1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Sunlight Intensity Concentrator - Idea to boost solar energy

  1. Apr 16, 2015 #1
    So I had this idea and I want to run it by some people and see if it's 1) possible 2) worthy of pursuing further 3) a good idea. I don't have a degree in engineering or physics, I'm currently studying chemistry and am taking physics 2 (E&M) right now, so excuse me if I don't use the correct language or formalities. Now for the idea-

    Since the sun's EM wave intensity is lost as the inverse square root of the distance to earth, only a very small fraction of it reaches us. We can dramatically increase this by putting a device close to the sun that focuses the intensity it "collects" into a narrow beam. Optimally this narrow beam will not lose any intensity over the long distance it travels to the earth. Now we have greatly increased the power the sun gives off that actually arrives at the earth.

    I have quickly sketched the overview and made a few calculations, which I attached. Some assumptions I made-
    -The concentrator will be placed 1 km from the sun, but only now I realize that any man-made device will probably not function in those kinds of temperatures. Having the concentrator in Mercury's orbit would not be worth it.
    -The power the sun gives off is 3.8e26 W. This is the value wikipedia gave for solar luminosity. I assume solar luminosity means power output

    If all my calculations and assumptions are correct we should be able to boost the power earth receives from the sun by 1.76e12%. This should boost all solar power we currently have (assuming 15% efficient devices) by 2.64e11%.

    Let me know what yall think
     

    Attached Files:

  2. jcsd
  3. Apr 16, 2015 #2
    It might be possible from an engineering point of view, but you wouldn't want one of those big mirrors going a bit adrift and frying a large city somewhere.
     
  4. Apr 16, 2015 #3

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    You would have to build something like a Dyson sphere to fully use the power of the sun. And it is impossible to focus all the sunlight on a spot as small as earth (not that it would be advisable anyway - it would fry everything in seconds).

    Systems closer to the sun have many additional problems - as an example, their orbital period won't be one year, so they do not stay aligned where you need them.
    Giant lenses are completely impractical and large mirrors are problematic as well. And you would need really gigantic structures to get a notable result.
     
  5. Apr 16, 2015 #4

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    What would be the point? There is no shortage of surface area on Earth, to put solar energy harvesting schemes. It's the cheapest place to build and maintain equipment. Space launches are (and will be, probably always) hideously expensive. How many kW does each member of the Earth's population need? That's the bottom line.
     
  6. Apr 16, 2015 #5
    I'm not saying we have to harvest every last bit of power the sun gives off, just a 100 sq meter portion of it. As for frying cities, would there not be a way to have a satellite closer to earth, splitting the energy up to a few other satellites and so on until it is reasonable to shot the power down to earth? As for the orbital problems put two devices on opposite sides of the sun. I guess my idea is kind of like a dyson swarm, but it's just one solider out of the whole army. And I guess it depends what you call gigantic. I assumed a device with an area of 100 sq meters.

    Would it be more cost effective to cover the earth in solar panels or to make one 100 sq meter solar panelish device to launch into space? It can't be that expensive to launch something into space, people do it at my school all the time. And there might not be a shortage of surface area on earth, but we could drastically improve the energy per area on earth (right now were getting about 13 W/m^2 when we could be getting 3e19 W/m^2!).
     
    Last edited: Apr 16, 2015
  7. Apr 16, 2015 #6

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    This only increases energy on the earth if you direct light that would otherwise miss the earth so that it hits it. For this to be significant, the size of the redirected area has to be comparable to the sun's surface area.
     
  8. Apr 16, 2015 #7

    russ_watters

    User Avatar

    Staff: Mentor

    Using mirrors to concentrate solar energy is already done on Earth, and plenty of people have proposed space-based collectors, so there isn't anything wrong with the idea conceptually. I don't see that it is necessary to locate a collector so near the sun, though.
     
  9. Apr 16, 2015 #8

    russ_watters

    User Avatar

    Staff: Mentor

    I'm not following your logic. Could you explain another way?
     
  10. Apr 17, 2015 #9

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    Redistributing the light that hits earth would help as well - you increase the radiation that hits your photovoltaic cells and reduce the radiation that hits the ground somewhere else.
    That is better done with things close to earth, however. Still, the very expensive space launches make that impractical for now. New ways to get to space (especially non-rocket launches) could change that picture.
     
