Backtracking algorithm for solar tracker

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Backtracking algorithm for solar tracker

Postby ajit.nayak87 » Mon Jan 06, 2014 6:34 pm

Dear all,

I am trying to do dual axis tracker with back tracking algorithm .Can someone share me list of formula envolved here
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Re: Backtracking algorithm for solar tracker

Postby Tracker » Tue Jan 07, 2014 1:27 pm

ajit.nayak87 wrote: dual axis tracker with back tracking algorithm


As the red-head would say... Please Explain.. ;)
Do you mean "return to start" , for the next day..

I would have thought that there would be no need for any algorithm, just a knowledge of where it is pointing at any one time, and then save the coordinates at a time just after it has locked on.. and return there, when first light is detected.. (assuming it parks at night - in case of bad weather)
(If you know what I mean) :oops:
..
.
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Re: Backtracking algorithm for solar tracker

Postby ajit.nayak87 » Tue Jan 07, 2014 2:11 pm

No . for your understanding http://www.suntrack.es/english/modelos4.html check this link.
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Re: Backtracking algorithm for solar tracker

Postby Tracker » Tue Jan 07, 2014 4:12 pm

..
It must be me... What is that saying..

Is backtracking, a means of going back to the AM start position, or is it a method of "Hunting" for the highest output..
..
.
Retired Engineer and keen PV experimenter - Always ready to learn and share.
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Governments won't save the world :-) They will just TAX it :-(
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Re: Backtracking algorithm for solar tracker

Postby ajit.nayak87 » Tue Jan 07, 2014 4:13 pm

Tracker wrote:..
It must be me... What is that saying..

Is backtracking, a means of going back to the AM start position, or is it a method of "Hunting" for the highest output..
..
.

it a method of "Hunting" for the highest output..
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Re: Backtracking algorithm for solar tracker

Postby Tracker » Wed Jan 08, 2014 5:53 am

ajit.nayak87 wrote:.......a method of "Hunting" for the highest output..


so, now that we understand the terminology, how does the existing control work.. one assumes that it is digitally controlled as you seek an algorithm..
I would have thought that most tracking was done by analogue control, by hunting for a max....

I don't know that you can believe the claims in that reference,.. was it a 9% claimed improvement..
consider that the claimed improvement of tracking over fixed is 30%..... I cant imangine how hunting a few degrees will add 9% ;)
Retired Engineer and keen PV experimenter - Always ready to learn and share.
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Re: Backtracking algorithm for solar tracker

Postby Warpspeed » Sun Jan 26, 2014 3:11 pm

Several (or many) degrees, error in directly pointing at the sun is not going to make any measurable difference to the collection of incident solar radiation.

Astronomers and celestial navigators have been doing this to extremely high precision since the age of sailing ships.

What you need is an equitorial mount with seasonally corrected elevation.
This seasonal correction only need be done a few times a year, by maybe moving an elevation locking pin to one of several alternative holes.
Then a single axis motor drive that would potentially rotate exactly 360 degrees in 24 hours.
It would ALWAYS be pointed directly at the sun, even when the Earth is in the way.
Not too difficult to interrupt that travel at a set hour around dusk, and get it to return to an anticipated set hour position somewhere around dawn, then start up the tracking motor at the appointed time.

You could track forwards for twelve hours, and reverse for twelve hours at the same speed would be the simplest.
But in summer there may be more than twelve hours of usable sun at very high latitudes.
Perhaps in such a case if the horizon is unobstructed, track for sixteen hours, then reverse at twice normal speed for eight hours, pretty easy to do with a small quartz driven stepper motor, and a very high ratio mechanical reduction.
Its not difficult, just requires some clear logical thinking and ingenuity.

The key to success is getting your single motor drive axis perfectly aligned with the earths actual rotation, which never changes.
To do this you only need to know your exact latitude and where true North is.

This "equatorial mount" and its motor drive can then be made a very rigid structure that never moves once correctly set up at a specific location. It would be sticking straight up vertical at the north or south pole, and be exactly horizontal with the ground right at the Equator, and always pointing exactly north/south. (In Melbourne it would be sloping up towards the south at 38 degrees)

The tilt of the earths axis requires the elevation of the panels with respect to the motor drive axis to be seasonally adjusted by plus and minus 22 degrees at summer and winter, and paralell with the drive axis spring and autumn. This small amount of correction, in practical terms, probably only need be made a very few times a year for our application.
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Re: Backtracking algorithm for solar tracker

Postby Privatteer » Mon Jan 27, 2014 3:19 am

The device I use is a lot more simplistic. 4 Photocells tilted and sensing strongest direction of light. Delay on east movement about 5 times that of west.
Its not perfect in high cloud but does a reasonable job.
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Re: Backtracking algorithm for solar tracker

Postby Warpspeed » Mon Jan 27, 2014 5:44 am

Simplest possible system would have to be a propane mass weight transfer tracker.
Next step up would be a SINGLE AXIS dc motor driven optical self seeking tracker.

Both require the panel tracking axis to be made parallel with the earths rotation, which my previous post attempts to explain.

A two axis tracker requires two of everything, double the mechanical complexity, twice as many problems, for no benefit.

Its just a case of working out how a single axis tracker needs to be correctly built and positioned initially.
And that is just latitude angle and knowing where the true north/south line is.
Even if its positioned with a few degrees of error, it will still work just fine.
Its not difficult !!!
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Re: Backtracking algorithm for solar tracker

Postby Warpspeed » Mon Jan 27, 2014 6:24 am

A few years ago when I was trying to get my head around all this sun tracking stuff, I built this small model of a sun tracker that was intended to reflect the sun onto a fixed target.
It used a 24 hour mains driven timer with a mirror glued onto the top, via a 45 degree wooden block.

The 45 degree mirror angle was supposed to reflect the sun back down the axis of rotation.
The whole thing was tilted upwards at 38 degrees (Melbourne latitude) and pointed due north.

It would have worked perfectly in spring or autumn, but a detail I missed at the time, was that the angle of the wooden block needed to be changed with the season for perfect tracking.

It was an interesting experiment, and I did learn from it.

If you can reflect the sun continuously onto one point, it would then be possible to reflect it again with a second fixed mirror onto the final target.
The second fixed mirror would only be required if you had multiple trackers spaced apart (to prevent mutual shading) all directing sunlight onto the same target.
It was just a crazy idea that I had at the time, that I just had to try out.
It "almost" worked, and would have worked perfectly if I had known to make my mirror elevation adjustable on the face of the 24 hour timer, instead of rigidly fixing it at 45 degrees.

Image
Last edited by Warpspeed on Mon Jan 27, 2014 7:12 am, edited 3 times in total.
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