Introduction: Portable Sun Tracking Solar Panel With a Windup Clock Drive

I've just designed and built a homemade solar tracker than can be easily set to accurately align to the altitude of the sun (as it changes daily, with the seasons), and also faithfully track the sun, from sunrise to sunset. The tracking ability of the panel provides about 40% more power than a fixed panel. Another little-known advantage of sun tracking solar panels is that they run cooler, which enhances their output, versus rooftop mounted panels, or panels flat on the ground, which tend to build up a considerable amount of heat.

The lightweight, but sturdy device is a real workhorse, ready to provide power in the field for contractors, third world homesteads, camping trips, vacation cabins, scientifc research field stations, recharging electric powered radio controlled model aircraft, and sound systems for park events.

The heart of the unit is a standard Intermatic wall timer (Model FD12HC), with a 21 tooth spur gear mounted on the 3/16" diameter timer knob shaft, and a 36 tooth spur gear mounted on the 1/4" threaded axis that holds and rotates the solar panel. The electrical contacts of the Intermatic timer were gutted to reduce drag. The massof the lightweight 12 Volt, 12 Watt mono-crystalline solar panel, delicately balanced, slows the speed of the clock mechanism about a third of one percent.

The spur gears were ordered from:
Sterling Instrument / Stock Drive Products
fax: 516-326-8827
Excellent schematics provided online for all gears.

21 tooth gear:
Part Number: A 1T 2-Y24021

36 tooth gear:
Part Number: A 1T 2-Y24036

Step 1: Articulated Foundation:

The foundation is designed to be lightweight, yet with rigid right angles at the corners, but is very flexible, parallel to the ground. In fact, a leg can be lifted almost 2 inches before another leg lifts. Four levels, one on each side, are required to accurately level the foundation to the ground. The photo shows the foundation knocked down for ease of stowage and transport.

Step 2: Pivot Mount for the Solar Panel:

The solar altitude "U" bracket (with geared clock drive) is hinge-mounted to the foundation, and angled to the proper solar elevation for the specific day, and snugged down with 2 thumb screws and a friction-fit wedge.

Step 3: Geared Clock Drive Details:

A standard off-the-shelf Intermatic Spring Wound Wall Timer (Model FD12HC), with a 21 tooth spur gear mounted on the 3/16" diameter knob shaft, and a 36 tooth spur gear mounted on the 1/4" threaded axis that holds and rotates the solar panel. The electrical contacts of the Intermatic timer were gutted to reduce drag.

It's important to note that these Intermatic™ clock timers are now in short supply, as the Intermatic™ website no longer seems to be running and hardware stores no longer stock these reliable and well-made devices. There are other brand(s) of household windup clock drive wall timers out there, but they are not well made and are unreliable, and are, simply, false economy. 

Step 4: Balancing and Mounting the Solar Panel:

A lightweight, 12VDC, 12 Watt solar panel was mounted to a wooden frame (varnished in advance) and carefully balanced, between two push-pins, to find the center of gravity, for the axis. Holes were then drilled and short 1/4" threaded shafts inserted and tightened down with nuts and large washers to provide an absolutely straight axis. The solar panel pivots on roller bearings, with internal greased ball bearings. The mass of the panel, the power-out cord, and the internal resistance of the grease, retards the speed of the geared down clock mechanism only about 1/3rd of one percent. But serendipity played its hand to perfectly match the rotation of the panel to the path of the sun.

A larger solar panel could be mounted on the rig, and solvent could be used to remove the grease from the ball bearings, and light machine oil added instead, to track at the same rate.

Two clock mechanisms, mounted in tandem, should work quite well for even larger solar panels -or a lightweight solar oven, mounted on a horizontal "lazy susan" ball bearing base. But, in the case of a solar oven, it seems that the best way, for a solar tracker, would have the cooking pot resting securely on a firm foundation, with a lightweight clock-driven reflector / glass window housing revolving around the heavy cooking pot. Only upper and lower reflectors would then be needed, to compensate for latitude and solar angle.

Let me know if you try this, as I have to move on to other projects and simply don't have time to develop and refine it. But I love to see how these things progress.

