User manual
Appendix II - Sunrise/Sunset Thresholds
Description:
The SunSaver MPPT uses the array voltage (Varray) to determine whether it is daytime or
nighttime. It is essential for the controller to know when transitions from day-to-night or night-to-
day occur in order to keep accurate control of the lighting/loads. To do this, the controller looks
for when Varray rises above a certain level or falls below a certain level.
During sunrise (assuming clear skies), Varray steadily climbs until it reaches its rated
maximum. The Sunrise Threshold is used to determine at what voltage the SSMPPT should
recognize a night-to-day transition. Conversely, during sunset, Varray steadily decreases as less
and less sunlight strikes the panels. The Sunset Threshold is used to determine at what voltage
a day-to-night transition should be recognized.
These thresholds are specied as percentages of the maximum seen Varray; the highest
array votlage recorded by the controller since the controller was last restarted. It can safely be
assumed that the maximum seen Varray is approximately the Open Circuit Voltage (Voc) rating
of the array (found on module datasheets). For example, if the Voc of the array is 20.0V and the
Sunrise Threshold is set to 60%, the controller will recognize sunrise as occurring when the array
voltage reaches 12.0V (20.0V * 0.6 = 12.0V).
The Sunrise Threshold percentage must always be set higher than the Sunset Threshold
percentage.
Tips for Use:
IMPORTANT: The default threshold percentages will be sufcient for the large majority
of systems. Only make changes to the percentages if absolutely necessary.
• Allow the system to operate in real-world conditions before considering changes to the
thresholds. After the system has been operating in the eld, changes can be made to the
threshold percentages in order to tweak exactly when the lights come on / go off.
• It is best to keep the sunrise and sunset percentages at least 10% away from each other.
If the percentages are too close, rapidly changing lighting (sunlight) conditions can cause
undesired light/load operation.
• During the day: Trees or other objects that cast shadows on the solar array tend to cause
‘mini-sunsets’ (where the array output voltage drops, but not as much as during true sun-
set). To prevent the controller from detecting a sunset event during temporary shading
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