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Solar Power Transmission

Solar Power Transmission

The idea of having a space station that beams down solar energy to earth has been a popular topic in many sci-fi communities, but it may not be fiction for much longer. Officials in the US and Japanese government have begun funding research into the creation of real space-based solar power stations.

In Japan, the space solar power system (SSPS) and the Japan Aerospace Exploration Agency (JAXA) are currently working together with 16 other companies (including Mitsubishi) on a geostationary solar space station. The station would collect the solar energy by way of photovoltaic cells and then transmit this energy to earth via laser or microwave form. This would then be converted into electricity for commercial power grids or stored energy as hydrogen. This space station could potentially transmit one gigawatt of energy to earth – equivalent to the output of a large nuclear plant [Source: Scientific American]. The US, along with the small island nation of Palau, also are working in conjunction to create an orbital solar power station and are planning to erect a “rectifying antenna,” to demonstrate the effectiveness of this technology. The antenna would be 260 feet in diameter and would be set up to collect 1 MW, enough energy to power over 1,000 homes, from a satellite orbiting some 300 miles above [Source: Treehugger].

How it Works
There are three parts to the solar space station:
1. solar cells or heat engines to collect energy
2. microwave or lasers to transmit energy to earth
3. rectennas (rectifying antennas) to collect the energy and distribute the energy on earth.

Most of the countries have opted for photovoltaic cells in order to collect th energy from the sun. One of the greatest advantages of having these cells out in space is that they can collect energy all the time. In space, the sun’s rays are never compromised by clouds or increment weather like on earth. Therefore, these stations can collect 144% more energy than any terrestrial solar panels [Source: Wikipedia]. Of course, there needs to be a a way to transmit this energy wirelessly, since having cables from space to earth is impractical. Japan has opted for laser transmission. The lasers use plates built from a ceramic material containing chromium, which absorbs sunlight and neodymium, which converts it into laser beams. These new lasers outperformed earlier demonstrating a solar-to-laser energy conversion efficiency of 42% [Source: Treehugger]. On the other hand, many other countries have opted for microwave transmission. In fact, with the use of a rectifying antenna, the microwave-to-electricity conversion is about 90% [Source: Wikipedia], making it much more efficient than lasers.

Problems and Solutions
Of course with any new technological advances, there are always downfalls. One of the major downfalls of building a space solar power station is the huge cost and space to make the technology work. With a rough estimation of $21 billion, this could be one of the most expensive alternative energy sources. The money would go towards “thin-film condenser mirrors, solar panels and a microwave transmitter…, as well as a 100-unit laser array of 5,000 metric tons that would be 10 kilometers long” [Source: Scientific American]. While the intial cost is expensive, Suzuki and his colleagues are aiming to produce stable, cheap power and hydrogen at a target price of 6.5 cents per kilowatt-hour, which is in-line with conventional power generation [Source: Scientific American]. And since the space station itself is in space, it will not suffer the effects of weather, making maintenance and upkeep much cheaper.

Of course, because it is in space, there are many extraterrestrial problems like meteroid or space junk collisions that could throw the station off course. This leads into another huge safety problem: stray microwave beams. While in theory 95% of the microwave radiation is directed towards the antenna, if it were to miss or become misdirected, these beams could affect nearby towns. While science says that these beams are 10 mW/cm2 -completely withing the OSHA workplace standard [Source: OSHA] – scientists and developers have introduced a fail-safe beam targeting by using a retrodirective phased array antenna. A “pilot” beam is directed towards the antenna which sets up the phase front. The antenna then compares the pilot beam’s phase front with an internal clock in order to control the phase of the outgoing signal. This centers the beam directly on the rectenna. If the pilot beam is lost for any reason (if the transmitting antenna is turned away from the rectenna, for example) the phase control value fails and the microwave power beam is automatically defocused [Source: Wikipedia].

While there is still a long way to go until the actual station is completed, the Japanese and US government expect a demonstration of the technology to reach completion in three to four years. Should the demonstration go successfully, space-based solar power stations may not be a thing of fiction after all.

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NASA
Jasmine Greene

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31 comments

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3:32PM PDT on May 28, 2011

This sounds like a really great idea and potentially help us produce huge quantities of green energy. A couple of things that concern me are the (green) cost of putting anything in to space (all those rocket motors) and what the effect might be of sening microwaves from space bearing huge amounts of electricity. I haven't studied physics since school but, as fae as I am aware, the only thing close to this is lightening which ceates ozone. Nothing is without cost but maybe we should be more aware of the real costs before signing up to this one!

7:07PM PDT on May 18, 2011

Spend some oil now to spend less in the future..

1:48PM PDT on Apr 1, 2011

Somebody has a better idea reported on by the Buckminster Fuller Insititute newsletter. Put a giant wind turbine on permanent magnet mounting on a retractable platform and send it up several miles to where winds blow perpetually.

1:44PM PDT on Apr 1, 2011

Mirror and magnifying glass used here on earth, not in outer space, sound safer.

1:44PM PDT on Apr 1, 2011

Microwaves and lasers from space sound like they are dangerous threats to the public health. this would be a violation of NEPA as are the nukes. Mirror and magnifying glass sound safer.

4:38AM PDT on Apr 5, 2010

This is a very interesting idea :) However, I'm not sure how I feel about having all this microwave energy beamed down around us...anyway, I really hope that this is something the scientists take into consideration...but all in all, environmentally it's a really great idea!

4:37PM PST on Jan 25, 2010

thanks

7:37AM PST on Jan 7, 2010

Thanks!

10:59AM PST on Dec 16, 2009

Great post - Thanks.

4:47PM PST on Nov 22, 2009

This is very interesting say the least.

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