$2 sun tracker circuit - healthy discussion!

Picture of $2 sun tracker circuit - healthy discussion!
My apologies to any of the 1400 or so people who've read this Instructable in the day since it was published; I described an idea I was sure would work, and I was so excited to get it out there where people could try it, that I didn't wait until I could get the parts I needed to fully test it myself, and I posted based on a partial test and an assumption about the performance of small motors that turned out not to be accurate.

Now normally I would take a faulty Instructable down (and run away and hide), but in this one instance I'm going to leave this online after editing it to correct my mistakes, because I thought that there was still a good idea here that could be developed even if it had to be by someone with more electronics experience than me, and I wanted to put this germ of an idea out there so that maybe it could inspire someone to come up with a solution that works.  I offered the 1Yr pro membership upgrade I received when this went front-page as a prize, and as you can see from the comments a lively discussion ensued.  (I gave the prize to jtlowe for his suggestion of using a clockwork rotating platform, but although there's no more prizes to give, I would still welcome any more suggestions you all can offer).

The problem is sun tracking: pointing a solar panel directly at the sun so that it can harvest significantly more light - and the difficult aspect of the problem is that the cost of adding a sun tracker to a solar panel in order to gain X% extra output has to be less than X% extra cost, otherwise it's more cost effective to simply add more solar panels.

The solution that I had was to take two small PV cells from a couple of solar garden lights, and connect them not in series or even in parallel, but head to head, connecting the ground lead from one to the ground lead from the other, and determining which of the two panels was receiving more light by looking at which one was able to generate more voltage than the other.  For instance if one generated 2V and the other generated 3V, then the voltage between the two positive outputs would be 1 volt, and that volt would be used to drive a DC motor to turn the platform in the direction of the cell that was reading the stronger light signal.  (Although in practice the voltage was actually less because driving current through a PV cell against its natural direction (since it acts a little like a diode) causes a voltage drop in excess of just the voltage that would be cancelled out, though that's not relevant to the problem)

Although that is indeed what happens which you can confirm by looking at the voltage on a voltmeter, what I didn't realize was that these panels don't generate enough amperage to drive even the smallest motor, as far as I can tell.  I'm talking about 3V motors that need so little power that they'll spin from a single half-dead AA battery!

So what I'm going to show you here is half a solution, and I'm asking the smart readers of Instructables to help come up with the other half.
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mikesnyd3 months ago

Could you throw in a small capacitor bank to run the motor? The motor isn't constanty running so the small panels would be able to keep a good enough charge in the bank.

gtoal (author)  mikesnyd3 months ago

The trekbot toys use a supercapacitor rather than a battery to store their charge, so they're definitely good enough to use as you suggest.

I always thought that if you connected the black wires together that the output fron the corresponding cells would be positive. The only way I can see getting a positive and a negative output is connecting the positive to a negative,thus giving you a positive output and a negative output. Love the instructable! I have been trying to find a simple solar tracker for my homemade solar panels, and this would fit the bill nicely. Maybe feed the 2 outputs to a camparator or even a couple of OpAmps then connect that to the motors via driving transistors. I dont know, but will post a instructable when I do figure it out!
gtoal (author) 1 year ago
I found out an interesting fact today, You can use an LED as a light sensor, especially the green ones. I have an old strip of Christmas lights that I cut up last year (I was converting them from 110V AC to 12V DC) - I put a green LED on my voltmeter on the lowest voltage scale and it does indeed reat to light, You'll either need an op-amp to am[lify the signal, or hook it up to an ADC (say in an Arduino) and add up several samples to reduce the noise.

This appears to be a fairly well documented technique (even here in Instructables) but it was new to me.
Have a look at my "hard drive solar tracker" it is an adaption of this method and can drive pretty much any motor you wish.

I've also got a transistor version, not sure if I posted it on my website though.
The parts will only cost around £8 if you get the dead HDD for free.
gtoal (author)  scraptopower1 year ago
I do certainly have no shortage of dead drives, that's for sure!

It's a nice simple circuit, but are you powering it from the panels that you're shining the light on or from that DC power supply I can see off to one side? :-)

I may build this for the fun of it, but the biggest thing I still want to implement is a cheap way to power the rotation (or control it if unpowered) using no more than the small PV cells. i think your design may need more power than I have spare.

