4.0 OPERATION
MORNINGSTAR CORPORATION
23
4.0
4.2 TrakStar
TM
MPPT Technology
The SS-MPPT utilizes Morningstar’s TrakStar Maximum
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
(V
mp
) 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
owing into the SS-MPPT and 5 Amps
of charge current
owing out to the battery. The SS-MPPT
does not create current! Rest assured that the power into
the SS-MPPT is the same as the power out of the SS-MPPT.
Since power is the product of voltage and current (Volts x
Amps), the following is true*:
(1)
Power Into the SS-MPPT = Power Out of the SS-MPPT
(2)
Volts In x Amps In = Volts Out x Amps Out
* assuming 100% efficiency. losses in wiring and conversion exist.
If the solar module’s V
mp
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.
High Voltage Strings and Grid-tie Modules
Another bene
t of TrakStar MPPT technology is the ability
to charge 12 Volt or 24 Volt batteries with solar arrays of
higher nominal voltages. A 12V battery bank can be charged
with a 12 V, 24 V, or 36 V 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 SS-MPPT 75 V maximum input voltage rating at
worst-case (coldest) 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 SS-MPPT.
An Advantage Over Traditional Controllers
Traditional controllers connect the solar module directly
to the battery when recharging. This requires that the
solar module operate in a voltage range that is below the
module’s V
mp
. In a 12 V system for example, the battery
voltage may range from 10 - 15 Vdc but the module’s V
mp
is
typically around 17 V. Figure 8 shows a typical current vs.
voltage output curve for a nominal 12V off-grid module.
CURRENT
VOLTAGE
10 V
15 V
MAXIMUM
POWER
POINT
{
BATTERY
VOLTAGE
RANGE
~17 V
Figure 8. Nominal 12 V Solar Module I-V curve
