection and conversion of sun's energy into an electromagnetic microwave
beam to transmit usable energy to large receiving antennas (rectennas) on Earth for
distribution.
y 1973: Dr.Peter Glaser was granted U.S. patent number 3,781,647 for his method oftransmitting power over long distances
y 1994: The United States Air Force conducted the Advanced Photovoltaic Experimentusing asatellite launched into low Earth orbit bya pegasus rocket.
y 19951997: NASA conducted a Fresh Look study of space solar power (SSP) concepts andtechnologies.
y 1998: Japan's space agency starts a program for developing a Space Solar Power System(SSPS), which continues to the present day.
y 1999: NASA's Space Solar Power Exploratory Research And Technology program begun.
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y 2001:NASDA (Japan's national space agency) announced plans to perform additionalresearch and prototyping by launching an experimental satellite with 10 kilowatts and 1
megawatt of power.
y 2009: Jaxa, the Japan Aerospace Exploration Agency announced plans to orbit solar powersatellites that will transmit energy back to earth via microwaves. They hope to have the first
prototype orbiting by 2030.
y 2010: Europe's largest space company EADS Astrium plans to put a solar-collecting demosatellite in space.
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4.DESIGN OF SPACE BASED SOLAR POWER SYSTEM:-
Space-based solar power essentially consists of three parts:
1. a means of collecting solar power in space, for example via solar cells2. a means of transmitting power to earth, for example via microwave3. a means of receiving power on earth, for example via a microwave antenna (rectenna).
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b)Wireless power transmission to the Earth
The microwave power transmission system consists basically of five essential parts: (1) the
efficient conversion of DC power into microwave power, (2) the efficient distribution of the
microwave power over the transmitting aperture to form the microwave beam, (3) the efficient
transfer of'microwave power through space to the receiving site, (4) the efficient collection of
microwave energy at the receiving site (5) the efficient conversion of that microwave energy back
into DC electrical power.The adjective "efficient" has been used appropriately in all five of these
elements because the product of the five efficiencies determines the overall- efficiency.
Fig-Microwave power transmission system
If power is transmitted in a lossless medium such as the vacuum of space the overall DC to
DC efficiency is independent of distance of transmission if the total aperture area is scaled up with
the increase in distance and the proper distribution of microwave power over the transmitting
aperture is maintained.Of course, scaling the system to the 23,000 mile distance that separates the
SPS satellite from the earth's surface leads to large transmitting and receiving apertures.; The
diameters of the transmitting and receiving apertures in the SPS reference system are one and
ten kilometers, respectively. It is the economical use of such large apertures that leads to the large
electrical capacity of a single SPS, typically three to eight Gigawatts.
It was theoretically and experimentally demonstrated almost two decades ago that microwave
power can be very efficiently transferred from one aperture to another in vacuuim. Figure below
demonstrates the relationship between aperture sizes and the tranfer efficiency. Efficiency of
Transmission from Transmitting to Receiving Aperture as a Function of Parameter .
At and Ar are transmitting and receiving aperture areas, is wavelength, and D is the separation
distance between the apertures.
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Microwave energy is not attenuatsed or scattered in avacuum but it is in the earth's
atmosphere. However, it is found that there is relatively low attenuatioh and scattering for a
microwave beam using the SPS reference designwavelength of 12.24 cm (2.45 GHZ). Under normal
atmospheric conditions the loss is about 1%. Under the heaviest rainfall conditions which represents
the worst condition for attenuation and scattering, the total loss may be as great as 10%. The SPS
reference frequency is 2.45GHZ.
Fig-the loss as a function of frequency and rainfall conditions.
The requirements placed upon the device that transforms DC power into microwave power
include very high efficiency, ability to radiate any waste heat occasioned by any inefficiency in the
conversion process into space, very low noise emissions, very long life, a low ratio of mass to
microwave power output, and compatibility with both the DC input power source and the microwave
radiating antenna.There are several devices which converts DC into microwave power.These devices
were klystrons, and two crossed-field devices, the amplitron and the magnetron.
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a)MAGNETRON:- The DC power convertion to microwave power at the transmitting end
of the system by using magnetron is considered. The magnetron is diode type electron tube, which
uses the interaction of magnetic and electric field in the complex cavity to produce oscillation of very
high peak power. It employs radial electric field, axial magnetic field, anode structure and a
cylindrical cathode.