Step 5: Pivot Mechanism:

The clock mechanism is fully wound and the solar panel is then carefully placed into the "U" brackets, and the gears meshed. The fluted wooden inserts are then inserted over the roller bearings and snugged down with rubber bands, to hold fast in high winds.

Step 6: Basic Lead-acid Battery Power Station:

A 12 Volt, 8.5 Amp-Hour sealed lead acid battery pack (a good match for the 12 Volt 12 Watt solar panel) is connected to the solar panel. The portable battery pack has an internal charge controller that prevents the solar panel from overcharging the battery. Lead acid batteries are also far more tolerant of fluctuating solar panel voltages than other types of battery packs. And the new breed of high rate sealed lead acid batteries have twice the capacity of those produced in the 1980's, making them a better choice than lithium-ion and nickel-metal hydride battery packs. The battery pack rests on a special, moveable rack, to provide heft and stability against gusting winds.

Step 7: Sun Tracking Solar Panel - Setup and Ready for Charging:

Portable 12 Volt, 12 Watt solar panel, a real work horse, is set up and now ready to generate power.

To quickly and accurately orient the sun tracker to true north, I prefer to use the "Sun Compass
version 1.8" (freeware), on my Palm TX pda. It's easy to initially set up: Just enter the time and select your city, from a long list on the program. And, when the program is opened, the "sun" will always appear in the exact position.
Holding the pda stylus perpendicular to the screen, to create a shadow across the screen, and
then rotating the pda until the thin shadow crosses both the "sun" and the center of the compass
rose, will provide highly accurate results.

A standard, traditional compass, even when set for magnetic declination, can all to often be
affected by nearby power lines and metallic objects, producing faulty readings. And my digital compass will not give readings if any magnetic interference is detected.

And my trusty vintage handheld GPS device will not funtion as a compass, when standing still.

Setting the tracker to the solar altitude, unlike orienting to North -or pivoting the solar panel to face the sun, is NOT intuitive. A solar altitude formula, or a solar altitude reference chart, is required to quickly and efficiently angle the solar panel to the seasonal angle of the sun. And, as the solar angle will vary wildly with the seasons, the angle of the solar panel should be carefully reset at least every two days.

Basically, the north-south rotating axis of the solar panel needs to always point north and skyward. There seems to be a common misconception that the axis always points directly to the north star, but that is not the case. The elevation of the north-south axis is always at a right angle to the sun's rays.

To orient the solar tracker to the seasonal altitude of the sun, the University of Oregon offers their "Online sun path chart program". It's the simplest, and most intuitive, I've found:

Entering your zip code will generate a chart that shows the angle of the sun, at high noon
(solar time), in your area, for different days of the year. Don't be distracted by the hours on the chart, as high noon is the only position you should be concerned about.

90 degrees, on the chart, is directly overhead. 0 degrees, on the chart, is on the horizon.
Subtracting the angle of the sun, from 90 degrees, will give you the proper angle of the solar
panel (perpendicular to the sun's rays), at high noon. The solar panel will now follow the sun, from sunrise to sunset.

Later on, I found a used Palm m515 pda, at a local flea market, for $ 5.00, and installed "RiseSet" program for the Palm OS, Version 2.1 (freeware). The program allows for setting up to 3 favorite locations with latitude, longitude, and GMT offset, to later provide a quick and easy reference for north-south orientation of the axis of the solar panel, as well as accurately setting the noon solar elevation.  For noon solar elevation, just be sure to set the time for "high noon", which can be 11:00am, or 12:00pm, or 1:00pm, depending on daylight savings time.  The vintage Palm m515 pda is now conveniently stored with the solar panel.

The tracker is designed to be fully functional, anywhere from the equator to the north pole. A simple modification of the clock drive position will allow it to also function in the southern hemisphere.

Also, being portable, the unit, if necessary, can be easily moved to another nearby location, to take advantage of the afternoon sun, if there is no area that receives full sunlight throughout the day.