Thanks for the link, your tracker works nicely.
I see, I was intending on running off the solar panel((20W) it will track, but I don't have a way to run it without a power source.
gtoal (author) 1 year ago

I have a one-year free pro membership available which I'll give to the person who comes up with the most elegant and cheapest way to use this circuit in an actual tracker!

gtoal (author)  gtoal1 year ago
Well, comments have finally trickled to a halt and this seems like a good time to award the 1Yr pro upgrade that I promised.

I was hoping someone would actually build something and try out their ideas, and if they had, that would have made the selection of a winner much easier!

However many good ideas were suggested and chosing a winner was tough - for example I thought Wroger-Wroger had a good grasp of the big picture; alarrrd and jtlowe made low-tech analog suggestions in the sprit of the instructable; perfo, eecharlie, and others contributed valuable detailed information on electronics that would definitely help in a scaled up version of this project. Every commenter had something helpful to say - there really were no bad ideas here.

In the end I decided to give the prize to jtlowe for his suggestion of using a wind-up clockwork mechanism, which was at the level of complexity that I was looking for and is what I'm going to work on next to improve the design.

Congratulations JT! I'll email you the code.

I would certainly agree with you that you don't have enough current to drive a motor. But I would say more importantly, you don't have enough power (voltage times current).
However, if you are using solar lights you have a readily available power source, the batteries.
And another thing is that all the solar lights I've seen have another sensor to turn off the lights during the day so that the batteries will charge more. I don't know if these are phototransistors or LDSs but I would think this would be a better source of your 'light' differential signal. So what I would try would be to run the differential signal into a transistor for gain. The transistor is powered by the battery or batteries and then you would have enough power to drive the motor. Since the motor isn't going to be moving that much, you should theoretically have your efficiency. Now you may have to connect two in series to get enough voltage for the motor.
Now, I'm not an analog guy or a motor guy but I think this would have a better chance of working.

gtoal (author)  msuzuki7771 year ago
The cheaper garden lights use the PV cell to determine the light level rather than using a separate sensor. I doubt that the part of the circuit that switches the LED off it draws much current.

I'm wondering if the pulse of power from the coil in the Joule Thief circuit is enough to turn the motor a little - it would be more like a stepper motor if it worked, as long as it didn't drive it too far past the optimum position.
The Joule Thief cannot add more energy than is already there.

Here's my suggestion. Take out the output LEDs from the solar lights, Leave the rechargeable batteries in. They will charge up to maybe 1.4V. Get a low voltage comparator. I know some can be powered by less than 1V. Power the comparator with one of the batteries. Now take the PV output from the two solar lights. This voltage is going to be higher than the battery so divide it down with a voltage dividers. Tie the two voltages to the comparator. Add hysteresis so the motor will stop when you get close. Now you know that the direction of the sun goes in only one direction so the motor needs to move in only one direction. Drive the output of the comparator to the motor. You might need a transistor to give it enough current but the battery should have any capacity to turn the motor especially since the duty cycle for the motor will be so low.

Now if this isn't enough power, you could tie two solar lights in series so the battery voltages would be about 2.8V.

By the way a cheaper solar light is the $1 solar light keychains sold on ebay. They actually put out 3 volts.

gtoal (author)  msuzuki7771 year ago
"The Joule Thief cannot add more energy than is already there."

maybe what I said didn't make sense out of context so let me explain what I was thinking: the motors need a higher current to get started turning than they do to keep turning. I know that the power output from the PV cells isn't enough to start the motors turning, but I was hypothesizing that if you collected the output and sent it all at once in a short pulse, it *might* be enough to overcome that initial inertia and turn the motor a little. I was also guessing it wouldn't turn far and wouldn't have enough duration to keep it turning with the risk of overshooting the target. Again - all assumptions, but ones I plan to test on Saturday morning in the heat of the day :-)

Now ideally I would suggest using a capacitor to build up charge, but since we have the JT circuit already - came with the $1 unit that the PV cells came in - we might as well reuse that if it would work. From what I read in another instructable, it looks like JT uses the collapsing field of a coil to generate a large pulse - at a voltage sufficient to charge a 1.2v battery, so it is plausible it would be enough to kick over a gearmotor since a AAA cell alone can do it even when the AAA cell is almost depleted.

I'll give it a try and report back. Chances are it won't work, but it's definitely worth the effort to try.
Yes, the JT circuit doesn't add energy but it will concentrate more in a pulse. I doubt it will work also.
But instead of adding a capacitor, you could probably add the battery as it's already part of the $1 cost anyway. The battery is going to act just like a capacitor.
By the way, we only have a Dollar Tree out here but I've never seen a solar light in there. Maybe I'm looking in the wrong place.

