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Is it possible to make sun light collimated in such a way, to increase energy density and keep it more less parallel?

like on the Earth we have intensity of sun approximately 1300 watt/m2. If we use some mirrors/lenses optical system, can we make it parallel (of course not ideal parallel) and increase density for example to 5000 watt/m2.

for example like shown in the pictures below enter image description here enter image description here

From other point there is this thing, which looks like makes it impossible https://en.wikipedia.org/wiki/Etendue#Conservation_of_etendue

or it is still possible and I did not understand Conservation of etendue correctly?

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    $\begingroup$ You could do this if sunlight was perfectly parallel, in which case the etendue would be zero - something that can not happen because of the wave nature of light and that does not happen because of the finite solid angle of the sun as seen from Earth. In reality the etendue of a beam of sunlight is a finite number and if you decrease the width of the beam, the angle will increase. Absolutely nothing stops you from reaching a power density of $5000W/m^2$, of course. Concentrated solar applications are often specified with 500x concentration! $\endgroup$
    – CuriousOne
    Commented May 20, 2016 at 9:07
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    $\begingroup$ It can't be done keeping the rays parallel, as you wrote, because of conservation of etendue. To put it simply, if you "smoosh" the rays together you will make them less parallel. For a nice discussion, read this: what-if.xkcd.com/145 $\endgroup$
    – valerio
    Commented May 20, 2016 at 9:20
  • $\begingroup$ But how etendue conservation correlates in case of point source and lens? If I have point source, I definitely can make parallel beam with lens, if point source in the focus. Of course in geometric optic approximation. $\endgroup$
    – Zlelik
    Commented May 22, 2016 at 11:03
  • $\begingroup$ Is it feasible to take 1m diameter parabolic mirror, make with extra lenses the beam 1cm diameter near this mirror and have it only 2cm in 100m distance? How usually can I solve this kind of task? Which formula and technic can I use? $\endgroup$
    – Zlelik
    Commented May 22, 2016 at 11:07
  • $\begingroup$ Looks like I understand about point source and etendue. If etendue dG=dSdSASomethingElse (dSA - solid angle), then for point source etendue is zero, because area dS is zero, and for parallel beam etendue is zero because Solid Angle is zero and this is why there is no any contradiction if we convert point source light to parallel beam. But if we use Optical Phase Conjugation (en.wikipedia.org/wiki/…) theoretically we can convert Sun light to the parallel beam. Or Optical Phase Conjugation is theoretical idea without real implementation? $\endgroup$
    – Zlelik
    Commented Jun 13, 2016 at 15:45

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So collimating sunlight to be exactly parallel seems difficult. but close enough for practical purposes might be possible. My idea is to have a large parabolic mirror with a hole in the center, then invert a much smaller parabolic mirror with focal points shared. it will give you a relatively straight beam back through the hole in the larger dish when the contraption is pointed directly at the sun. perhaps a lens can be made to compensate for the small angle difference in sunlight?

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  • $\begingroup$ If you have a new question, please ask it by clicking the Ask Question button. Include a link to this question if it helps provide context. - From Review $\endgroup$
    – Miyase
    Commented Oct 24, 2023 at 7:28

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