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21-01-2010, 11:16 PM
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solar power satellite full report

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ABSTRACT
The search for a new, safe and stable renewable energy source led to the idea of building a power station in space which transmits electricity to Earth. The concept of Solar Power Satellites (SPS) was invented by Glaser in 1968.Research is still going on in this field and NASA is planning to implement one by 2040. SPS converts solar energy into microwaves and transmit it to a receiving antenna on Earth for conversion to electric power. The key technology needed to enable the future feasibility of SPS is Microwave Power Transmission.
SPS would be a massive structure with an area of about 56 sq.m and would, weigh about 30,000 to 50,000 metric ton. Estimated cost is about $74 billion and would take about 30 years for its construction. In order to reduce the projected cost of a SPS suggestions are made to employ extraterrestrial resources for its construction. This reduces the transportation requirements of such a massive structure. However the realization of SPS concept holds great promises for solving energy crisis.

INTRODUCTION
The new millennium has introduced increased pressure for finding new renewable energy sources. The exponential increase in population has led to the global crisis such as global warming, environmental pollution and change and rapid decrease of fossil reservoirs. Also the demand of electric power increases at a much higher pace than other energy demands as the world is industrialized and computerized. Under these circumstances, research has been carried out to look into the possibility of building a power station in space to transmit electricity to Earth by way of radio waves-the Solar Power Satellites. Solar Power Satellites(SPS) converts solar energy in to micro waves and sends that microwaves in to a beam to a receiving antenna on the Earth for conversion to ordinary electricity.SPS is a clean, large-scale, stable electric power source. Solar Power Satellites is known by a variety of other names such as Satellite Power System, Space Power Station, Space Power System, Solar Power Station, Space Solar Power Station etc.[1].One of the key technologies needed to enable the future feasibility of SPS is that of Microwave Wireless Power Transmission.WPT is based on the energy transfer capacity of microwave beam i.e,energy can be transmitted by a well focused microwave beam. Advances in Phased array antennas and rectennas have provided the building blocks for a realizable WPT system [2].
WHY SPS
Increasing global energy demand is likely to continue for many decades. Renewable energy is a compelling approach “ both philosophically and in engineering terms. However, many renewable energy sources are limited in their ability to affordably provide the base load power required for global industrial development and prosperity, because of inherent land and water requirements. The burning of fossil fuels resulted in an abrupt decrease in their .it also led to the green house effect and many other environmental problems. Nuclear power seems to be an answer for global warming, but concerns about terrorist attacks on Earth bound nuclear power plants have intensified environmentalist opposition to nuclear power. Moreover, switching on to the natural fission reactor, the sun, yields energy with no waste products. Earth based solar panels receives only a part of the solar energy. It will be affected by the day & night effect and other factors such as clouds. So it is desirable to place the solar panel in the space itself, where, the solar energy is collected and converted in to electricity which is then converted to a highly directed microwave beam for transmission. This microwave beam, which can be directed to any desired location on Earth surface, can be collected and then converted back to electricity. This concept is more advantageous than conventional methods. Also the microwave energy, chosen for transmission, can pass unimpeded through clouds and precipitations.
SPS “THE BACKGROUND
The concept of a large SPS that would be placed in geostationary orbit was invented by Peter Glaser in 1968 [1].The SPS concept was examined extensively during the late 1970s by the U.S Department of Energy (DOE) and the National Aeronautics and Space Administration (NASA). The DOE-NASA put forward the SPS Reference System Concept in 1979 [2]. The central feature of this concept was the creation of a large scale power infrastructure in space, consisting of about 60 SPS, delivering a total of about 300GW.But, as a result of the huge price tag, lack of evolutionary concept and the subsiding energy crisis in 1980-1981, all U.S SPS efforts were terminated with a view to re-asses the concept after about ten years. During this time international interest in SPS emerged which led to WPT experiments in Japan.
RECENT NASA EFFORTS
Fresh look Study
During 1995-96, NASA conducted a re-examination of the technologies, system concepts of SPS systems [2],[3].The principal objective of this ËœFresh Look Studyâ„¢ was to determine whether a SPS and associated systems could be defined. The Fresh Look Study concluded that the prospects for power from space were more technically viable than they had been earlier.
SSP Concept Definition Study
During 1998, NASA conducted the SSP Concept Definition Study which was a focused one year effort that tested the results of the previous Fresh Look Study. A principal product of the efforts was the definition of a family of strategic R&T road maps for the possible development of SSP technologies.
SSP Exploratory and Research Technology Program
In 2000, NASA conducted the SERT Program which further defined new system concepts. The SERT Program comprised of three complementary elements:
¢ System studies and analysis
Analysis of SSP systems and architecture concepts to address the economic viability as well as environmental issue assessments.
¢ SSP Research and technology
Focused on the exploratory research to identify system concepts and establish technical viability
¢ SPS technology demonstration
Initial small scale demonstration of key SSP concepts and / or components using related system / technologies.
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 Earthâ„¢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 [4].
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 Earthâ„¢s surface would have been about 10 km in diameter [5].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.

Figure 1 Configuration of SPS is space.
The day-night cycle ,cloud coverage , atmospheric attenuation etc.reduces the amount of solar energy received on Earthâ„¢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 for ma 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 center around midnight [7].
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[7].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 [4].
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 [4]. SPS has all the advantage of ground solar, plus an additional advantage; it generates power during cloudy weather and at night. In other words 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 [8].

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 [9].

Figure 2
WIRELESS POWER TRANSMISSION
Transmission or distribution of 50 or 60 Hz electrical energy from the generation point to the consumer end without any physical wire has yet to mature as a familiar and viable technology.However, the reported works on terrestrial WPT have not revealed the design method and technical information and also have not addressed the full-scale potential of WPT as compared with the alternatives, such as a physical power distribution line [10]. However the main thrust of WPT has been on the concept of space-to-ground (extraterrestrial) transmission of energy using microwave beam.
Fig.3 shows the block diagram of a conceptual WPT system annexed to a grid [10].

Figure 3. conceptual model for a WPT system annexed to a grid.
The 50 Hz ac power tapped from the grid lines is stepped down to a suitable voltage level for rectification into dc. This is supplied to an oscillator fed magnetron. Inside the magnetron electrons are emitted from a central terminal called cathode. A positively charged anode surrounding the cathode attracts the electrons. Instead of traveling in a straight line, the electrons are forced to take a circular path by a high power permanent magnet. As they pass by the resonating cavities of the magnetron, a continuous pulsating magnetic field i.e., electromagnetic radiation in microwave frequency range is generated. After the first round of cavity-to-cavity trip by the electrons is completed the next one starts, and this process continues as long as the magnetron remains energized. Fig.4 shows the formation of a re-entrant electron beam in a typical six cavity magnetron. The output of the rectifier decides the magnetron anode dc voltage. This in turn controls the radiation power output. The frequency of the radiation is adjusted by varying the inductance or capacitance of the resonating cavities.

