29-05-2013, 03:59 PM
Power transmission Using Solar Powered Satellite and Rectenna Report
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Abstract
Can’t we use solar power at the night? This question may look somewhat absurd since there is obviously no meaning of “Using solar power at night”! Now-a-days we are using the solar power to generate electricity by the solar panels mounted on the earth. But, in outer space, the sun always shines brightly. No clouds block the solar rays, and there is no nighttime. Solar collectors mounted on an orbiting satellite would thus generate power 24 hours per day, 365 days per year. If this power could be relayed to earth, then the world's energy problems might be solved forever.
History of Free Space Power Transmission
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 invented and used for the microwave-powered helicopter. The first rectenna was composed of 28 half-wave dipoles terminated 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 % to 84 %. The highest record of 84 % efficiency was attained in the demonstration of microwave power transmission in 1975 at the JPL Goldstone Facility. Power was successfully transferred from the transmitting large parabolic antenna dish 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 the DOE/ NASA Satellite Power System Concept Development and Evaluation Program, started in 1977. The extensive study of the SPS ended in 1980, producing a 670 page summary document. The concept of the SPS was first proposed by P. E. Glaser in 1968 to meet both space-based and earth-based power needs. The SPS will generate electric power of the order of several hundreds to thousands of megawatts using photovoltaic cells of sizable area, and will transmit the generated power via a microwave beam to the receiving rectenna site.
Rectenna
Rectenna is an acronym for RECTifying anTENNA. It is a special type of antenna that rectifies the incoming microwave radiation into DC current and hence the name Rectenna.
A rectenna comprises of a mesh of dipoles and diodes for absorbing microwave energy from a transmitter and converting it into electric power. Its elements are usually arranged in a mesh pattern, giving it a distinct appearance from most antennae. A simple rectenna can be constructed from a schottky diode placed between antenna dipoles as shown in Fig. 1. The diode rectifies the current induced in the antenna by the microwaves. Rectenna are highly efficient at converting microwave energy to electricity. In laboratory environments, efficiencies above 90% have been observed with regularity.
Solar Energy: A limitless source of energy
The solar energy that reaches the Earth is about 10,000 times total human energy production today and the energy available in near-Earth space is limitless. Research is being done on many different ways of using solar power economically on Earth, and many of these will be successful. Terrestrial solar energy is going to become a colossal business. However, sunlight is diffuse and not available continuously at the Earth's surface. So one additional possibility is to collect solar energy 24 hours per day in space, and transmit it as microwave beams to receivers on Earth. Compared to solar power collected at the Earth's surface, SPS faces the extra costs of space transportation and microwave power transmission.
Conclusion
From the above presentation we concluded that through use of wireless power reception through Rectenna his helpful for power generation throughout 365 days in a year. With out any shortages so it is prefer to use this technique in developing countries like India for power generation.