TrackStar Technology

Traditional PWM vs Morningstar’s TrakStar™ MPPT Technology
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is precisely the time when batteries will benefit from an increased amount of charging current.
Environmental Considerations:
Environmental conditions will cause the Vmp of a solar array to fluctuate with partial array shading
and module temperature having the most impact. MPPT technology allows the system to track the
changing Vmp and maximize energy harvest in any environmental conditions.
Another noticeable increase in charging efficiency, or taking advantage of the voltage differential
“boost” will be seen in colder temperatures. As solar modules drop in temperature, their Vmp
increases (see Appendix). Using a standard PWM regulator, a decrease in temperature would
correspond in almost no change in power. Since the array current stays the same the charging current
picks nothing up from the increased voltage. However, an MPPT controller tracks the increasing Vmp
and converts the excess voltage being produced into additional charging current. In general, any rise in
Vmp will increase an MPPT controller’s harvest relative to a PWM controller. (Conversely, any drop in
Vmp will decrease an MPPT controller’s harvest relative to a PWM controller).
As seasons change, the angle of the sun striking a solar module will change as well (assuming
stationary modules). The greater the angle of incidence, the less power a module will ultimately
produce. During times of the year where the angle of incidence is greatest (and relative power output is
decreased), MPPT technology is very useful for harvesting the maximum amount of energy.
MPPT controllers can play a big role in helping improve system performance, especially autonomy
considerations, for keeping the batteries charged during the winter months with less daylight hours
and sometimes poor incident angle. Again, the additional “boost” is the greatest when it may be
needed the most.
Array Sizing for PWM Regulators:
The first consideration in sizing the array for a PWM controller is open circuit voltage (Voc). Every
controller has a maximum input voltage rating. The array must have a temperature compensated (see
Appendix) Voc less than the controller’s maximum input voltage rating. During PWM switching
cycles, the controller input is exposed to the array open circuit voltage. Using an array with a
temperature compensated Voc greater than the controller input rating will damage the controller.
Next, consider the maximum power voltage (Vmp). The Vmp of the array needs to be higher than
the battery’s maximum charging voltage.