Figure 4. Re-entrant electron beam in a six-cavity magnetron
The microwave power output of the magnetron is channeled into an array of parabolic reflector antennas for transmission to the receiving end antennas. To compensate for the large loss in free space propagation and boost at the receiving end the signal strength as well as the conversion efficiency, the antennas are connected in arrays. Moreover, arrayed installation of antennas will necessitate a compact size.
A series parallel assembly of schottky diodes, having a low standing power rating but good RF characteristics is used at the receiving end to rectify the received microwave power back into dc. Inverter is used to invert the dc power into ac.
A simple radio control feedback system operating in FM band provides an appropriate control signal to the magnetron for adjusting its output level with fluctuation in the consumers demand at the receiving side. The feedback system would switch of the supply to the oscillator and magnetron at the sending end if there is a total loss of load.
The overall efficiency of the WPT system can be improved by
¢ Increasing directivity of the antenna array
¢ Using dc to ac inverters with higher conversion efficiency
¢ Using schottky diode with higher ratings.


MICROWAVE POWER TRANSMISSION IN SPS
The microwave transmission system as envisioned by NASA and DOE would have had three aspects [5]:
1. The conversion of direct power from the photovoltaic cells, to microwave power on the satellites on geosynchronous orbit above the Earth.
2. The formation and control of microwave beam aimed precisely at fixed locations on the Earths surface.
3. The collection of the microwave energy and its conversion into electrical energy at the earthâ„¢s surface.
The ability to accomplish the task of efficiently delivering electrical power wirelessly is dependent upon the component efficiencies used in transmitting and receiving apertures and the ability to focus the electromagnetic beam onto the receiving rectenna.
Microwave WPT is achieved by an unmodulated, continuous wave signal with a band width of 1Hz. Frequency of choice for microwave WPT has been 2.45GHz due to factors such as low cost power components, location in the ISM band, extremely low attenuation through the atmosphere [2]. The next suggested band centered at 5.8GHz system reduces the transmitting and receiving apertures. But this is not preferred due to increased attenuation on higher frequency.

The key microwave components in a WPT system are the transmitter, beam control and the receiving antenna called rectenna .At the transmitting antenna, microwave power tubes such as magnetrons and klystrons are used as RF power sources. However, at frequencies below 10 GHz, high power solid state devices can also be used. For beam safety and control retro directive arrays are used. Rectenna is a component unique to WPT systems. The following section describes each of these components in detail.
TRANSMITTER
The key requirement of a transmitter is its ability to convert dc power to RF power efficiently and radiate the power to a controlled manner with low loss. The transmitterâ„¢s efficiency drives the end-to-end efficiency as well as thermal management system i.e., any heat generated from inefficiencies in the dc-RF conversion, should be removed from the transmitter as it reduces the life time of RF devices and control electronics [2]. Passive inter modulation is another field which requires critical attention. Filtering of noise and suppression of harmonics will be required to meet he regulatory requirement.
The main components of a transmitter include dc-to-RF converter and transmitting antenna. . The complexity of the transmitter depends on the WPT application. For the large scale WPT application such as SPS, phased array antennas are required to distribute the RF power sources across the aperture and electronically control the power beam. Power distribution at the transmitting antenna=v (1-r²), where r is the radius of antenna [7].
There are mainly three dc-to-RF power converters: magnetrons, klystrons and solid state amplifiers.

Klystron
Fig.5 shows the schematic diagram of a klystron amplifier [15].

Figure 5 Klystron amplifier schematic diagram.
Here a high velocity electron beam is formed, focused and send down a glass tube to a collector electrode which is at high positive potential with respect to the cathode. As the electron beam having constant velocity approaches gap A, they are velocity modulated by the RF voltage existing across this gap. Thus as the beam progress further down the drift tube, bunching of electrons takes place. Eventually the current pass the catcher gap in quite pronounce bunches and therefore varies cyclically with time. This variation in current enables the klystron to have significant gain. Thus the catcher cavity is excited into oscillations at its resonant frequency and a large output is obtained.
Fig.6 shows a klystron transmitter [2]. The tube body and solenoid operate at 300°C and the collector operates at 500°C. The overall efficiency is 83%. The microwave power density at the transmitting array will be 1 kW/m² for a typical 1 GW SPS with a transmitting antenna aperture of 1 km diameter. If we use 2.45 GHz for MPT, the number of antenna elements per square meter is on the order of 100. Therefore the power allotted to the individual antenna element is of the order of 10 W/element. So we must distribute the high power to individual antenna through a power divider [1].

Figure 6 Klystron transmitter
BEAM CONTROL
A key system and safety aspect of WPT in its ability to control the power beam. Retro directive beam control systems have been the preferred method of achieving accurate beam pointing.

As shown in fig.7 a coded pilot signal is emitted from the rectenna towards the SPS transmitter to provide a phase reference for forming and pointing the power beams [2]. To form the power beam and point it back forwards the rectenna, the phase of the pilot signal is captured by the receiver located at each sub array is compared to an onboard reference frequency distributed equally throughout the array. If a phase difference exists between the two signals, the received signal is phase conjugated and fed back to earth dc-RF converted. In the absence of the pilot signal, the transmitter will automatically dephase its power beam, and the peak power density decreases by the ratio of the number of transmitter elements.

Figure 7 Retro directive beam control concept with an SPS.
RECTENNA
Brown was the pioneer in developing the first 2.45GHz rectenna [2].
Rectenna is the microwave to dc converting device and is mainly composed of a receiving antenna and a rectifying circuit. Fig .8 shows the schematic of rectenna circuit [2]. It consists of a receiving antenna, an input low pass filter, a rectifying circuit and an output smoothing filter. The input filter is needed to suppress re radiation of high harmonics that are generated by the non linear characteristics of rectifying circuit. Because it is a highly non linear circuit, harmonic power levels must be suppressed. One method of suppressing harmonics is by placing a frequency selective surface in front of the rectenna circuit that passes the operating frequency and attenuates the harmonics.

Figure 8 Schematic of rectenna circuit.
For rectifying Schottky barrier diodes utilizing silicon and gallium arsenide are employed. In rectenna arrays, the diode is the most critical component to achieve higher efficiencies because it is the main source of loss. Diode selection is dependent on the input power levels. The breakdown voltage limits the power handling capacity and is directly related to series resistance and junction capacitance through the intrinsic properties of diode junction and material .For efficient rectification the diode cut off frequency should be approximately ten times the operating frequency.
Diode cut off frequency is given by Æ’=1/ [2pRsCj], where Æ’ is the cut off frequency, Rs is the diode series resistance, Cj is the zero-bias junction capacitance.

