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SolarPowerSatellite
SVPM’s college of engineering, Malegaon (Bk), Page 1
CHAPTER 1
1.1 Introduction
Can‟t we use solar power at the night? This question may look somewhat
absurd since there is obviously no meaning of “Using solar power at night”! Now-a-
days we are using the solar power to generate electricity by the solar panels mounted
on the earth. But, in outer space, the sun always shines brightly. No clouds block the
solar rays, and there is no night time. Solar collectors mounted on an orbiting satellite
would thus generate power 24 hours per day, 365 days per year. If this power could be
relayed to earth, then the world's energy problems might be solved forever. We
propose a new method for power generation in which the solar power is converted
into microwaves through satellites called Solar Power Satellites (SPS) and it is
received using a special type of antennae called rectenna, mounted on earth surface.
The concept of free space power propagation is not a new concept and it is the
topic of discussion for nearly four decades. In this paper we explain the same for the
generation and reception of electrical power using the rectennas. Rectennas are
special type of antennae that could convert the incoming microwave radiation into
electricity and this electricity can be sent to grids for storage and future usage.
SolarPowerSatellite
SVPM’s college of engineering, Malegaon (Bk) Page 2
1.2 History
The post-war history of research on free-space power transmission is well
documented by William C. Brown, who was a pioneer of practical microwave power
transmission. It washe who first succeeded in demonstrating microwave-powered
helicopter in 1964. A power conversion device from microwave to DC, called a
rectenna, was invented and used for the microwave-powered helicopter. The first
rectenna was composed of 28 half-wave dipole exterminated in a bridge rectifier
using point contact semiconductor diodes. Later, the point contact semiconductor
diodes were replaced by silicon Schottky-barrier diodes, which raised the microwave-
to-DC conversion efficiency from40 % to 84 %. The highest record of 84 %
efficiency was attained in the demonstration of microwave power transmission in
1975 at the JPL Goldstone Facility. Power was successfully transferred from the
transmitting large parabolic antenna dish to the distant rectenna site over a distance of
1.6 km. The DC output was 30 kW.
The concept of the SPS was first proposed by P.E. Glaser in 1968 to meet both
space-based an dearth-based power needs. The SPS will generate electric power of the
order of several hundreds to thousands of megawatts using photovoltaic cells of
sizable area, and will transmit the generated power via a microwave beam to the
receiving rectenna site. Among many technological key issues, which must be
overcome before the SPS realization, microwave power transmission (MPT) is one of
the most important key research issues. The problem contains not only the
technological development microwave of power transmission with high efficiency
and high safety, but also scientific analysis of microwave impact onto the space
plasma environment.
SolarPowerSatellite
SVPM’s college of engineering, Malegaon (Bk) Page 3
CHAPTER 2
Why To Use SPS?
The SPS concept arose because space has several major advantages over earth
for the collection of solar power. There is no air in space, so the satellites would
receive somewhat more intense sunlight, unaffected by weather. Ina geosynchronous
orbit an SPS would be illuminated over 99% of the time. The SPS would be in Earth's
shadow on only a few days at the spring and fall equinoxes; and even then for a
maximum of an hour and a half late at night when power demands are at their lowest
.This allows expensive storage facilities necessary to earth-based system to be
avoided In most senses the SPS concept is simpler than most power systems here on
Earth. This includes the structure needed to hold it together,which in orbit can be
considerably lighter due to the lack of gravity. Some early studies looked at solar
furnaces to drive conventional turbines but as the efficiency of the solar cell
improved, this concept eventually became impractical. In either case, another
advantage of the design is that waste heat is re-radiated back into space, instead of
warming the biosphere as with conventional sources The Solar Power Satellite (SPS)
concept would place solar power plants in orbit above Earth, where they would
convert sunlight to electricity and beam the power to ground-based receiving stations.
The ground-based stations would be connected to today's regular electrical power
lines that run to our homes, offices and factories here on Earth.
SolarPowerSatellite
SVPM’s college of engineering, Malegaon (Bk) Page 4
CHAPTER 3
Wireless Power Transmission To Earth
Wireless power transmission was early proposed to transfer energy from
collection to the Earth's surface. The power could be transmitted as either microwave
or laser radiation at a variety of frequencies depending on system design. Whatever
choice is made, the transmitting radiation would have to be non-ionizing to avoid
potential disturbances either ecologically or biologically if it is to reach the Earth‟s
surface. This established an upper bound for the frequency used, as energy per
photon. And so the ability to cause ionization, increases with frequency. Ionization of
biological materials doesn't begin until ultraviolet or higher frequencies so most radio
frequencies will be acceptable for this.
To minimize the sizes of the antennas used, the wavelength should be small
(and frequency correspondingly high) since antenna efficiency increases as antenna
size increases relative to the wavelength used. More precisely, both for the
transmitting and receiving antennas, the angular beam width is inversely proportional
to the aperture of the antenna, measured in units of the transmission wavelength. The
highest frequencies that be used are limited by atmospheric absorption (chiefly water
vapour and CO2) at higher microwave frequencies.
For these reasons, 2.45 GHz has been proposed as being a reasonable
compromise. However, that frequency results in large antenna sizes at the GEO
distance. A loitering stratospheric airship has been proposed to receive higher
frequencies (or even laser beams), converting them to something like 2.45 GHz for
retransmission to the ground. This proposal has not been as carefully evaluated for
engineering plausibility as have other aspects of SPS design; it will likely present
problems for continuous coverage.
SolarPowerSatellite
SVPM’s college of engineering, Malegaon (Bk) Page 5
CHAPTER 4
4.1 SPS A General Idea
Solar Power Satellites would be located in the geosynchronous orbit. The
difference between existing satellites and SPS is that an SPS would generate more
power-much more power than it requires for its own operation.
The solar energy collected by an SPS would be converted into electricity, then
into microwaves. The microwaves would be beamed to the Earth‟s surface, where
they would be received and converted back into electricity by a large array of
devices known as rectifying antenna or rectenna.(Rectification is the process by
which alternating electrical current ,such as that induced by a microwave beam , is
converted to direct current). This direct current can then be converted to 50 or 60 Hz
alternating current. Each SPS would have been massive; measuring 10.5 km long
and 5.3 km wide or with an average area of 56 sq.km. The surface of each satellite
would have been covered with 400 million solar cells. The transmitting antenna on
the satellite would have been about 1 km in diameter and the receiving antenna on
the Earth‟s surface would have been about 10 km in diameter. The SPS would weigh
more than 50,000 tons.
