Setting up your Solar Machine’s Reset Homing / Limit Switches


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This documentation is part of the Open Sun Harvesting Project.

This page will show you how to set up the limit switches on either a heliostat or a sun tracking machine when using the Sun Tracking / Heliostat Program.

You will need two switches for every sun tracker or heliostat. One for resetting the machine’s azimuth and the other for resetting the machine’s altitude.

Note that in this case the “limit” switches are actually being used as “homing” switches. They still tend to be called limit switches even when being used as homing switches though, so watch out for the difference.

When the program is first started, it has no idea what the current orientation of the machine is. Thus, the purpose of the homing switches is to allow the program to “feel out” the machine’s orientation by moving it until it triggers the switches which are set at a known angle. The program will repeat this process automatically once a day just in case the machine has become “lost” again.

Heliostat Normal

When setting up your homing switches, it is important to realize that the altitude and azimuth angles of the machine that are referred to throughout this page (and even the entire site) are measured using the normal of the mirror’s surface (or the surface of whatever type of solar collector that you happen to be using). Without getting into too much detail, a “normal” is essentially just an imaginary arrow that points out from the mirror’s surface and is also perpendicular to it. An example image is shown below.

As the machine moves to other orientations, the normal always remains perpendicular to the surface.

 

Altitude Homing Switch

We will first look at how to set up the altitude limit switch.

The picture on the left shows a machine at an altitude angle of zero. The altitude is considered to be zero when the normal (not shown) of the machine is parallel with the horizon. The picture on the right shows the machine after it has rotated in the negative altitude direction. The exact angle value you use is up to you (just don’t use zero). Once you have moved the the machine to the altitude angle you want the machine to reset at, set your homing switch so that it is triggered at that exact angle.

 

Note that you can also set the altitude homing switch so that it is triggered when the machine moves in the positive altitude direction. Typically, I tend not to set my homing switches here since it creates a lot of unneeded movement, but you can still do it this way if the need arises.

When setting the altitude homing switch, make sure it is set either at the extreme negative range of its motion or at its extreme positive range of motion.

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Azimuth Homing Switch

How you set up your azimuth homing switch differs slightly depending on whether you live in the northern or southern hemisphere. An explanation of these differences can be found on the Northern and Southern Hemisphere Differences in the Sun Tracking / Heliostat Program page.

Northern Hemisphere

(You can skip this section if you are in the southern hemisphere)

When in the northern hemisphere, the machine’s azimuth is at zero degrees when the normal points in the direction of geographic south. The machine’s azimuth becomes negative when it moves counter clockwise and positive when it moves clockwise.

When setting the azimuth homing switch, it is best to set it at a negative azimuth angle so that the machine is ready for the morning sun after the nighttime reset is finished.

In the below example, we have turned the machine to an azimuth of -70 degrees. We will assume that this is the furthest that this machine is physically capable of moving to, so the homing switch will be placed so that it is triggered when the machine reaches this angle during the reset.

 

 Southern Hemisphere

(You can skip this section if you are in the northern hemisphere)

When in the southern hemisphere, the machine’s azimuth is at zero degrees when the normal points in the direction of geographic north. The machine’s azimuth becomes negative when it moves clockwise and positive when it moves counter clockwise.

When setting the azimuth homing switch, it is best to set it at a negative azimuth angle so that the machine is ready for the morning sun after the nighttime reset is finished.

In the below example, we have turned the machine to an azimuth of -70 degrees. We will assume that this is the furthest that this machine is physically capable of moving to, so the homing switch will be placed so that it is triggered when the machine reaches this angle during the reset.

This documentation is part of the Open Sun Harvesting Project.

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