RECENTLY DEVELOPED MPT SYSTEMS
The Kyoto University developed a system called Space Power Radio Transmission System (SPORTS) [1]. The SPORTS is composed of solar panels, a microwave transmitter subsystem, a near field scanner, a microwave receiver. The solar panels provide 8.4 kW dc power to the microwave transmitter subsystem composed of an active phased array. It is developed to simulate the whole power conversion process for the SPS, including solar cells, transmitting antennas and rectenna system.
Another MPT system recently developed by a team of Kyoto University ,NASDA and industrial companies of Japan , is an integrated unit called the Solar Power Radio Integrated Transmitter (SPRITZ),developed in 2000 [1]. This unit is composed of a solar cell panel, microwave generators, transmitting array antennas and a receiving array in one package. This integrated unit as shown in fig.9 could be a prototype of a large scale experimental module in the orbit

Figure 9 SPRITZ (Solar Power Radio Integrated Transmitter 2000)
CONSTRUCTION OF SPS FROM NON TERRESTRIAL MATERIALS: FEASIBILITY AND ECONOMICS
SPS, as mentioned before is massive and because of their size they should have been constructed in space [5]. Recent work also indicate that this unconventional but scientifically well “based approach should permit the production of power satellite without the need for any rocket vehicle more advanced than the existing ones. The plan envisioned sending small segments of the satellites into space using the space shuttle. The projected cost of a SPS could be considerably reduced if extraterrestrial resources are employed in the construction [9].One often discussed road to lunar resource utilization is to start with mining and refining of lunar oxygen, the most abundant element in the Moon™s crust, for use as a component of rocket fuel to support lunar base as well as exploration mission. The aluminum and silicon can be refined to produce solar arrays [12].
A number of factors combine to make the concept of using non conventional materials appear to be feasible. Among them are the shallow gravity wells of the Moon and asteroids; the presence of an abundance of glass, metals and oxygen in the Apollo lunar samples; the low cost transport of those materials to a higher earth orbit by means of a solar-powered electric motor; the availability of continuous solar energy for transport, processing and living [12].
Transportation requirement for SPS will be much more needed for known for known commercial applications. One major new development for transportation is required: the mass driver [12].The mass driver is a long and narrow machine which converts electrical energy into kinetic energy by accelerating 0.001 to 10 kg slugs to higher velocities. Each payload-carrying bucket contains superconducting coils and is supported without physical contact by means of dynamic magnetic levitation. As in the case of a linear synchronous motor-generator, buckets are accelerated by a magnetic field, release their payload, decelerate with return energy and pick up another pay load for acceleration. The power source can be either solar or nuclear. The mass driver conversion efficiency from electrical to kinetic energy is close to 100 percent. The mass driver can be used as a launcher of lunar material into free space or as a reaction engine in space, where payloads are transferred from orbit to orbit in a spiral trajectory. The performance of the mass driver could match that of the space shuttle main engines. But the mass driver has the advantage that any material can be used as fuel and continuous solar power in space is the common power source.
An alternative to the use of lunar resources for space manufacturing is the use of earth-approaching asteroidal materials.
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 [13].
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 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 [12]. 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 [4]. 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 ambient temperatures the warming might be welcomed by birds and may present a nuisance attraction [13].
Serious discussions and education are required before most of mankind accepts this technology with global dimensions. Microwaves, however is not a Ëœpollutantâ„¢ but , more aptly , a man made extension of the naturally generated electromagnetic spectrum that provides heat and light for our sustence

ADVANTAGES AND DISADVANTAGES
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 [14]. 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 earthâ„¢s surface.
3. The zero gravity and high vacuum condition in space would allow much lighter, low maintenance structures and collectors [14].
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.
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 [15].
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[15].
CONCLUSION
The SPS will be a central attraction of space and energy technology in coming decades. However, large scale retro directive power transmission has not yet been proven and needs further development. Another important area of technological development will be the reduction of the size and weight of individual elements in the space section of SPS. Large-scale transportation and robotics for the construction of large-scale structures in space include the other major fields of technologies requiring further developments. Technical hurdles will be removed in the coming one or two decades. Finally, we look forward to universal acceptance of the premise the electromagnetic energy is a tool to improve the quality of life for mankind. It is not a pollutant but more aptly, a man made extension of the naturally generated electromagnetic spectrum that provides heat and light for our sustenance. From this view point, the SPS is merely a down frequency converter from the visible spectrum to microwaves.
REFERENCES
[1] Hiroshi Matsumoto, Research on solar power satellites and microwave power transmission in Japan, IEEE microwave magazine, pp.36-45, Dec 2002.
[2] James O. Mcspadden & John C. Mankins,Space solar power programs and microwave wireless power transmission technology, IEEE microwave magazine, pp.46-57, Dec 2002.
[3] J.C. Mankins,A fresh look at space solar power: new architectures, concepts and technologies in 38th Astronautical Federation.
[4] Seth Potter, Solar power satellites: an idea whose time has come [online] Available on http://www.freemars.org/history/sps.html, last updated on Dec.1998
[5] Consumer Energy Information: EREC Reference Briefs [online] Available on http://www.eere.gov/consumerinfo/rebriefs/123.html,last updated on Apr.03.
[6] Mc GrawHill Encyclopedia of Science and Technology, vol.16, pp.41.
[7] Om P.Gandhi,Microwave engineering and application, PHI.
[8] Geoffrey A.Landis,A super synchronous solar power , Presented at SPS-97: Space &electric power for humanity, 24-25 Aug 1997, Montreal, Canada.
[9] Geoffrey A.Landis,An evolutionary path to SPS, Space power, vol.9, no.4, pp.365-371, 1990.
[10] S.S.Ahmed, T.W.Yeong and H.B.Ahmad,Wireless power transmission and its annexure to the grid system, IEE Proc.-Gener.Transm.Distrib., Vol.150, No.2, March 2003.
[11]Kennedy Electronics Communication Systems, Tata McGraw Hill.
[12] B.Oâ„¢Leary,The construction of satellite solar power stations from non terrestrial materials: feasibity and economics, Alternative energy sources, Vol.3, pp.1155-1164.
[13] John M.Osepchuk,How safe are microwaves and solar power from space, IEEE microwave magazine, pp.58-64, Dec.2002.
[14] International Encyclopedia of Energy, Vol.4, pp.771.
[15] David M.Pozar,Microwave Engineering, Wiley




