Motor Control

Elevation tracking will work if you are 'near equator' (up one side and down the other) as that is close to an equatorial mount there. (40 degrees elevation sounds off for this though, and you will never find the sun at negative elevations, that's pointing downward). As you get more northern or southern, azimuth start to become more important (At the pole, you ONLY need azimuth tracking).

As Upsidedown said, an equatorial mount makes a good single axis operation. It won't correct for the seasonal north-south motion of the sun, but that is small enough, and slow enough that you might not need to automatically adjust for this. It does say that an accelerometer might not be the right sensor, as at higher latitudes you get less signal from it, a rotary encoder of some sort on the equatorial mount is more commonly used.

Having just a simple 'bang-bang' controller (on/off and direction), your control law will be fairly simple, If you are too far from the desired position turn on the motor in the needed direction, and when you get close, stop (don't wait for exactly equals, as you are going to overshoot).

One other issue with using an accelerometer for position measurement here is that while you are moving, that motion will affect the accelerometer reading, making it hard to decide when to stop.

Reply to
Richard Damon
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Hi,

You mentioned that as elevation tracking works if the tracker is near the equator but as we move more north or south azimuth becomes important.

I am confused that my solar tracking is single axis and my solar panel is facing East with tilt -40 degrees measured with my accelerometer, the solar panel will travel to +40 degrees facing the Sun in the west.

Since, its single axis tracking how can it follow azimuth angle at all. Because according to my understanding, I need dual axis motor to follow both azimuth ( north to south) and elevation ( east to west) to follow the Sun.

In single axis system I can only do east to west and follow just elevation angle. How can I follow azimuth with single axis?

Reply to
Jessica Shaw

You confuse me a lot with your misunderstandings. Azimuth is not a North/South measurement at all. Azimuth is the horizontal component (along the horizon like a compass measurement, 0 to 360 degrees) and elevation is the vertical (up from the horizon, 0 to 90 degrees).

What some here have tried to explain is that you can use an equatorial mount where the axis of the movement is aligned along the line parallel to the axis of the earth. Then the movement of your panel around this single axis will come fairly close to the path of the sun all through the year with some variation from season to season.

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Rick
Reply to
rickman

Ok. I appreciate that you are trying to teach me. But the thing is to point the solar panel towards the sun at 90 degrees requires dual axis motor.

My understanding is that with one axis control ( East to West) setup I can only do Elevation and not azimuth. I might be wrong.

Reply to
Jessica Shaw

Read up on equatorial mounts. No, a single axis won't follow the sun exactly, but on any given day the sun follows a straight line across the sky that you can track with a single axis. This straight line changes a tiny amount from day to day. So there will be some inaccuracy over the seasons, but you can either set the axis to a mid position which will minimize the average error... or you can provide for a periodic manual adjustment over the seasons... or you can use another motor to move the axis up and down a handful of degrees... or you can add a mechanism that will work from the first motor and each time it cycles through a day it takes a step in the right direction and reverses every 6 months.

Those are all my ideas. But before you will understand this very well I think you need to learn about equatorial mounts.

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Rick
Reply to
rickman

I will read about equatorial mount. But would you please look at the following video.

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Its a single axis horizontal tracker. Can I say that this tracker can only do Azimuth tracking not elevation tracker?

The following video shows vertical axis solar tracker. Can I say that this tracker can only do elevation tracking only?

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Reply to
Jessica Shaw

The trackers in the videos are not equatorial mounts. I am working with the tracker that is shown in the following video link, not exactly the same tracker but much smaller than this.

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This is not equatorial mount plus it can not follow azimuth but can only follow elevation. Am I right?

Reply to
Jessica Shaw

The axis of this unit is vertical. The movement is azimuth.

The axis of this unit is horizontal, most likely aligned north/south. The movement is elevation.

Near the equator an equatorial mount axis is horizontal like the elevation unit. At other latitudes an equatorial mount axis raises up from horizontal according to the longitude. The result is that as it sweeps the sky, it tracks pretty close to a direct line to the sun. It will vary a bit over the course of the year which will be less than either the horizontal axis mount or the vertical axis mount.

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Rick
Reply to
rickman

My tracker looks like the tracker in the following video aligned east / west.

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It starts at 40 degrees facing east and then travels to -40 degrees facing west and then stops.

So, it will follow only the elevation of the Sun. Because of horizontal axis it can only follow the elevation of the Sun. Am I correct?

Plus if I move it 15 degrees every hour then that would be enough to follow the Sun or is there any roam to do any fancy tracking algorithm stuff.

Does 15 degrees every hour elevation following will take care of all the seasons and months of the year?

Reply to
Jessica Shaw

One thing I don't get in this video is that they show all the panels lying flat at the midpoint. They would have better utilization of the panels if they were tilted out of the plane according to the latitude, at least it would be better during the middle of the day when the highest power is received and somewhat less in the early hours and late hours at some times of the year.