The reason that the SPS must be so large has to do with the physics of power
beaming. The smaller the transmitter array, the larger the angle of divergence of the
transmitted beam. A highly divergent beam will spread out over a large area, and
may be too weak to activate the rectenna. In order to obtain a sufficiently
concentrated beam; a great deal of power must be collected and fed into a large
transmitter array.
The day-night cycle ,cloud coverage , atmospheric attenuation etc .reduces the
amount of solar energy received on Earth‟s surface. SPS being placed in the space
overcomes this .Another important feature of the SPS is its continuous operation
i.e,24 hours a day,365 days a year basis. Only forma total of 22 in a year would the
SPS would be eclipsed for a period of time to a maximum of 72 min .If the SPS and
the ground antenna are located at the same longitude, the eclipse period will centre
SolarPowerSatellite
SVPM’s college of engineering, Malegaon (Bk) Page 6
around midnight. The power would be beamed to the Earth in the form of
microwaves at a frequency of 2.45 GHz. Microwaves can pass unimpeded through
clouds and rain .Microwaves have other features such as larger band width , smaller
antenna size, sharp radiated beams and they propagate along straight lines. Because
of competing factors such as increasing atmospheric attenuation but reducing size for
the transmitting antenna and the other components at higher frequency, microwave
frequency in the range of 2-3 GHz are considered optimal for the transmission of
power from SPS to the ground rectenna site. A microwave frequency of 2.45 GHz is
considered particularly desirable because of its present uses for ISM band and
consequently probable lack of interference with current radar and communication
systems. The rectenna arrays would be designed to let light through, so that crops or
even solar panels could be placed underneath it. Here microwaves are practically nil.
Figure 4.1 Design of Space based Solar Power (SBSP)
The amount of power available to the consumers from one SPS is 5 GW .the
peak intensity of microwave beam would be 23 MW/cm².So far, no non thermal
health effects of low level microwave exposure have been proved, although the issue
remains controversial . SPS has all the advantage of ground solar, plus an additional
advantage; it generates power during cloudy weather and at night. In other words
SolarPowerSatellite
SVPM’s college of engineering, Malegaon (Bk) Page 7
SPS receiver operates just like a solar array. Like a solar array, it receives power
from space and converts it into electricity. If the satellite position is selected such
that the Earth and the Sun are in the same location in the sky, when viewed from the
satellite, same dish could be used both as solar power collector and the microwave
antenna. This reduces the size and complexity of satellite.
However, the main barrier to the development of SPS is social, not
technological. The initial development cost for SPS is enormous and the construction
time required is very long. Possible risks for such a large project are very large, pay-
off is uncertain. Lower cost technology may be developed during the time required
to construct the system. So such a large program requires a step by step path with
immediate pay-off at each step and the experience gained at each step refine and
improve the risk in evolutionary steps.
4.2 Solar Energy Conversion
Two basic methods of converting sunlight to electricity have been studied:
photovoltaic (PV) conversion, and solar dynamic (SD) conversion. Most analyses of
solar power satellites have focused on photovoltaic conversion (commonly known as
“solar cells”). Photovoltaic conversion uses semiconductor cells (e.g., silicon or
gallium arsenide) to directly convert photons into electrical power via a quantum
mechanical mechanism.
Figure 4.2: solar cell use in SPS
Photovoltaic cells are not perfect in practice, as material purity and processing
issues during production affect performance; each has been progressively improved
SolarPowerSatellite
SVPM’s college of engineering, Malegaon (Bk) Page 8
for some decades. Some new, thin-film approaches are less efficient (about 20% vs.
35% for best in class in each case), but are much less expensive and generally lighter.
In an SPS implementation, photovoltaic cells will likely be rather different from the
glass-pane protected solar cell panels familiar to many from current terrestrial use,
since they will be optimized for weight, and will be designed to be tolerant to the
space radiation environment (it turns out fortuitously, that thin film silicon solar
panels are highly insensitive to ionizing radiation), but will not need to be
encapsulated against corrosion by the elements. They do not require the structural
support required for terrestrial use, where the considerable gravity and wind loading
imposes structural requirements on terrestrial implementations.
4.3 A DC To Microwave Converter
To convert the DC power to microwave for the transmission through antenna
towards the earth‟s receiving antenna, microwave oscillators like Klystrons,
Magnetrons can be used. In transmission, an alternating current is created in the
elements by applying a voltage at the antenna terminals, causing the elements to
radiate an electromagnetic field.
The DC power must be converted to microwave power at the transmitting end
of the system by using microwave oven magnetron. The heat of microwave oven is
the high voltage system. The nucleus of high voltage system is the magnetron tube.
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
SolarPowerSatellite
SVPM’s college of engineering, Malegaon (Bk) Page 9
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. Momentum is provided by negative
4000 V DC. This is produced by means of voltage doubler circuit. The electrons blast
off from cathode like tiny rocket.
As the electrons move towards their objective, they encounter the powerful
magnetic. The effect of permanent magnet tends to deflect the electrons away from
the anode. Due to the combined effect of electric and magnetic field on the electron
trajectory they revive 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 chare wheel 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. The low cost and readily available magnetron is used in ground.
The same principle would be used but a special magnetron would be developed
for space use. Because of the pulsed operation of these magnetrons they generate
much spurious noise. A solar power satellite operating with 10 GW of radiated power
would radiate a total power of one microwatt in a 400 Hz channel width.
4.3.1 Magnetron
The cavity magnetron is a high-powered vacuum tube that
generates microwaves using the interaction of a stream of electrons with a magnetic
field while moving past a series of open metal cavities (cavity resonators). Electrons
pass by the openings to these cavities and cause radio waves to oscillate within,
similar to the way a whistle produces a tone when excited by an air stream blown past
its opening. The frequency of the microwaves produced, the resonant frequency, is
determined by the cavities' physical dimensions. Unlike other vacuum tubes such as
a klystron or a traveling-wave tube (TWT), the magnetron cannot function as
an amplifier in order to increase the intensity of an applied microwave signal; the
magnetron serves solely as an oscillator, generating a microwave signal from direct
current electricity supplied to the vacuum tube.
