Solar tracking without an optical tracker

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jwax
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Post by jwax » Tue Dec 30, 2008 2:53 am

If I recall my amateur astronomy days, you only need to track with one motor to cancel the earths rotation, right? It will need tweeks during the year to keep the declination angle pointed at the sun, but tracking the sun on any given day only needs one drive motor, right?

haklesup- That is an amazing piece of hardware! Talk about a navigational aid! :smile:

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dacflyer
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Post by dacflyer » Tue Dec 30, 2008 7:12 am

basically yes, my solar tracker uses only 1 motor.
its a modified c-band satalite dish. you could use a 2nd motor to automatically adjust for tilt suring the year, but daily tracking just needs 1 motor..
i use a sun sensor from red rock energy, they have several moduals to choose from . ready made or in kit form, your choice.. i went for the kit, it was cheaper. but if i had to do it again. i'd spend a few more bucks for the ready made modual. the kit has very specific instructions, because the kit us very compact, parts are covering other parts. and solidering is very tight quarters.
but other then that its a very good kit.

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haklesup
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Post by haklesup » Tue Dec 30, 2008 11:31 am

Very timely discussion. Not more than half a day after I made comments about using GPS to track the sun I saw an example of the Science Channel last night. He is doing exactly what I was talking about (I never thought my comments were original but its nice to see I was making common sense)

This guy also invented a low cost plastic parabolic dish that may be worth looking into.

http://science.discovery.com/tv/ecopolis/ecopolis.html

See the "Harvesting Sunlight" video link on the right side of this page
http://science.discovery.com/video/ecopolis.html

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Forrest Mims III
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Post by Forrest Mims III » Thu Jan 01, 2009 9:16 am

MrAl,

You asked if the microcontroller method might be overkill.

Seems to me that simpler is better, but arguments can be made that either optical tracking or a microcontroller is simpler.

Perhaps I'm biased:

1. When taking various sunlight instruments to remote locations, I have to initiate them with a GPS or a keyboard. This provides the coordinates so the instruments knows the location of the sun. An optical tracker would simplify this process.

2. As I noted above, the sun is not necessarily the brightest object in the sky when clouds are blocking it. An optical tracker would correct for this. While this would enhance the output of the solar panel, the increase would be small.

This is an interesting question, and it would be good to hear from others who have built sun trackers.

Forrest

Forrest M. Mims III
www.forrestmims.org
www.sunandsky.org
www.twitter.com/fmims

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MrAl
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Post by MrAl » Fri Jan 02, 2009 9:17 am

Hi again Mr. Mims,


Oh yeah i see what you mean about the microcontroller initialization.
That would make setup a little more involved. I guess if it all worked
out this process could be automated to some degree, but probably
not cost effective to build in a GPS tracker (at least not in todays
marketplace).

Yes, it would be nice to hear from people who have actually built
a tracker and tested it over some period of time.

One other thing i wouldnt mind looking at is an algorithm for an
optical tracker. A question that comes up is does it always point
in the same direction, move with the panel, or can it search
the sky with it's own X-Y platform?
I ask this because i have to wonder if an optical sensor could
end up tracking the movement of the clouds and therefore get
'sidetracked' seeing only the western part of the sky when it
should be looking at the eastern part, or vice versa.
LEDs vs Bulbs, LEDs are winning.

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haklesup
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Post by haklesup » Fri Jan 02, 2009 1:15 pm

I think the Digital GPS based controller would mainly have an advantage if you were selling lots of them to randomly located customers. It would drastically reduce setup headaches for low cost systems in the hands of novice users as it has for telescopes.

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kheston
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Post by kheston » Sat Jan 03, 2009 11:33 am

Mr.Al,

I have the mechanism covered. I've salvaged two C-band dishes and the linear actuators that came with them. I think they have 12v steppers that even I can figure out how to control.

What I'm looking for is the best way to know my 8ft spun aluminum dish is pointed in the direction it needs to be pointed.
Kurt - SF Bay

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Externet
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Post by Externet » Wed Jan 07, 2009 2:49 pm

Hi.
Been away from the net for a while; getting to this thread somewhat late.

I did use an atomic clock receiver to drive the stepper motor to aim a mirror instead of using optical/photosensors. It may be of interest.

http://www.scienceforums.net/forum/show ... hp?t=26341

And had good suggestions in this thread about reading aiming position :

http://forum.servomagazine.com/viewtopi ... =heliostat


Miguel
- Abolish the deciBel ! -

rshayes
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Post by rshayes » Wed Jan 07, 2009 5:21 pm

I would suggest two solar cells, mounted back to back. Take the difference between the two photocurrents. This can be done by connecting the solar cells in parallel with one reversed with respect to the other (plus of first cell to minus of second cell; minus of first cell to plus of second cell. Connect one of the paralleled leads to ground and the other to a current amplifier, such as an op amp with a feed back resistor and only a small input resistor. Since the capacitance of the solar cells will be high, a capacitor across the feedback resistor will help stability.

When the sun is edge on to both cells, the output will be zero and the difference will be zero. If the sun moves to one side, the output of that cell will be greater, and the polarity of the output signal will indicate the direction of error. If the sun is on the other side, the polarity will reverse. This arrangement should be able to function over nearly 180 degrees.

Only one sensor would be needed for an equatorial mount (axis parallel to the earth's axis). An altazimuth mount would need two sensors, one for each axis.

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