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Concentrated solar power plants use reflecting surfaces to gather the sun rays for energy production.

enter image description here

Currently they sit idle at night and are not used for anything.

These have huge collection areas, so I'm wondering why are they not used at night for astronomical observations of some type?

Depending on the reflector type it can be as simple as raising a radio antenna on top of the tower.

Pros:

  • They already able to track celestial bodies in the sky.
  • They already build. So extending them for a scientific use would cost a fraction of the cost compared to building a new radio array.
  • They are huge.

enter image description here

Cons:

  • Limited Frequency Range

I have always been fascinated by the ability of astronomers to extract information from a couple of pixels of data. So I think that this idea can be beneficial to the scientific community.

What do you think? Am I missing something obvious that makes this impractical?

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    $\begingroup$ "Am I missing something obvious that makes this impractical?" Yes, pointing precision. If you'd observe one star with this array, there's no way you would recieve it as a point source. By design, all mirrors cannot be pointing at exactly one point in the calorimeter, lest it overheats. Besides, modern astronomical mirrors have insane standards of surface flatness, which those mirrors surely don't adhere to. Also you can't raise an antenna on top to do optical observations. $\endgroup$
    – AtmosphericPrisonEscape
    Commented Feb 23, 2022 at 14:41
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    $\begingroup$ The mirrors are flat, so they can't focus an image (even the ones that aren't flat, aren't optical quality parabolic). So even if you did manage to coordinate all of them accurately enough to focus one star on a pixel of a sensor, all of the rest of the image would be out of focus and interfere with the one pixel that was in focus. The Sun isn't a point source, so there's a lot of margin for error in the optical surface, and pointing accuracy. $\endgroup$
    – Greg Miller
    Commented Feb 23, 2022 at 15:13
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    $\begingroup$ @AtmosphericPrisonEscape I think you missed the point of the question. The OP already mentioned radio astronomy but perhaps you decided to comment too quickly without reading carefully? This arrangement can also be used to collect photons from cosmic ray showers. What it lacks in precision it makes up for in sheer size. If one of these was freely available I'm sure some observational astronomer(s) would put something on the tower and try to see if they could get some radio or cosmic ray shower data with low spatial resolution. $\endgroup$
    – uhoh
    Commented Feb 24, 2022 at 0:49
  • $\begingroup$ @GregMiller ditto. Since the mirrors are independently movable, it could collect from a larger area than the Sun, concentrating different areas of the sky on to different segments of the tower. The number of possible configurations is... astronomical! $\endgroup$
    – uhoh
    Commented Feb 24, 2022 at 0:50
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    $\begingroup$ An interesting night-time use of solar mirrors: Margaret by Moonlight. $\endgroup$
    – PM 2Ring
    Commented Feb 24, 2022 at 8:58

2 Answers 2

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Probably the most interesting thing that could be done is some kind of transient search in a small part of sky, like the "collect photons from cosmic ray showers" idea suggested by @uhoh's comment. The mirrors are optimized for optical light, so you could collect a highly amplified signal of a Sun-sized patch of sky, perhaps at a fast sampling rate, and look for cosmic ray effects within the atmosphere, or any other transient signal out in the Universe.

As mentioned in @Greg Miller's comment, the mirrors would have to be aligned to very high precision to produce an image, and it would be low quality. The only advantage would be the large collecting area.

The original question compares the solar concentrator to a radio array. There are a couple key differences:

  • The mirrors are optimized for visible light (where most of the Sun's energy is in the spectrum). At radio wavelengths, they may not reflect well.
  • In a radio interferometer array, each array element is a single dish and receiver. The signals from the receivers are correlated and combined digitally. The solar concetrator mirrors are the wrong shape for each one to focus onto its own receiver. Also, a significant part of the array cost is the receiver and correlator hardware.

If the mirror surfaces were good radio reflectors, the solar concentrator could serve as a crude single-dish radio telescope (think Aricebo). But with the flat collector shape, in addition to any individual mirror surface defects, the resulting telescope would not be able to measure polarization. So it would not be as good as regular dish-shaped radio telescopes.

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    $\begingroup$ Nice answer. I am surprised no one suggested using it as a day time solar telescope. Presumably, the operator must closely monitor temperatures and heat flows. Could this data be used somehow to measure solar activity? To me, these things look like giant bolometers. $\endgroup$
    – Connor Garcia ♦
    Commented Mar 7, 2022 at 23:35
  • $\begingroup$ @Conor Garcia - The advantages of telescopes are light-collecting power and angular resolution. But these collectors can't form a good image, and the Sun is such a bright target that smaller telescopes already collect plenty of signal. $\endgroup$
    – giardia
    Commented Mar 8, 2022 at 13:05
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Cosmic ray Cerenkov collection won’t work- it works physically, but the data would turn out useless.

The Sun is a single, small source, and so generating power, not signal, implies a single, small target (the receiver). Cerenkov observatories triangulate the cosmic ray, which might appear anywhere in a given sky patch. Using a single-transmit, single-receive geometry to study cosmic rays would be 1) grossly inefficient in ray collection, due to small observed patch, and 2) unable to triangulate substantially, to determine the ray properties.

You don’t shave with a sword, nor do you reap with a scalpel.

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