28-06-2012, 05:44 PM
Solar Power Satellite and Microwave Power Transmission
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INTRODUCTION
Solar Power Satellites would be located in the geosynchronous orbit. The difference between existing satellites and SPS is that an SPS would generate more power-much more power than it requires for its own operation. The solar energy collected by an SPS would be converted into electricity, then into microwaves. The microwaves would be beamed to the Earth’s surface, where they would be received and converted back into electricity by a large array of devices known as rectifying antenna or rectenna.(Rectification is the process by which alternating electrical current, such as that induced by a microwave beam , is converted to direct current). This direct current can then be converted to 50 or 60 Hz alternating current.
Each SPS would have been massive; measuring 10.5 km long and 5.3km wide or with an average area of 56 sq.km. The surface of each satellite would have been covered with 400 million solar cells. The transmitting antenna on the satellite would have been about 1 km in diameter and the receiving antenna on the Earth’s surface would have been about 10 km in diameter .The SPS would weigh more than 50,000 tons. The reason that the SPS must be so large has to do with the physics of power beaming. The smaller the transmitter array, larger is 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.
It is known that electromagnetic energy also associated with the propagation of the electro-magnetic waves. We can use theoretically all electro-magnetic waves for a wireless power transmission (WPT).Wireless power transmission occur in form of wave can be called as microwave power transmission (MPT). The difference between the WPT and communication systems is only efficiency.
The Maxwell’s Equations indicate that the electromagnetic field and its power diffuse to all directions. Although we transmit the energy in the communication system, the transmitted energy is diffused to all directions. Although the received power is enough for a transmission of information, the efficiency from the transmitter to receiver is quiet low. Therefore, we do not call it the WPT or MPT system.
Typical WPT is a point-to-point power transmission. For the WPT, we had better concentrate power to receiver. It was proved that the power transmission efficiency can approach close to 100%. We can more concentrate the transmitted microwave power to the receiver aperture areas with taper method of the transmitting antenna power distribution. Famous power tapers of the transmitting antenna are Gaussian taper, Taylor distribution, and Chebychev distribution. These taper of the transmitting antenna is commonly used for suppression of sidelobes. It corresponds to increase the power transmission efficiency. Concerning the power transmission efficiency of the WPT, there are some good optical approaches in Russia.
Future suitable and largest application of the WPT via microwave is a Space Solar Power Satellite (SPS). The SPS is a very huge satellite designed as an electric power plan orbiting in the Geostationary Earth Orbit (GEO). SPS consists of mainly three segments; solar energy collector to convert the solar energy into DC (direct current) electricity, DC-to-microwave converter, and large antenna array to beam down the microwave power to the ground. The first solar collector can be either photovoltaic cells or solar thermal turbine. The second DC-to-microwave converter of the SPS can be either microwave tube system or semiconductor system. It may be their combination. The third segment is a gigantic antenna array. An amplitude taper on the transmitting antenna is adopted in order to increase the beam collection efficiency and to decrease sidelobe level in almost all SPS design. A typical amplitude taper is called 10 dB Gaussian in which the power density in the center of the transmitting antenna is ten times larger than that on the edge of the transmitting antenna. The SPS is expected to realize around 2030. Before the realization of the SPS, we can consider the other application of the MPT.
History of Solar power satellite and Microwave Power Transmission
In 1864, James C. Maxwell predicted the existence of radio waves by means of mathematical
model. In 1884, John H. Poynting realized that the Poynting Vector would play an important role in quantifying the electromagnetic energy. In 1888, bolstered by Maxwell's theory, Heinrich Hertz first succeeded in showing experimental evidence of radio waves by his spark-gap radio transmitter. The prediction and Evidence of the radio wave in the end of 19th century was start of the wireless power transmission.
At the same period of Marchese G. Marconi and Reginald Fessenden who are pioneers of
Communication via radio waves, Nicola Tesla suggested an idea of the wireless power transmission and carried out the first WPT experiment in 1899. He said “This energy will be collected all over the globe preferably in small amounts, ranging from a fraction of one to a few horse-power.
One of its chief uses will be the illumination of isolated homes”. He actually built a gigantic coil which was connected to a high mast of 200-ft with a 3 ft-diameter ball at its top. He fed 300 kW power to the Tesla coil resonated at 150 kHz. The RF potential at the top sphere reached 100 MV.
