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Photovoltaic Effect and Solar Energy
(Page 3)
The Earth receives 174 petawatts (1 PW = 1,000,000,000,000,000 W) of incoming solar radiation at the upper atmosphere. Approximately 30% is reflected back to space while the rest is absorbed by clouds, oceans and land masses. See figure below.
Total Solar Energy Breakdown
Source: Wikipedia
The total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately 3,850,000 exajoules (EJ) per year. In 2002, this was more energy in one hour than the world used in one year.Photosynthesis captures approximately 3,000 EJ per year in biomass. The amount of solar energy reaching the surface of the planet is so vast that in one year it is about twice as much as will ever be obtained from all of the Earth's non-renewable resources of coal, oil, natural gas, and mined uranium combined.
The above graph shows the relative abundance of solar energy across the United States. Evidently, the potential of solar energy projects is limited by the geographical location. But for most areas of the United States, solar energy is a viable alternative to fossil fuels and even bio-diesel.
Of course, human creativity has never been limited by imagination. Almost 40 years ago to this date, the first astronauts were sent to the moon, a milestone in the history of space exploration. One can't help but thinking where would be a better place to collect the sunlight other than the space, some 20,000 miles above the earth, with no atmosphere to absorb or scatter the sunlight; no weather phenomena to affect the efficiency; no seasonal changes in the performance of the panels and above all, a considerably longer daytime. And to recall that electromagnetic waves are essentially photons packed with energies, solar energy collected in the space can be beamed back to the earth at a more efficient frequency (i.e. less energy loss during transmission) and bypass the grids directly to where the consumers are.
As reported in the December 4th, 2008 issue of The Economist magazine, space solar power (SSP) is no longer the imagination of mad scientists. Space solar power is an idea far ahead of its time, but the necessary technology already exists.Small scaled solar panels have been powering space shuttles and stations for many years. Power transmission via invisible electromagnectic radiations has been proved plausible. Although there may not be any technical difficulty with the idea, the economics are another matter. The initial cost of setting up the system in space may be prohibitive, but its strategic benefits, especially potentials in defense and national security make it an intriguing area of research.
It's the vision that drives technological advances. 40 years ago, before the oil crisis, few could foresee solar panels on the roofs of ordinary Americans. The development and wide adoption of solar energy is the living proof of how science and technology can overcome hurdles big or small and deliver amazing results. For scientific achievements, sky is the only limit. Or is it?
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<i>Courtesy of The Economist</i>
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