CONTENTS
INTRODUCTION¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦............. 01
WHY SPS¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦.............. 02
SPS-THE BACKGROUND¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦.. 03
SPS-A GENERAL IDEA¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦.......... 05
WIRELESS POWER TRANSMISSION ¦¦¦¦¦¦¦¦¦¦¦¦.. 09
MICROWAVE POWER TRANSMISSION IN SPS¦¦¦¦¦¦¦¦ 12
TRANSMITTER¦¦¦¦¦¦¦¦¦¦.. 13
BEAM CONTROL¦¦¦¦¦¦¦¦¦.. 15
RECTENNA ¦¦¦¦¦¦¦¦¦¦¦.. 16
RECENTLY DEVELOPED MPT SYSTEMS ........................................ 18
CONSTRUCTION OF SPS FROM NON TERRESTRIAL MATERIALS: FEASIBILITY AND ECONOMICS¦¦¦¦¦¦¦¦¦¦¦¦¦¦ 19
MICROWAVES-ENVIRONMENTAL ISSUES ¦¦¦¦¦¦¦¦. 21
ADVANTAGES AND DISADVANTAGES¦¦¦¦¦¦¦¦¦¦¦ 23
CONCLUTION¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦ 24
REFERENCES¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦ 25


ACKNOWLEDGEMENT
I extend my sincere gratitude towards Prof . P.Sukumaran Head of Department for giving us his invaluable knowledge and wonderful technical guidance
I express my thanks to Mr. Muhammed kutty our group tutor and also to our staff advisor Ms. Biji Paul for their kind co-operation and guidance for preparing and presenting this seminar.
I also thank all the other faculty members of AEI department and my friends for their help and support.

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21-02-2010, 01:09 PM
Post: #2
RE: solar power satellite full report

.pptx  SOLAR POWER SATELLITE.pptx (Size: 537.18 KB / Downloads: 792)

SOLAR POWER SATELLITE

solar power satellite

INTRODUCTION

The new millennium has introduced increased pressure for finding new renewable energy sources
Building a power station in space to transmit electricity to Earth by way of radio waves-the Solar Power Satellites.
Microwave Wireless Power Transmission
SPS is a clean, large-scale, stable electric power source


WHY SPS

Increasing global energy demand
Limitation of renewable energy sources
Environmental problems due to fossil fuels.

Overcome day & night effect and other factors such as clouds.
Overcome energy crisis.

SPS“ THE BACKGROUND

Peter Glaser invented the concept of a large SPS.
The U.S Department of Energy (DOE) and the
National Aeronautics and Space Administration
(NASA) examined the SPS concept extensively
during the late 1970s.
Fresh look Study, SSP Concept Definition Study.
SSP Exploratory and Research Technology
SPS- A GENERAL IDEA
It is located in the geosynchronous orbit.
Comparison between ordinary satellite.
Its operation.
About structure.
Comparison between terrestrial station

WIRELESS POWER TRANSMISSION

The 50Hz ac power tapped from grid line is stepped down to suitable voltage level for rectification in to dc.
The it is supplied to oscillator fed magnetron.
Magnetron consist of electrons supplied by cathode which are collected by positively charged anode.
The electrons are forced to move in a circular path by a high power permanent magnet.
Electromagnetic radiation in microwave range is generated

MICROWAVE TRANSMISSION IN SPS

The conversion of direct power to microwave power
The formation and control of microwave beam
The collection of the microwave energy and its conversion into electrical energy at the earthâ„¢s surface.
The key microwave components in a WPT system are the transmitter, beam control and the receiving antenna called RECTENNA

TRANSMITTER

The key requirement of a transmitter is its ability to convert dc power to RF power efficiently and radiate the power to a controlled manner with low loss.
The transmitterâ„¢s efficiency drives the end-to-end efficiency as well as thermal management system.
The main components of a transmitter include dc-to-RF converter and transmitting antenna.
The main dc-RF converter s are klystrons

KLYSRON TRASMITTER

The tube body and solenoid operate at 300°C and the collector operates at 500°C.
The overall efficiency is 83%.
The microwave power density at the transmitting array will be 1 kW/m² for a typical 1 GW SPS with a transmitting antenna aperture of 1 km diameter.
If we use 2.45 GHz for MPT, the number of antenna elements per square meter is on the order of 100.

BEAM CONTROL

A key system and safety aspect of WPT in its ability to control the power beam.
Retro directive beam control systems have been the preferred method of achieving accurate beam pointing.
A coded pilot signal is emitted from the rectenna towards the SPS transmitter to provide a phase reference for forming and pointing the power beams

RECTENNA

RECTENNA is the microwave to dc converting device .
It is mainly composed of a receiving antenna and a rectifying circuit.
Fig. shows schematic of RECTENNA. It consists of a receiving antenna, an input low pass filter, a rectifying circuit and an output smoothing filter.
In RECTENNA arrays, the diode is the most critical component to achieve higher efficiencies because it is the main source of loss.
Diode cut off frequency is given by Æ’=1/ [2pRsCj], where Æ’ is the cut off frequency, Rs is the diode series resistance, Cj is the zero-bias junction capacitance.
ADVANTAGES

The power could be directed to any point on the earthâ„¢s surface.
The power density would be uninterrupted by darkness, clouds, or precipitation, which are the problems encountered with earth based solar arrays.
The realization of the SPS concept holds great promises for solving energy crisis
No moving parts.
No fuel required.
No waste product.

DISADVANTAGES

The main draw back of solar energy transfer from orbit is the storage of electricity during off peak demand hours.
The frequency of beamed radiation is planned to be at 2.45 GHz and this frequency is used by communication satellites also.
The entire structure is massive.
High cost and require much time for construction.
Radiation hazards associated with the system.
Risks involved with malfunction.
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

CONCLUSION

The SPS will be a central attraction of space and energy technology in coming decades. However, large scale retro directive power transmission has not yet been proven and needs further development. Another important area of technological development will be the reduction of the size and weight of individual elements in the space section of SPS. Large-scale transportation and robotics for the construction of large-scale structures in space include the other major fields of technologies requiring further developments. Technical hurdles will be removed in the coming one or two decades. Finally, we look forward to universal acceptance of the premise the electromagnetic energy is a tool to improve the quality of life for mankind. It is not a pollutant but more aptly, a man made extension of the naturally generated electromagnetic spectrum that provides heat and light for our sustenance. From this view point, the SPS is merely a down frequency converter from the visible spectrum to microwaves.