  11. Apr 17, 2015 #10

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    I'm not sure where those figures come from. For a 100msq receiver to be close enough to the Sun to receive the same amount of Power that the Earth gets, it would need to be so close that it would fry, even if it reflected most of the received power. But who needs a whole hemisphere's worth of solar power?
    I looked at this link to get an idea of the cost of launching stuff just into low earth orbit and it's about 20k USD per kilogram. Your school is clearly a wealthy establishment if they really are having regular space launches. When you consider the cost of ground based solar cells, for the same price, you could get yourself an average of at least 10kW - and that ignores the cost of the space borne equipment, the control system etc etc.
    Any worthwhile engineering project has to address an actual requirement and you need to ask whether the system you propose would actually be needed. The sums can tell you the available power for a given space borne system (with a lot of speculative arm waving) but, until we are seriously pushed for available ground based solar sources, it is just not worth it, imo.
    Looking way into the future, there could be a case for considering how to get useful solar energy at great distances from the Sun, where the solar constant is a lot lower than 1kW/sqm. That could probably involve some massive reflector system.
     
  12. Apr 17, 2015 #11

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    Look at the sun. That's the light that is hitting your eye. If you place a small (with respect to the sun's disk) lens near the sun, it can rearrange the image of the sun, but it can't create any more light. The only way you get more light is by redirecting light that otherwise wouldn't hit your eye so that it hits your eye.

    We're used to thinking about magnifying glasses, but the properties of a lens near the target don't give us insight on the properties of a lens near the source.
     
  13. Apr 17, 2015 #12

    russ_watters

    User Avatar

    Staff: Mentor

    Ah, a lens between us and the sun - I was envisioning a mirror next to the sun (I suspect others were too). But looking at the drawing (I hadn't before), it looks more like what you describe. In that case, I agree with your analysis.
     
  14. Apr 17, 2015 #13
    I never did say anything about a mirror, I don't know where that idea originated. I'm thinking more along the lines of capturing the energy of the expanding sphere of sunlight before it dissipates to much. If you imagine the wavefronts of my drawing in 3-D you see how the closer we get the more sunlight will hit a piece of area.

    A good analogy would be an oil spill. You want to collect all the oil as soon as possible before it spreads out. By having an "oil sponge" close to the site of spillage you will collect more oil than if your "oil sponge" was further away.
     
    Last edited: Apr 17, 2015
  15. Apr 17, 2015 #14

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    I think most people on PF know about the Inverse Square Law. What you seem to be ignoring is that an area of 100msq, close enough to be picking the equivalent power that the Earth gets at its 150M km distance would be totally roasted. At least a mirror would be the most efficient way of redirecting the light and, hence, would roast slightly less.
    You are too fixated on your basic idea to see where it becomes impracticable, too expensive and probably not required.
     
  16. Apr 17, 2015 #15

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    Such an area does not exist at all. We have 1kW/m^2 at earth (a bit more, but we have atmospheric extinction in both cases). The surface of sun is at a radius of 0.0046 AU, you would need an area of 2750 km2 directly at its surface to get the same power as the whole power earth receives. And even then you would need some active components as passive lenses or mirrors cannot focus every light emitted from this area onto earth.

    A lens between sun and earth does not help - you cannot reduce the phase space of sunlight, and light is emitted in all directions.


    Frequent space launches? There are about 90 of them per year world-wide, and they cost tens of millions of dollars for a few tons of payload to low earth orbit. Sending stuff to interplanetary space is a factor 3-4 more expensive.
     
  17. Apr 17, 2015 #16

    russ_watters

    User Avatar

    Staff: Mentor

    Sorry....I assumed you meant a mirror because a mirror would work (and has been proposed before), whereas your idea really wouldn't.
     
  18. Apr 17, 2015 #17
    It's crazy because the Earth already intercepts far more energy than it (we) could ever use. The money spent on this would be better spent on increasing efficiency in PV. Also, the 'death ray' scenario that others upthread have noted is not a small thing. If this solar concentrator ever impinged directly on the Earth, it would wipe out all life it impinged upon.
     
  19. Apr 17, 2015 #18

    russ_watters

    User Avatar

    Staff: Mentor

    Yes, you are right: a mirror solar concentrator isn't thought of as a great idea either due to the "death ray" issue and launch costs.
     
  20. Apr 19, 2015 #19
    Where's this figure from?
     
  21. Apr 19, 2015 #20
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Sunlight Intensity Concentrator - Idea to boost solar energy
Loading...