14
POWER
VOLTAGE
10 15 1 7
TrackStar
Maximum
Power
Point
Traditional
Controller
Operating Range
CURRENT
VOLTAGE
10 15 1 7
Maximum
Power
Point
Typical Battery
Voltage Range
12 Volt Module
Current vs. Voltage
12 Volt Module
O utput Power
Figure 4-1. Nominal 12 Volt Solar Module I-V curve and output power graph.
The array V
mp
is the voltage where the product of output current and voltage (Amps x Volts) is
greatest, which falls on the “knee” of the solar module I-V curve as shown on the left in Figure
4-1.
Because traditional controllers do not always operate at the V
mp
of the solar array, energy is
wasted that could otherwise be used to charge the battery and power system loads. The greater
the difference between battery voltage and the V
mp
of the module, the more energy is wasted.
MPPT technology will always operate at the maximum power point
resulting in less wasted
energy compared to traditional controllers.
Conditions That Limit the Effectiveness of MPPT
The V
mp
of a solar module decreases as the temperature of the module increases. In very hot
weather, the V
mp
may be close or even less than battery voltage. In this situation, there will be
very little or no MPPT gain compared to traditional controllers. However, systems with modules of
higher nominal voltage than the battery bank will always have an array V
mp
greater than battery
voltage. Additionally, the savings in wiring due to reduced solar current make MPPT worthwhile
even in hot climates.
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