There are several reasons for aiming things at the sun. For example to increase the power output of solar panels and solar collectors that focus the sun’s energy need to track the sun precisely.

Many good mechanical designs exist for moving solar collectors so they aim at the sun but I wasn’t able to find a good, reliable, simple method to detect the sun’s position and compare the collector’s direction to the sun’s position. What I found was:

· Rotating or moving sensors that track the sun. These can track the sun very precisely and when mounted on the collector they compare the collector’s direction to that of the sun. But, they have on fatal flaw. They have a very narrow acquisition range. For example, when they track the sun from east to west, the sensor is aimed west and can’t see or acquire the sun when it rises in the east. The same happens when clouds obscure the sun for a time, the sun can move out of acquisition range. This problem means you need a secondary tracking mechanism. It could be a second sensor with a wider acquisition range or a clock that predicts where the sun should be. But these have other problems and they increase the complexity.

· Fixed (non moving) sensors can locate the sun anywhere in the sky but they don’t compare this to collector’s position. A second sensor is required to keep track of where the collector is aimed. It could a POT on the collector that varies it’s resistance with direction, or stepper motors so the control keeps track of where the collector is aimed, or others. But it comes down to you need a second mechanism to monitor the collector's position and then some logic to compare the two and make corrections.

I wanted a simple method to compare the collector’s direction to the sun’s position that would work through 180° such that it could acquire the sun anywhere in the sky and provide a error signal that I can use to aim the collector. I was prepared to have 2 sensors, one for horizontal and the other for vertical as this matches the mechanical methods for moving the collector.

I started with a fixed sensor. It acquires the sun anywhere in the sky. I then added a method to compare the collector’s direction. How? A shade over the fixed sensor. The shade moves with the direction of the collector. The sensor simply gives me an east value and a west value (or up and down values) that are equal when the collector is aimed at the sun but the east signal is greater when the sun is east of the collector or the west signal is greater when the sun is west of the collector.

This really should be patented but I am publishing it without a patent because I already have patents and they turn out to be quite useless unless you are a big corporation who can afford to defend them. Maybe I’ll win and actually get some compensation for this invention.

That’s enough theory. How do we make this?

Step 1: Get a Couple Solar Cells

I have several practical designs. The first one uses small photo voltaic cells that I get at the dollar store. Get a couple of these (or similar) solar toys;

Step 2: Pry Them Open

Pry them open.

Step 3: Unsolder the Leads

Unsolder the leads

Step 4: Install the Cells in the Frame

I designed and printed a frame for 2 photovoltaics(I have uploaded the .STL file). Here it is with just one cell installed.

Step 5: Install the Shield

Next make a shade (I call it a ‘Shield’). Here is the sketch. You can make it from thin aluminum. I have a big roll but you can use a pop can. Be careful not to cut yourself. Paint the inside flat black to minimize reflected light.

Here is my assembled sensor for vertical tracking.

Step 6: Make a Second One

Here is my sensor for horizontal tracking.

The horizontal sensor is the same but I have different mechanisms to move the shield. Sorry about the background clutter in the lab. I have many projects on the go.

Step 7: Mount Them

The vertical sensor is fixed on a stationary arm and the shield is driven by several shafts such that it follows the vertical rotation.

The horizontal sensor is mounted on the vertical arm, so it moves in the one axis, but it’s shield is moved with the horizontal rotation.

That’s the mechanics of the Solar Sensor.

Step 8: Install the Solar Collector

Here is the finished tracking solar collector. As you can tell from the shadows it tracked the sun to it's afternoon position.

Step 9: Supplementary Information

Please remember that this instructable is on the sensor the rest of this and the pictures below showing my implementation are all supplementary.

I’ve uploaded the file for the sensor frame and a second sensor frame I designed for Light Dependent Resistors (much smaller).

I use an arduino with a H bridge module to control the motion. I’ve uploaded the arduino code too. Of course you know that the photo voltaics give a voltage. I just connect this to an ADC. And make decisions based on the voltages. If you use LDRs you’ll have to put them into a voltage divider and provide a voltage.

Here is the collector drive mechanism without the collector (main photo voltaic panel).