Unfortunately, he failed because the transmitted power was diffused to all directions with 150 kHz radio waves whose wave length was 21 km. To concentrate the transmitted power and to increase transmission efficiency, we have to use higher frequency than that used by Tesla. In 1930s, much progress in generating high-power microwaves, 1-10 GHz radio waves, was achieved by invention of the magnetron and the klystron.
After World War II, high power and high efficiency microwave tubes were advanced by
development of radar technology. We can concentrate a power to receiver with microwaves.
We call the wireless power transmission with microwaves as microwave power transmission
(MPT). Based on the development of the microwave tubes during the World War II, W. C. Brown started the first MPT research and development in 1960s.
First of all, he developed a rectenna, rectifying antenna which he named, for receiving and rectifying microwaves. The efficiency of the first rectenna developed in 1963 was 50 % at output 4WDC and 40% at output 7WDC, respectively. With the rectenna, he succeeded in MPT experiments to wired helicopter in 1964 and to free-flied helicopter in 1968 . In 1970s, he tried to increase MPT demonstration to helicopter with W. C.
Brown DC-RF-transmission-RF-DC total efficiency with 2.45 GHz microwave. In 1970, overall DC-DC total efficiency was only 26.5 % at 39WDC in Marshall Space Flight Center. In 1975, DC-DC total efficiency was finally 54 % at 495WDC with magnetron in Raytheon Laboratory . In parallel, He and his team succeeded in the largest MPT demonstration in 1975 at the Venus Site of JPL Goldstone Facility . Distance between a transmitting parabolic antenna, whose diameter was 26m, and a rectenna array, whose size was 3.4mx 7.2 m, was 1 mile. The transmitted microwave of 2.388GHz was 450 kW from klystron and the achieved rectified DC power was 30 kWDC with 82.5% rectifying efficiency. Based on the Brown’s work, P. E. Glaser proposed a Solar Power Satellite (SPS) in 1968.
In 1980s, Japanese scientists progressed the MPT technologies and research. In 1983 and 1993,
Hiroshi Matsumoto’s team carried out the first MPT experiment in space. The rocket experiment were called MINIX (Microwave Ionosphere Nonlinear Interaction eXperiment) in 1983 and ISY-METS (International Space Year – Microwave Energy Transmission in Space) in 1993, respectively.
They focused nonlinear interaction between intense microwave and ionospheric plasmas. In the MINIX experiment, they used cooker-type 800W-2.45GHz magnetron for microwave transmitter. New wave-wave-particle interaction phenomenons were observed in the MINIX. Plasma theory and computer experiments supported the observations. After 1990s, many MPT laboratory and field experiments were carried out in the world.
THE ABOVE DAIGRAM SHOWS HOW SOLAR ENERGY COME TO PANEL AND HOW MICROWAVE BEAMS TRANSMITTED AND RECTENNA ALSO SHOWS WHO RECIEVES THIS BEAMS.
Recent Technologies and Researches of Wireless Power Transmission – Antennas and Transmitters
.Antennas for Microwave Power Transmission
All antennas can be applied for both the MPT system and communication system, for example, Yagi-Uda antenna, horn antenna, parabolic antenna, microstripantenna, phased array antenna or any other type of antenna. To fixed target of the MPT system, we usually select a large parabolic antenna, for example, in MPT demonstration in 1975 at the Venus Site of JPL Goldstone Facility and in ground-to-ground MPT experiment in 1994-95 in Japan . In the fuel-free airship light experiment with MPT in 1995 in Japan, they changed a direction of the parabolic antenna to chase the moving airship.
However, we have to use a phased array antenna for the MPT from to moving transmitter/receiver which include the SPS because we have to control a microwave beam direction accurately and speedy. 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 is possible to steer the direction of the microwave beam. The antenna elements might be dipoles, slot antennas, or any other type of antenna, even parabolic antennas. In some MPT experiments in Japan, the phased array antenna was adopted to steer a direction of the microwave beam.
All SPS is designed with the phased array antenna. We consider the phased array antenna for all MPT system.
ANTENNA FOR MICROWAVE POWER TRANSMISSION WITH RECTENNA
Here microwave power source who has frequency 2.45ghz as shown in figure is transmitted means here microwave power is transmitted through satellite with the help of transmitter.waves are transmitted in the form of circular waveguide as shown in figure and rectenna is a receiver who receives this power and convert it into electrical power.