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25-03-2010, 11:29 AM
Post: #3
RE: solar power satellite full report
great work thanks man.keep it up

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30-03-2010, 12:43 PM
Post: #4
RE: solar power satellite full report
thanks a lot for help!!
03-04-2010, 10:52 PM
Post: #5
RE: solar power satellite full report
Abstract
The selling price of electrical power varies with time. The economic viability of space solar power is maximum if the power can be sold at peak power rates, instead of baseline rate. Price and demand of electricity was examined from spot-market data from four example markets: New England, New York City, suburban New York, and California. The data was averaged to show the average price and demand for power as a function of time of day and time of year. Demand varies roughly by a factor of two between the early-morning minimum demand, and the afternoon maximum; both the amount of peak power, and the location of the peak, depends significantly on the location and the weather . The demand curves were compared to the availability curves for solar energy and for tracking and non-tracking
satellite solar power systems, in order to compare the market value of terrestrial and solar electrical power.
In part 2, new designs for a space solar power (SSP) system were analyzed to provide electrical power to Earth for economically competitive rates. The approach was to look at innovative power architectures to more practical approaches to space solar power. A significant barrier is the initial investment required before the first power is returned. Three new concepts for solar power satellites were invented and analyzed: a solar power satellite in the Earth-Sun L2 point, a geosynchronous no-moving parts solar power satellite, and a nontracking geosynchronous solar power satellite with integral phased array. The integral-array satellite had several advantages, including an initial investment cost approximately eight times lower than the conventional design.
1. Introduction
The Solar Power Satellite (or "Space Solar Power," SPS) is a concept to collect solar power in space, and then transport it to the surface of the Earth by microwave beam, where it is converted into electrical power for terrestrial use. In space, collection of the Sun's energy is unaffected by the day/night cycle, weather, seasons, or the filtering effect of Earth's atmospheric gases. Average solar energy per unit area outside Earth's atmosphere is on the order of ten times that available on Earth's surface.
The collection of solar energy in space for use on Earth introduces the new problem of transmitting energy from the collection point, in space, to the place where the energy would be used, on Earth's surface. Since wires extending from Earth's surface to an orbiting satellite would be impractical, many SPS designs have proposed the use of microwave beams to transmit power wirelessly. The collecting satellite would convert solar energy into electrical energy, which would then be used to power a microwave emitter directed at a collector on the Earth's surface. Dynamic solar thermal power systems are also being investigated.
Many problems normally associated with solar power collection would be eliminated by such a design, such as the high sensitivity of conventional surface solar panels to corrosion and weather, and the resulting maintenance costs. Other problems may take their place though, such as cumulative radiation damage or micrometeoroid impacts.
Producing electricity from sunlight in space is not a new or untried technology. Many space faring craft are covered in solar cells, such as rovers and shuttles, and hundreds of operating satellites use solar energy as their main source of power. What has never been tried before is transmitting that power back to Earth for our use.
Being a clean and safe energy design, space-based solar power has the potential to play a significant role in solving global energy and environmental problems. It utilizes space outside of Earth's ecological system, and may essentially produce no by-products.
2. History
The SPS concept, originally known as Satellite Solar Power System ("SSPS") was first described in November 1968. In 1973 Peter Glaser was granted U.S. patent number 3,781,647 for his method of transmitting power over long distances (e g from an SPS to the Earth's surface) using microwaves from a very large (up to one square kilometer) antenna on the satellite to a much larger one on the ground, now known as a rectenna.
Glaser then worked at Arthur D. Little, Inc., as a vice-president. NASA signed a contract with ADL to lead four other companies in a broader study in 1974. They found that, while the concept had several major problems -- chiefly the expense of putting the required materials in orbit and the lack of experience on projects of this scale in space, it showed enough promise to merit further investigation and research.
Between 1978 and 1981 the US Congress authorized DOE and NASA to jointly investigate. They organized the Satellite Power System Concept Development and Evaluation Program. The study remains the most extensive performed to date. Several reports were published investigating possible problems with such an engineering project. They include:
¢ Resource Requirements (Critical Materials, Energy, and Land)
¢ Financial/Management Scenarios
¢ Public Acceptance
¢ State and Local Regulations as Applied to Satellite Power System Microwave Receiving Antenna Facilities
¢ Centralization/Decentralization
¢ Mapping of Exclusion Areas For Rectenna Sites
¢ Economic and Demographic Issues Related to Deployment
¢ Meteorological Effects on Laser Beam Propagation and Direct Solar Pumped Lasers
¢ Power Transmission and Reception Technical Summary and Assessment
¢ Space Transportation
The Office of Technology Assessment concluded
Too little is currently known about the technical, economic, and environmental aspects of SPS to make a sound decision whether to proceed with its development and deployment. In addition, without further research an SPS demonstration or systems-engineering verification program would be a high-risk venture.
More recently, the SPS concept has again become interesting, due to increased energy demand, increased energy costs, and emission implications.
3. Sert
In 1999 NASA's Space Solar Power Exploratory Research and Technology program (SERT) was initiated for the following purpose:
¢ Evaluate studies of the general feasibility, design, and requirements.
¢ Create conceptual designs of subsystems that make use of advanced SSP technologies to benefit future space or terrestrial applications.
¢ Formulate a preliminary plan of action for the U.S. (working with international partners) to undertake an aggressive technology initiative.
¢ Construct technology development and demonstration roadmaps for critical Space Solar Power (SSP) elements.
It was to develop a solar power satellite (SPS) concept for a future gigawatt space power systems to provide electrical power by converting the Sunâ„¢s energy and beaming it to the Earth's surface. Subject to studies it proposed an inflatable photovoltaic gossamer structure with concentrator lenses or solar dynamic engines to convert solar flux into electricity.
Some of SERT's conclusions include the following:
¢ The environmental impact of conventional power plants and their impact on world energy supplies and geopolitical relationships can be problematic.
¢ Renewable energy is a compelling approach, both philosophically and in engineering terms.
¢ Space solar power systems appear to possess many significant environmental advantages when compared to alternative approaches.
4. Design
Space-based solar power essentially consists of three parts :
1. a means of collecting solar power in space, for example via solar cells or a heat engine
2. a means of transmitting power to earth, for example via microwave or laser
3. a means of receiving power on earth, for example via a microwave antennas (rectenna)
The space-based portion will be in a freefall, vacuum environment and will not need to support itself against gravity other than relatively weak tidal stresses. It needs no protection from terrestrial wind or weather, but will have to cope with space-based hazards such as micrometeorites and solar storms. 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.
4.1. Supersynchronous Solar Power Satellite :
It is proposed here to analyze a solar power satellite put into a completely different orbit, the Earth-sun L-2 halo orbit. The location of the Earth-sun L2, and a typical halo orbit around it. This is referred to as a super synchronous" location for a solar power satellite, since it is located beyond synchronous orbit. While the halo orbits around the lagrangian points are slightly unstable, the instability is so weak that several space probes have used the L1 halo orbit for operational use, with only minimal amounts of propellant needed to keep them in position. At first consideration, it would seem that the Earth-sun L2 point is a poor choice for a space solar power system transmitter. At a distance of point 1.5 million kilometers from the Earth, it will be forty times further away from the Earth than a satellite placed in geosynchronous orbit. However, it turns out that this orbit allows design simplifications to the satellite solar power design that more than compensate
for this disadvantage. Thus, it is perfectly suited to fill in night power to solar arrays which receive solar power during the daytime. This allows a ground-based solar array field to be "upgraded" to a 24-hour power source, and hence, by upgrading the status of the power from "intermittent" to "baseload," increases the selling price of the power from low intermittent power levels, to higher baseload power levels.
Design Details: Since the sun and Earth are nearly the same direction, it can feature:
Integrated solar concentrator dish/microwave transmission dish
Integrated solar cell/solid state transmitters
No rotating parts or slip-rings
Frequency: 30 GHz
transmitter diameter: 3 km
receiver diameter: 6 km
3 ground sites, receive 8 hours per day
Total Mass 1,300 tonnes
At assumed transmitter efficiency 33% (todayâ„¢s technology): 1 GW power output
At assumed transmitter efficiency 67% (future technology): 2 GW power output.
4.2. Fixed Geosynchronous Solar Power Satellite :

