Jane Doe7th semester

Electrical EngineeringRegd.no.xxxxxxxxxx

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OUTLINE

Introduction Solar Power Satellite Microwave Power Transmission Issues Conclusion

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INTRODUCTION

A great concern has been voiced in recent years over the extensive use of energy, the limited supply of resources, and pollution of the environment from the use of present energy conversion systems. Thus the search for alternative sources of energy is being encouraged. The solar power satellite (SPS) concepts envisions using the constant availability of light in space to generate baseload electricity on Earth.

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The SPS is a gigantic satellite designed as an electric power plant orbiting in the Geostationary Earth Orbit (GEO). It consists of mainly three segments; solar energy collector to convert the solar energy into DC (direct current) electricity, DC-to-microwave convert-er, and large antenna array to beam down the microwave power to the ground.

More intense sunlight.SPS would be illuminated over 99% of the

time.No need for costly storage devices.Power can be beamed to the location

where it is needed.No air or water pollution is created in the

process.

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POSSIBLE DESIGNS

www.spacedaily.com/images/solar-sps-satellite-bg.jpg

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www.ssi.org/assets/images/slide02.jpg

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PROBLEMS AND POSSIBLE SOLUTIONS

Cost of transporting materials to space can be minimized by using materials from moon or asteroids .Difficulty in construction can be overcome by using International space station or moon as construction base.Routine maintenance can be carried out using robots.

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How to transmit power to earth?

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The beamed microwave power transmission system can be used to transmit power to earth. Its major advantage is its ability to transfer energy across large distances.

Basic Parts of beamed microwave power transmission system are:-1.DC to microwave conversion2.A beam forming antenna.3.Free space transmission4.Reception and reconversion to DC

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Beamed microwave power transmission system

DC to microwav

e conversio

n

Beam formin

g antenn

a

Free space transmission

Reception Conversion to DC

70-90% 70-97% 5-95% 85-92%

Maximum possible DC-DC efficiency --- 76%Experimental DC-DC efficiency ---54%

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The solar energy collected is converted into electrical energy by the solar PV cells. To transmit the power to earth the SPS converts the DC electricity into microwaves using an onboard cavity magnetron which is same as an microwave oven magnetron except being modified so as to provide directional beam with less noise.

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Now the microwave produced needs to be transmitted so as to be received on earth. The efficiency of transmission, wavelength used and the distance depends upon the transmitter and receiver aperture.

The relationship between aperture to aperture efficiency and character ר

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The microwaves are transmitted using phased array antenna as we have to control the microwave beam direction accurately and speedily. The phased array is a directive antenna which generate a beam form whose shape and direction by the relative phases and amplitudes of the waves at the individual antenna elements. It has low efficiency but it steers electrically and thus has no moving parts

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For accurate target detection and high efficient beam forming retro-directive system is used. Usually they have phase conjugate circuits in transmitter or receiver antenna. A pilot signal transmitted by the target is received and re-radiated from the phase conjugate circuit. If the pilot signal is received back by the target then it is set and power is transmitted.

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RECTENNA It is an unique device which spreads over receiv- ing area and combines the function of antenna and rectifier. A simple rectenna element consists of a dipole antenna with an RF diode connected across the dipole elements. The diode rectifies the AC current induced in the microwave to produce DC power. The rectenna will be used as an array for high power MPT because one rectenna element rectifies a few W only. The SPS requires a rectenna array whose diameter is over km. It has an overall efficiency of about 85%. It has low specific mass of 1-2 kg for each KW of DC power.

www.powersat.com/image_library.html

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ENVIRONMENTAL ISSUESA suggested microwave beam would have a maximum intensity at its center of 23 mW/cm^2, which is comparable to the OSHA safety limit of 10 mW/cm^2. Over 95% of the beam energy will fall on the rectenna. The remaining microwave energy will be absorbed and dispersed well within standards currently imposed upon microwave emissions around the world.Rectennae are supposed to be located at remote areas.

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LEGAL ISSUESSPS needs to be allocated a slot in the geosynchronous orbit which has limited capacity. LEO(Low Earth Orbit) can come as a possible solution.Another legal concern of using SPS is whether the satellites that beam energy to Earth are allowed under international treaties that prohibit military uses of outer space.Microwaves may interfere with the communication signals.Handling space debris related to SPS may cause legal concerns.

Too little is currently known about the technical, economic and environmental aspects of SPS to make a decision about

it’s deployment. An SPS research program could ultimately assure an adequate

information base for these decisions. If future demand growth is expected to be

high, SPS might be needed early in the 21st century, and an increase in research effort

would be justified.

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www.bu.edu/law/central/jd/organizationswww.bvucoepune.edu.in/pdf'swww.sspi.gatech.edu/wptshinohara.pdfOffice of Technology Assessment (OTA),

Princeton, workshop on solar power satellitewww.spacedaily.comwww.ssi.orgwww.wikipedia .comIEEE transactions on microwave theory and

techniques, vol. 40, no. 6, june 1992

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