Solar Power Satellite (Sps)

8/2/2019 Solar Power Satellite (Sps)

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A TECHNICAL PAPER PRESENTATION ON

SOLAR POWER SATELLITE (SPS)


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ABSTRACT


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This paper reports on the futuristic advances in power transmission through microwaves. Sun is a limitless

ource of Energy. A Space Power Satellite (SPS) orbiting round the earth traps solar energy and generates electric

ower using photovoltaic cells of sizable area. SPS transmits the generated power via a microwave beam to the

eceiving Rectenna site on earth. A RECTENNA (RECtifying anTENNA) comprises of a mesh of dipoles and diodes

or absorbing microwave energy from a transmitter and converts it into electric power. We can in fact directly convert

olar energy into electrical energy with the use of solar cells, but this process will be affected by day/night cycles,

weather, and seasons. We are aware of the fact that light is an electromagnetic wave. Light rays never diffuse in space

& if by any means these rays can be transmitted from space to earth then it will be a perfect solution for our desired

eed of 24 hrs power supplies. The 21st century endeavors and approaches for establishing human race in space can

ome true only if the basic requirement of human beings is satisfied i.e. 24hrs power, which can be efficiently served by

ectenna. This paper presents the concept & evolution of satellite power system, SPS2000 (a research work by ISAS)


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nd the impact of Microwave Power Transmission (MPT) on space plasma. In near future conventional power sources

annot meet total power demand, for which SPS is a best solution.

Recent Trend in power generation Using S.P.S And Rectenna


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. INTRODUCTION


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The post-war history of research on free-space power transmission is well documented by William C. Brown,

who was a pioneer of practical microwave power transmission. It was he who first succeeded in demonstrating a

microwave-powered helicopter in 1964. A power conversion device from microwave to DC, called a rectenna, was

nvented and used for the microwave-powered helicopter. The first rectenna was composed of 28 half-wave dipoles

erminated in a bridge rectifier using point-contact semiconductor diodes. Later, the point contact semiconductor diodes

were replaced by silicon Schottky-barrier diodes, which raised the microwave-to-DC conversion efficiency from 40 %

o 84 %. The highest record of 84 % efficiency was attained in the demonstration of microwave power transmission in

975 at the JPL Goldstone Facility. Power was successfully transferred from the transmitting large parabolic antenna

ish to the distant rectenna site over a distance of 1.6 km. The DC output was 30 kW.

An important milestone in the history of microwave power transmission was the three-year study program called


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he DOE/ NASA Satellite Power System Concept Development and Evaluation Program, started in 1977. The extensive

tudy of the SPS ended in 1980, producing a 670 page summary document. The concept of the SPS was first proposed

y P. E. Glaser in 1968 to meet both space-based and earth-based power needs. The SPS will generate electric power of

he order of several hundreds to thousands of megawatts using photovoltaic cells of sizable area, and will transmit the

enerated power via a microwave beam to the receiving rectenna site. Among many technological key issues, which

must be overcome before the SPS realization, microwave power transmission (MPT) is one of the most important key

esearch issues. The problem contains not only the technological development microwave of power transmission with

igh efficiency and high safety, but also scientific analysis of microwave impact onto the space plasma environment.

. SOLAR POWER SATELLITE:

The concept of the Solar Power Satellite (SPS) is very simple. It is a gigantic satellite designed as an electric


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ower plant orbiting in the Geostationary Earth Orbit (GEO).

Fig. 1

t consists of mainly three segments.

) Solar energy collector to convert the solar energy into DC (direct current) electricity


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) DC-to-microwave converter,

) Large antenna array to beam the microwave power to the ground.

The solar collector can be either photovoltaic cells or a solar thermal turbine. The DC-to-microwave

onverter of the SPS can be either a microwave tube system or a semiconductor system, or their combination. The third

egment is a gigantic antenna array. The SPS system has that advantage of producing electricity with much higher

fficiency than a photovoltaic system on the ground. Since SPS is placed in space in GEO, there is no atmospheric

bsorption, the solar input power is about 30% higher density than the ground solar power density, and power is

vailable 24 hours a day without being affected by weather conditions. It is confirmed that the eclipses would not cause

problem on a grid because their occurrences are precisely predictable.