SolarPowerSatellite
SVPM’s college of engineering, Malegaon (Bk) Page 10
Figure 4.3 Magnetron
Magnetron, diode vacuum tube consisting of a cylindrical (straight
wire) cathode and a coaxial anode, between which a dc (direct current) potential creates
an electric field. A magnetic field is applied longitudinally by an external magnet.
Connected to a resonant line, it can act as an oscillator. Magnetrons are capable of
generating extremely high frequencies and also short bursts of very high power. They
are an important source of power in radar systems and in microwave ovens.
4.4 Transmitting Antenna
Power transmission via radio waves can be made more directional, allowing
longer distance power beaming, with shorter wavelengths of electromagnetic
radiation, typically in the microwave range. Power beaming using microwaves has
been proposed for the transmission of energy from orbiting solar power satellites to
Earth and the beaming of power to spacecraft leaving orbit has been considered. The
size of the components may be dictated by the distance from transmitter to receiver
distance, the wavelength and the Rayleigh Criterion or diffraction limit, used in
standard radio frequency antenna design, which also applies to lasers. In addition to
the Rayleigh criterion Airy's diffraction limit is also frequently used to determine an
approximate spot size at an arbitrary distance from the aperture.
The Rayleigh criterion dictates that any radio wave microwave or laser beam
will spread and become weaker and diffuse over distance; the larger the transmitter
antenna or laser aperture compared to the wavelength of radiation, the tighter the
SolarPowerSatellite
SVPM’s college of engineering, Malegaon (Bk) Page 11
beam and the less it will spread as a function of distance (and vice versa). Smaller
antennae also suffer from excessive losses due to side lobes. However, the concept of
laser aperture considerably differs from an antenna. Typically, a laser aperture much
larger than the wavelength induces multi-mode radiation and mostly collimators are
used before emitted radiation couples into a fibre or into space.
Ultimately, beam width is physically determined by diffraction due to the dish
size in relation to the wavelength of the electromagnetic radiation used to make the
beam. Microwave power beaming can be more efficient than lasers, and is less prone
to atmospheric attenuation caused by dust or water vapour losing atmosphere to
vaporize the water in contact. Then the power levels are calculated by combining the
above parameters together and adding in gain losses to antenna an due characteristics
d the transparency of the medium through which the radiation passes. That process is
known as calculating a link budget,
However, the above mathematics does not account for atmospheric absorption
which can be Severe damping effect on propagating energy in addition to causing
severe fading and loss of Quos.
4.5 TRANSMISSION
As the electro-magnetic induction and electro-magnetic radiation has
disadvantages we are going for implementation of electrical conduction and resonant
frequency methods. Of this, the resonant induction method is the most implement able
due to the reasons given later. In the distant future this method could allow for
elimination of many existing high tension power transmission lines and facilitate the
inter connection of electric generation plants in a global scale. The microwave source
consists of microwave oven magnetron with electronics to control the output power.
The output microwave power ranges from 50w to 200w at 2.45GHz. A coaxial cable
connects the output of the microwave source to a coax-to-wave adaptor. This adapter
is connected to a tuning waveguide ferrite circulator is connected to a tuning
waveguide section to match the wave guide impedance to the antenna input
impedance. The slotted wave guide antenna consists of 8 waveguide sections with 8
slots on each section. These 64 slots radiate the power uniformly through free space to
the rectifying antenna (rectenna). The slotted waveguide antenna is ideal for power
transmission because of its high aperture efficiency (>95%) and high power handling
SolarPowerSatellite
SVPM’s college of engineering, Malegaon (Bk) Page 12
capability. Microwaves are situated on the electromagnetic spectrum with frequencies
ranging from 0.3 to 300 GHz.
The energy transmitted by a microwave is very diffusive in nature, such that the
receiving antenna area must be very large when compared to the transmitter.
Although the use of microwaves to transmit energy from space down to earth is
attractive, most part of the microwaves receives significant interference due to
atmosphere. Still there are certain frequency windows in which these interactions are
minimized. The frequency windows in which there is a minimum of atmospheric
signal attenuation are in the range of 2.45-5.8GHz, and also 35-38GHz; specifically
we might expect losses of 2-6%, and 8-11% respectively for these two microwave
signal ranges. As the microwave power is beamed towards a particular point (Point to
point) using parabolic antennas (Drum antennas) the free space path loss (FSPL) is
not in a considerable amount Wireless Power Transmission (using microwaves) is
well proven. Experiments in the tens of kilowatts have been performed at Goldstone
in California in 1975 and more recently (1997) at Grand Bassin on Reunion Island.
These methods achieve distances on the order of a kilometre.
Microwave Laser
Frequency (Wave length) 5.8GHz 1.06µm
Atmospheric/ionosphere
transmission (clear sky)
97% 80%
Dc to RF(laser)
conversion efficiency
80%(expected) 60%(expected)
RF(laser) to dc
conversion efficiency
80%(expected) 60%(expected)
Table 4.1 Comparison of Microwave and Laser Power Transmission for SPS
4.6 Ground Segment – Reception
The SPS system will require a large receiving area with a Rectenna array and
the power network connected to the existing power grids on the ground. Although
each rectenna element supplies only a few watts, the total received power is in the
Giga watts (GW).
SolarPowerSatellite
SVPM’s college of engineering, Malegaon (Bk) Page 13
A Rectenna may be used to convert the microwave energy back into electricity.
Rectenna conversion efficiencies exceeding 95% have been realized. The word
“Rectenna” is formed from rectifying circuit and antenna. A rectifying antenna called
rectenna receives the transmitted power and converts the microwave power to direct
current (DC) power. The rectenna is a passive element with a rectifying diode, and is
operated without any extra power source. The rectenna has a low-pass filter between
the antenna and the rectifying diode to suppress re-radiation of higher harmonics. It
also has an output smoothing filter. This demonstration rectenna consists of 6 rows of
dipole antennas, where 8 dipoles belong to each row. Each row is connected to a
rectifying circuit which consists of low pass filters and a rectifier. The rectifier is a
GA-As Schottky barrier diode, that is impedance matched to the dipoles by allow pass
filter. The 6 rectifying diodes are connected to the light bulbs for indicating that the
power is received. The light bulbs also dissipate the received power.
