Turns out that in the summer months at the location (latitude) of the cottage, if we simply turn the solar panels on an axle -- pointing east when the sun rises, and following it across the sky all day to point straight up at noon, and due west at sunset -- we will double the amount of electricity we take in. I found that out by looking at this website: http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/ If you play with the applet on this site, you can see why using solar panels in Mexico in the winter makes a lot more sense than using them in Iowa during the winter. Interestingly, the benefit you get from tracking the sun in the two places is not the same percentage.
Anyway, if I can double my output, I can halve the number of solar panels I need, saving lots of money. The question is how. Turns out commercial trackers cost as much money as simply buying all the extra solar panels. If you have the room, it is a lot easier to just put in more panels and not worry about tracking.
But what fun is that? So I have been trying to track the sun with a homemade tracker that is CHEAP. ( www.redrok.com has all kinds of crazy home-brewed stuff for tracking the sun, cooking turkey's with the sun, you name it. this guy is out there.)
Here is a photo of what it looks like so far:
It is long and close to the ground so that storms can't blow it away. The axle is really an axle -- like from a boat trailer. A simple steel rack was used to extend the axle. This works really well so far.
I've got two more problems to solve before this thing works:
1) I need a computer to tell the motor when to turn on and off. That means I need a computer (actually, a "programmable logic controller") like they use in factories for making stuff. (These are way cheap: http://web5.automationdirect.com/adc/Home/Home). You can use trigonometry to figure out when sunrise and sunset will be ( I used this site: http://squ1.org/wiki/Solar_Position_Calculator). I'll program that into the computer. ...there are more details here about sensors and stuff. Post your questions if you have them.
2) The other problem is what kind of mechanism will the computer turn on and off to make the solar panels move.
Here is one close up of the mechanism I am working on for turning the panels from east to west.
That big black thing is an actuator -- which basically is just an arm that pushes in and out with lots of force. (This one cost $50 and could almost pick up a car. I read somewhere on the web that this is what they use for rock and roll shows to raise people through the floor and stuff. It is usually for moving those giant old satellite dishes that people in the country used to have.)
Here is another close up of the gears:
I think this looks cool, but I tell you what: it doesn't work. Let me tell you what I was thinking when I did it.
Take a look at this diagram I did while figuring this out:
Here is what I (thought I) knew: I needed gears because, if you try and turn the lever arm 180 degrees, the actuator's push arm crashes into the axle when the lever travels far away from the actuator. (Imagine the lever arm going around the diameter above. Let me know if you don't get it, I'll post a better picture.)
Playing with the picture above, I decided that the actuator would have a good angle for leverage for about a 90 degree turn of the lever arm (as shown above). That means I needed a 2:1 gear. I was talking to my brother who is a mechanic and he told me that cam gears from cars have a 2:1 ratio. They are tough. Cheap (the one you see cost $25). The right size. Even better, I could use the same type of sensor as they use in cars to read how much the gear had turned (by sensing when a gear tooth traveled by). ....off I went. It was a match made in heaven.
What I FAILED to do was to ask myself what is DIFFERENT about my application and a cam shaft in a car. Not good. Here's why:
Think about a car. The engine always turns the same way. So the chain is always tight on one side and always loose on one side. (Like on your bike: it is tight on the top and loose on the bottom.) As soon as I tried to turn my solar panels, one side of the chain (no matter how tightly I installed it) got loose. The the loose side flips up off the teeth of the gear and the whole thing starting skipping -- just like a loose chain on a bike.
Well, they thought of that in cars. They put a chain tension-er in on the loose side to keep the chain from skipping. Like this:
BUT tracking the sun and running an engine are different: tracking the sun goes back and forth, running an engine always goes the same way. The loose side is always the same on an engine. A solar tracker turns both ways since it goes back and forth from sunrise to sunset. Sometimes one side is loose, sometimes the other. If you through in wind rocking the thing all around, you have total chaos. (I've given up on trying to come up with a two-side tensioner. Other approaches are better. This is a rat hole.)Long story short: I thought I could borrow the solution from cars and put it in a solar tracker. But I did not really test whether that was true. It was the old square peg, round hole kind of problem solving.
The one thing I did right, though, was to get out and try something. I know a lot more about my mechanism problem now than I did before I messed up. I now know that an essential quality of my machine is that it has load in two directions. Actually, knowing that my problem is harder than I thought has given me much more elegant ideas for simpler mechanisms than when I thought the problem was easy. I'll share those some other time.