. DC TO MICROWAVE GENERATION AND AMPLIFICATION


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The technology employed for generating microwave radiation is extremely important for the SPS system. It

hould be highly efficient, very low noise, and have an acceptable weight/power ratio. A microwave energy transmitter

ften uses 2.45 GHz in the ISM band. There are two types of microwave generators and amplifiers, the microwave tube

nd the semiconductor amplifier. These have contrasting electric characteristics. The microwave tube magnetron can

enerate and amplify high power microwaves (over kilowatts) with a high voltage (over kilovolts). It is very

conomical. The semiconductor amplifier generate low power microwave (below 100W) with a low voltage (below

ifteen volts). It currently is still expensive. The microwave tube has higher efficiency (over 70%) and the semiconductor

as lower efficiency (below 50%). The weight of the MPT system is also important for reducing the transportation cost

f the SPS. Microwave tube is lighter than a semiconductor amplifier when we compare the weight by power-weight

atio (kg/kW) because the microwave tube can generate and amplify higher power microwaves than can the

emiconductor amplifier.


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. RECTENNA

RECTifying anTENNA rectifies received microwaves into DC current. A rectenna comprises of a mesh of


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ipoles and diodes for absorbing microwave energy from a transmitter and converting it into electric power. Its

lements are usually arranged in a mesh pattern, giving it a distinct appearance from most antennae. A simple rectenna

an be constructed from a Schottky diode placed between antenna dipoles as shown in Fig. 1. The diode rectifies the

urrent induced in the antenna by the microwaves. Rectenna are highly efficient at converting microwave energy to

lectricity. In laboratory environments, efficiencies above 90% have been observed with regularity. In future rectennas

will be used to generate large-scale power from microwave beams delivered from orbiting SPS satellites.

.1. Schottky Barrier Diode:

A Schottky barrier diode is different from a common P/N silicon diode. The common diode is formed by


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onnecting a P type semiconductor with an N type semiconductor, this is connecting between a semiconductor and

nother semiconductor; however, a Schottky barrier diode is formed by connecting a metal with a semiconductor. When

he metal contacts the semiconductor, there will be a layer of potential barrier (Schottky barrier) formed on the contact

urface of them, which shows a characteristic of rectification. The material of the semiconductor usually is a

emiconductor of n-type (occasionally p-type), and the material of metal generally is chosen from different metals such

s platinum, tungsten etc. Sputtering technique connects the metal and the semiconductor.

A Schottky barrier diode is a majority carrier device, while a common diode is a minority carrier device. When a

ommon PN diode is turned from electric connecting to circuit breakage, the redundant minority carrier on the contact

urface should be removed to result in time delay. The Schottky barrier diode itself has no minority carrier, it can

uickly turn from electric connecting to circuit breakage, its speed is much faster than a common P/N diode, so its

everse recovery time Trr is very short and shorter than 10 ns. And the forward voltage bias of the Schottky barrier


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iode is under 0.6V or so, lower than that (about 1.1V) of the common PN diode. So, The Schottky barrier diode is a

omparatively ideal diode, such as for a 1 ampere limited current PN interface. Below is the comparison of power

onsumption between a common diode and a Schottky barrier diode:

P =0.6 x 1 = 0.6 W

P =1.1 x 1 = 1.1 W

It appears that the standards of efficiency differ widely. Besides, the PIV of the Schottky barrier diode is

enerally far smaller than that of the PN diode; on the basis of the same unit, the PIV of the Schottky barrier diode is

robably 50V while the PIV of the PN diode may be as high as 150V. Another advantage of the Schottky barrier diode

s a very low noise index that is very important for a communication receiver; its working scope may reach 20 GHz.


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. Solar Power Satellite of SPS2000:

SPS2000 is a model of solar power satellites with microwave power output of 10 MW, which was proposed by

he SPS working group of the Institute of Space and Astronautically Science (ISAS). The primary objective of

PS2000 research is to show whether SPS could be realized with the present technology and to find out technical

roblems. The conceptual study of SPS2000 is now being carried out under the assumption that the first construction

will be started before the beginning of the twenty first century. SPS2000 transforms the DC power generated by huge

olar arrays to microwave power at 2.45 GHz and transmits it to the rectennas on the earth while it moves from west to

ast in an equatorial low earth orbit (LEO) of 1100 km altitude. Transmission is possible when the rectenna can be in

he field of view of the controllable microwave beam from SPS2000. Therefore, SPS2000 should always detect the

ocation of the rectenna and direct a microwave beam toward the rectenna. In order to perform the beam scan, the


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pacetenna should have a function of a phased-array antenna. We discuss a configuration of spacetenna of SPS2000. On

he basis of the spacetenna proposed above, we design a functional system model of SPS2000 as a demonstration model

nd construct microwave circuits employing silicon (Si) semiconductors since there are many advantages in Si

echnology compared with others in terms of cost reduction, robustness of the system and extraterrestrial resources.