While the size and the electrical generation profile with the Earth-sun L2 solar power satellite make it a poor choice for a financially successful design, one aspect of the design remains extremely attractive: the absence of a rotary joint makes the L2 solar power satellite a design with no moving parts. The baseline figure of merit for this design was to examine how the power production profile fits with the demand (and price) profile for terrestrial electrical power ,assuming that the power is to "fill in" for a ground solar power system.
The satellite designed with the same design criteria: maximum simplicity; no moving parts; mission is to power when ground solar power is not available. A fixed microwave transmitter is permanently mounted on a bifacial solar array, which can be illuminated from either side. Figures shows that this concept produces maximum power at dawn and at dusk, with zero power production at noon and at midnight.
By employing a fixed transmitter attached to the solar array, the power management and distribution system size can be greatly simplified and reduced in mass. The difficulties associated with power transfer from the array to the transmitter are minimized, and the mass and cost of the SPS are reduced. The new SPS needs only gravity-gradient stabilization to ensure that the transmitter remains pointed to the rectenna site on the Earth.
4.3. Fixed Design with integrated microwave transmitter:
If the design constraint of a single array is relaxed, two arrays can be base lined, and the arrays can be tilted outward to accommodate the actual demand peak (after subtraction of solar) at 8 AM and 4 PM .With the addition of tilt, it is no longer true that the microwave beam is perpendicular to the solar arrays. The backside of each solar array is in the view of the Earth. A significant difficulty of the earlier design is the fact that the initial size of the system requires an extremely high initial investment. The redesign of the solar power satellite opens the possibility of integrating the solar array directly to the microwave transmission. By placing solid-state microwave transmitters directly on the back of the solar array, power management and distribution, as well as all voltage conversion, is eliminated.
Figure shows the conceptual design for a satellite to deliver maximum power at 8 AM and 4 PM, where the back side of each array is an integrated microwave transmitter. The advantages of integration of the solar arrays and the transmitter are discussed in reference and by integrating solar array with the microwave transmitter, the transmitter aperture becomes as large as the solar array area. This results in a narrower beam. A narrow beam allows smaller rectenna areas, thereby permitting much smaller solar power satellites. The smaller scale reduces the initial capital investment.
V-shaped fixed orientation solar power satellite to provide fill-in power for a ground solar installation
4.4. Solar energy conversion (solar photons to DC current):
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. Photovoltaic cells are not perfect in practice, as material purity and processing issues during production affect performance; each has been progressively improved 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, but will not need to be encapsulated against corrosion by the elements. They may not require the structural support required for terrestrial
use, where the considerable gravity loading imposes structural requirements on terrestrial implementations.
5. WIRELESS POWER TRANSMISSION (WPT)
BACKGROUND
5.1. Introduction:
A major problem facing Planet Earth is provision of an adequate supply of clean energy. It has been that we face ...three simultaneous challenges -- population growth, resource consumption, and environmental degradation -- all converging particularly in the matter of sustainable energy supply. It is widely agreed that our current energy practices will not provide for all the world's peoples in an adequate way and still leave our Earth with a livable environment. Hence, a major task for the new century will be to develop sustainable and environmentally friendly sources of energy.
Projections of future energy needs over this new century show an increase by a factor of at least two and one Half, perhaps by as much as a factor of five. All of the scenarios from reference 3 indicate continuing use of fossil sources, nuclear, and large hydro. However, the greatest increases come from "new renewables" and all scenarios show extensive use of these sources by 2050. Indeed, the projections indicate that the amount of energy derived from new renewables by 2050 will exceed that presently provided by oil and gas combined. This would imply a major change in the worldâ„¢s energy infrastructure. It will be a Herculean task to acquire this projected amount of energy. This author asserts that there are really only a few good options for meeting the additional energy needs of the new century in an environmentally acceptable way.
One of the so-called new renewables on which major reliance is almost certain to be placed is solar power. Solar power captured on the Earth is familiar to all. However, an alternative approach to exploiting solar power is to capture it in space and convey it to the Earth by wireless means. As with terrestrial capture, Space Solar Power (SSP) provides a source that is virtually carbon-free and sustainable. As will be described later, the power-collecting platforms would most likely operate in geosynchronous orbit where they would be illuminated 24 hours a day (except for short eclipse periods around the equinoxes). Thus, unlike systems for the terrestrial capture of solar, a space-based system would not be limited by the vagaries of the day-night cycle. Furthermore, if the transmission frequency is properly chosen, delivery of power can be carried out essentially independent of weather conditions. Thus Space Solar Power could provide base load electricity.
The vision of achieving WPT on a global scale was proposed over 100 years ago when Nikola Tesla first started experiments with WPT, culminating with the construction of a tower for WPT on Long Island, New York, in the early 1900s. Tesla's objective was to develop the technology for transmitting electricity to anywhere in the world without wires. He filed several patents describing wireless power transmitters and receivers. However, his knowledge of electrical phenomena was largely empirical and he did not achieve his objective of WPT, although he was awarded the patent for wireless radio in 1940.
The development of WPT was not effectively pursued until the 1960s when the U.S. Air Force funded the development of a microwave-powered helicopter platform. A successful demonstration of a microwave beam-riding helicopter was performed in 1965. This demonstration proved that a WPT system could be constructed and that effective microwave generators and receivers could be developed for efficient conversion of microwaves into DC electricity.
The growing interest in solar energy conversion methods and solar energy applications in the 1960s and the limitations for producing cost-effective base load power caused by adverse weather conditions and diurnal changes led to the solar power satellite concept in 1968 as a means to convert solar energy with solar cell arrays into electricity and feed it to a microwave generator forming part of a planar, phased-array antenna. In geosynchronous orbit, the antenna would direct a microwave beam of very low power density precisely to one or more receiving antennas at desired locations on Earth. At a receiving antenna, the microwave energy would be safely and very efficiently reconvened into electricity and then transmitted to users.
The first technical session on solar power satellites (SPS) was held in 1970 at the International Microwave Power Institute Symposium at which representatives of Japan,
European countries, and the former Soviet Union were present. Based on preliminary studies, a plan for an SPS program was prepared by an NSF/NASA panel in 1972 and the first feasibility study of SPS was completed for NASA/Lewis Research Center in 1974.
Shortly after the "oil shock" of October 1973, Japan staned to implement the Sunshine Plan to develop renewable energy sources. Japan's Plan included, as a long-term objective, the development of SPS. Back in the U.S. in 1975, a successful demonstration of microwave wireless power transmissions was performed at the NASA Deep Space Antenna facility at Goldstone, California. In this demonstration of point-to-point WPT, 30 kW of microwaves were beamed over a distance of one mile to a receiving antenna. Microwaves were converted directly into DC at an average efficiency of 82%, confounding critics who claimed that such high conversion efficiencies could not be achieved. By 1976 engineering, environmental and economic analyses of several SPS concepts had been performed by NASA the office of Management and Budget, in its deliberations on the Fry 1977 budget, directed that further study of this concept be the responsibility of the Energy Research and Development Administration (ERDA), which subsequently became the Department of Energy (DoE). The SPS Concept Development and Evaluation Program (CDEP), performed by DoE/NASA and its contractors, used a NASA-developed SPS Reference System configuration as a basis for conducting environmental, societal, and comparative economic assessments, The DOE/NASA assessment team, as well as a majority of scientists, engineers, and analysts who participated in the CDEP recommended that the program be continued at a modest funding level, and SPS assessments directed at resolving or reducing significant uncertainties associated with microwave radiation effects and SPS design considerations, and to continue some promising experiments. By 1980 the CDEP was brought to its scheduled conclusion and not continued in a follow-on program, partly because the economic pressures of the oil crisis had passed, partly because of changed priorities for renewable energy development, and partly because of expectations that nuclear and eventually fusion power would meet future growth in energy demands.
A substantial body of work, both analytical and experimental, has established the technical feasibility of wireless transmission of useful amounts of power. Wireless transmission of power is similar in concept to information transmission by communications satellites, but at a higher intensity. However, because the radio frequency power beam is engineered for conversion back to electricity at very high efficiency, useful amounts of power could be transmitted at intensities less than that of sunlight. Experimental transmissions of power in amounts up to 30 kW have been accomplished over short distances (1.6 km) with conversion efficiencies in excess of 85% from incoming radio frequency power into electrical power.