Good Luck.

gtoal (author)  msuzuki7771 year ago
The $1 lights at the Dollar Tree are only an occasional item. I bought enough to line my whole garden last time they were here :-)  Apparently you can order online and get a case shipped to your local store.
I will keep an eye out for them. Personally, I like the $0.99 solar keychain as they have 3V batteries and include 3LEDs. I bought some on Newegg but they're cheaper on ebay.
While this is an interesting theoretical project, I question the practical application. As you said it's not very practical outdoors.
The problems I see indoors are first, you probably need an unobstructed south facing window. Even with that I don't think there would be much tracking involved.
I have a south facing window but when the sun is out, I always have my blinds down and there ain't no room for a moving panel.
I would think a slightly larger panel would cover any charging panel.
Other questions, how much is solar charging a cellphone going to save over plugging it in.
By the way, I charge my solar keychains under a lamp. Well, these solar lights charge under room lighting? Guess I've never tried it.

I guess if you're going 'Green' I would say a bigger solar panel is more efficient as you are not wasting energy moving the panels.

A question, however. Since a solar panel is taking energy from the sun, will it be cooler? In theory, I would think that since some of the energy is being converted to electricity, there would be less heat.

There are a couple of tricks to this - I have designed commercial units for larger solar collectors.
Here are a couple of the tricks.

Your PV cells should be polycrystalline with a resistor load, so that they work as solar power sensors not solar energy sensors. A mono crystalline cells needs full light cover to generate a poly- doesn't. Measure the voltage across the PV cell to measure exposure to the sun.

This will work for adjusting alignment but you need to turn back east when it gets dark (night time).

To save power only turn east-west.

Use a polar mount to get your panels roughly parallel to the earth's axis. Dont bother adjusting the north- south alignment, there isn't enough to gain.

I hope this helps
Not quite true. Re gains from accurate tracking.

It's pretty simple to prove, Get one easy to handle solar panel, and hook up to a digital multimeter, and then log the voltages with pencil to paper and accurate estimates of angular alignment to sun in say 5* Degree increments.

I have found that as long as solar panels are within about 15* of true alignment to the sun there is very little difference between being pointed directly at the sun AND being 15* out of alignment with the sun.

It was after that, that the power gained started to drop off..

In regards to accurate tracking and the North South Alignment - this I would say is NOT an issue at or near the equator, as setting the tracking to the North South alignment, at the equinox or between the summer and winter day light lenghts, would keep the sun within the 15* of alignment.

But when ones location is in the lower or higher latitudes, for instance, the sun is at 29* above the horizon at the winter solstice, and it's 75* above the horizon at the summer soltace.

That is a difference of 36*, so in saying if the panels are pointed at the sun, within 15* of true perependicular alignment to the sun, and more especially so in winter, where the say light is weaker, the days are far shorter etc...

At the worst, having the panels set for the summer solstace alignment, would cause a dramatic loss of harvesting capacity in winter, and vis vera for alignment with the winter solstace.

If one were to set the panels at the suns noon equinox angle of 56* (where I live), there would be an appreciable loss at the solstace periods, because the panels will be more than 15* off set to the sun in winter, which is the most important time to have reasonably accurate alignment and also with the summer sun.

So my take is, the lower or higher your location latitude wise, is to get up and clean the panels and service the equipment, on at least a monthly basis, and to manually set the angles to point the panels at the more or less noon sun, for that part of the year - especially in winter.

Cleaning the panels, especially in dusty locations, makes a HUGE difference to the amount of gain as well.

Get out in the early morning or late afternoon sun, and also the winter sun and then align a panel with the sun and measure the voltage drop, the more the panel is out of perpendicular alignment with the sun.

I do know that absolutely perfect tracking systems, that align with the sun on a minute by minute basis, are a waste of time....

I do believe that a simple stepped tracking of turning the panels, to lead the sun by 5 degrees, and then when the panels lag the sun by 5 degrees, to make another turn of the panels, is about optimum.

But keeping the panels adjusted for north south alignment, this issue is basically irrelevant at or near the equator, but it becomes progressively more and more important, especially seasonally, and the further you are away from the equator and are closer you are to the poles.

gtoal (author)  Wroger-Wroger1 year ago
Agree 100%
It's not only very clever, but if you had done some more research you would have found that it's very common. Not dissing the effort, though.

Actually, if you put your mind to the problem and get away from the solution, you will come to conclude that the traverse we make around the sun is quite regular.

All you need to "track" the sun for a fixed solar array is a timer and some small adjustment as the seasons change.

