19-10-2010, 10:18 AM
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This article is presented by:R .Venkatesh
L .Krishnam Raju
SOLAR POWER SATELLITES
ABSTRACT:
Can’t we generate solar power during night times? Yes my paper suggests a solution to generate solar power during night times. It is probably well known that we are running out of fossil fuel. Most of the energy sources we are using are non renewable. Oil and gas are not to last longer than about fifty years, whereas coal will probably last another two or three centuries. Uranium and nuclear plants will not last forever either. So, in order to provide the generations to come with energy, we have to find the way to use unlimited sources. And this is where SPS gets in action. It provides solutions to use one of the most renewable and unlimited source on earth: the SUN.
Still someone might ask why using SPS and not solar panels on the surface of the earth? With the SPS, problems such as daylight and bad-weather conditions, which one might have to deal with, when using solar panels, do not exist. Neither does the need of storage in order to have continual provision of energy and especially considering our inability for adequate energy storage on earth. With SPS the maximum energy loss due to eclipses is only a hundred and twenty hours a year. Furthermore the energy received by the rectennas on earth is ten times more than that received by solar panels of the same surface.
The solar panels used on the surface of the earth prevent sun beams to go through them and consequently prevent any kind of cultivation of the earth under them. But with SPS the photo voltaic cells are in space, so we have no problem with the area needed. In addition the rectennas on earth are semi-transparent allowing sun light to go through them and making possible the cultivation of the soil. So we have no waste of space.
Probably in the future there will be other sources of energy such as fusion, in fact we are already using renewable sources like either hydroelectricity or geothermal energy. SPS might be one of several renewable energies we will use in the future.
Now that we have seen several reasons why SPS could be a great project, let's keep our feet on the ground. There are still some problems to solve before we can see the first SPS working.
INTRODUCTION TO SPS:
The Solar Power Satellite (SPS) concept would place solar power plants in orbit above Earth, where they would convert sunlight to electricity and beam the power to ground-based receiving stations. The ground-based stations would be connected to today's regular electrical power lines that run to our homes, offices and factories here on Earth.
Why put solar power plants in space? The sun shines 24 hours a day in space, as if it were always noontime at the equator with no clouds and no atmosphere. Unlike solar power on the ground, the economy isn't vulnerable to cloudy days, and extra generating capacity and storage aren't needed for our nighttime needs. There is no variation of power supply during the course of the day and night, or from season to season. The latter problems have plagued ground based solar power concepts, but the SPS suffers none of the traditional limitations of ground-based solar power.
INTRODUCTION TO RECTENNA:
A rectenna is a rectifying antenna, a special type of antenna that is used to directly convert microwave energy into DC electricity. 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. The diode rectifies the current induced in the antenna by the microwaves. Schottky diodes are used because they have the lowest voltage drop and therefore waste the minimum power.
Rectennae are highly efficient at converting microwave energy to electricity. In laboratory environments, efficiencies above 90% have been observed with regularity. Some experimentation has been done with inverse rectennae, converting electricity into microwave energy, but efficiencies are much lower—only in the area of 1%.