As an added bonus, this solar tracking device could also be set up on a picnic table and used, at night, by the casual amateur astronomer. To function as a true equatorial mount, the north-south rotating axis of the solar panel needs to be re-positioned to point directly at the north star. But be advised that windy nights may blow the telescope back and forth, +/- 1 degree on the geared axis. While such tolerances are acceptable for solar panels, it is not suitable for serious astronomy.


azlan187 (author)2014-04-14

this is great!

kellykelly97 (author)2013-07-17

I wanted to know what the numbers on the rod stand for, do they correspond to the angles of the sun?

shastalore (author)kellykelly972013-07-18

Yes. Solar angle: 0 degrees is the horizon, while 90 degrees is directly above.

The lower the solar angle, the higher you go "up" the calibrated arm, to properly align the solar panel to the sun.

gaiatechnician (author)2010-03-09

I have a new video on equatorial mount that you might find helpful  and also I have a picture showing a liquid piston tracker.
Do you think the clockwork could do the job of timing for something like the liquid piston tracker?


Your link for this doesn't work. Could you check it out and post a correction? Thanks.

author should help and should help too. I made the second one and it worked. But centre of gravity issues make it difficult to keep the motion even. The 2nd one should overcome any issues with centre of gravity. Actually I just looked and all my tracking ideas are on including diagrams and some nasty old video Thanks Brian.

kellykelly97 (author)2013-06-27

Do you happen to have a list of all the materials you used to make this????

shastalore (author)kellykelly972013-06-28

No, I don't have a list of materials on any of my projects, as I see all of them as experimental, and always subject to future changes and improvements.

Some of my projects are quite dangerous, if not put together properly, or carelessly handled while in use. So, in these cases, I would rather make it just a little difficult for the casual user, who might not delve deeply into the project, and might end up seriously injuring themselves and others.

I have also been approached about posting detailed schematics, with a list of materials, as well as step-by-step assembly details. But I decline, for the same reasons.

All of my projects start out with only basic sketches and ideas, with preliminary math, and any additional info gleaned from the internet (which is usually seems to be quite sparse, for all of my projects). And are then quickly thrown together, often with cardboard and hot glue, and the results carefully tested and measured. My initial math always gets me in the ballpark, but things are then quickly fine-tuned with an x-acto knife and masking tape. The experimental project is then produced from wood, using the crude, hot glued cardboard prototype for all dimensions and revisions.

My Instructables posts are mainly intended to show that such projects are possible, and also to inspire others to improve on them. And post their results on Instructables for all.

celestiallarry (author)2009-08-06

For readers who find this project of interest, you may want to see this fellow's electric sundial. I would imagine the output from his device could be used as a controller for a sun tracker.

grayhead (author)celestiallarry2011-12-31

You are right. Hi has already made it by himself. See

elrodqfudp (author)2011-03-25

To make a more powerful tracker, for larger panels, you might try using the clock works from a water heater timer powered via an inverter.

Gramjen (author)2011-02-28

Wow, this looks like a great accomplishment in engineering, especially since it uses materials that can be made within an average residence. What a cool tool to be able to use.

gaiatechnician (author)2009-11-11

Thank you for posting the instructable. 
The geared clock should be ideal for running the "clock based dripper tracker" 
I have been looking for a better clock for over a year!
Some Normal wall clocks can run it but they are so hard to take apart that most of the time I have damaged them and many of them are very weak.
The advantage of the dripper trackers is that there if the wind gets strong, your clock is not directly connected to the panel and the wind cannot damage the clock.  Also, with the dripper tracker, you clock could do the timing for several panels at once if you wanted.
If you are using solar panels, you can use a little of the power to run a 12 volt sump pump and reset the drippers at the end of the day.
Alternatively you could put several panels on one dripper tracker if you used big barrels of water instead of little buckets like I did.

pfiddle (author)2009-10-25

 This may yet prove to be a serious contender for a prize. Beaut. Simple. Workable. MY only concern is dust and dirt getting into the works. 
One way to avoid it is a trick my mother taught me - put some oiled-paper under the clockwork. It attracts dirt that sticks to it and we've often gotten clocks to start up again after years of disuse by this "trick".

