Frequently Asked Questions

• Does the Trac-Stat SL1 need to have a computer connected to it?
• Does the SL1 require a power source?
• How do I know that the SL1 is aligned to my tracker?
• What is the sampling period of the SL1?

Q: Does the Trac-Stat SL1 need to have a computer connected to it?

No, the SL1 can be configured in an automatic (standalone) mode where it records sun data on some pre-set period.

Q: Does the SL1 require a power source?

Yes, the SL1 must either be powered over the USB port (by connection to an on-site computer), or with a DC voltage source between 5 and 24V. A power supply, solar panel, or battery could be used to power the SL1. GreenMountain provides a cable terminated with the appropriate weatherproof connector and information on the connector (a standard off-the-shelf component available from Digikey and other vendors).

Q: How do I know that the SL1 is aligned to my tracker?

You have multiple options:

1. The SL1 is provided with precisely machined reference surfaces, and has been factory-calibrated to a known accuracy relative to these mounting surfaces. If you have a surface on your tracker which is suitably flat and well-aligned to your tracker or CPV axis of interest, you can mount the SL1 directly to this surface.

2. The SL1 allows a “software calibration/zero”. In this mode, you can use any method to align the CPV module and tracker with the sun (by looking for maximum current output, for example), and then send a “calibrate now” command to the sensor. The sensor records the sun position and stores this as a zero position to which all future readings will be references. This method also lets you take advantage of the SL1’s higher accuracy when used in a relative measurement mode.

Q: What is the sampling period of the SL1?

There are two components to this answer.

First, the SL1 has a “sample period” configurable via the USB interface that sets how often it locates the sun, reports the pointing error, and saves this value to the internal nonvolatile memory. This period can be set to a wide range of values (we find many customers use 30-60 seconds), but typically can not be set to any shorter than 5-15 seconds, depending on other sensor settings. This time limitation is due to various processing and communications performed on the sensor for each reading.

However, the portion of this time spent acquiring of the sun position itself is much quicker, typically 1-2 seconds at the very beginning of the sampling period, so there is no need to worry about the sun moving significantly during the reading (and the reading is not a “time-averaged position” over the entire sample period—it is the sun position at the beginning of the sample period).