Recent studies indicate that collection and transmission of power from space could become an economically viable means of exploiting solar power within the next couple of decades. A substantial maturation of certain technologies is needed and, most importantly, the cost of launching material to space must be significantly reduced. Very active efforts are being pursued in the aerospace community to achieve both of these goals.
Two types of WPT:
1) Ground based power transmission
2) Space based power transmission
But Space-based power transmission is preferred over Ground-based power transmission.
Ground is (obviously) cheaper per noontime watt, but:
¢ Space gets full power 24 hours a day
“ 3X or more Watt-hours per day per peak watt
“ No storage required for nighttime power
¢ Space gets full power 7 days a week “ no cloudy days
¢ Space gets full power 52 weeks a year
“ No long winter nights, no storms, no cloudy seasons
¢ Space delivers power where it™s needed
“ Best ground solar sites (deserts) are rarely near users
¢ Space takes up less, well, space
“ Rectennas are 1/3 to 1/10 the area of ground arrays
“ Rectennas can share land with farming or other uses
5.2. Wireless power transmission to the 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 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 can be used are limited by atmospheric absorption (chiefly water vapor and CO2) at higher microwave frequencies.
Conceptual model for a WPT system annexed to a grid.
The 50 Hz ac power tapped from the grid lines is stepped down to a suitable voltage level for rectification into dc. This is supplied to an oscillator fed magnetron. The microwave power output of the magnetron is channeled into an array of parabolic reflector antennas for transmission to the receiving end antennas. To compensate for the large loss in free space propagation and boost at the receiving end the signal strength as well as the conversion
efficiency, the antennas are connected in arrays. A series parallel assembly of schottky diodes, having a low standing power rating but good RF characteristics is used at the receiving end to rectify the received microwave power back into dc. Inverter is used to invert the dc power into ac.A simple radio control feedback system operating in FM band provides an appropriate control signal to the magnetron for adjusting its output level with fluctuation in the consumers demand at the receiving side.
5.3. Evolving WPT Markets:
Markets that will be made accessible with WPT will have a profound influence on global business activities and industry competitiveness. The following are examples of the future commercial opportunities of WPT:
1. Roadway powered electric vehicles for charging electric batteries with WPT from microwave generators embedded in the roadway while a vehicle is traveling at highway speed, thus eliminating stops to exchange or recharge batteries greatly extending travel range.
2. High-altitude, long-endurance aircraft maintained at a desired location for weeks or months at 20 km for communications and surveillance instead of satellites, at greatly reduced costs.
3. Power relay satellites to access remote energy sources by uncoupling primary electricity generation from terrestrial transmission lines (15). Power is transmitted from distant sites to geosynchronous orbit and then reflected to a receiver on Earth in a desired location.
4. Solar power satellites in low-Earth or geosynchronous orbit or on the Moon to supply terrestrial power demands on a global scale.
6. Spacecraft sizing
The size of an SPS will be dominated by two factors. The size of the collecting apparatus (eg, panels, mirrors, etc) and the size of the transmitting antenna which in part depends on the distance to the receiving antenna. The distance from Earth to geostationary orbit (22,300 miles, 35,700 km), the chosen wavelength of the microwaves, and the laws of physics, specifically the Rayleigh Criterion or Diffraction limit, used in standard RF (Radio Frequency) antenna design will all be factors.
It has been suggested that, for best efficiency, the satellite antenna should be circular and the microwave wavelength should be about 1 kilometers in diameter or larger; the ground antenna (rectenna) should be elliptical, 10 km wide, and a length that makes the rectenna appear circular. Smaller antennas would result in increased losses to diffraction/sidelobes. For the desired (23mW/cm²) microwave intensity these antennas could transfer between 5 and 10 gigawatts of power.
To be most cost effective, the system should operate at maximum capacity. And, to collect and convert that much power, the satellite would require between 50 and 100 square kilometers of collector area (if readily available ~14% efficient monocrystalline silicon solar cells were deployed). State of the art (currently, quite expensive, triple junction gallium arsenide) solar cells with a maximum efficiency of 40.7% could reduce the necessary collector area by two thirds, but would not necessarily give overall lower costs for various reasons.
6.1. LEO instead of GEO
A collection of LEO (Low Earth Orbit) space power stations has been proposed as a precursor to GEO (Geostationary Orbit) space power beaming systems. There would be both advantages (much shorter energy transmission path lengths allowing smaller antenna sizes, lower cost to orbit, energy delivery to much of the Earth's surface, assuming appropriate antennas are available, etc.) and disadvantages (constantly changing antenna geometries, increased debris collision difficulties, requirement of many more power stations to provide continuous power delivery at any particular point on the Earth's surface, etc.). It might be possible to deploy LEO systems sooner than GEO because the antenna development would take less time, but it would certainly take longer to prepare and launch the number of required satellites. Ultimately, because full engineering feasibility studies have not been conducted, it is not known whether this approach would be an improvement over a GEO installation.
6.2. Earth-based infrastructure(Rectenna)
The Earth-based receiver antenna (or rectenna) is a critical part of the original SPS concept. It would probably 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. Rectennas would be multiple kilometers 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, so such a rectenna would not be as expensive in terms of land use as might be supposed.
7. Comparison of Power Sources
Power
Generation Costs Cost/Watt Pros Cons
Nuclear Power State of the art facilities can generate up to 366 Gigawatts 3-5 billion for the facility $61.32 Extensive scientific data available
Technology has been established and used for decades
No greenhouse effects Nuclear proliferation
Larger capital costs
Security and risks of containment breaches
Fossil Fuels Dependent upon usage Currently oil is at $100 a barrel and expected to rise $53.42 Inexpensive and established
Currently Abundant and highly Versatile Pollution , acid rain and global warming
Extensive transportation
Limited Supply Increasing costs
Solar Power 19-56 watts per square meter. Max power generation limited only by size at a rate of <$1.00, dependent upon the size of the station <$1.00 (employing new technologies) Free as long as sunlight is available Requirement of special materials
Current technology requires large amounts of land for small amounts of energy generation
Solar Powered Satellites 230 watts per square meter up to 8.75 terawatts 70-80 billion including launch costs <$1.00 (employing new technologies) Can produce electricity 24 hours a day, 7 days a week.
Satellite can transmit power to different areas globally Extremely expensive
8. Advantages & Disadvantages
8.1. Advantages:
The SPS concept is attractive because space has several major advantages over the Earth's surface for the collection of solar power. There is no air in space, so the collecting surfaces would receive much more intense sunlight, unaffected by weather. In geostationary 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 75 minutes late at night when power demands are at their lowest. This characteristic of SPS based power generation systems to avoid the expensive storage facilities (eg, lakes behind dams, oil storage tanks, coal dumps, etc) necessary in many Earth-based power generation systems. Additionally, an SPS will have none of the polluting consequences of fossil fuel systems, nor the ecological problems resulting from many renewable or low impact power generation systems (eg, dam retention lakes).
Economically, an SPS deployment project would create many new jobs and contract opportunities for industry, which may have political implications in the country or region which undertakes the project. Certainly the energy from an SPS would reduce political tension resulting from unequal distribution of energy supplies (eg, oil, gas, etc). For nations on the equator, SPS provides an incentive to stabilise and a sustained opportunity to lease land for launch sites.
Developing the industrial capacity needed to construct and maintain one or more SPS systems would significantly reduce the cost of other space endeavours. For example, a manned Mars mission might only cost hundreds of millions, instead of tens of billions, if it can rely on an already existing capability.
Space solar power would be the only means of acquiring direct solar energy to supplement the burning of fossil fuels or nuclear energy sources under the most extreme conditions of a global catastrophic volcanic winter (or similarly, nuclear winter).
1. Unlimited energy resource.
2. Energy delivered anywhere in the world.
3. Zero fuel cost.
4. Zero CO2 emission.
5. Minimum long-range environmental impact.
6. Solar radiation can be more efficiently collected in space.
8.2. Disadvantage:
1. 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 initial cost and require much time for construction.
5. Radiation hazards associated with the system.
6. Launch costs.
7. Capital cost even given cheap launchers.
8. Would require a network of hundreds of satellites.
9. Possible health hazards.
10. The size of the antennas and rectennas.
11. Geosynchronous satellites would take up large sections of space.
12. Interference with communication satellites.


