Operation
ProStar MPPT Operator’s Manual
37
36
4.0
4.1 TrakStar
TM
MPPT Technology
The ProStar MPPT utilizes Morningstar’s TrakStar Maxi-
mum Power Point Tracking technology to extract maximum
power from the solar module(s). The tracking algorithm
is fully automatic and does not require user adjustment.
Trakstar technology will track the array maximum power
point voltage (Vmp) as it varies with weather conditions,
ensuring that maximum power is harvested from the array
through the course of the day.
Current Boost:
In many cases, TrakStar MPPT technology will “boost” the
solar charge current. For example, a system may have 2
amps of solar current flowing into the ProStar MPPT and
5 amps of charge current flowing out to the battery. The
ProStar MPPT does not create current! Rest assured that the
power into the ProStar MPPT is the same as the power out
of the ProStar MPPT. Since power is the product of voltage
and current (Volts x Amps), the following is true*:
(1) Power Into the ProStar MPPT = Power Out of the ProStar
MPPT
(2) Volts In x Amps In = Volts Out x Amps Out
* assuming 100% efficiency i.e. if no losses in wiring and
conversion existed.
If the solar module’s Vmp is greater than the battery voltage,
it follows that the battery current must be proportionally
greater than the solar input current so that input and output
power are balanced. The greater the difference between the
maximum power voltage and battery voltage, the greater
the current boost. Current boost can be substantial in
systems where the solar array is of a higher nominal voltage
than the battery as described in the next section.
4.0 OPERATION
High Voltage Strings and Grid-tie Modules
Another benefit of TrakStar MPPT technology is the ability
to charge 12 or 24 volt batteries with solar arrays of higher
nominal voltages. A 12 volt battery bank can be charged
with a 12, 24, 36 or 48V nominal off-grid solar array. Certain
grid-tie solar modules may also be used as long as the
solar array open circuit voltage (V
oc
) rating will not exceed
the ProStar MPPT 120V maximum input voltage rating at
worst-case (lowest) module temperature. The solar module
documentation should provide V
oc
vs. temperature data.
Higher solar input voltage results in lower solar input
current for a given input power. High voltage solar input
strings allow for smaller gauge solar wiring. This is especially
helpful for systems with long wiring runs between the solar
array and the ProStar MPPT.
An Advantage Over Traditional Controllers
Traditional controllers connect the solar module directly
to the battery when recharging. This requires that the so-
lar module operate in a voltage range that is below the
module’s V
mp
. In a 12V system, for example, the battery
voltage may range from 10 - 15 Vdc but the module’s V
mp
is
typically around 17V. Figure 4.1 shows a typical current vs.
voltage output curve for a nominal 12V off-grid module.
Figure 4.1. Nominal 12 volt solar module I-V curve and output power
graph
PO
WER
VOLTAGE
10
15 17
TrackStar
Maximum
Power
Point
Traditional
Controller
Operating Range
CURRENT
VOLTAGE
10
15 17
Maximum
Power
Point
Typical Battery
Voltage Range
12 Volt Module
Current vs. Voltage
12 Volt Module
Output Power