4
INTRODUCTION
1.3
Clarification around the purpose and connection of the MPPT
.
What is the main purpose of the MPPT?
The MPPT allows you to take advantage of the mathematics behind power conversion and allows
maximum power delivery from the panel.
Let’s look at a typical solar panel (the values will be adjusted to make reading/maths easier).
Open circuit voltage = 22 V (Voc)
Power point voltage = 17 V (Vmp)
Short Circuit current = 10.1 Amp (Isc)
Max Charge current = 10.0 Amp (Imp)
Max Power = 170 W
What do these values mean?
Open circuit voltage:
If the panel is exposed to sunlight while the panel is not connected to anything the voltage will be 22
volts.
Power point voltage:
If we connect the panel to the MPPT the panel will be kept around 17V (depending on the
temperature of panel, angle of sun etc.) as long as the MPPT has a flat battery to charge.
This is the point at which the panel voltage multiplied by the panel current = max wattage (not max
amps or max voltage but the combination of the two).
Short circuit current:
If the panel + and panel
– touches, this current will flow.
The panel will be at 10amp when panel voltage is at 17V. If the panel voltage is forced lower, the
current will increase.
As voltage decreases, when the panel voltage reaches 0 V then the current will = 10.1 amps.
Max charge current:
As long as the sun gives you 1000 W/m2 and the panel is kept at 25° C (P.S. panel temp rises when
a current is flowing) and the panel voltage is kept at Vmp then the Imp will = 10 amps.
Max Power:
Vmp x Imp = 170 W
What Happens When You Charge a Battery?
•
Power cannot be created out of nothing and cannot be destroyed,
so input = output and Vbattery x Ibattery must = Vpanel x Ipanel
•
With a MPPT regulator the panel voltage is controlled independently from the battery voltage
and the panel voltage is kept at Vmp allowing Imp to flow. Refer to table 1.3
•
With a PWM regulator the panel is connected to the Battery while charging, forcing Vpan to =
Vbat, a current slightly higher than Imp will flow, because the panel is directly connected to
battery the current must be equal in both, if the current is limited to Imp then the power is
limited to Vpan (or Vbat) x Imp. Refer to table 1.4
Table 1.1
Table 1.2
MPPT
PWM
Vbat Ibat
Vpan Ipan
Power
Vbat Ibat
Vpan Ipan
Power
10v
17 Amp
17v
10 Amp
170w
10v
10.05 Amp 10v
10.05 Amp 100w
12v
14.2 Amp 17v
10 Amp
170w
12v
10.05 Amp 12v
10.05 Amp 120w
14v
12.2 Amp 17v
10 Amp
170w
14v
10.05 Amp 14v
10.05 Amp 140w