The Earth-based receiver antenna (or rectenna) is a critical part of the original
SPS concept. It would consist of many short dipole antennas, connected via diodes.
Microwaves broadcast from the SPS will be received in the dipoles with about 85%
efficiency. With a conventional microwave antenna, the reception efficiency is still
better, but the cost and complexity is also considerably greater, almost certainly
prohibitively so. Rectenna would be multiple kilometres across. Crops and farm
animals may be raised underneath a rectenna, as the thin wires used for support and
for the dipoles will only slightly reduce sunlight, or non-arable land could be used, so
such a rectenna would not be as expensive in terms of land use as might be supposed.
This rectenna has a 25% collection and conversion efficiency, But rectennas have
been tested with greater than 90%.
SolarPowerSatellite
SVPM’s college of engineering, Malegaon (Bk) Page 14
Figure 4.4 Design of Earth Receiving Station (Rectenna)
4.7 Rectenna
Rectenna is an acronym for Rectifying antenna. It is a special type of antenna
that rectifies the incoming microwave radiation into DC current and hence the name
Rectenna. A rectenna comprises of a mesh of dipoles and diodes for absorbing
microwave energy from a transmitter and converting it into electric power. Its
elements are usually arranged in a mesh pattern, giving it a distinct appearance from
most antennae. A simple rectenna can be constructed from a schottky diode placed
between antenna dipoles as shown in Fig. 4.The diode rectifies the current induced in
the antenna by the microwaves. Rectenna are highly efficient at converting
microwave energy to electricity. In laboratory environments, efficiencies above 90%
have been observed with regularity. In future rectenna will be used to generate large-
scale power from microwave beams delivered from orbiting SPS satellites.
Figure 4.5 Rectenna Circuit
SolarPowerSatellite
SVPM’s college of engineering, Malegaon (Bk) Page 15
Figure 4.6 Rectenna
SolarPowerSatellite
SVPM’s college of engineering, Malegaon (Bk) Page 16
CHAPTER 5
Compare BetweenOther Sources
Table 5.1 Comparison between SPS and Other Sources
SolarPowerSatellite
SVPM’s college of engineering, Malegaon (Bk) Page 17
CHAPTER 6
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 possess 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.
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 sitting rectenna in environmentally insensitive locations,
such as in the desert, over water etc. The classic rectenna design would be
transparent in sunlight, permitting growth and maintenance of vegetation under the
rectenna.
However, the issues related to microwaves continue to be the most pressing
environmental issues. On comparing with the use of radar, microwave ovens ,
police radars, cellular phones and wireless base stations, laser pointers etc. public
exposures from SPS would be similar or even less. Based on well-developed
antenna theory, the environmental levels of microwave power beam drop down to
0.1μW/cm². Even though human exposures to the 25 mW/cm²will, in general, be
avoided, studies shows that people can tolerate such exposures for a period of at
least 45 min. So concern about human exposure can be dismissed forthrightly.
Specific research over the years has been directed towards effects on birds, in
particular. Modern reviews of this research show that only some birds may
experience some thermal stress at high ambient temperatures. Of course, at low
SolarPowerSatellite
SVPM’s college of engineering, Malegaon (Bk) Page 18
ambient temperatures the warming might be welcomed by birds and may present a
nuisance attraction.
Serious discussions and education are required before most of mankind
accepts this technology with global dimensions. Microwaves, however is not a
„pollutant‟ but, more aptly, a man made extension of the naturally generated
electromagnetic spectrum that provides heat and light for our sustence.
SolarPowerSatellite
SVPM’s college of engineering, Malegaon (Bk) Page 19
CHAPTER 7
7.1 ADVANTAGES
The 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 expect when the sun
is eclipsed by the earth. Thus about five times energy could be collected,
compared with the best terrestrial sites
2. The power could be directed to any point on the earth‟s 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 moving parts.
7. No fuel required.
8. No waste product.
7.2DISADVANTAGES
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 drawback 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 and this
frequency is used by communication satellites also.
3. The entire structure is massive.
4. High cost and require much time for construction.
5. Radiation hazards associated with the system.
6. Risks involved with malfunction.
7. High power microwave source and high gain antenna can be used to deliver
an intense burst of energy to a target and thus used as a weapon.
SolarPowerSatellite
SVPM’s college of engineering, Malegaon (Bk) Page 20
CHAPTER 8
Conclusion
One of the key technologies needed for implementing an SPS is microwave
power transmission from the geosynchronous orbit to the ground. The SPS requires
new microwave technologies for achieving a high power conversion efficiency of
more than 80% from/to dc and an extremely high precision beam control with 10-
radaccuracy from the 2-km2 array antenna. These requirements are significantly
challenging, and hence, considerable effort is needed for proper research and
development of the technologies. The technologies are to be partially verified in the
ground demonstration experiment within several years, and they are to be fully
verified in the space experiments within ten years. Ongoing research and development
activities according to the technology roadmap are expected to lead to the beginning
of the new SPS era in the 2030s.
SolarPowerSatellite
SVPM’s college of engineering, Malegaon (Bk) Page 21
CHAPTER 9
References
1. J. O. Mcspadden and J. C. Mankins, “Space solar power programs and
microwave wireless power transmission technology,” IEEE Microwave Mag.,
pp. 46–57, Dec. 2002.
2. IOSR Journal of Electronics and Communication Engineering (IOSR-JECE)
ISSN: 2278-2834, ISBN: 2278-8735, PP: 59-64.
3. Susumu Sasaki, Koji Tanaka, and Ken-ichiro Maki, “Microwave Power
Transmission Technologies for Solar Power Satellites, “Proceedings of the
IEEE | Vol. 101, No. 6, June 2013.