The cylindrical cathode is surrounded by an anode with cavities and thus a radial electric
field will exist. The magnetic field due to two permanent magnets which are added above and
below the tube structure is axial. The upper magnet is North Pole and lower magnet is South Pole.
The electron moving through the space tends to build up a magnetic field around itself. The
magnetic field on right side is weakened because the self-induced magnetic field has the effect of
subtracting from the permanent magnetic field. So the electron trajectory bends in that direction
resulting in a circular motion of travel to anode. This process begins with a low voltage being
applied to the cathode, which causes it to heat up. The temperature rise causes the emission of more
electrons. This cloud of electrons would be repelled away from the negatively charged cathode. The
distance and velocity of their travel would increase with the intensity of applied voltage. The effect
of permanent magnet tends to deflect the electrons away from the anode. Due to the combined
affect of electric and magnetic field on the electron trajectory they move to a path at almost right
angle to their previous direction resulting in an expanding circular orbit around the cathode, which
eventually reaches the anode. The whirling cloud of electrons forms a rotating pattern. Due to the
interaction of this rotating space with the configuration of the surface of anode, an alternating
current of very high frequency is produced in the resonant cavities of the anode. The output is taken
from one of these cavities through waveguide and it will be routed to output antenna.
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The general arrangement of the magnetrons and the sections of slotted waveguide array with
which they are associated is shown in Figure. The magnetrons are shown with a single fin radiator
that efficiently conducts the heat generated by any inefficiency'a a from the magnetron and
radiates it directly into space.The magnetron and the inner edge of the radiating fin operate at a
temperature of 3400C and the size of the fin is dimensioned to radiate 560 watts under this condition.
If the tube is operating with an efficiency of 85%, the microwave power that is generated is 3.2 kW.
Although the fin is made from pyrographite, the most efficient conductor and radiator per unit mass
of material, the fin begins to dominate the combined mass of the tube and its radiator at power levels
much in excess of 3 kW. At this unit power level more than 2,000,000 tubes may be needed in one
SPS satellite, providing a high degreeof redundancy if some should fail.
Fig-assembly of packaged magnetron
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b)RETRODIRECTIVE ANTENNA ARRAY:-
For efficient microwave power transmission the beam must be highly collimated which
requires that the phase of the microwave power as it is launched from the antenna have a high degree
of phase uniformity. This uniformity is achieved by dividing the entire transmitting antenna into
subarrays. The phase of the output of the subarrays is controlled by means of the retrodirective array
principle in which a reference phase across the face of the transmitting antenna is provided by a pilot
beam launched from the center of the rectenna array on the earth's surface. A second reference or
"clock" phase is provided within the transmitting antenna itself. The difference in these two
references at each subarray position is used to cause that subarray to radiate in phase with the others,
even though the subarrays may be out of line mechanically with each other, to create a highly
collimated beam that is pointed directly at the rectenna.
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c)RECTENNA:-
The rectenna is a unique device that was conceived and developed for beamed microwave power
transmission. The functions of rectenna are power collecting ,harmonic filtering and rectification
into DC power. Rectenna rectifies received microwaves into DC current. It spread out over the
receiving aperture area and combines the function of an antenna and a rectifier. In its simplest
from rectenna consist of a collection of rectenna elements, each with a half wave dipole that
feeds a low pass filter circuit terminated in a rectifying diode. The output of the diode in the local
region feeds into a common DC bus.
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5.LOCATION OF SATELLITE:-
a)GEOSTATIONARY ORBIT
A geostationary orbit (or Geostationary Earth Orbit - GEO) is a geosynchronous orbit directly
above the Earth's equator (0 latitude), with a period equal to the Earth's rotational period .An object
in a geostationary orbit appears motionless, at a fixed position in the sky, to ground observers. The
main advantage of locating a space power station in geostationary orbit is that the antenna geometry stays
constant, and so keeping the antennas lined up is simpler.
fig-GEO
b)LOW EARTH ORBIT(LEO)
It requires less energy to place a satellite into a LEO and the LEO satellite needs less powerfulamplifiers for successful transmission and there will be a less transmission path. But its
disadvantages are frequent changes in antenna geometries and more power stations needed to receivepower continuously. It might be possible to deploy LEO systems sooner than GEO because the
antenna development would take less time, but it may take longer to prepare and launch the number
of required satellites.
