TrakStar MPPT Technology and Maximum Input Power

Morningstar’s TrakStar™ MPPT Technology & Maximum Input Power
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o Limiting charging current for smaller battery banks without exceeding the maximum charging
current.
System details can be examined to determine if operating closer to the MPPT controller’s full capacity will be cost
effective. For example, a 10% loss for 5% of the time when it is not needed may be more like a 0.5% net charging
loss. The ability to oversize the array gives the PV designer more choices.
Q4. Besides STC Power, what array details are important when sizing an MPPT controller?
There are two critical values that must be carefully evaluated.
 The array’s temperature compensated minimum Vmp should stay above the battery maximum Vb for
consistent charging to occur.
 The array’s temperature compensated maximum Voc should never exceed the maximum voltage ratings
of the controller (as that will damage the controller).
These minimum and maximum voltage levels are related to the temperature coefficient of the PV cells (Cell
temperature can be much higher than the ambient temperature). Morningstar’s sizing calculator
(http://www.morningstarcorp.com/en/strings/calc.php) can provide minimum and maximum voltage levels for
an array based on minimum record low temperature and maximum average high temperatures. Using this
sizing tool, with your controller and module of choice, will help to ensure its correct and reliable operation.
Q5. Can I use a 240 Watt (60 Cell / Vmp ≅ 30V) PV module with a SunSaver MPPT™
controller?
Yes. Even though the SunSaver MPPT™ controller in a 12V system is nominally rated for a 200W PV array, you
can use a larger PV module e.g. a 240W PV module.
 For 12V systems the SunSaver MPPT controller is an acceptable option due to its ability to convert the
module voltage down and charge a 12V battery very effectively. (Fact: all Morningstar MPPT controllers
are buck converters—they can convert voltage down but not up, which is known as a boost
converter. For this reason, the Vmp of the module must be above the battery voltage at all times or
charging will cease).
 For 24V systems the use of this module with a SunSaver MPPT controller is not an option since the
voltage (Vmp≈30V) is too low for a single module to charge correctly (Vmp too low) and Voc is too high
for two modules in series—as this would exceed the controllers 75Voc maximum.