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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