Fig-inner layer-LEO
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6.LAUNCHING SATELLITE IN SPACE
All satellites today get into orbit by riding on a rocket or by riding in the cargo bay of the Space
Shuttle. For most satellite launches, the scheduled launch rocket is aimed straight up at first. This
gets the rocket through the thickest part of the atmosphere most quickly and best minimizes fuel
consumption. After a rocket launches straight up, the rocket control mechanism uses the inertial
guidance system to calculate necessary adjustments to the rocket's nozzles to tilt the rocket to the
course described in the flight plan. Once the rocket reaches extremely thin air, at about 120 miles
(193 km) up, the rocket's navigational system fires small rockets, just enough to turn the launch
vehicle into a horizontal position. The satellite is then released. At that point, rockets are fired again
to ensure some separation between the launch vehicle and the satellite itself.
One problem for the SBSP concept is the cost of space launches and the amount of material
that would need to be launched.Power beaming from geostationary orbit by microwaves carries the
difficulty that the required 'optical aperture' sizes are very large. For example, the 1978 NASA SPS
study required a 1-km diameter transmitting antenna, and a 10 km diameter receiving rectenna, for a
microwave beam at 2.45 GHz. These sizes can be somewhat decreased by using shorter wavelengths,
although they have increased atmospheric absorption and even potential beam blockage by rain or
water droplets.
Building from space
Gerard O'Neill, noting the problem of high launch costs in the early 1970s, proposed building
the SPS's in orbit with materials from the Moon.Launch costs from the Moon are potentially much
lower than from Earth, due to the lower gravity. Due to the lack of partially self-replicating systems
on the lunar surface under remote control of workers stationed on Earth, this idea is expected to take
more time.
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7.MICROWAVES-ENVIRONMENTAL ISSUES
The price of implementing a SPS includes the acceptance of microwave beams as the link of
that energy between space and earth. Because of their large size, SPS would appear as a very bright
star in the relatively dark night sky. SPS in GEO would show more light than Venus at its brightest.
Thus, the SPS would be quite visible and might be objectionable.
SPS posses many environmental questions such as microwave exposure, optical pollution that
could hinder astronomers , the health and safety of space workers in a heavy-radiation (ionizing)
environment , the potential disturbance of the ionosphere etc.The atmospheric studies indicate that
these problems are not significant , at least for the chosen microwave frequency [2.45GHZ]. On the
earth, each rectenna for a full-power SPS would be about 10 km in diameter. This significant area
possesses classical environmental issues. These could be overcome by siting rectenna in
environmentally insensitive locations, such as in the desert, over water etc. The classic rectenna
esign would be transparent in sunlight, permitting growth and maintenance of vegetation under the
rectenna.
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8.ADVANTAGES AND DISADVANTAGESThe idea collecting solar energy in space and returning it to earth using microwave beam has
many attractions.
1. The full solar irradiation would be available at all times.Thus about five times energy could becollected, compared with the best terrestrial sites.
2. The power could be directed to any point on the earths surface.
3. The zero gravity and high vacuum condition in space would allow much lighter, low maintenance
structures and collectors.
4. The power density would be uninterrupted by darkness, clouds, or precipitation, which are the
problems encountered with earth based solar arrays.
5. The realization of the SPS concept holds great promises for solving energy crisis
6. No waste product.
The concept of generating electricity from solar energy in the space itself has its inherent
disadvantages also. Some of the major disadvantages are:
1. The main draw back of solar energy transfer from orbit is the storage of electricity during off peak
demand hours .
2. The frequency of beamed radiation is planned to be at 2.45 GHz
3. The entire structure is massive.
4. High cost and require much time for construction.
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9.REFERENCES
1. SOLAR POWER SATLLITE By United States. Congress. Office of TechnologyAssessment.
2. SOLAR POWER SATELLITE AS A SOURCE OF BASE LOAD ELECTRICALPOWER(IEEE Transaction on power apparatus and
System,vol.pas.100,no.6,june1981)
3. SOLAR POWER SATELLITE INFERENCER ASSESSMENT(ieee microwavemagazine 2002)
4. AN OVERVIEW OF THE SOLAR POWER SATELLITE OPTION(IEEE transactionon microwave theory and techniques,vl.40,no.6,june1992)
5. SOLAR POWER SATELLITE-THE EMERGING ENERGY OPTION.PETEREDWARD GLASER,FRANK PAUL DAVIDSON
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