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Gadget Freak Case #217: Finding the Sun With a Microcontroller

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Droid
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Has the sun gone wobbly?
Droid   6/25/2012 9:47:10 AM
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This is really cool. However, since when did the position of the sun become unpredictable requiring us to "find" it. By the way - you could also look up "fearlessthinker" on youtube.  He has built a similar sun tracker.

ervin0072002
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Gold
Re: Solar tracker
ervin0072002   6/25/2012 9:55:48 AM
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Hm NREL.GOV has a C source code available to the public to track the sun using time stamp and a single microcontroller. The only problem is the feedback loop. LVDT's or RVDT's can get expensive so it might be simpler to have an array of 10cent phototransistors with a microcontroller I don't know? And have a direct feedback loop between light intensity and position of sensor (assuming that sensor is in the same plane as your collector (dish or trough is fine). as to this being a non-problem I disagree. Current systems (reflector and aim mechanism) are way too expensive. It is roughly 200% of the current competing costs. It's hard to invest in solar because of the initial investment. I think cheaper ways to solve this problem are always a big plus.

John E
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Silver
Not very simple
John E   6/25/2012 11:10:10 AM
The solar trackers that I have seen all had a much simpler tracking system.  The rough aiming was done with a simple timer and the fine control done with 4 photodiodes placed in the sided of an x shaped metal or plastic extrusion that extended 3or 4 inched outward, and shaded the diodes that were pointed fathest away from the sun.  The tracker moved towards whichever diode had the most light on it.  This was all done with analog circuitry. 

78RPM
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Gold
Re: Solar tracker
78RPM   6/25/2012 11:26:12 AM
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The position of the sun is not as simple a problem as you might think. Go to www.analemma.com as a start.  Did you know that the longest day of the year has neither the earliest sunrise nor the latest sunset? For your learning fun, just browse for "Solar Position." It is tempting to say our collecter position is close and that's good enough, but in this day when engineers try to get energy efficiency on the order of microwatts, we want all the energy we can attain.  I hope the other suggested uses for the multiplexing project do not get lost in the discussion.

Jerald Cogswell

kf2qd
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Platinum
A question of efficiency
kf2qd   6/25/2012 12:21:53 PM
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I have thought about a solar tracker - say you have a day when it starts out sunny, but gets heavy overcast. Do you keep tracking, hoping for sun, or do you shut down your tracker because there isn't enough power coming off the panel to replace wha the tracker uses? Or the day starts off cloudy and the sun comes out at noon. If 2 of these days some in sequence it was cheaper to quit tracking when the sun faded, and start tracking when the sun reached some minimum intensity.

 

For solar power you really need to consider the total power budget of every component. If a given component uses too much power, and a tracker running when there is no sun is a total waste of power, then it means you won't have power for other, possibly more important uses. If I don't run the tracker on a day with no sun, I have power for lights that night so a disabled resident can see their way to the restroom.

 

So - on a day with plenty of sun, solar tracking is a plus. An a day with no sun, tracking the "non-existant" sun is a total loss.

78RPM
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Gold
Re: A question of efficiency
78RPM   6/25/2012 1:01:12 PM
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to kf2qd, I agree that the MCU program should include inputs and logic to stop tracking when the sun is dim. BTW, I've messaged the editor to include my source code in the link. There should also be a hysteresis in searching, i.e., consider letting the MCU and motors sleep for 2 or 3 minutes before making a correction. Hysteresis is more important for a small collector than a big array. And let's remember that not all collectors are flat panels. If we use a parabolic channel to focus light along a pipe, we need high aiming accuracy -- and we need to stop tracking when ambient conditions or temperature say it's a waste of energy.

Jerald Cogswell

herbissimus
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Silver
non electrical tracking solution
herbissimus   6/25/2012 1:43:53 PM
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zomeworks, a company in new mexico has a totally non electrical solution to the tracking problem thats quite popular with cattle ranchers with desert watering holes that uses 2 canisters of freon (or similar) connected with piping so that when the panels shade one it becomes heavier tilting the panels appropriately. there's lots of ways to skin this cat !

http://www.zomeworks.com/photovoltaic-tracking-racks/

Rob Spiegel
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Blogger
Re: A question of efficiency
Rob Spiegel   6/25/2012 2:58:30 PM
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Just to let everyone know, the source code will soon be posted. 

Gregarious2
User Rank
Iron
Re: Not very simple
Gregarious2   6/25/2012 5:58:22 PM
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I've used the quad cell method ( both analog and digital ) with concentrator systems and it works quite well as part of a servoed tracker. Digital was a bit easier to cope with the sun behind clouds, sunset vs sunrise positions, etc... conditions. Hamamatsu once sold a photodetector array ( S9132  ) that output XY position of a bright spot using an on board row column multiplexer scheme. You clocked the chip and looked for maxval on the x and y data streams. I think it was under $30.

One thing I've noticed here in Hawai'i with a huge boom on PV systems. ( we currently pay .45 / kwh ) Most of the installers seem to go for aesthetics rather than efficiency. Driving through any neighborhood, you will see most PV arrays are flat to the roof pitch  in whatever direction the house is pointed. The lucky folks face south.

78RPM
User Rank
Gold
Re: Not very simple
78RPM   6/25/2012 6:49:00 PM
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Hi, Gregarious2.  Aloha, Brah. I lived in Hawaii for 22 years.

It's fun to see people think of all the alternative solutions. There is no one right way. It depends upon your application and design goals.

My problem with analog quad cell was that the motors were constantly being nagged, "this way; oops cloud; this way." The MCU could be programmed with some hysteresis / forgiveness and sleep to save energy. Again, if you are using a parabolic channel to focus along a water pipe, you need high accuracy. In Hawaii, you have solar power to waste. Here in Montana we want that boy aimed as accurately as we can.

Hey, Dudes: anybody want to comment about applications for multiplexing apart from the solar application?

Jerald Cogswell

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