9. Conclusion
The economic case for a solar power satellite is most compelling if the solar power satellite can generate power that sells at peak, rather than average, price.. Several new designs for solar power satellites were considered, in an attempt to maximize the amount of power produced at peak rates. This study has given researchers a remarkable insight into uncertain future of development of power from space.
There is little doubt that the supply of energy must be increased dramatically in coming decades. Furthermore, it appears almost certain that there will be a shift toward renewable sources and that solar will be a major contributor. It is asserted that if the energy system of the world is to work for all its people and be adequately robust, there should be several options to develop in the pursuit of and expanded supply. While the option of Space Solar Power may seem futuristic at present, it is technologically feasible and, given appropriate conditions, can become economically viable. It is asserted that it should be among those options actively pursued over coming decades. The challenges to the implementation of Space Solar Power are significant, but then no major expansion of energy supply will be easy. These challenges need to be tackled vigorously by the space, energy and other communities.
Finally, it should be emphasized that if we fail to develop sustainable and clean energy sources and try to limp along by extrapolating present practices, the result is very likely to be thwarted development of economic opportunities for many of the Earth's people and, almost certainly, adverse changes to the planetary environment.
The resolve of the synthesis problem of the WPT shows that WPT efficiency may be improved by using special current discontinuous distribution on the antenna. Here we have three possibilities:
1. To use a discontinuous equidistant array with the quasi Gauss distribution.
2. To use a discontinuous non-equidistant array with the uniform distribution.
3. To use uniform continuous phase synthesis antenna array.
All of these methods are original and they have been modeled only in the frame of International Science and Technology Center Project.
The possibility of decrease of the wave beam expansion permits to make the WPT systems less expensive. Such approach to the problem of the continuous radiators and of the real antennas, which can be created, is new.
Due to high launch costs, SPS is still more expensive than Earth-based solar power and other energy sources. Yet, even now, a small SPS system could be economically justified to provide otherwise unavailable emergency power for natural disaster situations, urban blackouts and satellite power failures.
10. Reference
1. P.E. Glaser «Method and Apparatus for Converting Solar radiation toElectrical Power», U.S. Patent 3 781 647, 1973.
2. R. Bryan Erb, "Space-Based Solar Power - How Soon and How Much", 49th Congress of the International Astronautical Federation, Paper IAF-98-R.2.02, Melbourne, Australia, September 28 - October 2, 1998.
3. WEC/IIASA, Global Energy Perspectives, Nakicenovic, Nebojsa, et al, Cambridge University Press, 1998.
4. P. E. Glaser, "An overview of the solar power satellite option," IEEE Transactions on Microwave Theory and Techniques, vol. 40, no. 6, pp. 1230-1238, June 1992.
5. W. C. Brown and E. E. Eves, "Beamed microwave power transmission and its application to space," IEEE Transactions on Microwave Theory and Techniques, vol. 40, no. 6, June 1992.
6. World Energy Council, "Energy for Tomorrowâ„¢s World - Acting Now", WEC Statement 2000, http://www.worldenergy.org.
7. http://www.nspri.com


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