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Fig.3

The general configuration of SPS2000 has the shape like a triangular prism as shown in Figure 2 The power


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ransmission antenna, spacetenna, is built on the bottom surface facing to the earth, and the other two surfaces are used

o deploy the solar panels. SPS2000 moves on an equatorial LEO at an altitude of 1100km. The choice of the orbit

minimizes the transportation cost and the distance of power transmission from space. The spacetenna is constructed as a

hased-array antenna. It directs a microwave power beam to the position where a pilot signal is transmitted from a

round-based segment of power system (RECTENNA). Therefore, the spacetenna has to be a huge phased-array

ntenna in size with a retro directive beam control capability. So, microwave circuits are connected to each antenna

lement and driven by DC power generated in the huge solar panels. A frequency of 2.45 GHz is assigned to transmit

ower to the earth. Figure 2 also shows a scheme of microwave beam control and rectenna location. SPS2000 can serve

xclusively the equatorial zone, especially benefiting geographically isolated lands in developing nations.


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Fig.4. Configuration of the Spacetenna


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Figure 4 illustrates a configuration of the Spacetenna. The Spacetenna has a square shape whose dimension is

32 meters by 132 meters and which is regularly filled with 1936 segments of sub array. The sub array is considered to

e a unit of phase control and also a square shape whose edges are 3 meters. It contains 1320 units of cavity-backed

lot antenna element and DC-RF circuit. Therefore, there will be about 2.6 million antenna elements in the spacetenna.


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Fig. 5 Block Diagram of the Spacetenna

Figure 5 illustrates a block diagram of the spacetenna. The spacetenna is composed of pilot signal receiving

ntennas followed by detectors finding out the location of the rectenna on the earth, power transmission antenna

lements and phase control systems. The left and right hand sides in Fig.4 correspond to parts of power transmission

nd direction detection, respectively. The antenna elements receiving the pilot signal have a polarization perpendicularo the antenna elements used in the power transmission so as to reduce effectively interactions between both antenna

lements. Moreover, the pilot signal frequency and a frequency for the energy transmission are different from each

ther. Using two kinds of frequency for the power transmission and the pilot signal prevents each other from interfering

nd makes it possible to find out the accurate direction of a specified rectenna.


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Fig. 6.1


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Fig. 6.2


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Fig. 6.3

A Solar Power Satellite (SPS) with a thoroughly energized Earth in the background. One of the first things we

will begin doing once we are using space resources is constructing a SPS, a vast solar array which gathers the constant

olar power in orbit and beams energy to Earth in the form of a safe, low-density microwave beam.


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Fig. 6.4

On Earth, the beam is intercepted by a rectenna several miles across, where it is converted back into electricity.

The electricity is then rectified to AC, and fed into the power grid. The goal is to undersell power generated by fossil

uels or nuclear energy.


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Fig. 6.5

The Rectenna will be huge, but the land underneath need not go to waste. Since the array absorbs the microwaves, but

llows sunlight and rainfall through, the land could be used for farming or ranching. Or, as in this case, the rectenna

ould be built as a vast set of greenhouses, feeding millions.


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. CONCLUSION

In the future Rectenna stands as a milestone among non conventional energy resources. This technology is more

eliable than ground based solar power. In order for SPS to become a reality it several things have to happen:

Cheaper launch prices

Involvement of the private sector

. REFERENCES

Glaser, Peter E.. "Method And Apparatus For Converting Solar Radiation To Electrical Power".

Satellite Power System Concept Development and Evaluation Program July 1977 - August 1980.

DOE/ET-0034, February 1978.

Satellite Power System Concept Development and Evaluation Program Reference System Report.


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DOE/ER-0023, October 1978.

Satellite Power System (SPS) Resource Requirements (Critical Materials, Energy, and Land). HCP/R-4024-02,

October 1978


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Solar Power Satellite (Sps)