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Freeing Gases For Cheap Fuel Cells With Orbiting Laser Cannons (cont.)
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So far, Japanese laboratories have reported an energy efficiency of 16 percent in converting sunshine into hydrogen using visible light. But Mori's laser-oriented team now boasts of a more substantial 30 percent rate. But the satellite solar power boosters note the NASDA effort must still play catch up to match traditional space-based systems. The Space Studies Institute puts the bar at a steep 80 percent.
"We are now confident of being able to deliver to the electrical grid about 90 percent of the energy transmitted from a power satellite since that was demonstrated in real world systems 27 years ago. That is not to say that this is the only possible solution, it is one solution that is known to work. It MAY be possible that there will be other, economically superior, ones developed," writes Dr. Lee Valentine, Executive V.P. of the Princeton, N.J. think tank and space commercialization advocacy group.
"If…the conversion efficiency of the power beam to hydrogen is about 80 percent or so, and assuming the capital costs for the receiving structures are the same then they would be economically equivalent. The reasoning is as follows: The net conversion of transmission beam energy to grid electrical energy is about 90 percent and the conversion efficiency of electrical energy to hydrogen using the best present-day electrolytic cells is also about 90 percent...Ninety percent times 90 percent is about 80 percent, so an 80 percent conversion efficiency of beam energy to hydrogen would then be equivalent to the classic SSP microwave transmission followed by an hydrolysis step to produce hydrogen."
 | | TECH WEDNESDAY | | | | | | |  | Images |
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| NASDA diagram of the hydrogen production facility, using an orbiting laser to electrolyze the water.
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| A detailed diagram of NASDA's hydrogen-producing laser concept. Click to enlarge.
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|  | TODAY'S DISCUSSION | | | | | | |
And it's not clear that NASDA's idea conforms to other standards laid out for solar power satellites – that they should be environmentally benign and unusable as a weapon.
But Valentine notes, "There is another, minor, advantage that the photolytic system of hydrogen production has over direct electrical production. One is that the hydrogen production system provides an easy storage method to buffer the power outages caused by Earth's shadow falling on geostationary orbit. Those last up to about 25 minutes and occur daily for a few days twice yearly at the time of the equinoxes."
Tomlin Coggeshall, Vice President of the Hydrogen Energy Center, wasn't familiar with the specifics of the NASDA plan, but thinks that some other innovative idea, like using bacteria to break hydrogen out from compounds, could hold promise too. Nonetheless, Coggeshall wrote in an email that, "If it is feasible, our organization would approve of this method because it produces hydrogen renewably from solar power and water. I believe it is not too far-fetched (but it sounds expensive)."
But the "miserable science" of economics is as real as physics when it comes to erecting new energy infrastructures, and so some folks in the hydrogen crowd are watching the Japanese program skeptically, at least for now.
"It does sound far-fetched. I doubt it would be practical in the near term future, but it does sound interesting for large-scale hydrogen generation in the future," says Barbir.
Valentine doesn't think that day is too far off. The way he sees it, the moon and asteroids are waiting to be turned into power plant hardware, maybe even for hydrogen production to replace crude oil.
"The costs should not boggle the mind. Petroleum infrastructure on the Earth will cost about one trillion dollars over the next decade and will be useless for producing energy when the oil runs out," argues SSI's Valentine. "A similar investment in SSPs built of non-terrestrial materials would give us an inexhaustible energy source and open the universe for settlement, too."
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