SunSaver Manual
MORNINGSTAR CORPORATION 31
4.0
High Voltage Strings and Grid-tie Modules
Another benet 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