Now, if you want some sort of "robotic" style sun tracker, then you'll probably need more than $2 worth of parts.

Keep trying.
True you can just pick up the phone with credit card in hand and have an all singing all dancing solar array auto tracking in a jiffy. But then where's the fun in that. This post is in the spirit of the site and that is doing stuff or at least trying with hack able components and investigating different ways to do it.
True but there are a lot of projects put on here just to win a prize offered. Some are the equivalent of cutting out paper dolls, gluing on a resistor for a hand and taping 9v batteries on for feet! "Look what I did! An electronic robot!"

Even this author clearly states that he posted a project that he hadn't really even built ("...I described an idea I was sure would work, and I was so excited to get it out there where people could try it, that I didn't wait until I could get the parts I needed to fully test it myself, and I posted based on a partial test..."), but he still won the prize. Projects here are a lot about winning prizes. You just have to sort out the junk.

I applaud this author for admitting his mistake and posting the retraction.
gtoal (author)  texasclodhopper1 year ago
Appreciate the comment, thank you. I don't mind looking like an idiot occasionally though I try not to make a habit of it :-) It is weird what gets popular and what languishes. I actually find it a little embarassing (and frustrating) that this post about a 30-minute hack has been the most popular one I've ever made, yet the post I did about CNC art which is actually something original and reflected maybe 6 months of hard work has gone virtually unnoticed :-) Still, this has sparked a lively discussion and I'm really pleased to see that. I actually was able to use this discussion at the university where I work yesterday as an example of the design process - building on your mistakes and all - to a visiting class of high school kids that we were trying to persuade to become engineering students next year.
Well, if looks were important then I'd be in trouble all the time.

I've been vilified on here at times, because I can't always find a way to "be nice" with some of these projects. Criticism is not being un-nice, but can be quite constructive. I got flamed for pointing out that one project was based on a stolen shopping cart. Many argued that the store that owned it was OK with it being converted to something else for the "author." Why present projects that teach the wrong thing?

You take criticism well and must be a good instructor to those around you. Thanks for that!
Point taken I can see what you mean about alteria motive. I don't think they apply in this case but I can see how they could with others.
gtoal (author)  texasclodhopper1 year ago
Actually I confess that I am deliberately doing exactly what you criticise me of - working back from a solution in search of a problem. Because as you point out there is indeed a lot of prior art and just about everything has been thought of before. My goal isn't specifically to build a solar tracker - if that's all I wanted I'd follow one of the existing Instructables. My goal is to see if the one original idea I had here is something that can be exploited somehow. The very minor intuitiion that you could use using two $1 solar garden lights to determine the direction of a lighty source is the only original thing I lay claim to here, and what I'm hoping is that there *may* be a way to exploit it that is cheap and easy, because the other trackers I've looked at (and I've read about many of them) are generally either not cheap in component terms or in terms of man hours it takes to build them.

The basic rule of thumb I'm exploring here is whether it's cheaper to add tracking or to add more solar panels. For huge panels it's a no-brainer. For medium panels it's borderline. For small ones like cell phone chargers, I'll be interested if you can show me *any* existing tracker designs that give you a bigger win than just adding another panel for the cost. Honestly the only cheap efficiency improvements I can think of that are ways of concentrating the sunlight by mirrors or lenses but those are bulky and fine for outdoors but not so practical for say behind an office window.
If your panels are ground based, it should be cheaper to add tracking (in summer.)
But in winter the sun is low in the sky and (here it is cloudy) so it doesn't much matter where the panel points. It will perform badly no matter what!
There is a helpful site called sollumis that shows where the light comes from all day. If you track well, you must beat a stationary panel by a long ways.
I heard an interview (I thiink with the guy from red rock). He claims that the statistics for cloudy days and sunny days are just averaged over wide areas and you local climate is far more important than you would think. If you are in a sunny area, work at tracking. If you are cloudy, it might not be worth it.
gtoal (author)  gaiatechnician1 year ago
I live near McAllen Texas. We don't have a Winter here :-)
gtoal (author)  texasclodhopper1 year ago
No offence taken, after all my profile says "Favorite activity: reinventing the wheel" :-)