4. N. Shinohara, “Wireless Power Transmission for Solar Power Satellite
(SPS)”
5. ShubhamR.Gawande, “WIRELESS POWER TRANSMISSION THROUGH
SOLAR POWER SATELLITES (S.P.S),” ISSN (PRINT): 2393-8374,
(ONLINE): 2394-0697, VOLUME-3, ISSUE-3, 2016

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Space Based Solar Power Satellite

  • 1. SolarPowerSatellite SVPM’s college of engineering, Malegaon (Bk), Page 1 CHAPTER 1 1.1 Introduction Can‟t we use solar power at the night? This question may look somewhat absurd since there is obviously no meaning of “Using solar power at night”! Now-a- days we are using the solar power to generate electricity by the solar panels mounted on the earth. But, in outer space, the sun always shines brightly. No clouds block the solar rays, and there is no night time. Solar collectors mounted on an orbiting satellite would thus generate power 24 hours per day, 365 days per year. If this power could be relayed to earth, then the world's energy problems might be solved forever. We propose a new method for power generation in which the solar power is converted into microwaves through satellites called Solar Power Satellites (SPS) and it is received using a special type of antennae called rectenna, mounted on earth surface. The concept of free space power propagation is not a new concept and it is the topic of discussion for nearly four decades. In this paper we explain the same for the generation and reception of electrical power using the rectennas. Rectennas are special type of antennae that could convert the incoming microwave radiation into electricity and this electricity can be sent to grids for storage and future usage.
  • 2. SolarPowerSatellite SVPM’s college of engineering, Malegaon (Bk) Page 2 1.2 History The post-war history of research on free-space power transmission is well documented by William C. Brown, who was a pioneer of practical microwave power transmission. It washe who first succeeded in demonstrating microwave-powered helicopter in 1964. A power conversion device from microwave to DC, called a rectenna, was invented and used for the microwave-powered helicopter. The first rectenna was composed of 28 half-wave dipole exterminated in a bridge rectifier using point contact semiconductor diodes. Later, the point contact semiconductor diodes were replaced by silicon Schottky-barrier diodes, which raised the microwave- to-DC conversion efficiency from40 % to 84 %. The highest record of 84 % efficiency was attained in the demonstration of microwave power transmission in 1975 at the JPL Goldstone Facility. Power was successfully transferred from the transmitting large parabolic antenna dish to the distant rectenna site over a distance of 1.6 km. The DC output was 30 kW. The concept of the SPS was first proposed by P.E. Glaser in 1968 to meet both space-based an dearth-based power needs. The SPS will generate electric power of the order of several hundreds to thousands of megawatts using photovoltaic cells of sizable area, and will transmit the generated power via a microwave beam to the receiving rectenna site. Among many technological key issues, which must be overcome before the SPS realization, microwave power transmission (MPT) is one of the most important key research issues. The problem contains not only the technological development microwave of power transmission with high efficiency and high safety, but also scientific analysis of microwave impact onto the space plasma environment.
  • 3. SolarPowerSatellite SVPM’s college of engineering, Malegaon (Bk) Page 3 CHAPTER 2 Why To Use SPS? The SPS concept arose because space has several major advantages over earth for the collection of solar power. There is no air in space, so the satellites would receive somewhat more intense sunlight, unaffected by weather. Ina geosynchronous orbit an SPS would be illuminated over 99% of the time. The SPS would be in Earth's shadow on only a few days at the spring and fall equinoxes; and even then for a maximum of an hour and a half late at night when power demands are at their lowest .This allows expensive storage facilities necessary to earth-based system to be avoided In most senses the SPS concept is simpler than most power systems here on Earth. This includes the structure needed to hold it together,which in orbit can be considerably lighter due to the lack of gravity. Some early studies looked at solar furnaces to drive conventional turbines but as the efficiency of the solar cell improved, this concept eventually became impractical. In either case, another advantage of the design is that waste heat is re-radiated back into space, instead of warming the biosphere as with conventional sources The Solar Power Satellite (SPS) concept would place solar power plants in orbit above Earth, where they would convert sunlight to electricity and beam the power to ground-based receiving stations. The ground-based stations would be connected to today's regular electrical power lines that run to our homes, offices and factories here on Earth.
  • 4. SolarPowerSatellite SVPM’s college of engineering, Malegaon (Bk) Page 4 CHAPTER 3 Wireless Power Transmission To Earth Wireless power transmission was early proposed to transfer energy from collection to the Earth's surface. The power could be transmitted as either microwave or laser radiation at a variety of frequencies depending on system design. Whatever choice is made, the transmitting radiation would have to be non-ionizing to avoid potential disturbances either ecologically or biologically if it is to reach the Earth‟s surface. This established an upper bound for the frequency used, as energy per photon. And so the ability to cause ionization, increases with frequency. Ionization of biological materials doesn't begin until ultraviolet or higher frequencies so most radio frequencies will be acceptable for this. To minimize the sizes of the antennas used, the wavelength should be small (and frequency correspondingly high) since antenna efficiency increases as antenna size increases relative to the wavelength used. More precisely, both for the transmitting and receiving antennas, the angular beam width is inversely proportional to the aperture of the antenna, measured in units of the transmission wavelength. The highest frequencies that be used are limited by atmospheric absorption (chiefly water vapour and CO2) at higher microwave frequencies. For these reasons, 2.45 GHz has been proposed as being a reasonable compromise. However, that frequency results in large antenna sizes at the GEO distance. A loitering stratospheric airship has been proposed to receive higher frequencies (or even laser beams), converting them to something like 2.45 GHz for retransmission to the ground. This proposal has not been as carefully evaluated for engineering plausibility as have other aspects of SPS design; it will likely present problems for continuous coverage.
