Author Topic: The other kind of heliostats...  (Read 1409 times)

Externet

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The other kind of heliostats...
« on: February 11, 2014, 02:27:05 PM »
Hi all.
As we know, we can instal one mirror, get one sun reflected to the spot we want to illuminate, or two or more mirrors aimed to that same spot for greater illumination intensity, or two or more mirrors for an expanded area.
Going to a parabolic mirror, the target spot gets smaller, concentrating much more light on the same spot.  It may become uncomfortably bright.

Heliostats means keeping the target illuminated while the sun travels on the sky.  If that is the objective, well, there is another way; by using a convex or more than one convex mirror to aim somewhat dimmer sunlight or several ĺayers of sunlight one on top of the other or stacked one above the other.
A single convex mirror yields less illumination intensity, but may get rid of tracking mechanisms to a good degree.  Several convex mirrors can add to the intensity or to the target area.

So. I will be ordering a 4' x 8 x 1/4" plastic mirror to play with, like these people do:
--->http://www.cleardomesolar.com/solareflexpanels.html

Using it single or cutting it to yield two stacked 2' x 8' could be interesting.  The curvature to which the mirror be flexed, will define the target bandwidth spread and the sun angle-hours that will work without tracking.
I see it as a cheaper alternative, not much risk of breaking it, unpowered, no failprone mechanism$, no need for post, bearings.
Please let me know your experienced pros and cons of what I will be missing here, like spraying some protective backcoating.

Now, what if by the nobility of plastic, it could be somewhat flexed both vertically and horizontally, like a section of a bubble face ?
OR :  using something like this instead : ---> http://shard3.1stdibs.us.com/archivesD/upload/8880/30/XXX_8880_1269871137_1.jpg
For the purpose of mild, large illuminated area with no tracking ?


Gabriel

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Re: The other kind of heliostats...
« Reply #1 on: February 14, 2014, 07:42:54 AM »
That is actually a cool idea. I hadn't seen this one before. You wouldn't get much heat energy from it since most of the reflected light doesn't make it in the window, but sunlight has a lot of, well, light in it so it should still do a decent job of illuminating a room.

 I guess the amount of energy you would get depends a lot on the size of the window, but I would estimate that the window in the picture is probably receiving less than 20% of the total energy that would be available from the midday sun to a surface that size, assuming the window if facing north.

I'm not so sure about the "bubble face" idea. Yes you could technically illuminate a larger area, but at that point the light would be so spread out that I don't think it would do much significant lighting, at least not to justify the expense of the reflector.

 


Externet

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Re: The other kind of heliostats...
« Reply #2 on: February 14, 2014, 10:26:20 AM »
Hello.
Heliostats can have two purposes; illuminating or heating.
The convex approach would not be for heating, obviously.  Heating would take more than one mirror aimed to the same spot.

It will take me a while to figure out a formula with the parameters for target distance, convex mirror radius, 'bubble' arc, span of lighted band, and number of hours of exposure it would yield without tracking.
Will be back at some point with whatever I come up with.

The evolution from bending the convex mirror on a single axis ---> to bending in two axis ---> to single 'bubble'  ---> to multiple 'bubbles' ---> may end as a satin flat mirror; as a sanded sheet of aluminium or stainless.   Sort of what photographers use for uniform illumination, that reflective satin umbrella.
That should provide a softer illumination to an entire north side wall without beaming an uncomfortable intense lightspot from the sun into a window.

Gabriel

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Re: The other kind of heliostats...
« Reply #3 on: February 18, 2014, 07:57:55 PM »
It would definitely be interesting to see the formula once you have it worked out!