One Man's Adventures into Renewal Energy
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Solar Tracker Sensor - MK II

23rd August 2012

Solar Tracker Sensor
The MK1 sensor wasn't too great in my opinion, so I've decided to completely re-think the Solar Sensor.

MK2's idea is to use some light tunnels to shadow the sensors. When shadowed, the sensor forces to tracker to move.

In my rather crude diagram you can see in Fig.A that both sensors are getting the same amount of light, so no movement of tracker is needed.
However, in Fig.B you can see the Sun has moved across the sky, resulting in sensor B becoming shadowed. The tracker then has to move to the left to get both sensors back in the Sun.

The following instructions will show how to make this.

Solar Tracker Sensor
This is an encapsulated LDR (light dependent resistor)

The benefit it has over normal LDRs is that it is 'encapsulated' in a dome of plastic. This obviously makes it much more impervious to inclement weather conditions.

Solar Tracker Sensor
I'm going to mount the LDRs in "tunnels".
A tunnel for each LDR.
The tunnels will have the effect of shadowing the Sun as it moves across the sky.
It's a bit hard to describe...but hopefully all will become clear as we progress.

The LDRs will be glued in the tunnels(tubes).

I found some steel tube that as an inside diameter exactly the same as the LDRs (13mm). I would have liked Aluminium or plastic for better weathering, but steel is all I had in the garage.
I cut the tube into 4 pieces, approx 60mm long.

Solar Tracker Sensor
Use some insulation tape to tape two tubes together.
Place the taped tubes on a flat surface and use something heavy to make sure they are perfectly flat on the table... this will ensure they will be perfectly aligned with each other.

Use epoxy to glue the tubes together.

Leave overnight.

Solar Tracker Sensor
The epoxy will harden and you should now have two sets of two tubes glued together.

Wait for the epoxy to harden...

Solar Tracker Sensor
After the epoxy has hardened, use some tape to join the two sections together.
Make sure everything is perfectly square and use some more epoxy to join the two sections together.

Wait for the epoxy to harden...

Solar Tracker Sensor
After the epoxy has hardened, you should end up with something like this.
Four perfectly cut, perfectly square tunnels (tubes), nicely epoxy'd together.

Solar Tracker Sensor
Top down view of the Tunnels.
You can see mine are nice and square with each other.

Solar Tracker Sensor
I finished it off with a spray of Hammerite (rust prevention spray paint).
Obviously - If you managed to get hold of aluminium or plastic, you might not want to do this.
But even so, I think a nice layer of black paint finishes it off nicely!

Solar Tracker Sensor
The next stage is to glue in the LDRs.
You need each LDR in each tunnel to be exactly the same depth.
I've devised a cunning method for doing this.
Get something that will snugly fit in each tunnel - AA batteries happen to be perfect diameter for my sensor.
Line each battery up so that they end up approx 15mm from the end.
Use tape to secure all four batteries in place.

Solar Tracker Sensor
Slide in each LDR into position.
Make sure each has slid all the way down till they meet the end of the battery.
Use epoxy to glue each in place. - I guess you could also use's up to you.

Note - Notice I've used a decent amount of insulation tape to ensure nothing shorts out onto the case of the tunnels. It doesn't look particularly great, but it's functional!

Solar Tracker Sensor
And here you go!

Each LDR nicely glued into each tunnel...all exactly at the same depth.

watch this space for rest of instructions...

Next - How did I make the Vertical Axis


LOUKAS KAKKOS - 10/03/2019 19:26:15
I have from 1985 this way of tracker sensor.If you want to sale as part or completed device with the electronics let me know. I have ore 5 versions new sensor from the same year 1985.

Wubbe - 05/11/2017 10:38:01
Hello,I have donate 2 pound can you sent me the zipfile from the solar tracker please Thank in advance,Wubbe

TJ Wheeler - 10/06/2016 18:47:20
what about a clear cap at the top of the tube ? Is there any mechanical alignment needed ? (except as shown) Where to get the encapsulated LDR ?

Websonic - 11/09/2014 23:32:02
Hi there, Great stuff. Being not that good with programming arduino I must ask: What code have you used to drive relays?

Mike Blake - 03/02/2013 00:48:37
I use some heavy rubber/silicon hose pieces that are a snug fit in the tubes. That way the device can be removed and also while working out the length of the tubes the device can be moved up or down or the tube replaced etc.


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