Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Energy from space?

  1. Jun 14, 2009 #1
    Why can't we seek to develop a mean to with draw energy from outerspace? Using solar.. Neuclar or other sources and transfer that power back via something similar to what's proposed for "the space elevator"?
     
  2. jcsd
  3. Jun 14, 2009 #2

    russ_watters

    User Avatar

    Staff: Mentor

    That's a jumbled mess of unrelated ideas there....

    Short answer, though - people are seeking to develop solar energ!
     
  4. Jun 14, 2009 #3

    Nabeshin

    User Avatar
    Science Advisor

    The only one of these that makes sense is the solar power idea. Obviously a solar power station in space would receive the sun's rays in full force 24 hours a day. There's no advantage to nuclear power in space, really, except that the waste would already be in space...

    The main reason we don't have a solar panel farm is that it's still quite expensive to put things in space. And, like you said, we need a mechanism to transit the power to Earth, and without something akin to a space elevator, we don't have a good way to do that either.
     
  5. Jun 19, 2009 #4
    Microwaves can do the job just fine. The problem is convincing nervous Nellies that it's safe to do so.
     
  6. Jun 19, 2009 #5

    Wallace

    User Avatar
    Science Advisor

    The energy required to actually put solar panels in orbit would never ever get repayed over the usefull life of said solar panels, so this is not a practial means of generating energy, regardless of how you want to get the energy they do produce back to Earth.

    Even with a space elevator, the economics of putting solar panels in space is dubios to say the least.
     
  7. Jun 19, 2009 #6
    Wallace, innumeracy is the cause of many ills and silly arguments. Current solar power satellite plans call for arrays with a mass-to-power-received density of between 500-4000 W/kg. To get to orbit via chemical rocket requires about 4 times the energy of the payload mass being in orbit, which is about 30 MJ/kg. Thus the payload needs to return ~120 MJ/kg to pay for getting it to orbit in energy terms. How long does that take? At 500 W it takes 120,000 kJ/0.5 kJ/s = 240,000 seconds. For the other case it takes 120,000 kJ/4 kJ/s = 30,000 seconds.

    Thus you're quite in error. Assuming a 15-30 year lifespan you're out by a factor of ~15,800 - 32,000.
     
  8. Jun 19, 2009 #7

    Wallace

    User Avatar
    Science Advisor

    I wish you were my accountant ;) You are forgetting much of the total energy budget, including the manufacturing costs (in terms of energy) of the solar cells in the first place, as well as the full costs of manufacturing and mantaining whatever you are using to get them into orbit. Present day solar cells barely pay themselves off (at least the high end ones in terms of efficiency) in terms of their production costs to lifetime energy generation. Plus, even if a design calls for a specific W/Kg ratio, the question is whether that is realistic or not.
     
  9. Jun 20, 2009 #8

    Chronos

    User Avatar
    Science Advisor
    Gold Member

    Assumes facts not in evidence, Wallace. Constructing a space elevator is doable. Devisng a cheap method for manufacturing nanotube fibers is the only issue. They used to say the same thing about computer chips. Extracting energy from 'empty' space, on the other hand, is impossible.
     
    Last edited: Jun 20, 2009
  10. Jun 20, 2009 #9
    Wallace, manufacturing anything requires energy. Make a fair comparison. Besides the embodied energy of an ultralight space PV array will be rather low compared to the energy cost of orbitting it. But there's another advantage that space-based systems have - continuous exposure to the power-source means a system in space collects, when bad weather and the seasons are factored in, at least 4.8 times what is collected on Earth and 8-12 times more versus higher latitude sites. Plus solar concentrators can be used minimising the energy cost of making PV cells.

    As for the old saw that terrestrial solar systems don't return their embodied energy... it's old oil-industry truism. The most recent analysis I saw claimed an energy return of 5-10 times in high latitudes and even more so in sunnier climes. The return is much, much higher for concentrator arrays.

    So next time you make ill-informed claims do some research.

    BTW I'm actually pro-nuclear power myself, if you're wondering. Usually I hear the old propaganda anti-solar lines from pro-nukers who want to discredit renewables, so your claim sounded familiar. Solar power is, of course, using the only working fusion reactor we have - the Sun - and thus being anti-nuclear is kind of idiotic. Of course, to be really renewable nuclear fuels would need to come from the sea and we'd need to use high efficiency fission power cycles to maximise energy extracted and minimise the waste quantity and storage time. Thus it's not inconsistent to be pro-nuclear but anti-enriched uranium fuel-cycles - the most waste-full nuclear cycle of all. But I'm happy for them to be used as a precursor leading up to burning up the waste in better fuel cycles.
     
  11. Jun 20, 2009 #10
    thank you for you'r sarcasim! It was simpley a question I had in my mind and through no help from you I got a reasoniable answer ! so again thank you sir!
     
  12. Jun 20, 2009 #11

    russ_watters

    User Avatar

    Staff: Mentor

    You're quite welcome, though you apparently still need some help with the concept of sarcasm, as there wasn't any in that post....(You may detect some in this post, though.)

    I was hoping my post would prompt you to reword your question into something that made more sense. Perhaps I could have added "could you rephrase the question" to the end, there, but I guess I figured it was implied.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Energy from space?
  1. Pictures from Space (Replies: 7)

Loading...