Kaiven (author)2009-10-02

Cool! I was just talking about this with someone the other day, except with a parabolic food cooker!

shastalore (author)Kaiven2009-10-02

Alright! Do it! 'Cause I haven't had time to get around to it yet. But I did toy with the idea. The most promising approach seems to be a stationary black cooking pot, resting on a solid base, on a slender pedestal, with a lightweight aluminum parabolic reflector, properly angled for the latitude and day of the year, with the clockdrive faithfully tracking the sun from sunrise to sunset. But the device would also need a heat resistant glass panel to contain the solar heat, as well as a clever way to seal everything against drafts, which complicates getting the weak and tiny windup clockdrive to track everything. Be sure to post it on if and when you complete it.

Kaiven (author)shastalore2009-10-03

Oh, well I didn't say I would make one. We were just thinking :P Sorry for giving up your hopes, but maybe someone would be interested in doing this for us? haha

shastalore (author)Kaiven2009-10-05

That's ok. Actually, the soIar oven possibility, I described above, was really a design for a solar water heater, with a black cylinder (with reflector and heat resistant glass) replacing the solar panel, but still carefully angled for latitude and season. If one was to build a solar oven, with a windup clock-driven sun tracker, adjustments, for latitude and season, are not needed, as the "L" shaped side view accepts all sunlight anyway. But the clock drive would require a little more planning (an eccentric cam), as a simple 180 degree rotation would not faithfully track the sun, since the axis of the pivot would be perpendicular to the ground.

eyeball_kirkenbach (author)2009-10-02

Iceman94 (author)2009-08-10

Is there any way to scale this up to say, a 3'x3' panel?

shastalore (author)Iceman942009-08-11

I don't feel that a 3' x 3' solar panel would be a good candidate for a simple scale-up. You see, a lightweight solar panel would weigh at least 12-1/2#, and that would be too much mass for the simple clock drive to handle. Even if you were to mount two clock drives, at opposite ends of the panel, it would be straining things. And would probably be an awkward setup, juggling both clock drives and building a larger, cumbersome rig for the wide and unwieldy swing of the solar panel. And be aware that buffeting winds, on a 3' x 3' panel, will also put a damaging strain the delicate clock drives.

A state-of-the art 3' x 3' solar panel will probably generate about 85 watts, which seems extravagant for packing into a remote site or cabin. You might want to take a second look at the current usage of your 12VDC accessories and see if low drain devices are available.

My original plans called for two solar panels: 12 Volts 12 Watts each, in-line, on a longer axis, for a convertible 12 Volt - 24 Volt system. The entire rig wouldn't be much larger than my existing one. But the lightweight Russian-made panels were in short supply and I could only get my hands on one of them, at the time. I now have three of these lean-and-mean panels for my projects.

You might want to consider building two of these 12VDC 24 Watt rigs I just described. Combined, they would generate 48 Watts of power. They would also have the advantage of a lower profile (= less wind resistance) than a 3' x 3' device. And if you are truly setting up in a remote site, 2 units would provide the advantage of a redundant power system, in case one malfuntions, or becomes damaged.

I tend to favor small portable, rugged 12VDC battery power stations: One charging on the solar panel + one charging on the portable wind generator, plus one or two extra 12VDC power stations in use. That way, the portable power stations can be switched back and forth for charging, and set up in the area(s) of the camp or research station that they're needed. Very convenient.

Iceman94 (author)shastalore2009-08-13

cool, thanks. What was the approximate cost of the finished rig?

shastalore (author)Iceman942009-08-13

I don't really know how much it would cost you to build this rig, as it's homemade. Of course, once one thinks about it, our time is the most expensive commodity on these things. And the special, lightweight 12 Volt 12 Watt Russian solar panels will actually cost about 4 times what I paid for them, once they get their production up. But there are other brands out there that are readily available, are also lightweight, weatherproof, and you have many wattage / sizes to choose from.

About This Instructable




Bio: Industrial Arts, Appalachian State University. Recession has dried up my field (commercial printing & packaging), but have found new work in staging, lighting, sound systems, sets ... More »
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