Why just 40 degrees each way? Unless there are obstructions, there would be useful power available over a much wider range of motion.

I'm not crazy about your terminology using the word "elevation". If you have the elevation and azimuth of the sun, the elevation will not match the angle of elevation of your mechanism. But I guess you are describing it correctly otherwise.

The sun moves over an arc of 180 degrees in an average of 12 hours which amounts to 15 degrees per hour. Your device will only follow the sun for less than 6 hours.

With significant error in pointing at all times.

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Rick
Reply to
rickman

My mechanical system allows only 40 degrees tilt on both sides.

How can I map the Sun's angle of elevation to my mechanism? I am controlling the motor with micro. and feed back is an accelerometer.

If I go with less than 15 degrees every hour then will I be able to follow the Sun for more hours.

So, with this horizontal axis tracker, there will be significant errors that can not be taken care of by any means. I can not change the mechanical setup of this tracker in any ways. Am I correct?

What are your thoughts about " Back Tracking" as sown in the following link

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Any suggestions on avoiding the shadow casting of one panel on another!

Reply to
Jessica Shaw

First, it sounds like you are measuring Zenith angle, not Elevation (they are related but measured differently). Elevation is 0 when pointing at the horizon, and goes up to 90 when pointing straight up.

Zenith is 0 when pointing straight up, and goes to 90 degrees at the horizon (and sign can be used to distinguish direction of rotation).

One way to see why you can use elevation nearer the Equator and Azimuth nearer the Poles is look at what happens as we move off the idea point and get to mid latitudes. At (local) noon, the panels with the Elevation mount will be pointing straight up, but the sun will not be not be straight up, but will have a zenith angle roughly equal to the latitude (give or take about 23 degrees based on season). This gives you about

70% efficiency {cos(45 deg)}, slightly better in summer, worse in the winter. As you move towards morning and evening, you have a similar angle, but the math gets complicated.

If we wanted to convert the system to an Equatorial type mount, you raise the Northern end (assuming you are north of the equator) so that at noon the panels point directly at the sun at noon (this tip angle will again be equal to the latitude). Now the rotation angle is aligned with the rotation axis of the earth, and this is called equatorial. For solar panels, the question will come at what point does it pay to do this. For a large array, the end will get very high which has its own problems, or you need to break up the array into smaller pieces with more controller expenses.

Reply to
Richard Damon

I am stuck with the following solar panel mount

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It moves from east to west. It has a horizontal axis. I can not do equatorial. All I wanted to know that this solar panel setup can not do azimuth and zenith at all. It can only follow elevation.

What are your thoughts about " Back Tracking" as sown in the following link

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Any suggestions on avoiding the shadow casting of one panel on another! Any suggestion on the algorithm that I can use to solve this problem.

Reply to
Jessica Shaw

The OP is clearly a troll. The task looks like some university homework.

In any civilized country (I do not know about the USA), persons with so little mathematical and physics knowledge would be admitted to study. .

Reply to
upsidedown

Any suggestions on avoiding the shadow casting of one panel on another!

Any suggestion on the algorithm that I can use to solve this problem. I found the following link

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Reply to
Jessica Shaw

zenith is measuring angle from vertical, elevation is measuring angle from horizontal, so they are just different ways of talking about the same thing. The angles you quoted where 0 straight up, which is a zenith angle (it may be that the manufacturer is using the wrong word in their description, giving you the wrong idea).

Note that the system listed can do a limited form of equatorial, as they allow a 15 degree tip of the array. Depending on where you are, that might help some (or depending on how big, it might get things too high, which is why they talk about for south facing hillsides).

It is basically simple math once you can compute the suns position. You limit the angle of the arrays so that the ray from the sun that just hits the back edge of the first panel also just hits the front edge of the second panel.

i suspect it helps as the efficiency of a panel is best when it is uniformly illuminated (not shadowed).

Reply to
Richard Damon

Thanks for the reply! Can you give me the formula or Do you know a website or a simple paper where I can find the formula for back tracking. I looked as much as I could but was unable to find one. I found some papers but the math was too complicated.

Reply to
Jessica Shaw

I haven't had to work out the formula, so don't have it handy. The most complicated part is working out the Sun angle (projected onto your panels), but you needed that before.

For back tracking, it is simple Geometry using the spacing between rows of panels, the size of the panels, and the angle of the sun to figure out what angle to place the panels so they are just on the verge of shadowing each other. (There are two possible solutions when you want to use backtracking, but you want the 'flatter' one)

Reply to
Richard Damon

I don't see how the back tracking shown in your link has much advantage. The panels intercept the same amount of sun when backtracking... no, they intercept less sun. If you keep the panels aimed as closely to the sun as possible, they will receive more sun along the edges which don't overlap.

The solution to shadow casting is to space the panels further apart. That's pretty simple, no?

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Rick
Reply to
rickman

Why would you want to use backtracking? I think it results in less sunlight being collected by the panels.

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Rick
Reply to
rickman

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