  • 5. SolarPowerSatellite SVPM’s college of engineering, Malegaon (Bk) Page 5 CHAPTER 4 4.1 SPS A General Idea Solar Power Satellites would be located in the geosynchronous orbit. The difference between existing satellites and SPS is that an SPS would generate more power-much more power than it requires for its own operation. The solar energy collected by an SPS would be converted into electricity, then into microwaves. The microwaves would be beamed to the Earth‟s surface, where they would be received and converted back into electricity by a large array of devices known as rectifying antenna or rectenna.(Rectification is the process by which alternating electrical current ,such as that induced by a microwave beam , is converted to direct current). This direct current can then be converted to 50 or 60 Hz alternating current. Each SPS would have been massive; measuring 10.5 km long and 5.3 km wide or with an average area of 56 sq.km. The surface of each satellite would have been covered with 400 million solar cells. The transmitting antenna on the satellite would have been about 1 km in diameter and the receiving antenna on the Earth‟s surface would have been about 10 km in diameter. The SPS would weigh more than 50,000 tons. The reason that the SPS must be so large has to do with the physics of power beaming. The smaller the transmitter array, the larger the angle of divergence of the transmitted beam. A highly divergent beam will spread out over a large area, and may be too weak to activate the rectenna. In order to obtain a sufficiently concentrated beam; a great deal of power must be collected and fed into a large transmitter array. The day-night cycle ,cloud coverage , atmospheric attenuation etc .reduces the amount of solar energy received on Earth‟s surface. SPS being placed in the space overcomes this .Another important feature of the SPS is its continuous operation i.e,24 hours a day,365 days a year basis. Only forma total of 22 in a year would the SPS would be eclipsed for a period of time to a maximum of 72 min .If the SPS and the ground antenna are located at the same longitude, the eclipse period will centre
  • 6. SolarPowerSatellite SVPM’s college of engineering, Malegaon (Bk) Page 6 around midnight. The power would be beamed to the Earth in the form of microwaves at a frequency of 2.45 GHz. Microwaves can pass unimpeded through clouds and rain .Microwaves have other features such as larger band width , smaller antenna size, sharp radiated beams and they propagate along straight lines. Because of competing factors such as increasing atmospheric attenuation but reducing size for the transmitting antenna and the other components at higher frequency, microwave frequency in the range of 2-3 GHz are considered optimal for the transmission of power from SPS to the ground rectenna site. A microwave frequency of 2.45 GHz is considered particularly desirable because of its present uses for ISM band and consequently probable lack of interference with current radar and communication systems. The rectenna arrays would be designed to let light through, so that crops or even solar panels could be placed underneath it. Here microwaves are practically nil. Figure 4.1 Design of Space based Solar Power (SBSP) The amount of power available to the consumers from one SPS is 5 GW .the peak intensity of microwave beam would be 23 MW/cm².So far, no non thermal health effects of low level microwave exposure have been proved, although the issue remains controversial . SPS has all the advantage of ground solar, plus an additional advantage; it generates power during cloudy weather and at night. In other words
  • 7. SolarPowerSatellite SVPM’s college of engineering, Malegaon (Bk) Page 7 SPS receiver operates just like a solar array. Like a solar array, it receives power from space and converts it into electricity. If the satellite position is selected such that the Earth and the Sun are in the same location in the sky, when viewed from the satellite, same dish could be used both as solar power collector and the microwave antenna. This reduces the size and complexity of satellite. However, the main barrier to the development of SPS is social, not technological. The initial development cost for SPS is enormous and the construction time required is very long. Possible risks for such a large project are very large, pay- off is uncertain. Lower cost technology may be developed during the time required to construct the system. So such a large program requires a step by step path with immediate pay-off at each step and the experience gained at each step refine and improve the risk in evolutionary steps. 4.2 Solar Energy Conversion Two basic methods of converting sunlight to electricity have been studied: photovoltaic (PV) conversion, and solar dynamic (SD) conversion. Most analyses of solar power satellites have focused on photovoltaic conversion (commonly known as “solar cells”). Photovoltaic conversion uses semiconductor cells (e.g., silicon or gallium arsenide) to directly convert photons into electrical power via a quantum mechanical mechanism. Figure 4.2: solar cell use in SPS Photovoltaic cells are not perfect in practice, as material purity and processing issues during production affect performance; each has been progressively improved
  • 8. SolarPowerSatellite SVPM’s college of engineering, Malegaon (Bk) Page 8 for some decades. Some new, thin-film approaches are less efficient (about 20% vs. 35% for best in class in each case), but are much less expensive and generally lighter. In an SPS implementation, photovoltaic cells will likely be rather different from the glass-pane protected solar cell panels familiar to many from current terrestrial use, since they will be optimized for weight, and will be designed to be tolerant to the space radiation environment (it turns out fortuitously, that thin film silicon solar panels are highly insensitive to ionizing radiation), but will not need to be encapsulated against corrosion by the elements. They do not require the structural support required for terrestrial use, where the considerable gravity and wind loading imposes structural requirements on terrestrial implementations. 4.3 A DC To Microwave Converter To convert the DC power to microwave for the transmission through antenna towards the earth‟s receiving antenna, microwave oscillators like Klystrons, Magnetrons can be used. In transmission, an alternating current is created in the elements by applying a voltage at the antenna terminals, causing the elements to radiate an electromagnetic field. The DC power must be converted to microwave power at the transmitting end of the system by using microwave oven magnetron. The heat of microwave oven is the high voltage system. The nucleus of high voltage system is the magnetron tube. 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
  • 9. SolarPowerSatellite SVPM’s college of engineering, Malegaon (Bk) Page 9 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. Momentum is provided by negative 4000 V DC. This is produced by means of voltage doubler circuit. The electrons blast off from cathode like tiny rocket. As the electrons move towards their objective, they encounter the powerful magnetic. The effect of permanent magnet tends to deflect the electrons away from the anode. Due to the combined effect of electric and magnetic field on the electron trajectory they revive 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 chare wheel 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. The low cost and readily available magnetron is used in ground. The same principle would be used but a special magnetron would be developed for space use. Because of the pulsed operation of these magnetrons they generate much spurious noise. A solar power satellite operating with 10 GW of radiated power would radiate a total power of one microwatt in a 400 Hz channel width. 4.3.1 Magnetron The cavity magnetron is a high-powered vacuum tube that generates microwaves using the interaction of a stream of electrons with a magnetic field while moving past a series of open metal cavities (cavity resonators). Electrons pass by the openings to these cavities and cause radio waves to oscillate within, similar to the way a whistle produces a tone when excited by an air stream blown past its opening. The frequency of the microwaves produced, the resonant frequency, is determined by the cavities' physical dimensions. Unlike other vacuum tubes such as a klystron or a traveling-wave tube (TWT), the magnetron cannot function as an amplifier in order to increase the intensity of an applied microwave signal; the magnetron serves solely as an oscillator, generating a microwave signal from direct current electricity supplied to the vacuum tube.
