The Sun's path across the sky has been known and has been predictable for a very long time. People with solar panels and solar cookers take either a high tech approach to solar tracking (light detecting electronics, etc or they manually adjust the cooker or panel. High tech is very expensive and manual adjustment is majorly error prone.
Low tech cheap tracking could improve solar performance substantially.
Low tech tracking would be valuable in really poor countrys for solar cooking and perhaps save many trees from the cooking fires.
This instructable describes my tracker that I made from an old and ugly clock.
This is a collaboration so if you have an old clock lieing around, please set it up with a gearwheel as I did and see how sturdy it is. If we can find a strong robust one, It could be bulk ordered for appropriate tech solar timing projects.
Step 1: Stripping the clock
First thing I had to do was to take the hands off the clock.
The hands are attached to 3 concentric shafts that are connected to the gear wheels in the clock
I had to find the wheels inside that turned the minute and second hand and cut off the pieces that went up through the middle. therefore I was left with the shaft that turns the hour hand. The hour hand is friction fit onto the shaft.
I wanted something stuck on much more firmly!
Unfortunately I dropped the clock during my taking it apart and I cracked the connection to its face.
Step 2: Fitting a "gearwheel" to the clock.
Here is the central post of the hour hand. I will fit the piece of plastic tube to it and use the peice of tiewire to join them together really strongly! Then I slipped an old medicine contianer lid over it, screwed it to the plastic and put on the top pice of the medicine container. This now was the timing device for the new tracker!
As the clock turned, the twine slowly unrapped from the lid. The lid was almost exactly 2 inches wide. This means it releases (2 pi r) 6.28 inches of string in 12 hours.
My tracker has a float in water which has 8 inches of travel before it hits the bottom. This means I can track the sun for 15 hours with this clock!
clocks are weak but the weak tick, tick, tick movement is slowed and strengthened by 60 times to move the minute hand and slowed and strengthened another 60 times to move the hour hand. 3600 times the strength should be able to move what I want!
Step 3: The float and container.
A float 6 inches high is made from a bucket. This float is then attached to a metal holder and put in a slightly bigger (wider) bucket. This float will weigh 5 or 6 kg when it is full of water.
The container bucket will have a little hole screwed in its bottom and a pipe will be inserted. This pipe will be attached to the string from the clock. As the clock turns, the string comes down the pipe drops and water drips out through it from the container!
There is more.
The float drops, and pulls the green string, this turns the solar cooker and pulls up the counterweight (the one liter drink bottle).
You can see the solar cooker on the next page.
Step 4: The solar cooker.
It can be a funnel cooker, a panel cooker, or something like what i made here. Tracking is not perfect with this simple tracker but good enough for these types of cookers and a whole lot better than no tracking at all!
I used a lazy susan. I had some waste thin plywood, I bent it to the curve of the susan, and cut some off the 2 ends from the middle to the edge at the bottom so it leans forward a bit.
Then I used flour paste to stick the kitchen foil to it. This sends the light down to the mason jar (which is covered by a plastic bag to slow heat loss.
I had to join a 4 inch diameter cylinder at the bottom of the lazy susan to act as a gear.
4 inches because the clock turns at 30 degrees per hour but the sun moves at only 15 degrees per hour. The coffee container was the perfect size!
Step 5: Testing testin testing!
I used this clock to do a demonstration once before but this is the first time I set it up to actually run a solar cooker. My test was run from about 5 30 in the evening till about 7 pm. Not the ideal times, to be sure.
Here are some pics from the first test. With the sun heating up some molasses in a mason jar covered in a crinkly plastic bag.
It started off cool but soon got up there!
To reset your clock for the morning, all you have to do is wind on the string twice (That coresponds to 24 hours) and fill the bucket with water. It will start tracking in the morning again at exactly the same time! So you can heat up water for a nice cup of solar tea when you get up!
Note, this does not exactly follow the sun. To do that, either one of the wheels would have to be eliptical (for more accuracy) or for great accuracy, the solar cooker should be mounted on an Equatorial or Polar mount. (2 different names for the same thing!).
I used the lazy susan to recycle it and because I did not have to deal with centre of gravity issues (as I would have to do on equatorial mount) and because this instructable is chiefly about the simple clock based tracker.