PWM vs. TrakStar MPPT Technology

Traditional PWM vs Morningstar’s TrakStar™ MPPT Technology
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Appendix - Temperature Compensation:
It is important to take into account temperature compensation and understand how it relates to
both the output voltage and output current of a solar module.
Solar modules have performance ratings under standard test conditions (STC); normally a cell
temperature of 25°C and 1000W/m2 irradiance. Actual operating conditions will, of course, vary from
STC. Manufacturers publish temperature coefficients which can be used to determine module output
current/voltage under expected conditions. The two most important are the Voc and Isc Temperature
Coefficients.
The Voc temp coefficient, specified in volts per °C (or °F), is a negative value. This indicates
that the open circuit voltage of the module has an inverse relationship with temperature (Voc decreases
with increasing temperature and increases with decreasing temperature). When determining if the Voc
of an array is appropriate for the controller’s maximum input voltage, it is essential to take into account
temperature effects. In warm weather, the Voc of a module may be low enough to use with a certain
controller. However, as seasons change and temperature drops, the Voc may rise past a voltage safe to
use with that controller.
Worst case temperature effects should always be used when sizing an array. For example: the
Voc of a module under STC (25°C) is 21V. The Voc temp coefficient is -0.05V/°C. If the record low
temperature for the area in which the module will be placed is -10°C, the worst case (highest) Voc will
be 22.75Voc:
-10°C - 25°C = -35°C
-35°C * -0.05V/°C = 1.75V
21V(@STC) + 1.75V = 22.75V(@-10°C)
The Isc temp coefficient, specified in amps per °C (or °F), is a positive value. This indicates
that the short circuit current will rise with increasing temperature and fall with decreasing
temperature. Normally, the Isc coefficient is small enough to be neglected.