  • 10. SolarPowerSatellite SVPM’s college of engineering, Malegaon (Bk) Page 10 Figure 4.3 Magnetron Magnetron, diode vacuum tube consisting of a cylindrical (straight wire) cathode and a coaxial anode, between which a dc (direct current) potential creates an electric field. A magnetic field is applied longitudinally by an external magnet. Connected to a resonant line, it can act as an oscillator. Magnetrons are capable of generating extremely high frequencies and also short bursts of very high power. They are an important source of power in radar systems and in microwave ovens. 4.4 Transmitting Antenna Power transmission via radio waves can be made more directional, allowing longer distance power beaming, with shorter wavelengths of electromagnetic radiation, typically in the microwave range. Power beaming using microwaves has been proposed for the transmission of energy from orbiting solar power satellites to Earth and the beaming of power to spacecraft leaving orbit has been considered. The size of the components may be dictated by the distance from transmitter to receiver distance, the wavelength and the Rayleigh Criterion or diffraction limit, used in standard radio frequency antenna design, which also applies to lasers. In addition to the Rayleigh criterion Airy's diffraction limit is also frequently used to determine an approximate spot size at an arbitrary distance from the aperture. The Rayleigh criterion dictates that any radio wave microwave or laser beam will spread and become weaker and diffuse over distance; the larger the transmitter antenna or laser aperture compared to the wavelength of radiation, the tighter the
  • 11. SolarPowerSatellite SVPM’s college of engineering, Malegaon (Bk) Page 11 beam and the less it will spread as a function of distance (and vice versa). Smaller antennae also suffer from excessive losses due to side lobes. However, the concept of laser aperture considerably differs from an antenna. Typically, a laser aperture much larger than the wavelength induces multi-mode radiation and mostly collimators are used before emitted radiation couples into a fibre or into space. Ultimately, beam width is physically determined by diffraction due to the dish size in relation to the wavelength of the electromagnetic radiation used to make the beam. Microwave power beaming can be more efficient than lasers, and is less prone to atmospheric attenuation caused by dust or water vapour losing atmosphere to vaporize the water in contact. Then the power levels are calculated by combining the above parameters together and adding in gain losses to antenna an due characteristics d the transparency of the medium through which the radiation passes. That process is known as calculating a link budget, However, the above mathematics does not account for atmospheric absorption which can be Severe damping effect on propagating energy in addition to causing severe fading and loss of Quos. 4.5 TRANSMISSION As the electro-magnetic induction and electro-magnetic radiation has disadvantages we are going for implementation of electrical conduction and resonant frequency methods. Of this, the resonant induction method is the most implement able due to the reasons given later. In the distant future this method could allow for elimination of many existing high tension power transmission lines and facilitate the inter connection of electric generation plants in a global scale. The microwave source consists of microwave oven magnetron with electronics to control the output power. The output microwave power ranges from 50w to 200w at 2.45GHz. A coaxial cable connects the output of the microwave source to a coax-to-wave adaptor. This adapter is connected to a tuning waveguide ferrite circulator is connected to a tuning waveguide section to match the wave guide impedance to the antenna input impedance. The slotted wave guide antenna consists of 8 waveguide sections with 8 slots on each section. These 64 slots radiate the power uniformly through free space to the rectifying antenna (rectenna). The slotted waveguide antenna is ideal for power transmission because of its high aperture efficiency (>95%) and high power handling
  • 12. SolarPowerSatellite SVPM’s college of engineering, Malegaon (Bk) Page 12 capability. Microwaves are situated on the electromagnetic spectrum with frequencies ranging from 0.3 to 300 GHz. The energy transmitted by a microwave is very diffusive in nature, such that the receiving antenna area must be very large when compared to the transmitter. Although the use of microwaves to transmit energy from space down to earth is attractive, most part of the microwaves receives significant interference due to atmosphere. Still there are certain frequency windows in which these interactions are minimized. The frequency windows in which there is a minimum of atmospheric signal attenuation are in the range of 2.45-5.8GHz, and also 35-38GHz; specifically we might expect losses of 2-6%, and 8-11% respectively for these two microwave signal ranges. As the microwave power is beamed towards a particular point (Point to point) using parabolic antennas (Drum antennas) the free space path loss (FSPL) is not in a considerable amount Wireless Power Transmission (using microwaves) is well proven. Experiments in the tens of kilowatts have been performed at Goldstone in California in 1975 and more recently (1997) at Grand Bassin on Reunion Island. These methods achieve distances on the order of a kilometre. Microwave Laser Frequency (Wave length) 5.8GHz 1.06µm Atmospheric/ionosphere transmission (clear sky) 97% 80% Dc to RF(laser) conversion efficiency 80%(expected) 60%(expected) RF(laser) to dc conversion efficiency 80%(expected) 60%(expected) Table 4.1 Comparison of Microwave and Laser Power Transmission for SPS 4.6 Ground Segment – Reception The SPS system will require a large receiving area with a Rectenna array and the power network connected to the existing power grids on the ground. Although each rectenna element supplies only a few watts, the total received power is in the Giga watts (GW).
