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DIY Motorized Solar Tracking Using an MBED

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Tom Murphy
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Shady Business
Tom Murphy   7/23/2013 6:06:43 PM
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I wonder, instead of using the shade, wouldn't it have been better to simple put a light-absorbing filter over the photovoltaic cells?  The shade would shift in angle, exposing more of one cell than the other, while a filter would keep them even -- replicating Florida in Arizona. 

Caleb Kraft
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Re: Shady Business
Caleb Kraft   7/23/2013 6:15:44 PM
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The entire point was to make them uneven so that the array would shift to put them back in an even state. Without the shade, both panels reached saturation at all times. The shade gives a mechanical means of increasing the disparity between the two. 

Tom Murphy
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Re: Shady Business
Tom Murphy   7/23/2013 6:22:00 PM
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I know that's what he meant, Caleb, but I was confused by this part:

The MBED reads voltage from two small photovoltaic cells placed at right angles to each other. It rotates until the voltages on the two panels match. However, Davis found that this did not work in the Arizona sun as well as it did on his Florida workbench. The sun was too bright, and the difference between the panels was too minimal at any angle.

 

That made me wonder, if the Arizona sun was too bright, then why not make it less bright with a filtering lens? Wouldn't an opaque shade cast a longer and longer shadow as it tilts, thereby throwing off the direction more and more?  I'm not getting that part.

Caleb Kraft
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Re: Shady Business
Caleb Kraft   7/23/2013 6:54:29 PM
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Sorry, He was using a lightbulb on his workbench for testing which is much more directional than the sun (ar at least a smaller source in relation to the sensor)

Tom Murphy
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Re: Shady Business
Tom Murphy   7/23/2013 7:06:07 PM
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I get it. So the problem wasn't that the sun was brighter, but was more evenly distributed -- the distance from one side of the board wasn't any different from the other side. That makes sense. I'm still not sure how he keeps the increasing angle of the sun against the shade from increasingly throwing off the calibration, but I'll just accept the notion that he found a solution. Thanks!

Luis Sanchez
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This reminds me of my school project
Luis Sanchez   7/23/2013 11:59:13 PM
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We at school tried to do this almost same thing. But We were using a stepper motor and it was more of a simulation as we didn't have real solar panels. 

But, reading about this makes me question... how about using the same current that the solar panel yields as a measure or as the level to judge if the panel is receiving the light at the expected levels. Mmmm just by thinking on it I guess it would be more difficult as some variations are added to the system like the fact that the sunlight varies in the course of the day and also varies with the seasons. 

Thus, perhaps this is something to consider for using all that horse power in the MBED brain ... to make it able to get the weather info and from that define a range of sunlight intensity. Then wage that with some tables which model the expected intensity during the day and season and vuola! now you can spare some hardware and save some bucks! If it's mass produced then you'd be saving a lot of dollars man! 

There, first Feature Requirement for v 2.0 ;-)

Caleb Kraft
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Re: This reminds me of my school project
Caleb Kraft   7/24/2013 12:08:09 AM
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Yeah, a stray cloudy patch could put the system into a mode where it thought it was out of allignement (without some way to determine based on direction).


Some companies have abandoned flat panels because of these issues and gone to cylindrical ones with reflectors behind them. That is considerably more difficult in your home though.

Tom Murphy
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Re: This reminds me of my school project
Tom Murphy   7/24/2013 11:45:59 AM
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Good thoughts, Luis, and it made me think of another approach. Why not put a tube slightly greater than the diameter of the solar cell that would channel the maximum amount of sunlight when the tube is pointed directly at the sun? Then the rig could be calibrated to maintain the maximum voltage from the cell, which would keep it aimed at the sun.

Caleb Kraft
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Re: This reminds me of my school project
Caleb Kraft   7/24/2013 11:58:30 AM
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this is exactly what one company did recently. Instead of having rotating solar cells, they were cylindrical with a reflector below them that was also cylindrical. When done in a larger quantity this is much more efficient than rotating a flat panel (they claim). 

Here they are if you're curious. http://www.solyndra.com/technology-products/

wwbrown
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Re: This reminds me of my school project
wwbrown   7/24/2013 12:34:48 PM
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It is easy to calculate the position of the sun very accurately based on location and time.  I do not understand why an optimization algorithm is used when you could just calculate the position.  The MBED has an on board real time clock and the location could be input each time it was moved so a dedicated GOS unit on the tracker would not be required. 

An on GPS could easily be used if the designer thought the drift on the RTC was too great.  The location of the system could be read in from the GPS when started at a new location.  Measurements of the location could be read in for a pre-determined period and the location would then just be the average of those results, this would provide a better location.  Given the distances involved any location the GPS gave you would suffice anytime the GPS had a lock.

rick merritt
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Tracking the sun and star
rick merritt   7/24/2013 8:48:03 AM
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Now if Mike got together with the guy tracking satellites  (http://www.eetimes.com/author.asp?section_id=36&doc_id=1318979&)  they could collaborate on a system to track the sun and the stars ;-)

prabhakar_deosthali
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North-South tracking
prabhakar_deosthali   7/24/2013 10:34:29 AM
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The way the correction has been applied to rotate the panels to get maximum sunlight thruout the day, a similar correction can be done to track the sun's north south movement during the year. This is especially required for the regions which are away from the equatorial regions.

Caleb Kraft
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Re: North-South tracking
Caleb Kraft   7/24/2013 10:36:36 AM
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Indeed. He talked about that a little bit, stating that he didn't need it at this point.

It seems like a linear actuator on the taller end of the base would achieve this pretty easily. 

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