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‘It’s always sunny in space’

That was the title of a paper by Dr Susumu Sasaki of the Japan Aerospace Exploration Agency, proposing a radical solution for the world's energy needs — space-based solar energy. It's been the stuff of science fiction for years, but as Omair Ahmad explains, the power plants of the future are almost here.

OMAIR AHMAD  30th Aug 2014

NASA plans to build ‘Sun Towers’, such as the one depicted above, to capture solar power and beam it back to the Earth.

t an India-Pakistan conference on water issues in 2010, a senior journalist made an impassioned plea. "Water and all the issues related with hydro-electric power are a thing of the past," he said. "We are fighting over yesterday's technology. The solar power potential of J&K is far greater than the hydropower of the state." It was a startling statement, and most of the dour experts around the table, unused to optimism of any sort, were unsure of how to deal with the idea. When the journalist mentioned that the technology had not been perfected, however, the attendees gave up on even discussing the idea, and went back to muttering about Hafiz Saeed and his outrageous statements such as, "Either water will flow or blood will flow."

The dream of solar power has been with us for a long time, whether it is build solar arrays in the high, clear mountain climate of Ladakh or the dry but eminently sunny climes of Rajasthan and Gujarat, or Desertec, the proposed solar project in North Africa that is supposed to take care of all the energy needs of Europe. The dreams have always outstripped the reality, though. And the biggest dream of all is, of course, solar panel arrays in space.

One of the key constraints of solar panels is that they are on earth, behind the haze that we call our atmosphere, which keeps us from burning to death. Without our thick atmosphere life on earth would be impossible, true, but it also makes solar power generation that much more difficult. About 30% of solar radiation is reflected back into space, and a great deal more is either absorbed or refracted by clouds and other matter in the upper atmosphere. Nevertheless, more solar energy reaches the earth in one hour than is used by humans throughout the year.

Solar energy manifests itself across many wavelengths, and at best solar panels manage to catch only a small percentage of the total energy — the newest ones have conversion ratios of about 20–30%. If we could catch this energy in space itself, without the atmosphere disturbing it, we would have so much more to play with, and the low conversion ratios would not matter at all.

Scientists have dreamt of tapping the potential of this energy coursing through space, seemingly only a hand's breadth away, since the early 1950s. We have done this most successfully with satellites, using solar cells to power the many communications and other satellites orbiting the Earth. Probably the most beautiful demonstration of this is the International Space Station, whose main power source is the large array of solar panels spread around it like the wings of a gorgeous metallic insect. A special extra is that the solar panels not only collect the energy from the sun, but the rear-facing panels also collect the energy reflected off the Earth. 

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The basic technology needed to convert solar energy into a focussed laser beam is smaller than a kitchen table. A prototype of this type of laser was tested at the Lawrence Livermore National Laboratory in the United States in 2002, and a working model is under production.

It is not just satellites orbiting around the Earth that use solar power. The Juno mission, which took off from Cape Canaveral in 2011 and is due to arrive at Jupiter in 2016, is solar powered. Jupiter is five astronomical units away from the sun, or approximately 750 million kilometres away. No spacecraft has used solar panels at a distance further than 300 million kilometres from the sun before, but improvements in technology mean that for the first time, we will have an orbiting satellite operating at some two-and-a-half times that distance. 

An Ancient Art Goes inTo SpaceSanshey Biswas

With all these breakthroughs in the science of solar energy, the obvious question is this: how do we use these advances in space to benefit us on Earth? Of course, some of the technical feats have been transferred already. The improvements in solar technology that power the satellites are used to build improved solar panels, but the gold standard would be to transfer the energy caught in space straight to the Earth. The only question is how to do it. It isn't as if we could launch a satellite with a long set of wires running back to the Earth.

Over time, scientists have come up with two ways to do this. The first would be to convert the light into laser power. A moderate-sized satellite could be launched into a low-Earth orbit — about 400 kilometres up — and once assembled, would beam a focussed laser beam back to a generating system on earth. The basic technology needed to convert solar energy into a focussed laser beam is smaller than a kitchen table. A prototype of this type of laser was tested at the Lawrence Livermore National Laboratory in the United States in 2002, and a working model is under production.

The key thing about such satellites is how small and cheap they would be. Each one would weigh about 10 tons, and cost as little as $500 million. (Yes, this is "little" in space terms — the average space shuttle flight cost anywhere from 1.2 to 1.5 billion dollars. From 1971 to 2010 a total of $173 billion dollars was spent on the space shuttle programme. Of course, the US Department of Defence spends four times that much every year.) Such satellites could be launched by a single rocket, and made to self-assemble.

The International Space Station is equipped with solar panels that both capture energy from the sun as well as that reflected back by the Earth.

The problems, though, are also obvious. Imagine a laser-beaming satellite in space! Actually, you don't have to; Hollywood already did that with the James Bond movie Die Another Day, where a satellite called Icarus trained an enormously powerful laser to cut through icebergs and trigger off all the mines in the Demilitarised Zone between North and South Korea. Of course, such a powerful laser would be next to impossible to build in real life, and the smaller lasers would often be blocked by clouds or other atmospheric matter. Even if you had groups of such lasers, their effectiveness would be uneven and limited.

A more powerful space-based solution would be a satellite that converted sunlight into microwave radiation and beamed it down to the Earth. Microwave radiation cannot be blocked by clouds and would therefore not be affected by the weather, but building such a satellite would be a massive task. Such a satellite would weigh close to 100,000 tons, and have to be placed in geostationary orbit 35,000 kilometres above earth. (In comparison, the International Space Station is in on a low-Earth orbit at about 420 kilometres. Its construction began in 1998 and is still not complete.)

Nevertheless if you can imagine it, somebody is bound to try and make it, and in this case it is the Japanese who are on the go, or more specifically, the Japan Aerospace Exploration Agency (JAXA). Not only does JAXA plan on building such a satellite over the next 25 years, it is also building a three-kilometre man-made island to receive the microwave radiation in a safe manner.

The bill will be, no doubt, astronomical, but it will be the engineering to create the huge solar arrays kilometres in length, or free-floating mirrors flying in sequence, that will determine success or failure. Breakthroughs, such as the origami-style folding of solar panels by Brian Tease at NASA, are slowly turning this dream into an achievable reality. Hopefully, India, with one of the most cost-efficient space programs in the world, will also be involved. Maybe then the dour experts that manage our world would finally allow themselves an optimistic smile.

 
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