  • 13. SolarPowerSatellite SVPM’s college of engineering, Malegaon (Bk) Page 13 A Rectenna may be used to convert the microwave energy back into electricity. Rectenna conversion efficiencies exceeding 95% have been realized. The word “Rectenna” is formed from rectifying circuit and antenna. A rectifying antenna called rectenna receives the transmitted power and converts the microwave power to direct current (DC) power. The rectenna is a passive element with a rectifying diode, and is operated without any extra power source. The rectenna has a low-pass filter between the antenna and the rectifying diode to suppress re-radiation of higher harmonics. It also has an output smoothing filter. This demonstration rectenna consists of 6 rows of dipole antennas, where 8 dipoles belong to each row. Each row is connected to a rectifying circuit which consists of low pass filters and a rectifier. The rectifier is a GA-As Schottky barrier diode, that is impedance matched to the dipoles by allow pass filter. The 6 rectifying diodes are connected to the light bulbs for indicating that the power is received. The light bulbs also dissipate the received power. The Earth-based receiver antenna (or rectenna) is a critical part of the original SPS concept. It would consist of many short dipole antennas, connected via diodes. Microwaves broadcast from the SPS will be received in the dipoles with about 85% efficiency. With a conventional microwave antenna, the reception efficiency is still better, but the cost and complexity is also considerably greater, almost certainly prohibitively so. Rectenna would be multiple kilometres across. Crops and farm animals may be raised underneath a rectenna, as the thin wires used for support and for the dipoles will only slightly reduce sunlight, or non-arable land could be used, so such a rectenna would not be as expensive in terms of land use as might be supposed. This rectenna has a 25% collection and conversion efficiency, But rectennas have been tested with greater than 90%.
  • 14. SolarPowerSatellite SVPM’s college of engineering, Malegaon (Bk) Page 14 Figure 4.4 Design of Earth Receiving Station (Rectenna) 4.7 Rectenna Rectenna is an acronym for Rectifying antenna. It is a special type of antenna that rectifies the incoming microwave radiation into DC current and hence the name Rectenna. A rectenna comprises of a mesh of dipoles and diodes for absorbing microwave energy from a transmitter and converting it into electric power. Its elements are usually arranged in a mesh pattern, giving it a distinct appearance from most antennae. A simple rectenna can be constructed from a schottky diode placed between antenna dipoles as shown in Fig. 4.The diode rectifies the current induced in the antenna by the microwaves. Rectenna are highly efficient at converting microwave energy to electricity. In laboratory environments, efficiencies above 90% have been observed with regularity. In future rectenna will be used to generate large- scale power from microwave beams delivered from orbiting SPS satellites. Figure 4.5 Rectenna Circuit
  • 15. SolarPowerSatellite SVPM’s college of engineering, Malegaon (Bk) Page 15 Figure 4.6 Rectenna
  • 16. SolarPowerSatellite SVPM’s college of engineering, Malegaon (Bk) Page 16 CHAPTER 5 Compare BetweenOther Sources Table 5.1 Comparison between SPS and Other Sources
  • 17. SolarPowerSatellite SVPM’s college of engineering, Malegaon (Bk) Page 17 CHAPTER 6 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 possess 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. 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 sitting rectenna in environmentally insensitive locations, such as in the desert, over water etc. The classic rectenna design would be transparent in sunlight, permitting growth and maintenance of vegetation under the rectenna. However, the issues related to microwaves continue to be the most pressing environmental issues. On comparing with the use of radar, microwave ovens , police radars, cellular phones and wireless base stations, laser pointers etc. public exposures from SPS would be similar or even less. Based on well-developed antenna theory, the environmental levels of microwave power beam drop down to 0.1μW/cm². Even though human exposures to the 25 mW/cm²will, in general, be avoided, studies shows that people can tolerate such exposures for a period of at least 45 min. So concern about human exposure can be dismissed forthrightly. Specific research over the years has been directed towards effects on birds, in particular. Modern reviews of this research show that only some birds may experience some thermal stress at high ambient temperatures. Of course, at low
  • 18. SolarPowerSatellite SVPM’s college of engineering, Malegaon (Bk) Page 18 ambient temperatures the warming might be welcomed by birds and may present a nuisance attraction. Serious discussions and education are required before most of mankind accepts this technology with global dimensions. Microwaves, however is not a „pollutant‟ but, more aptly, a man made extension of the naturally generated electromagnetic spectrum that provides heat and light for our sustence.
  • 19. SolarPowerSatellite SVPM’s college of engineering, Malegaon (Bk) Page 19 CHAPTER 7 7.1 ADVANTAGES The 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 expect when the sun is eclipsed by the earth. Thus about five times energy could be collected, compared with the best terrestrial sites 2. The power could be directed to any point on the earth‟s 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 moving parts. 7. No fuel required. 8. No waste product. 7.2DISADVANTAGES 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 drawback 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 and this frequency is used by communication satellites also. 3. The entire structure is massive. 4. High cost and require much time for construction. 5. Radiation hazards associated with the system. 6. Risks involved with malfunction. 7. High power microwave source and high gain antenna can be used to deliver an intense burst of energy to a target and thus used as a weapon.
  • 20. SolarPowerSatellite SVPM’s college of engineering, Malegaon (Bk) Page 20 CHAPTER 8 Conclusion One of the key technologies needed for implementing an SPS is microwave power transmission from the geosynchronous orbit to the ground. The SPS requires new microwave technologies for achieving a high power conversion efficiency of more than 80% from/to dc and an extremely high precision beam control with 10- radaccuracy from the 2-km2 array antenna. These requirements are significantly challenging, and hence, considerable effort is needed for proper research and development of the technologies. The technologies are to be partially verified in the ground demonstration experiment within several years, and they are to be fully verified in the space experiments within ten years. Ongoing research and development activities according to the technology roadmap are expected to lead to the beginning of the new SPS era in the 2030s.
  • 21. SolarPowerSatellite SVPM’s college of engineering, Malegaon (Bk) Page 21 CHAPTER 9 References 1. J. O. Mcspadden and J. C. Mankins, “Space solar power programs and microwave wireless power transmission technology,” IEEE Microwave Mag., pp. 46–57, Dec. 2002. 2. IOSR Journal of Electronics and Communication Engineering (IOSR-JECE) ISSN: 2278-2834, ISBN: 2278-8735, PP: 59-64. 3. Susumu Sasaki, Koji Tanaka, and Ken-ichiro Maki, “Microwave Power Transmission Technologies for Solar Power Satellites, “Proceedings of the IEEE | Vol. 101, No. 6, June 2013. 4. N. Shinohara, “Wireless Power Transmission for Solar Power Satellite (SPS)” 5. ShubhamR.Gawande, “WIRELESS POWER TRANSMISSION THROUGH SOLAR POWER SATELLITES (S.P.S),” ISSN (PRINT): 2393-8374, (ONLINE): 2394-0697, VOLUME-3, ISSUE-3, 2016