One thing that's cool about an active follower rather than a fixed path tracker is that it works fairly well indoors for pointing at the indirect illumination through your window. And it's cool for demos where you can make it follow a flashlight :-)
Chiana_Rei1 year ago
If your only problem is generating enough voltage why not just wire in a small capacitor, or bank of capacitors that the small solar panel will keep charged and and the motor will turn slowly, as you have quite a few hours of slow very tiny movement. Then set your light following sensor right in the middle of the panel or use 4 one on each side to get 4 values and the motor turns towards the two with the highest value. and stops turning when the value drops, all you need is a way to read 4 values and come up with directional values to send to a motor driver circuit on a stepper motor. Alternately if pins are an issue then you could do the same thing with just two sensors and have the panel turn till the values across the two are the same. Then just use one panel as the master position finder and the rest have a driver circuit that gets the the turn command then you only have t create one sensor circuit. Ill have to look about but I think the easiest light seeking circuit I have ever built was the one from Mousey the Junkbot out of Make, you might even be able to use an IR mouse to build it and save some money if you can get eh values off of it, maybe using a USB to RS232 thingie. and I have now exhausted all the electronics design knowledge I might have.
jtlowe1 year ago
It sems to me that we are making htis way to complicated. Because the sun with be in a fixed position per each moment of time on a clock, why have a tracking system when you can use an old wind up clock and a gear mechanism instead? The only draw back is the return 12 hours while the sun is down and the winding the clock regularly.
Winding may be driven by a wind operated device.
If it is turning a gear against a pring force, then a reset switch can be activted onlce it reaches a set position and return the mechanism to its start postion waiting for another switch to engage the start of the days tracking activity.
Perhaps this too is too simple an idea as clock mechanisms do not move that large of a mass.
"We need to come in around $5 to be worth the effort."

This is the entirely wrong approach.

In life you get what you pay for.

In terms of the TIME and RESOURCES used in buying the parts, transporting the parts, doing the design and assembling and then making it all work, then all the adjusting and repairs and problems etc..

Then you get all the time spent in getting up and down ladders, with the risks of falls, injuries and disabilities or death.

I think it's better to do it properly in the first place, and to make the unit so it works without flaw for the next 50 years, or pay someone who has done all of the research and development, and has amortised the costs of this, across thousands of units.

I want strategic long term investments, of my time and finances, and limiting the consideration to "coming in to under $5" leaves out all of the other really important issues.

Sure I don't want to pay $900 for a controller, that has $25 worth of parts in it and I can build it in 3 - 5 hours myself.... but I want really good outcomes for whatever I do.

Why not? This is an experiment that may or may not work so what is wrong with setting one of your overall design goals as cost? It isn't the best approach for a lot of good project designs I agree but that's the fun of ibles like this. The author sets his own goals no matter how relevant others think of them, and then tries to achieve it.
As for your adage "in life you get what you pay for" if only that where true. You have to work like a (insert something that is renowned for working a lot in here) just to get something anywhere near what you pay for as most manufactures sell for what they can get not what it's worth which can be the same thing but can also be very different.
gtoal (author)  Wroger-Wroger1 year ago
I'm well aware that time is money, which is why I suggested maybe 20 minutes for putting this together. We're talking about a quick hack made out of $1 junk from a dollar store after all, not a beautifully engineered project with Kickstarter funding and a factory to build it. If you're willing to pay for a long term investment (although the life span of solar panels is what? 10 years?) then there are lots of people out there who'll sell you what you want. But this effort is to let a hobbyist have a little fun one afternoon and also produce something that they can use.

Truth is the best strategy is do nothing and look at what's available in a few years time when efficiency is way up and cost is way down. But meanwhile let us have our fun, after all that's what instructables is all about.


kubulai1 year ago
Dude. I'd just feed the output of the two opposing photovoltaic cells into +/- inputs on a cheap op amp (via resisters), and run the output of the op amp to a transistor to drive the motor. It's a good idea. A LM741 op amp is cheap -- a few cents.
gtoal (author)  kubulai1 year ago
Cool. That's In1+ and In1- taken care of. Now,where does Vcc and Vee come from?
snobound21 year ago
If I read this right you want to use this circuit/device to point a larger array of solar cells. If that is the case, then scale the idea up a bit (or a lot!) and make the entire array the sensor. Split it in half or quarters and stick to your original concept (w/ some of the tweaks offered) . The large array will supply the adequate power to drive the motors for positioning and with blocking diodes (to prevent other segments from interfering w/ the positioning process) arranged properly the segments can be summed together for your final output.

- Ed
The problem with using your actual main array as the sensor is by design none of your panels will be in the sweet spot. The purpose of a tracker is to get the PV panels off the main array as spot on as possible to maximise the output. Using half the array tipped one way and the other half the other will work as a control solution but will always keep the array off the optimised position so sorta negates the point a little.

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