Northern and Southern Hemisphere Differences in the Sun Tracking / Heliostat Program


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Sun trackers and heliostats oftentimes have a restricted range of motion due to constraints in their design. For example, a certain machine might only be able to move from -70 degrees to + 70 degrees along its azimuth. If oriented incorrectly, this machine would have poor access to the sun as it moves across the sky.

The Sun Tracking / Heliostat Program offers two possible orientations for your machine, one designed for the northern hemisphere and the other for the southern hemisphere.

Note: It may be helpful to look at the images at this link to get a better idea of how the sun travels across the sky at different latitudes before continuing.

Northern Hemisphere

In the northern hemisphere, the sun is mostly to the south, so it would be best to orient the machine so that south is the direction where the azimuth equals zero. This is shown in the picture below.

Also notice for future reference that negative angles point more east and positive angles point more west.

Southern Hemisphere

In the southern hemisphere, the opposite is true. Here, the sun is mostly to the north, so it would be best to orient the machine so that north is the direction where the azimuth equals zero. This is shown in the picture below.

Notice that the positive and negative angles seem reversed from how they were in the above northern hemisphere example. Negative angles still point more east and positive angles still point more west however. Warning! This is not standard. If you try to match the calculated sun’s azimuth output when using the southern hemisphere setting (useNorthAsZero), it’s not going to match other programs.

Note: Another way of looking at the previous two pictures is that negative angles point more towards the direction of the rising sun regardless as to whether the machine is located in the northern or southern hemisphere.

Close to the Equator and using Heliostats

If you live close to the equator and are using a heliostat, there can be some ambiguity as to whether north or south is the best direction to have the azimuth equal zero. Averaged over the course a year, the path of the sun isn’t strongly biased one way or the other in this situation.

In this case, it might be better to let the location of your target decide which to use. So if the location of the target relative to the heliostat is more to the south, then it might be best to use the northern hemisphere example above, even if you are technically in the southern hemisphere. If the target is more to the north though, then the southern hemisphere example might be best.

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